2017 Schoenborn Graduate Research Symposium

January 23, 2017

Continental Breakfast / Welcome 8:30 – 9:00 AM

Oral Presentations 9:00 – 10:20 AM

 9:00 AM J. Zachary Mundy

Background: Functional textile materials are found in wide-ranging applications –from energy storage and filtration to wearable electronics and personal protection. In this work, we present methods for the integration of chemical sensing functionality into pre-formed nonwovens using liquid-and vapor-phase deposition methods. Typically, so-called conductometric sensors, which undergo some measurable change in electrical properties upon chemical exposure, are used in these applications. However, as they are often based on metal oxide films, conductometric sensors require not only high operating temperature but also rigid supports to mitigate film fracture, thereby limiting their implementation into low-power, flexible applications. Organic semiconducting polymers, such as polyaniline, may be used as a sensing medium in place of metal oxides owing in part to its flexibility and room-temperature operation. Easily formed via the polymerization of aniline, polyaniline exhibits both an electrical and colorimetric switch upon exposure, from the conductive, green emeraldine salt form to the non-conductive, blue emeraldine base. [1] Herein, we demonstrate an in-situ polymerization method which results in thin coatings of polyaniline on nonwoven substrates along with novel vapor-phase deposition techniques enabling us to monitor the electrical properties of the polyaniline.[2]Results: Polyaniline-coated nonwovens are obtained after submerging in the polymerization solution during the reaction. Though the fiber diameter and fractional mass gain both increase with polymerization time, effective conductivity does not, indicating that a conformal film is formed in as little as 30 minutes. The coated nonwovens show a linear electrical response to dilute ammonia vapor, though an apparent delay in the response suggests mass transport limitations at the fiber surface. Additionally, we show that low-temperature metallic atomic layer deposition maybe used to form highly conductive nonwovens with minimal mass gain for monitoring the electrical state of the polyaniline.Conclusions: A novel in-situ polymerization technique results in preformed nonwovens coated with a polyaniline thin film for use in chemical sensing applications. Proof of concept demonstrations show a linear response to ammonia vapor but indicate some mass transport limitations. Additionally, to monitor the polyaniline-based sensors, we developed an atomic layer deposition process for depositing ultrathin, highly conductive metal films onto polymer substrates. When combined, these methods allow for the formation of an integrated, textile-based chemical sensor.References:

1.McQuade, D. Tyler, Anthony E. Pullen, and Timothy M. Swager (2000). Conjugated Polymer-Based Chemical Sensors. Chemical Reviews, 100: 2537-2574.

2. Mundy, J. Zachary, Arya Shafiefarhood, Fanxing Li, Saad A. Khan, and Gregory N. Parsons (2016). Low temperature platinum atomic layer deposition on nylon-6 for highly conductive and catalytic fiber mats. Journal of Vacuum Science and Technology A, 34: 01A152

 9:20 AM Russell W. Mailen
Background: Shape memory polymers (SMPs) represent a class of active materials that can change shape in response to external stimuli such as heat, light, pH, solvents, and magnetic fields. Although SMPs have many applications, we are primarily interested in using the material as environmentally responsive actuators for self-folding origami structures. Thermally activated SMPs can change shape in response to heat, and are desirable due to their low cost and tailorable properties. Self-folding can be used to obtain three-dimensional (3D) structures from planar sheets for an array of applications, including medical stents, antennas, and engineered, origami applications, such as space telescopes.Previously, we developed a method to activate SMPs using light. [1] To do this, we pattern black ink onto pre-strained polystyrene sheets. When placed under an infrared (IR) light, the black ink absorbs light more efficiently than the unpatterned regions of the polymer sheet. This local light absorption results in localized heating beneath the ink, and produces a temperature gradient through the thickness of the sheet. The material shrinks locally wherever the activation temperature, Ta, is exceeded. Because there is a gradient in temperature, there is a gradient in shrinkage, and the material deforms out-of-plane.Results: We investigate the thermo-mechanical response of heat activated SMPs by extending a previously developed finite element model [2] to account for both external and internal heat sources. The SMP can heat due to external heat sources, such as light, or from internal viscous heating. Viscous heating affects significantly the response of SMP sheets by increasing the temperature during pre-strain which accelerates stress relaxation. This stress relaxation results in a slower shrinking rate when the SMP is reheated. Viscous heating also causes a significant increase in temperature during unconstrained recovery. Our model shows how the coupled thermo-mechanical loading conditions affect folding and unfolding of SMP sheets in response to localized heating in a ‘hinged’ region. We conduct a parametric study of sheet thickness, hinge width, degree of pre-strain, and hinge surface temperature, and we demonstrate methods for generating 3D, curved structures.Conclusions: We show the importance of accounting for both external and internal heat sources when predicting the shape of SMP sheets that respond to light. Furthermore, complex shapes can be obtained by carefully designing the placement and darkness of ink on the sheet. The results can be used to set guidelines for the design of functional, self-folding SMP structures.References:

  1. Ying Liu, Y., Boyles, J., Genzer & Michael D. Dickey. Self-folding of polymer sheets using local light absorption. Soft Matter 8, 1-6 (2012).
  1. Mailen, R.W., Liu, Y., Dickey, M.D., Zikry, M. & Genzer, J. Modelling of shape memory polymer sheets that self-fold in response to localized heating. Soft Matter 11, 7827-7834 (2015).
 9:40 AM  Joseph Lavoie
Background: The creation of superhydrophobic and superoleophobic surfaces is a technical challenge that is applicable to many different industries, including automotive, consumer electronics, adhesion and many others. In particular, oil repellent nonwoven materials have been designed for the protection of charged electret filters from loss of charge, however alcohol exposure of these products still pose a significant issue. [1] Due to their extremely low surface tension compared to water and many oils, the creation of a surface which induces a significantly increased contact angle with alcohol is extremely challenging. With this in mind, this study sought to utilize many of the principles developed for superhydrophobic and oleophobic surfaces and apply them to the unique challenge of alcohol repellency in nonwoven filter materials.Results: Two approaches for surface modification have been developed and characterized. First, a conformal, layer-by-layer coating method was developed, utilizing soy protein isolate as an activation layer for the polypropylene (PP) substrate. Subsequent layers were formed using ionic interactions composed of poly(diallyldimethylammonium chloride) (pDADMAC) and fumed silica nanoparticles. The resultant silica surface was functionalized with a perfluorinated moiety, using a facile chemical vapor deposition (CVD) approach. The final, coated nonwoven yields significantly increased repellency due to its extremely rough and fluorinated surface, with apparent oil contact angles in excess of 110° and moderate increases to alcohol contact angles. Second, surface active, fluorochemical melt additives have been utilized to generate nonwoven substrates with increased oil and alcohol repellency. X-ray Photoelectron Spectroscopy (XPS) was used to characterize the kinetics of the changing surface composition of the nonwoven fibers, as migration of the additive to the surface occurs over time. This changing composition was then related to repellency via contact angle data.Conclusions: Two methods for surface modification of PP nonwoven substrates have been demonstrated and characterized. Both approaches were shown to exhibit improved repellency towards oils and alcohols. Multilayer coatings composed of soy protein, pDADMAC and silica nanoparticles were shown to generate rough, conformal coatings, that can be easily functionalized with low surface energy compounds. Nonwovens containing fluorochemical melt additives were generated and the kinetics of additive migration were characterized. It was shown that changing surface composition due to migration resulted in increased repellency. Samples with sufficient surface concentration of additive prevent wetting by isopropyl alcohol (IPA) and are therefore able to survive IPA vapor discharging tests in order to maintain filtration efficiency performance.References:

  1. Kim, J., Hinestroza, J. P., Jasper, W. & Barker, R. L. (2009) . Effect of Solvent Exposure on the Filtration Performance of Electrostatically Charged Polypropylene Filter Media. Text. Res. J. 79, 343–350.
10:00 AM Gilbert Castillo
Background: The ability to modify the surface of PET in controllable fashion is an important asset to alter surface energy, improve chemical inertness, induce surface cross-linking, increase or decrease surface roughness and hardness, enhance surface lubricity and electrical conductivity, impart functional groups at the surface for specific interactions with other functional groups, and/or provide anti-fouling properties1. Addition of reactive functional groups to PET surfaces can serve as a means of generating anchoring points for grafting materials onto the PET surface, which can be utilized to further tune its surface characteristics. Surface modification of PET aims to take advantage of its inherent mechanical and optical properties, its malleability retain its low cost and ease of manufacturing.Results: We show that PET surfaces react with 3-aminopropyltriethoxysilane in aqueous solutions, and the reaction is much slower in other solvents (alcohols, tetrahydrofuran, and toluene). The procedure described here creates a uniform coverage of hydrolyzed APTES layer on PET surfaces as shown by thickness measurements and ToF-SIMS imaging, which has a lateral resolution of 60 nm. Water is an attractive solvent as it is non-flammable, non-toxic, and inexpensive, and thus makes this process suitable for scale-up. The formation of islands or cross-linked APTES aggregates was not observed either in AFM images or ToF-SIMS images. Furthermore, the described procedure should also be applicable to polyester fibers.Conclusions: The activation of PET with APTES followed by silicate films deposition serves as a platform to endow the surface with various functionalities by taking advantage of excess hydroxyl moieties present on the surface. These surface functionalities include (but are not limited to) (1) biocidal, anti-fouling, hydrophilic coatings for biomedical applications; (2) biocidal and anti-fouling finishes for filtering applications; and (3) hydrophobic surfaces for self-cleaning applications.References:

  1. Chan, C. M. Polymer Surface Modification and Characterization; Carl Hanser, GmbH & Co.: 1994

Coffee Break 10:20 – 10:50 AM

Oral Presentations 10:50 – 12:10 PM

 10:50 AM Jonathan M. Conway
Background: Caldicellulosiruptor species are anaerobic bacteria that are the most thermophilic (Topt = 70-75°C) microorganisms currently known to degrade lignocellulosic biomass, making them of interest as platform microorganisms for engineering the conversion of unpretreated plant biomass to bio-based fuels and chemicals. To date, the genomes of 12 Caldicellulosiruptor species have been fully sequenced and genomic, transcriptomic, proteomic, and phenotypic analysis has revealed genes of interest for evaluating and manipulating the native attachment, degradation, and conversion mechanisms of Caldicellulosiruptor species. Of particular interest are the large (~170-220 kDa), multi-domain enzymes produced by Caldicellulosiruptor species containing catalytic glycoside hydrolase (GH) and carbohydrate binding module (CBM) domains [1]. A subset of these enzymes also contains surface layer homology (SLH) domains, which associate these enzymes with the bacterial surface layer (S-layer).Results: Full-length and truncated recombinant versions of several of these enzymes have been produced in E. coli and C. bescii for characterization in vitro [2]. Crystal structures for GH and CBM domains from these enzymes have also been determined, providing structural information to complement the biochemical characterization. In addition to these in vitro analyses, genetic manipulations in C. bescii are being performed, using improved genetic tools [3], to test hypotheses about the role of these enzymes in vivo and to engineer improved plant biomass degradation in this non-model host. A strain of C. bescii expressing a xylanase from C. kronotskyensis showed improved ability to degrade xylan substrates and the enzyme was correctly localized on the cell surface within the S-layer [2]. To probe the role of enzymes involved in cellulose degradation, strategic subsets of enzymes in the glucan degradation locus, a locus of cellulases conserved in cellulolytic Caldicellulosiruptor species, were deleted from the genome. The ability of these strains to degrade crystalline cellulose and plant biomass was evaluated to elucidate the role of these enzymes in the degradation of varied substrates.Conclusions: These complementary in vitro and in vivo approaches are providing an improved fundamental understanding of the native mechanisms of plant biomass recruitment, degradation, and conversion in Caldicellulosiruptor species. Using the advancing genetic tools for manipulating C. bescii, we are leveraging this understanding to engineer strains with improved biomass degradation ability looking towards the production of bio-fuels and bio-chemicals from lignocellulosic feedstocks.References:

  1. Conway, J.M., J.V. Zurawski, L.L. Lee, S.E. Blumer-Schuette, R.M. Kelly. (2015) Lignocellulosic Biomass Degradation by the Extremely Thermophilic Genus Caldicellulosiruptor. In: Thermophilic Microorganisms. Fuli Li, editor. Caister Academic Press. pp 91-120.
  1. Conway, J.M., W.S. Pierce, J.H. Le, J.H. Wright, G.W. Harper, A.L. Tucker, J.V. Zurawski, L.L. Lee, S. E. Blumer-Schuette, R.M. Kelly. (2016) Multi-Domain, Surface Layer Associated Glycoside Hydrolases Contribute to Plant Polysaccharide Degradation by Caldicellulosiruptor J. Biol. Chem. 291, 6732-6747.
  1. Lipscomb, G.L., J. M. Conway, S.E. Blumer-Schuette, R.M. Kelly, and M.W.W. Adams. (2016) Highly Thermostable Kanamycin Resistance Marker Expands the Toolkit for Genetic Manipulation of Caldicellulosiruptor bescii. Appl. Environ. Microbiol. 82(14), 4421-4428.
 11:10 AM Brittany Mertens
Background: We characterize the colloidal interactions of human norovirus reconstituted virus-like particles (VLPs) in aqueous suspension and on surfaces and seek means to control and modify them by using various classes of surfactants. The fundamental understanding of these interactions will aid in practical formulation of novel mixtures for virus inactivation and removal from contaminated surfaces. In aqueous solution, we characterize the effects of solution pH and surfactant type and concentration on virus particle aggregation, dispersion, and disassembly using dynamic light scattering (DLS) and electrophoretic light scattering (ELS). We also characterize the effects that copper ions have on virus integrity to explain empirical data indicating virus inactivation by copper alloy surfaces, and to develop novel metal ion-based virucides.Results: We observe that a strong ionic surfactant above its critical micelle concentration (CMC) causes capsid disassembly and breakdown of aggregates. Below CMC, surfactant adsorption onto the virus capsid follows simple adsorption models, depending on the charge of the surfactant and the net charge of the capsid. Ionic surfactant adsorption leads to modified apparent surface charge and subsequent aggregation or dispersion, depending on the surfactant charge. High concentrations of Cu(II) ions have little effect on the infectivity of human norovirus surrogates, so we use sodium ascorbate as a reducing agent to generate unstable Cu(I) ions from solutions of copper bromide. Low concentrations of monovalent copper ions (~0.1 mM) cause permanent capsid protein damage that prevents human norovirus capsid binding to cell receptors and induces a greater than 4log reduction in infectivity of Tulane Virus, a human norovirus surrogate. We demonstrate the oxidative mechanisms of virus damage, including capsid protein backbone cleaving by SDS-PAGE and RNA degradation by RT-qPCR.Conclusions: Micelles formed from strong ionic surfactants can disrupt interactions between capsid protein dimers and cause capsid disassembly. Adsorption of ionic surfactants below CMC leads to modified apparent surface charge and subsequent aggregation or dispersion, depending on the surfactant charge. Divalent copper ions mixed with a reducing agent such as sodium ascorbate generate virucidal Cu(I) ions capable of inactivating human norovirus surrogates. Significant differences in the susceptibility of different human norovirus strains to deactivation by copper ions indicate that capsid proteins bind copper with biological specificity. The infectivity and colloidal stability data reported here could enable the design of effective and benign virucidal formulations based on copper ions
 11:30 AM Deepti Srivastava
Background: It is well established that confinement within a nano-porous material, such as an activated carbon, carbon nanotube, or porous oxide can affect reaction yield, reaction rate and even the mechanism of the  reaction [1,2]. These effects arise from the strong intermolecular forces between the various reacting species and the pore walls, but are poorly understood. There has also been evidence that nanophases can exhibit high pressures when adsorbed within nanoporous materials due to confinement effects [5]. While the pressure in the bulk is a scalar quantity, the pressure inside a pore is a second-order tensor with both normal and tangential components, with respect to the wall. Molecular simulations for simple fluids in pores has shown the presence of high local tangential pressures, even at lower bulk pressures.Results: We report a molecular simulation study of the effects of confinement within a nanoporous carbon material on the equilibrium yield of the nitric oxide dimerization reaction, 2NO = (NO)2. This reaction is chosen for study both because of its importance in atmospheric chemistry and biology, and because experimental data is available for the reaction within carbon materials. At the experimental conditions the yield of dimer in the gas phase in equilibrium with the pore phase was less than 1 mol%, whereas the yield within the pores was 100 mol% within the accuracy of the experiment [3,4]. Monte Carlo simulations reported [5] found a large increase in the yield within slit-shaped pores due to the confinement, but the calculated yield was well below the experimental value.Conclusions: We conducted a Reactive Monte Carlo study of the NO dimerization reaction in slit-shaped carbon pores of various widths and over a range of temperatures. In particular, we show that the force fields used for both the monomer-wall and dimer-wall interactions were in error and were a primary cause of the discrepancy between the simulations and experiment.  Using ab initio calculations, we report revised force fields for these interactions, and show that the use of these leads to agreement with experimental results. In addition, we also investigate the relationship between the high in-pore tangential pressures and the higher reaction conversion yields under confinement.References:

  1. C.H. Turner, J.K. Brennan, J.K. Johnson and K.E. Gubbins, “Effect of Confinement by Porous Materials on Chemical Reaction Kinetics”, Journal of Chemical Physics, 116, 2138-2148 (2002).
  2. K. Kaneko, N. Fukuzaki, K. Kakei, T. Suzuki and S. Ozeki, Langmuir, “Enhancement of NO Dimerization by Micropore Fields of Activated Carbon Fibers”, 5, 960-965 (1989).
  3. O. Byl, P. Kondratyuk and J. T. Yates, “Adsorption and Dimerization of NO inside Single-Walled Carbon Nanotubes – An Infrared Spectroscopic Study”, J. Phys. Chem. B, 2003, 107, 4277-4279.
  4. C. H. Turner, J. K. Johnson and K. E. Gubbins, “Effect of Confinement on Chemical Reaction Equilibria: The Reactions 2NO = (NO)2 and N2+3H2 = 2NH3 in Carbon Micropores”, J. Chem. Phys., 114, 1851-1859 (2001).
  5. Yun Long, Jeremy C. Palmer, Benoit Coasne, Małgorzata Śliwinska-Bartkowiak and Keith E. Gubbins, “Pressure enhancement in carbon nanopores: A major confinement effect”, Physical Chemistry Chemical Physics, 13, 17163-17170 (2011)
11:50 AM Sara Jo Taylor
Background: We use molecular-beam mass spectrometry (MBMS) to identify and quantify the products of catalyzed acetic acid pyrolysis. MBMS is especially useful for detecting unstable species, such as ketene (H2C=C=O), one of the main products of acetic acid pyrolysis. MBMS requires successive stages of vacuum, partitioned by axially aligned sampling and skimmer cones. In our system, a reactor can be positioned in the primary vacuum chamber such that its exhaust is sampled and forced to undergo supersonic free-jet expansion due to the critical pressure drop across the sampling-cone orifice. With expansion, the internal energy of the reacting molecules is converted to translational energy, forming a directed beam of molecules frozen in chemistry [1]. The molecular beam is focused as it passes through the skimmer cone into the ionization chamber, where it undergoes electron ionization, producing ions that are separated by their mass-to-charge ratios via quadrupole filtering. The detected ions produce a signal proportional to their concentration and ionization cross-section, σ(eV).Results: Quantum-chemically predicted rate constants are compared with new experimental measurements (via MBMS) for pyrolysis of acetic acid. Previously, Padmanabhan et al. [2] measured first-order kinetics with respect to acetic acid concentration, reporting rate constants for the consumption of acetic acid and for ketene formation. Grottoli et al. [3] developed a different kinetic scheme, fitting Padmanabhan’s data to non-first order rate expressions for ketene formation, decarboxylation, and ketene decomposition. In the present work, we measure conversion of acetic acid in a tubular flow reactor using the homogeneous catalyst triethyl phosphate that was studied by Padmanabhan and by Grottoli. MBMS analysis of the reactor exhaust allows us to infer overall rate coefficients using plug-flow and CSTR models. We also compute gas-phase thermochemistry of species and transition states then calculate kinetics for several pathways of phosphoric-acid-catalyzed conversion of acetic acid to ketene and water. Structures, vibrational frequencies, and energies are computed by quantum chemistry with Gaussian 09. Using the Gaussian output files, rate coefficients are computed with the NIST ChemRate code or MESMER (Master Equation Solver for Multi-Energy well Reactions, open-source). Finally, we model our tubular flow reactor as a PFR in CHEMKIN, building the chemistry set from the elementary reaction steps in our hypothesized mechanisms.Conclusions: Low-barrier transition states, as well as pathways with irreversible steps which promote ketene formation, have been identified. In pursuit of a complete mechanism with rate constants and conversions congruent with our experimental data, we are searching for other pathways that proceed at a faster rate than those included thus far.References:

  1. Miller, D. R. (1988). Free-jet Sources. In G. Scoles (Ed.), Atomic and molecular beam methods, I (pp. 14-22). Oxford University Press.
  1. Padmanabhan, N. P., P. K. Deshpande, and N. R. Kuloor (1968). Catalytic Cracking of Acetic Acid to Acetic Anhydride. I & E C Process Design and Development, 7: 511-516.
  1. Grottoli, M. G., O. Loiacono, E. Ranzi (1991). Simulation Model for Ketene Productions via Acetic Acid. Computer Oriented Process Engineering (pp. 203-208). Elsevier Science Publishers, Amsterdam.

Lunch 12:10 – 1:50 PM

 12:40 PM Dr. David Ollis
Announcement of 2016 Stannett Award
 12:50 PM Todd Skare, Praxair CTO
Announcement of Fall 2016 Praxair Exceptional Teaching Assistant Award
 1:00 PM Keynote Address: Dr. Elizabeth Wilder
Procter and Gamble, Senior Scientist
“Beyond Technical Mastery:  The leadership skills that can make you stand out”             

Oral Presentations 1:50 – 3:30 PM

 1:50 PM Paul Lemaire
Background: The semiconductor industry foresees multiple challenges in designing and manufacturing the 7 and 5-nm nodes. Standard patterning techniques, such as lithography, become much less applicable because of challenges maintaining edge definition and alignment to the underlying features. In addition, semiconductor devices typically utilize three dimensional designs, creating complex high-aspect-ratio features. Current atomic layer etching (ALEt) techniques typically require argon bombardment, plasmas, or other energy-enhanced species, all of which can damage sensitive transistor features. Accordingly, industry is looking towards controllable thermally-driven etching techniques to supplement thin film deposition techniques currently used by the semiconductor industry.Results: We show that tungsten hexafluoride (WF6) can be used to selectively etch titania (TiO2) films versus other oxides including alumina (Al2O3). Results from quartz crystal microbalance (QCM), ellipsometry, and x-ray photoelectron spectroscopy (XPS) analysis, show TiO2 etching at 220°C and little to no etching at the lower process temperature of 120°C. These results are in agreement with thermodynamic modeling of bulk etching of TiO2 with WF6 which shows that WF6 forms volatile TiF4 and WOF4 species at 220°C, but not at 120°C. XPS shows evidence for a WOxFy layer that forms on of the TiO2 films during the etch process. This WOxFy layer in turn can be volatilized by dosing tin acetylacetonate (Sn(acac)2) or boron trichloride (BCl3). These two self-limiting reactions, 1) WF6 adsorption and 2) Sn(acac)2/BCl3 activation were combined to create an atomic layer etching (ALEt) process.Conclusions: WF6 selectively etches TiO2 films by forming volatile TiF4 and WOxFy without the need for energy-enhanced species. WF6 forms a WOxFy layer on TiO2, acting as a porous surface surfactant layer that fluorinates the TiO2 and allows the volatilization of etching product. At lower process temperatures, WF6 reacts with TiO2 without creating volatiles etch products. By operating at lower process temperatures and incorporating a co-reagent such as Sn(acac)2 or BCl3, we were able to develop a thermally-drive ALEt process.
 2:10 PM Matthew Melillo
Background: Poly(dimethylsiloxane) (PDMS) is one of the most common elastomers, with applications ranging from vibration damping shock absorbers and waterproof sealants to contact lenses, cosmetics, apparel, and cooking materials. Its siloxane backbone endows it with inherently high flexibility compared to the more rigid carbon-carbon backbone found in most polymers, giving it an effective operating range of approximately -100 to 300°C. Fundamental understanding of how small molecule liquids spread on the surface of and absorb into and out of PDMS networks is of critical importance for the design and use of another application – medical devices. Often, researchers use a commercial product from Dow Corning, Sylgard® 184, to make networks of varying degrees of softness or rigidness for studying cell adhesion and migration, but they lack the molecular-level topological and chemical knowledge of the networks. To address this gap, we have systematically studied the effects of polymer molecular weight, loading of tetra-functional crosslinker, end-group chemical functionality, and the extent of dilution of the curing mixture on PDMS network properties and benchmarked our results to the commercial Sylgard product. By applying several swelling and gelation theories to our results, we have demonstrated multiple avenues for estimating the molecular weight between effective crosslinks and have gained fundamental insights into how the molecular-level architecture influences both bulk mechanical and surface properties of model end-linked PDMS.Results: We have produced networks with a wide range of elastic properties, ranging in storage modulus from ~ 50 kPa to ~ 5 MPa, without the addition of filler particles or solvents. The degree of water wetting on these networks was shown to depend on both the modulus of the sample as well as the gel and sol fractions (i.e., the amount of material chemically bound and unbound to the network, respectively). In most aspects, Sylgard and model PDMS behaved similarly, generally following established theories with respect to swelling and modulus. However, some important distinctions do exist. Namely, tougher materials that maintain their damping ability were possible with Sylgard but were nearly impossible to make over the range of variables tested with model PDMS. Additionally, the water contact angles depended strongly on equilibration time with the substrate, taking several minutes to equilibrate, and the degree of hydrophobicity varied significantly depending on minor changes in network formulation.Conclusions: By tuning the aforementioned variables over a wide range, we have developed a “cookbook” of recipes for making PDMS networks of desired gel and sol fractions, storage and loss moduli, and degree of liquid swelling and water wetting. This provides users with the chemical formulations needed to create materials of sufficient mechanical and surface properties that fill their application requirements while maintaining full knowledge of the chemical composition of their materials, which isn’t possible using Sylgard. Furthermore, we have demonstrated multiple approaches to determining the molecular weight between effective crosslinks, an incredibly critical parameter that dictates, in large part, the network topological structure and thus, the bulk mechanical properties of the material. These findings will aid in the design and use of safe PDMS-based materials for medical devices and a variety of other applications that involve liquids interacting with PDMS.
 2:30 PM Daniel Armstrong
Background: Dielectric elastomers (DEs) are a class of electromechanical transducers that can act as actuators, sensors and energy capture devices. They are promising candidates for soft robotics applications due to the potential for large actuation strains (>300%), high coupling efficiency (>60%) and fast (Hz-kHz) response times. Recent breakthroughs in material design using acrylic elastomers[1] and silicone elastomers with carefully tailored architecture[2] have led to free standing actuators that are capable of high performance exceeding that of mechanically preloaded actuators that have historically been required for high performance.Results: A previously unexplored class of materials has been evaluated for applications as dielectric elastomers. Specifically, the material of interest is semi-crystalline olefinic thermoplastic elastomer (OTPEG) that has been softened with the addition of soft-block selective solvent.[3] The elastomer gel is soft, while incredibly tough, and unlike other elastomers used as DEs, these materials have significant strain set and undergo nanoscale restructuring upon strain. We have shown that this can impart two interesting properties for DE actuator applications: 1) inherent mechanical and electromechanical anisotropy for unidirectional actuation designs, and 2) an electromechanical response that suppresses electromechanical instability and snap through instability. Under anisotropic conditioning, uniaxial strains are relatively large (~20% linear) with significant strain anisotropy (>10:1) under no pre-load.Conclusions: Some properties of OTPEGs are not ideal for DEs. These OTPEGs in particular have some limitations due to mechanical integrity of gels at low weight fraction (~25 wt% polymer) and low dielectric constant. Acrylic and silicone elastomers traditionally perform better than polybutadiene and other olefin based rubbers as DEs. The singularly important finding of this work is the potential to control strain stiffening behavior by mechanical conditioning. This design paradigm applies to any elastomer that undergoes substantial hysteresis. We propose to apply this conditioning other semi-crystalline elastomers and elastomer gels (e.g. polyurethane elastomers) with desirable dielectric and mechanical properties for DE actuator applications.References:
1. Niu, Xiaofan, Hristiyan Stoyanov, Wei Hu, Ruby Leo, Paul Brochu, and Qibing Pei (2013) Synthesizing a New Dielectric Elastomer Exhibiting Large Actuation Strain and Suppressed Electromechanical Instability without Prestretching. J. Poly. Sci. Part B: Polymer Physics, 51:197-206.
2. Mohammad Vatankhah-Varnoosfaderani, William F. M. Daniel, Alexandr P. Zhushma, Qiaoxi Li, Benjamin J. Morgan, Krzysztof Matyjaszewski, Daniel P. Armstrong, Richard J. Spontak, Andrey V. Dobrynin, and Sergei S. Sheiko (2016) Bottlebrush Elastomers: A New Platform for Freestanding Electroactuation. S. S. Nat. Mater., 15:183−189.
3. Armstrong, Daniel P., Kenneth P. Mineart, Byeongdu Lee, and Richard J. Spontak (2016) Olefinic Thermoplastic Elastomer Gels: Combining Polymer Crystallization and Microphase Separation in a Selective Solvent. ACS Macro Lett., 5:1273-1277.

2:50 PM Duncan Davis
We created a novel system to macroscopically fold poly methyl meth acrylate sheets using only household, child-safe materials. Using uniform heat, we can fold the sheets into complex 3D origami-derived shapes. These sheets can be folded reliably, precisely, reversibly, and repeatedly. We also created models that predict bending angle of our sample as a function of the rubber band strain, and a model that balances the forces in the system to predict how the sheet will respond to heat and rubber band strain. These models can predict the dihedral angle, onset of folding, final shape, and temperature of the oven. Finally, we created a new programming method that changes how our samples unfold; allowing our samples to unfold into a complex shape the sheet previously held.References:

  1. Davis, D., Dickey, M. D. and Genzer, J. Repeatable Reversible 3D Bilayer Shape Programming with Ablated Hinges (Manuscript in preparation).
3:10 PM Tim Shay
Background: The use of wearable devices in healthcare can greatly benefit from the development of new microfluidic sampling methods for sensing biomarkers in sweat. Sweat contains many useful bioindicators that could enable traditional blood based testing techniques in a non-invasive wearable device. These indicators include glucose (for diabetes monitoring), cortisol (stress monitoring), various ionic species (Na+, K+, Cl for hydration sensing), lactate (athletic performance monitoring) as well as many other biochemicals. Current commercial wearable devices are limited to a combination of motion and heart rate sensors, which provide little insight to the health of the user. There are a few academic endeavors that are creating patches that measure sweat that is released from the body. While these devices are making great progress, they all still have the drawback that they only work during periods of high sweat rate and cannot manage the flow of fluid to direct it away from the sensor after testing. We aim to combine hydrogels with a paper microfluidic network to enable sweat sensing in wearable devices to mitigate both of these problems. Hydrogels will be doped with glycerol to use a high osmotic pressure difference with the body to pump sweat from the body and into our device. Paper microfluidics will then be used to guide the fluid flow through our sensing platform and ultimately evaporate the fluid off on the backside to allow for long-term continual sensing.Results: A microfluidic device was combined with thin biocompatible hydrogel discs equilibrated in saline or glycerol. The hydrogel interfaces with a water-permeable membrane, mimicking skin permeability. The high concentration of solute in the hydrogel creates an osmotic pressure difference across the membrane driving fluid flow through the membrane and into the microfluidic device. The release of this solute from the hydrogel autonomously pumps the fluid into an adjacent microfluidic channel. The osmotic strength of the hydrogel and its interfacial contact area with the membrane controls the flowrate. Continuous withdrawal of the fluid dilutes the concentration of solute in the hydrogel, which decreases the flowrate over time. Initial testing has shown that this sensing platform can pump biologically relevant and accurate levels of glucose across the membrane and through a microchannel to a reservoir interfacing a glucose sensor. We have also created a test method where flowrate through paper microfluidic strips could be observed based on evaporative pumping on the back end. Both flow rate and the operational limits based on hydrodynamic resistances and salt accumulation were modeled and verified through experimental testing. Electrical and colorimetric sensing were both demonstrated on these paper strips. Lastly, we have combined these paper microfluidic strips with our osmotically doped hydrogels and have begun testing these devices on human subjects.Conclusions: We have demonstrated the ability of hydrogel and paper microfluidics to be used to passively pump fluid in a lab setting. Initial testing on human subjects has been performed with promising results. Future work will involve embedding glucose and lactate electrodes into the microfluidic platform to allow for continual real-time sensing on the body.

Poster Session/Mixer 3:30 – 5:30 PM


Biotechnology

David Chang 

Background: Mammalian cells are commonly cultured in commercial 10,000 L bioreactors to produce therapeutic proteins for treatment of diseases such as arthritis, multiple sclerosis, and diabetes. As the biotechnology industry continues to push culture densities higher to maximize product yield, higher aeration levels are required. Additional aeration leads to harsher environments for cells, leading to the need for improved shear protection strategies to minimize cell damage. Nonionic surfactants are routinely used in mammalian cell culture to protect cells from the hydrodynamic conditions of sparged bioreactors. We investigate surfactant-cell interactions by characterizing cell membrane fluidity at various surfactant concentrations using fluorescence anisotropy. We also demonstrate the application of a novel concentric cylinder mixer (CCM) assay to quantify the relative shear sensitivity of a CHO cell line in a production bioreactor.

Results: Despite the widespread use of surfactants for shear protection in cell culture, the mechanism of protection is poorly understood. We show that membrane rigidity increases steeply with increasing surfactant concentration, eventually reaching a plateau at high concentrations. The membrane rigidity correlates with cell shear resistance measured using CCM. This assay is based on release of lactase dehydrogenase (LDH), an enzyme marker for cellular damage. Compared with other methods to characterize shear sensitivity, the CCM assay requires low sample volume and minimal processing time. Additionally, a time course study of cells in a production bioreactor indicates that cell shear sensitivity dramatically increases upon reaching peak viable cell density. This increased sensitivity may be a result of depletion of surfactant, accumulation of waste in the medium, or physiological changes in the cell. With a simple shift in shear protectant concentration, we demonstrate increased harvest viability resulting in decreased cellular debris, decreased foam stability, and a two-fold reduction in LDH upon harvest.

Conclusions: Our results expand the fundamental understanding of surfactant-cell interactions to guide further optimization of shear protection in mammalian cell culture. The application of our novel shear assay can aid in optimizing process parameter set points, enhancing medium formulations for process robustness, and also for the selection of shear resistant cell lines for process development.

Jason Coffman 

Vaccine technologies have evolved over the 20th century shifting away from whole or attenuated pathogens to pathogen protein, subunit, vaccines that are safer and more cost efficient to produce [1]. However, while subunit vaccines are safer, the subunit alone generally is not in proper context nor does it generate strong enough immune response to create long term immunity [1]. Particles provide a platform for displaying the protein subunits, increasing their immunogenicity and mimicking their natural display on a live virus [2]. While nanoparticles represent a great platform for optimizing and displaying proteins very few particles allow for the optimizing of multiple parameters. Particle Replication In Non-wetting Templates (PRINT) technology allows for the creation of polymeric nanoparticles with exact size, shape, and polymeric composition [3]. Using PRINT technology we have engineered the particle size/shape, charge, and protein conjugation/ adsorption for a recombinant E protein of the dengue virus (DV-recE). Particle size/shape was first tested as a particulate vaccine in vivo by adsorbing DV-recE to PLGA nanoparticles. In order to test particle conjugated DV-recE buffer conditions were found that minimized adsorption to a hydrogel particle formulation. With adsorption controlled recE was either conjugated (EDC/s-NHS) or adsorbed to cationic or anionic hydrogel PRINT particles, which were tested as a particulate vaccine in vivo.

Results: 80 x 320 nm cylindrical nanoparticles have been chosen for the particle size/shape. A buffer of 0.15% Tween-20 (v/v) and 2.5% glycerol (v/v) was found to stabilize the recE protein and minimize adsorption background under conjugation conditions. RecE conjugated anionic nanoparticles have higher IgG and neutralizing antibody titers than all other options.

Conclusions: 80 x 320 nm anionic hydrogel particles with recE conjugated to the particle surface in protein stabilizing buffer shows better results than adsorbed or conjugated recE cationic nanoparticles and will be optimized further.

References:

  1. Marie-Luce De Temmerman, Joanna Rejman, Jo Demeester, Darrell J. Irvine, Bruno Gander, and Stefaan C. De Smedt (2011). Particulate vaccines: on the quest for optimal delivery and immune response. Drug Discovery Today., 16: 13-14, 569,-582
  1. Martin F. Bachmann and Gary T. Jennings (2010). Vaccine delivery: a matter of size, geometry, kinetics and molecular patterns. Nature Reviews Immunology., 10, 787-796
  1. Jason P. Rolland, Benjamin W. Maynor, Larken E. Euliss, Ansley E. Exner, Ginger M. Denison, and Joseph M. DeSimone (2005). Direct fabrication and harvesting of monodisperse, shape-specific nanobiomaterials. Journal of the American Chemical Society., 127, 10096-10100

C.J. Duran 

Background: Methane (CH4) gas is often vented or flared at sources such as oil wells and landfills because the low value as a fuel does not justify building infrastructure to collect and transport the gas. The value of CH4 gas could be increased by conversion into valuable liquid products which are more economically feasible to collect and transport. Bacteria called methanotrophs can assimilate and convert CH4 carbon into valuable liquid products, but common industrial fermentation techniques have the following problems: They need large amounts of water, require a high power input to achieve gas-liquid mass transfer of poorly soluble CH4 gas, and require energy intensive separation of product from waste biomass. Our lab addresses these problems by immobilizing microorganisms in thin coatings on the surface of an inexpensive, porous, and flexible substrate such that biocatalysis can take place in a continuous falling film reactor (FFR). A FFR can be operated using very little water and with a low power input because the gas has only a thin layer of liquid to pass through to contact the cells. Because the cells are immobilized and unable to multiply, no waste biomass is generated and the secreted product is separated from biomass and accumulates in the flowing liquid phase. We have chosen the methanotroph Methylomicrobium alcaliphilum 20Z which is being engineered by collaborators at DO NREL (Golden, CO) to convert CH4 into valuable liquid products. The aim of this project is to develop a prototype FFR and optimize reactivity by efficiently immobilizing M. alcaliphilum 20Z as a biocatalyst.

Results: A small prototype reactor was constructed and a method to quantify adhesion of cells to a paper substrate was developed. Preliminary results show that M. alcaliphilum 20Z has the highest affinity for a very rough, cotton fiber paper which retains 90% of cells under a shear stress of 5 N/m2. Cell retention also decreases as the shear stress is increased. The prototype FFR has uniform falling liquid films for low Reynolds number (Re from 20-100) where many other chemical FFR with metal surfaces typically struggle with film uniformity. Oxygen transfer is studied in the system at low Re. The mass transfer coefficient at low flow (Re=20) was determined to be > 7.0×10-5 m s-1 which compares favorably with empirically predicted values.

Conclusions: Surface structure and chemical attributes of the paper substrate are shown to significantly affect adhesion of cells to the surface. The effects will be studied more thoroughly in the future by creating custom substrates with controlled parameters. Greater adhesion may also be achieved by expressing surface proteins in M. alcaliphilum 20Z with high affinity towards cellulose. Falling films at low Re have been well studied because the mass transfer coefficients always exceed what is predicted by theory. The mass transfer is very efficient at low Re due to the nature of the wavy liquid-gas interface. The prototype FFR performs as predicted by empirical correlations in literature and will help achieve efficient CH4 conversion at low power input if M. alcaliphilum 20Z can be optimally immobilized. This research will help create a new energy efficient biological route for greenhouse gas remediation and carbon recycling by engineering highly reactive biocatalysts for recovering CH4 from a variety of sources such as oil wells, landfills, and agricultural waste.

Thomas Jacobsen 

Background: Tools for regulating gene expression have been widely developed for single-celled organisms, such as bacteria and yeast. However, these genetic tools are currently limited or have yet to be established in more complex organisms.

Results: Here we describe a potential gene regulatory tool to be adapted in Drosophila melanogaster: self-cleaving hammerhead ribozymes. Self-cleaving ribozymes are natural RNA constructs that can undergo a phosphodiester cleavage reaction, resulting in mRNA cleavage and degradation. To implement fine-tuning capabilities for this genetic tool, various “competing sequences” can be cloned upstream of the ribozyme. Depending on thermodynamics, these “competing sequences” can interact with a major stem of the ribozyme through Watson-Crick base pairing, thus allowing for various conformational changes of the ribozyme structure. Since the cleavage activity of the ribozyme is largely dependent on the kinetics of the cleavage reaction, as well as the thermodynamics of the “competing sequences”, the level of gene expression can be predicted and tuned using various sequences.

Conclusions: Multiple ribozyme constructs were cloned either upstream or downstream of gfp, which was under the control of a constitutive promoter. These constructs were transiently transfected into HEK293T cells. The addition of different “competing strands” resulted in variable expression of GFP, but also appeared to interfere with its translational activity. Future work will be conducted to analyze the thermodynamics of the “competing sequences”, as well as to incorporate these tools to study a synthetic network mimicking the Bicoid/hunchback network.

Ashton Lavoie 

Background: Capture of host cell proteins (HCP) from typical protein expression systems is important for a wide variety of applications in biotherapeutics. Concerns regarding HCP impurities stem from a wide variety of possible risks that they pose, including immunogenic response, [1] reduced efficacy, [2] and low shelf-life due to enzymatic cleavage. [3] As a result of these concerns, purification processes generally require the removal of 3 to 5 logs of HCP. For downstream processing (DSP) of many biotherapeutics, the removal of impurities including HCP is largely achieved through capture of the product of interest in bind-and-elute chromatography steps, which allow non-binding impurities to flow through thus achieving both impurity removal and concentration of the target product. [4,5,6] While product capture can be highly effective in the removal of impurities, it introduces a number of concerns for bioprocesses that could be addressed with a robust flow through (FT) chromatography processing step coupled with a concentration step(s). FT chromatography involves the specific binding of impurities to the stationary phase, allowing the product of interest to flow through and enabling “straight-through” processing that could reduce processing time, buffer usage, and formation of product-related impurities in downstream processing.

Results: Removal of individual HCP species was tracked by LC-MS/MS relative quantification using iBAQ methods to determine removal over commercially available chromatography resins, including Capto Q, Capto DEAE, Capto Adhere, Capto S, CM Sepharose FF, and Capto MMC, in addition to novel HCP-binding peptide ligands identified by phage display, synthesized, and coupled to a chromatographic resin. By Bradford analysis, commercial resins showed < 0.5 LRV with the exception of Capto Adhere at ~ 1 LRV, while all peptide resins tested showed > 0.5 LRV.

Conclusions: Our results indicate that commercially available technologies are not sufficient for removing extracellular HCP when operating strictly in flow-through mode, as the maximum log reduction observed under the conditions tested was ~1 LRV, and a total of 24 proteins were identified as poor binders on all six commercial resins tested, including highly abundant species. HCP-binding peptide ligands were found to have equivalent or better HCP clearance compared to commercial resins without resin optimization.

References:

  1. Wang, X. et al. (2009) Bioeng. 103 (3), 446–458.
  1. Mechetner, L. et al. (2011) Chromatogr. B 879 (25), 2583–2594.
  1. Lee, K. et al. (2015) Reduction of Lipase Activity in Product Formulations.
  1. Shukla, A. et al. (2007) Chromatogr. B 848, 28–39.
  1. Tao, Y. et al. (2014) Bioeng. 111 (7), 1354–1364.
  1. Maria, S. et al. (2015) Chromatogr. A 1393, 57–64.

Laura L. Lee 

Background: Extremely thermophilic organisms have a promising, but yet unrealized, role to play in the deconstruction of lignocellulose for microbial biofuel production. Discovery of their potential has been pursued through genomics, pan-genomics, and metagenomics to further characterize ‘Caldi World’.

Results: First, three new species’ genomes (Caldicellulosiruptor sp. str. Rt8.B8, Caldicellulosiruptor sp. str. Wai35.B5, and Caldicellulosiruptor sp. str. NA10) were examined for the presence of novel glycoside hydrolases (GH) and surface layer homology (SLH) domain proteins. One of the most interesting finds was a multi-modular enzyme with a GH12 domain. These species were also investigated for the main Caldicellulosiruptor glucan degradation locus, where different arrangements of CAZyme gene domains were identified, as well as novel cellulose binding proteins (tāpirins) [1]. Next, we characterized the Caldicellulosiruptor core and pan-genomes with the GET_HOMOLOGUES [2] software in order to determine the genetic diversity. The core genome size is slowly decreasing, reaching a plateau (1284 genes). However, the pan-genome is open, the size still increasing as the number of sequenced isolates grows. Finally, samples from Obsidian Pool in Yellowstone National Park were metagenomically sequenced to identify thermophilic cellulases. 16S rRNA and Illumina DNA sequences revealed novel enzymes and organisms of interest, while PacBio sequencing has been used to obtain longer reads and potentially closed genomes. Due to subculture growth at higher temperatures and selection for cellulose degradation, the complex metagenomics samples were found to become primarily co-cultures containing at least one Caldicellulosiruptor species. Preliminary solubilization assays on switchgrass showed that most of the enriched metagenomic communities performed better than the native Caldicellulosiruptor obsidiansis and one sample, also consisting of a Caloramator species, degraded more than the highly cellulolytic Caldicellulosiruptor bescii.

Conclusions: While the decreasing core genome indicates that our understanding of what genes classify a microbe as a ‘Caldi’ is growing, we are still identifying novels genes, as indicated by the new species’ novel GH12 domains, open pan-genome, and enriched metagenomic cultures.

Overall, these results bring a more comprehensive understanding of the Caldicellulosiruptor genus, as well as shed light on novel CAZymes and proteins in both characterized and novel species, which could have important roles in how these microbes degrade polysaccharides.

References:

  1. Blumer-Schuette SE, et al., “Caldicellulosiruptor core and pan genomes reveal determinants for non-cellulosomal thermophilic deconstruction of plant biomass,” Bacteriol. 194(15), 4015-4028, 2012.
  2. Contreras-Moreira B, Vinuesa P., “GET_HOMOLOGUES, a versatile software package for scalable and robust microbial pan-genome analysis,” Appl. Environ. Microbiol. 79(24), 7696-7701, 2013.

 

Shah Md Toufiqur Rahman 

Background: Signal transduction is a complex and highly conserved intracellular process that regulates important biological responses and cell fate decisions. The ability of a cell to perceive and correctly respond to its extracellular environment is the basis of tissue homeostasis and normal physiological functions. Three important mitogen-activated protein kinase (MAPK) signaling pathways — which control cellular proliferation, differentiation, apoptosis and survival — are extracellular signal regulating kinase (ERK), c-Jun N-terminal kinase (JNK) and stress activated protein kinase (p38/SAPK). Dysregulation of these MAPKs are commonly implicated in different types of cancer. It is widely hypothesized that the three canonical MAPK cascades are co-regulated, but the dynamics of each MAPK pathway responding to activation of another have yet to be systematically evaluated. Using an optogenetic approach [1], we aim to dissect these important MAPK signaling cascades and elucidate crosstalk and shared feedback mechanisms between them.

Results: Experimental observation reveals a unique mechanism of p21-activated protein kinases (PAKs) mediated non-canonical activation of MEK/ERK signaling. We have also been able to investigate the negative cross-talk between ERK and p38 signaling pathways using photo-activatable caged MKK6. Uncaging of MKK6 only activates p38 MAPK, not JNK stress activated protein kinase and it also reduces ERK kinase activities which do not recover after p38 kinase activity inhibition.

Conclusions: Leveraging optogenetic approach, we have been able to introduce specific and acute gain in function perturbation on a single node of entire signaling network. This new experimental strategies reveals more cleanly distinct modes of crosstalk among three MAPK cascades.

References:

  1. Gautier, A., Deiters, A., & Chin, J. W. (2011). Light-activated kinases enable temporal dissection of signaling networks in living cells. Journal of the American Chemical Society, 133(7), 2124-2127.

Adam Wallace 

Background: We intend to engineer Chlamydomonas reinhardtii to survive dry-storage and retain photosynthetic reactivity upon rehydration in thin, adhesive coatings as a route to increase photoefficiency and decrease algal water requirements. Using convective sedimentation assembly (CSA), we are depositing closely packed, non-growing C. reinhardtii CC125 as adhesive films that exceed the density of photobioreactors. A C. reinhardtii paste, high Tg latex particles, low Tg latex binder particles, and osmo-protective disaccharides are combined and deposited by CSA on flexible polyester (PE). PE pre-coating with low Tg latex binder is used to improve adhesion and enable uniform deposition. Through immobilization and restricting growth, cells can be stabilized as CO2-absorbing biocatalysts for 100s to 1,000s of h [1]. These coatings can have a highly organized nanoporous microstructure and combine different cell types to minimize water requirements and maximize incident sunlight and CO2 absorption [2, 3].

Results: We have taken the first steps in demonstrating novel adhesive, flexible, and photoreactive coatings of algae. CSA biocomposite coatings of C. reinhardtii were made on flexible PE using acrylic/divinylbenzene particles (~5 µm diameter, 2.2% solids), biocide-free Setaqua 6776 (Nuplex BV) acrylic latex binder (~96 nm diameter, 5% solids), sucrose (0.1 g/mL), and C. reinhardtii CC125 (5-10 µm diameter, 9.8% dry solids). The PE was pre-coated with a 4.0±2.3 µm thick primer layer of 6776 binder. Coating void space (>1/2 cell diameter) measured by image analysis was 39.8±8.8%, and dry thickness was 10.2±0.9 µm. Coatings were uniform and did not crack or delaminate upon sharp angle flexing. Coatings demonstrated 9.57±0.001% absorptance of 400-700nm light measured by integrating sphere spectrophotometry. While this absorptance is low, it should be expected for a single monolayer of cells and particles.

Conclusions: CSA-deposited coatings of C. reinhardtii, and bimodal blend latex particles with sucrose on flexible polyester are feasible. A mechanistic understanding of particle deposition and ordering is required to increase cell packing per unit area. Future work will focus on optimizing light interaction, light absorption, and reactivity. Additionally multi-layer coatings will be made, and algae will be engineered for desiccation tolerance to preserve reactivity during dry storage.

References:

  1. Bernal, O.I.; Mooney, C.B.; Flickinger, M.C. (2014). “Specific Photosynthetic Rate Enhancement by Cyanobacteria Coated Onto Paper Enables Engineering of Highly Reactive Cellular Biocomposite “Leaves””. Biotechnology and Bioengineering 111, no. 10: 1993-2008.
  1. Gosse, J.L.; Engel, B.J.; Hui, J.C-H.; Harwood, C.S; Flickinger, M.C. (2010). “Progress Toward a Biomimetic Leaf: 4,000 h of Hydrogen Production by Coating-Stabilized Nongrowing Photosynthetic Rhodopseudomonas palustris”. Biotechnology Progress 26, no. 4: 907-918.
  1. Flickinger, M.C., Bernal, O.I., Schulte, M.J., Jenkins Broglie, J., Duran, C.J., Wallace, A., Mooney, C.B., Velev, O.D. 2016. “Biocoatings: Challenges to Expanding the Functionality of Waterborne Latex Coatings by Incorporating Concentrated Living Microorganisms”. Journal of Coating Technology and Research (submitted).

Matthew Waller 

Kye Won Wang 

Background: Hydrogels are three-dimensional, cross-linked networks of water-soluble chains. They have been studied as a drug delivery carrier for the benefits to be biologically harmless to the body when they are degraded. Among the many forms of hydrogels, hydrogel which is made from oligonucleotide modified polymer has attracted a lot of interest since DNA base pairs serve as a cross-linking agent and a network structure is formed automatically. We develop an implicit-solvent and coarse grained DNA model that enables molecular dynamics simulation of the spontaneous self-assembly between an oligonucleotide and its complementary strand. We model four different nucleotides that make up an oligonucleotide as single coarse grained molecules each and design to follow the base paring rules; adenine always pairs with thymine and cytosine always pairs with guanine. We also model two types of star-shaped poly(ethylene glycols) (PEG-A and PEG-B) precursors covalently functionalized on all ends with two different oligonucleotides and a third oligonucleotide chain (aptamer cross-linker) which is complementary to the sequence of the oligonucleotides in PEG-A and PEG-B to understand the formation of hydrogels.

Results: Preliminary simulation results show that the association and dissociation transitions between single-stranded and double stranded conformations of an oligonucleotide are reproduced, and the transition temperature has changed according to the sequence of nucleotides. Initially-uncrosslinked PEG-A, PEG-B, and cross-linker oligonucleotide bind to each other and form a network structure below the transition temperature due to their Watson-Crick pairing. Finally, the physical properties such as percolation and pore size of the already-formed hydrogel are analyzed. These simulations are being used to supplement experiments for Dr. Tania Betancourt and coworkers at Texas State University who have shown that the DNA functionalized hydrogels are suitable for use in drug delivery applications.

Conclusions: A coarse grained DNA model for describing its thermal stability is developed, and this model is expanded to the crosslink of DNA conjugated hydrogel precursors. The network structure via DNA hybridization is analyzed and investigated to apply to drug delivery applications.

Benjamin Zeldes 

Background: Members of the crenarchaeal order Sulfolobales are thermoacidophiles, growing best in water above 70°C and below pH 3. Members of the order exhibit unique metabolisms that help adapt them to their extreme environment. Many are capable of lithotrophic growth by oxidation of sulfur, and all share genes and a regulatory system for the 3-hydroxypropionate/4-hydroxybutyrate (3HP/4HB) carbon fixation cycle [1], which appears to be unique to the crenarchaeota. Current understanding of sulfur lithotrophy and carbon fixation pathways in the Sulfolobales is a result of a combination of genomic, transcriptomic, and enzyme activity studies in the native organisms, as well as recombinant expression of individual enzymes. Our lab has expanded this work using newly developed genetic systems to clone recombinant lithoautotrophic pathways into archaeal hosts, allowing us to study how multiple genes interact, and how activity of these pathways affects the organism as a whole.

Results: Recombinant versions of the first three enzymes of the 3HP/4HB cycle were functional in Pyrococcus furiosus, but we were able to show that additional accessory enzymes were necessary for maximal activity [2]. For more recent studies we have taken advantage of a new genetic host within the Sulfolobales themselves: Sulfolobus acidocaldarius. While current lab strains of S. acidocaldarius do not grow autotrophically, comparison with the genomes of related species that do suggests only a few genes are missing. A single gene insertion was sufficient to allow S. acidocaldarius to oxidize elemental sulfur to sulfuric acid, and we expect a few additional genes to allow it to conserve energy from this process, conceivably recovering fully autotrophic growth.

Conclusions: A metabolically engineered lithoautotrophic S. acidocaldarius strain could use energy from sulfur oxidation to produce chemicals from CO2. However, a more thorough understanding of the metabolic steps is needed and we are making headway in that regard. In future work, we will connect sulfur oxidation to a thermophilic pathway for acetone production to demonstrate the proposed concept.

References:

  1. Leyn, S.A., Rodionova, I.A., Li, X., and Rodionov, D.A. (2015). Novel Transcriptional Regulons for Autotrophic Cycle Genes in Crenarchaeota. Bacteriol. 197: 2383–2391.
  1. Lian, H., Zeldes, B., Lipscomb, G., Hawkins, A., Han, Y., Loder, A., Nishiyama, D., Adams, M., Kelly, R. (2016) Ancillary contributions of heterologous biotin protein ligase and carbonic anhydrase for CO2 incorporation into 3-hydroxypropionate by metabolically engineered Pyrococcus furiosus. Biotechnol. Bioeng. 113: 2652–2660.

Kinetics and Materials

Prajesh Adhikari 

Background: In the past decade, nanodiamonds (ND’s) have emerged as a novel class of 0-D nanofillers due to its unique properties such as high surface area, tailorable surface functionality, biocompatibility, superior hardness, mechanical strength and thermal conductivity. However, much remains unknown about ND dispersion behavior and its response to nanocomposite processing techniques. Tuning interfacial energy of these 0-D nanofillers to promote dispersion and enhance nanofiller-polymer wetting in the nanoscale is an essential prerequisite in designing polymer nanocomposites with reinforced macroscopic properties. To this end, we hypothesize that comparison of adhesion energies between polymer-nanofiller and cohesion energies between nanofillers could serve as one of the essential predictors of final performance of polymer-ND nanocomposites.

Results: Herein, we investigate the extent of polymer nanofiber composite property enhancement using nanodiamond fillers with different functionalities. Polyvinyl alcohol (PVA) nanodiamond dispersions prepared using solution intercalation technique was used to synthesize PVA nanofibers containing up to 3 wt.% loadings of carboxylated and hydroxylated nanodiamonds using facile electrospinning. The resulting polymer nanofiber composites show drastically different macroscopic properties. For carboxylated nanodiamonds, the thermal stability of the system was observed to increase due to a strong interaction between filler and the polymer via hydrogen bonding as observed in spectroscopy. However, thermal stability of hydroxylated nanodiamonds decreased possibly due to changes in crystallinity in the material. We explain these differences using surface energies of the nanofillers, wherein a balance between adhesive and cohesive energies dictates the final performance of the material. We further propose modification of nanoparticle with matrix polymer to promote interfacial adhesion between polymer-nanofiller.

Conclusions: The findings of this study could offer additional insight into the design of interfaces for functional polymer-ND nanocomposite materials.

Stephen Barilovits 

Background: The Biax Spunblown® process is a unique variant of the meltblowing process. Molten polymer is extruded from an array of outlets each of which is individually surrounded by a concentric high velocity air stream. The Spunblown® process purportedly accommodates a wide range of polymer resins, produces fibers of similar size to meltblown, and uses reduced air volume as compared to traditional meltblowing. However, despite the aerodynamic differences from traditional meltblowing, the Spunblown® web formation process has been the study of little published research.

Results: Infrared thermography has been used to determine fiber temperature during the spinning process and may be used to estimate fiber attenuation and determine appropriate die-to-collector distance. A detailed three dimensional air temperature and velocity profile has been established for an array of supplied temperatures and air cavity pressures. The effect air temperature, polymer temperature, air speed, and polymer throughput have been related to fiber diameter distribution and distance to solidification. Fiber diameter distributions have been investigated as a functions of an array of processing conditions and spinning stabilities.

Conclusions: Results from IR image analysis indicate substantial heat transfer occurs between the air and molten polymer prior to spinning. Additionally, IR thermography demonstrates that larger fibers cool more slowly than more narrow fibers. Air profiling reveals that air heat dissipates more quickly than does air momentum, which is especially true very close to the spinnerets. Decreases in polymer throughput most significantly reduced fiber diameters, but higher air temperature also lowered diameters substantially, and higher air pressures to a lesser extent. Spinning instability may significantly contribute to fiber size reduction.

Arnab Bose 

Background: Hemicellulose is one of the major components of lignocellulosic biomass. Torrefaction of hemicellulose is an important process because it provides a potential approach to prepare the fast pyrolysis feedstock [1]. A recent study has shown that in the torrefaction-process temperature- range (200°C to 300°C), hemicellulose decomposes to higher degree than cellulose and lignin; the two other components of lignocellulosic biomass [2]. On the other hand, due to the wide variability in the amounts of constituent monomers and polymers in hemicellulose, torrefaction-kinetics of hemicellulose is complex and it is not well-understood [3]. Thus, xylose, mannose and other monomer components of hemicellulose are adopted as the model compounds to explore the torrefaction kinetics of hemicellulose. The present study is mainly focused on the torrefaction of mannose, a hexose constituent of hemicellulose.

Results: Torrefaction of mannose is investigated over the temperature-range of 200°C to 300°C. Overall torrefaction kinetics is measured by thermogravimetric analysis and calorimetry (SDT Q600, TA Instruments) with linearly ramped temperature increase such as 5, 10, 15 and 20°C/min. Pyrolysis products from the fast pyrolysis (Pyroprobe 5200, CDS Analytical) at different temperatures (200, 250 and 300°C ) are analyzed in two dimensional gas chromatography and time-of-flight mass spectroscopy (Pegasus 4D, Leco). Major products at 250°C are shown to include anhydro-sugars, hydroxymethylfurfural, dihydroxyacetone, glycidol, acetic acid and carbon dioxide. Product distribution is observed to be more complex at higher temperature. Differences in the molecular weights between mannose and the identified products reveal the occurrences of pericylic reactions such as water, hydrogen, formaldehyde eliminations, ring breakage and their combinations. Simultaneously, computational quantum chemistry (Gaussian 09 and GaussView) is used to predict transition states. The transition states have been modeled and associated activation energies are calculated at a B3LYP/6-31 G(d,p) level of theory.

Conclusions: Torrefaction kinetics of mannose consists of various pericylic reaction pathways. At higher temperatures, accessibility to larger numbers of reaction pathways leads to higher numbers of products. However, quantum chemistry modeling needs to be done in order to build reaction pathways leading to the major observed products and to describe the reaction observations made by experiments.

References:

  1. Chew, J. J., Doshi, V., (2011), Recent Advances in Biomass Pretreatment – Torrefaction Fundamentals and Technology, Sustain. Energy Rev., 15, 4212–4222.
  1. Chen, W.H., Kuo, P.C., (2011), Torrefaction and Co-torrefaction Characterization of Hemicellulose, Cellulose and Lignin as well as Torrefaction of Some Basic Constituents in Biomass, Energy, 36, 803–811.
  2. Zhou, X., Li, W., Mabon, R., Broadbelt, L. J., (2016), A Critical Review on Hemicellulose Pyrolysis, Energy , Wiley Online Library, DOI: 10.1002/ente.201600327

Jennifer Clark 

Background: In order to reduce the computational cost of molecular dynamics simulations, atoms are often grouped into coarse-grained beads. The force-field parameters for these groups of atoms must represent all nonbonded interactions, except the coulombic potential. Top-down methods of parameterizing are an attractive option to define these interactions, as fitting from experimental data rather than theoretical models, ideally ensures proper description of the forces at play. All parameters then require experimental data for each bead-bead interaction and an iterative fitting routine. By expanding the Berthelot combining rules to include all nonbonded interactions, we produce a bottom-up parameterization method. Coarse-grained parameters are directly calculated from ab initio determined properties, greatly reducing parameterization effort. We can derive combining rules for any pair potential model, although this work focuses on their application for the Mie potential. Our combining rules will predict Mie potential cross-interaction parameters that have been fit to experimental data.

Results: We find that our combining rules qualitatively reproduce interaction energy as a function of bead type. This is a notable improvement when compared to the values predicted from the Berthelot combining rules. However, the resulting parameters are not satisfactory in quantitatively matching the parameters fit from experimental data. This difference becomes greater in the case of ionic systems where a dielectric constant is implemented in the simulation.

Conclusions: Our combining rules offer a limited ability to replicate experimentally fit interaction parameters. We can improve our method in two ways. First, by altering the expression of solvent effects in the combining rules. Second, by reassessing how ab initio calculations are used to determine bead properties. If implementation of these improvements does not produce adequate results, these combining rules have the potential to be the basis of a new coarse-grain force-field that is more easily implemented than the currently available alternatives.

Cathryn Conner 

Background: Our group is developing a new generation of functionalized environmentally benign nanoparticles for biotechnology. Nanoparticles are being increasingly used in industries such as agriculture, but the present nanoparticles are usually inorganic and toxic to the environment; although they can successfully deliver nutrients and active ingredients, they remain in the environment long after they have fulfilled their purpose. Unlike these traditional nanoparticles, environmentally benign nanoparticles (EbNPs) made of lignin can degrade after they have been used, so there is no toxic effect. These nanoparticles were developed in my group by Alexander Richter and have already been investigated as a form of biomedical treatment [1]. Silver ions were infused into the lignin core and coated with polyelectrolyte for use as an antibacterial; this was done to reduce the usage of silver nanoparticles, which remain in the environment causing damage by continuously releasing more silver ions. An ideal coating to change the surface charge of these nanoparticles would be one made of bioadhesives, including the biopolymers chitosan and cutin.

Results: We are currently investigating the properties of chitosan to change the surface charge of EbNPs from negative to positive to help them adhere to the negatively- charged surfaces of leaves. Our model surface demonstrates pronounced differences in adhesive properties and spreading patterns between non-functionalized nanoparticles and EbNPs coated with chitosan.

Conclusions: We have found that coating EbNPs with chitosan successfully changes surface charge and spreading pattern on glass slides. We aim to target specific features on leaf surfaces, such as trichomes and stomata, based on customized nanoparticle-leaf component interactions.

References:

Richter, Alexander P., Joseph S. Brown, Bhuvnesh Bharti, Amy Wang, Sumit Gangwal, Keith Houck, Elaine A. Cohen Hubal, Vesselin N. Paunov, Simeon D. Stoyanov, and Orlin D. Velev. “An Environmentally Benign Antimicrobial Nanoparticle Based on a Silver-infused Lignin Core.”Nature Nanotech Nature Nanotechnology 10.9 (2015): 817-23.

Ryan B. Dudek 

Background: Increased availability of light alkanes from shale gas has sparked interest in producing critically important olefins (e.g. ethylene, propylene) from the corresponding alkane feedstocks. Steam cracking of ethane and propane are promising processes for producing olefins from corresponding paraffins, but yields are thermodynamically limited by the reaction equilibia [1], [2]. The current study investigates an alternative approach to olefin production in which a metal oxide-based redox catalyst is employed in a cyclic redox process to drive greater-than-equilibrium olefin yields via selective hydrogen combustion (SHC) [3]. The incorporation of exothermic SHC leads to improvements in both material and energy efficiency. Here, we aim to establish tunable SHC behavior in metal oxide redox catalysts; we use materials based on manganese due to their attractive redox properties in related applications [4]. The effects of promoters on the SHC properties of these metal oxides are comprehensively evaluated [5].

Results: Selective hydrogen combustion (SHC) properties of the tested redox catalysts can be tuned by changing (a) bulk metal oxide; (b) type and weight loading of promoters; and (c) operating temperature. Optimal temperature for SHC behavior increases over the range 600°C to 800°C by changing the oxide substrates. Addition of promoters are shown to effectively tighten the SHC temperature range by inhibiting carbon oxidation and improves upon SHC performance of unpromoted bulk metal oxides across all materials tested. The amount of hydrogen combusted can be controlled by varying gas contact time and operating temperature. Reduced gas residence time and reduced reaction temperature generally lead to higher H2 combustion selectivity.

Conclusions: The materials tested in this study are suitable for application in a cyclic redox process for the production of ethylene and propylene from the corresponding paraffins. Promoted Mn oxides may be employed as redox catalysts along with dehydrogenation catalysts to selectively combust hydrogen and increase olefin yields while offsetting energy requirements for the endothermic dehydrogenation reaction. These redox catalysts can be designed and implemented to operate optimally at process conditions where olefin formation is favored, granting flexibility in process design.

References:

  1. Cavani, F.; Ballarini, N.; Cericola, A. “Oxidative dehydrogenation of ethane and propane: How far from commercial implementation?” Catalysis Today. 2007, 127, 113–131.
  1. Grasselli, R.K.; Stern, D.L.; Tsikoyiannis, J.G. “Catalytic dehydrogenation (DH) of light paraffins combined with selective hydrogen combustion (SHC). II.” Applied Catalysis A: General. 1999, 189, 9–14.
  1. Late, L.; Thelin, W.; Blekkan, E.A. “Selective combustion of hydrogen in the presence of hydrocarbons. Part 2. Metal oxide based catalysts.” Applied Catalysis A: General. 2004, 262, 63–68.
  1. Mattisson, T.; Jing, D.; Lyngfelt, A.; Ryden, M. “Experimental investigation of binary and ternary combined manganese oxides for chemical-looping with oxygen uncoupling (CLOU).” Fuel. 2016, 164, 228–236.
  1. Neal, L.M.; Yusuf, S.; Sofranko, J.A.; Li, F. “Oxidative Dehydrogenation of Ethane: A Chemical Looping Approach.” Energy Technology. 2016, 4 (10), 1200–1208.

Barbara V. Farias 

Background: Root-knot nematodes are economically devastating parasites which are able to infect a wide variety of crops[1]. Many commonly used nematicides suffer from poor target specificity and are often toxic and environmentally unsafe[2]. Abamectin is a widely-used nematicide which has shown low toxicity to non-target organisms, with many studies supporting its safe agricultural use[3][4]. However, abamectin’s poor mobility in soil makes it unable to fully protect the root system[5]. To address this issue, we have developed a method for more localized delivery of abamectin by coating soybean seeds with electrospun polymer nanofibers containing abamectin. Electrospinning consists of applying an electrical field to a polymer solution to draw out fibers, which collect to form nonwoven mats. The fiber diameters are within the nanoscale range, causing the coatings to have a high surface-to-volume ratio that facilitates delivery applications.

Results: We were able to directly electrospin polymer nanofiber mats on seeds by turning and rotating their position periodically. We performed germination trials on coated soybean seeds and showed that the presence of the nanofiber coating does not prevent germination. Active ingredient release studies from the nanofibers containing abamectin show slow release over time without an initial burst.

Conclusions: The polymeric nonwoven mats are suitable for sustained, localized delivery of active compounds to the root system of soybean seeds.

References:

  1. Koenning, S. R. (2010). Suppression of soybean yield potential in the continental United States by plant diseases from 2006 to 2009. Online. Plant Health Progress.
  1. Chitwood, D. J. (2002). Phytochemical based strategiesfor nematode control, Annu. Rev. Phytopathol., 40: 221-249.
  1. Putter, I., Mac Connell, J.G., Preiser, F.A., Haidri, A.A.; Ristich, S.S., and Dybas, R.A (1981). Avermectin: novel insecticides, acaricides and nematicides from a soil microorganism. Experientia, 37(9): 963-964.
  1. Cao,J., Guenther, R.H., Sit, T. L., Lommel, S. A., Opperman, C. H. and Willoughby, J. A. (2016). Development of abamectin loaded lignocellulosic matrices for the controlled release of nematicide for crop protection. Cellulose, 23 (1): 673-687.
  1. Faske, T. R. and Starr, J. L. (2007). Cotton Root Protection from Plant-Parasitic Nematodes by Abamectin-Treated Seed. J.Nematol., 39 (1): 27-30.

Koohee Han 

Background: Microbotics may play a breakthrough role for biomedical micron-scale manipulation and surgery, yet the field is still in its infancy because of the lack of means for building robots on the micron scale and supplying power for their actuation. Application of external fields to anisotropic colloidal particles is an innovational approach to address these requirements by assembling structures with desired complexity as well as feasible tunability on the patterns.

Results: We show how polymeric, cube-shaped microparticles with a cobalt (Co) patch along one face can be used in the assembly of a new class of microbotic components that can be dynamically reconfigured and spatially maneuvered using external magnetic fields. Application of external magnetic field may selectively magnetize the Co-coated facets and assemble the metallo-dielectric cubes into linear, multi-cube chains where the Co patches are oriented in series along the center of the assembled chains. More importantly, the polarization patterns of the Co patches can be modulated by tuning field parameters (e.g., field strength, frequency and direction), leading to dynamic reconfiguration of the assembled chains. On this basis we have demonstrated how such field-directed reconfigurable assemblies can be used as a novel micromanipulation tool by making microbot prototypes. Firstly, their potential is illustrated by making a micro-grabber capable of grabbing and transporting microscale objects (e.g., biological cells). The micro-grabber can be remotely and precisely controlled by combining uniform magnetic field controlled folding actuation and field gradient driven spatial navigation. We have also shown that such field-driven microbot assemblies can serve as an analytical tool for colloidal and biological systems.

Conclusions: The dynamic reconfigurability of the assembled clusters at micron-scale can be used to locally probe their microenvironment such as investigating the local organization of liquid crystal molecules and measuring the rigidity of microscopic specimens (e.g., living cells, vesicles). Field-manipulated microrobot clusters may find applications in microsurgery, biological separations and bioinspired colloidal origami. Given the enormous variety of shapes and structures of colloidal building units that can be used in such reversibly actuated active structures, it is likely that they can address a broad range of applications from robotics and micromanipulation to active microswimmers that can be magnetically reconfigurable on-demand.

Vasudev Haribal 

Background: Among the various processes for sustainable hydrogen generation, solar thermochemical water-splitting based on redox cycles of metal oxides represents an attractive approach. A key challenge for this process is the high temperatures needed for thermal decomposition of the metal oxide (>1200 °C) [1]. In addition, the need to balance the oxygen release and water-splitting properties of metal oxides often leads to low steam conversion. A hybrid solar-redox redox process for cogeneration of hydrogen and liquid fuels using methane and solar energy operates at lower temperatures and higher steam conversions [2]. In such a process, a reduced metal-oxide based redox catalyst is used to split water, producing concentrated hydrogen. The resulting (oxidized) redox catalyst is subsequently used to partially oxidize methane (POx step), forming syngas for Fischer-Tropsch synthesis. Over 58% syngas yield in the POx step and 77% steam to hydrogen conversion in the water-splitting step are achieved in a layered reverse-flow reactor configuration using La0.8Sr0.2FeO3-δ (LSF) supported Fe3O4 as the redox catalyst [2], [3]. Further improvements in syngas yield and steam-to-hydrogen conversion are desirable to improve the overall process efficiency.

Results: Density  Functional  Theory (DFT)  calculations  reveal  that  the  equilibrium  oxygen partial pressure (PO2) and oxygen vacancy formation energy (∆Evacancy) of perovskite-structured BaMnxFe1-xO3-δ are significantly different from those of FeO and MnO, and can be manipulated by varying the Fe:Mn ratios in the B-sites. These studies indicate that BaMn0.5Fe0.5O3-δ possesses desirable properties for the hybrid solar-redox scheme. Fluidized bed experiments demonstrate over 90% steam conversion in the water-splitting step and higher than 90% syngas yield in the methane POx step. In-situ XRD experiments show the activity and regenerative capability of BaMn0.5Fe0.5O3-δ under redox conditions. ASPEN Plus® simulations indicate the potential to obtain higher efficiencies than the state-of-the-art hydrogen and liquid fuel production processes with lower CO2 emissions.

Conclusions: We proposed and validated a rational strategy to optimize transition metal oxide based redox catalysts for water-splitting and syngas generation via a hybrid solar redox scheme.

References:

  • C. Chueh et al., “High-Flux Solar-Driven Thermochemical Dissociation of CO2 and H2O Using Nonstoichiometric Ceria,” Science, vol. 330, no. 6012, pp. 1797–1801, Dec. 2010.
  • F. He, J. Trainham, G. Parsons, J. S. Newman, and F. Li, “A hybrid solar-redox scheme for liquid fuel and hydrogen coproduction,” Energy Env. Sci, vol. 7, no. 6, pp. 2033–2042, 2014.
  • F. He and F. Li, “Perovskite promoted iron oxide for hybrid water-splitting and syngas generation with exceptional conversion,” Energy Env. Sci, vol. 8, no. 2, pp. 535–539, 2015.

Amber Hubbard 

Background: Folding and bending are common phenomena found in nature, prominent in the formation of structures ranging from plants to proteins. By harnessing the potential of man-made materials, self-folding structures have applications in everything from biomedical engineering to transportation methods. Past research has focused on the ability to understand self-folding mechanisms of thermoplastics for use in robotic structures or simplistic shape formation [1-3]. Particular interest in self-bending materials has focused on the ability to control bimorph systems composed of hydrogels or elastomeric materials [4-5]. However, hydrogels and elastomers lack the strength needed for many practical applications. This work takes inspiration from nature to design thermoplastic structures that mimic natural systems through the generation and control of self-automated folds and global curvature. By increasing the complexity of possible designs, we can have a greater impact and generate final structures with a wider range of overall applications.

Results: We induce self-actuation into our materials by patterning pre-strained polystyrene films with ink from an inkjet printer. The polystyrene sheets are pre-strained to shrink by ~ 55% when heated above their activation temperature (Ta ~ Tg) which is ~ 103°C. By patterning inked regions along the surface of the material localized heating, and therefore shrinkage, is achieved via strain gradients through the thickness of the material [1]. The design of these inked regions (i.e., ink darkness and distribution) determines the direction of folding, onset actuation time, and final structure. These results are compared with finite element modeling as a predictive tool [6].

Conclusions: An indirect and direct mechanism of curvature were identified and systematically studied with our self-actuated polystyrene material. This global curvature control is useful for the production of positive and negative Gaussian curvature from planar polymer sheets. The degree of curvature is directly related to the ink distribution and darkness of each sample as well as the aspect ratio and geometry of the starting substrates. Experimental and computational results were quantitatively and qualitatively compared with excellent agreement for the production of biologically-inspired gripping devices with the ability to hold ~ 925x their own weight.

References:

  1. Liu, Y., Boyles, J., Genzer, J., & Dickey, M. Self-folding of polymer sheets using local light absorption. Soft Matter. 8, 1-6 (2012).
  2. Felton, S., al., Self-folding with shape memory composites. Soft Matter 9, 7688-7694 (2013).
  3. Liu, Y., Mailen, R., Zhu, Y., Dickey, M., & Genzer, J. Simple geometric model to describe self-folding of polymer sheets. Rev. E 89, 1-8 (2014).
  4. Eugonov, A., Korvink, J., Luchnikov, V. Polydimethylsiloxane bilayer films with an embedded spontaneoud curvature. Soft Matter 12, 45-52 (2016).
  5. Abdullah, A., Braun, P., Hsia, K. Programmable shape transformation of elastic spherical domes. Soft Matter 12, 6184-6195 (2016).
  6. Mailen, R., Liu, Y., Dickey, M., Zikry, M., Genzer, J. Modelling of shape memory polymer sheets that self-fold in response to localized heating. Soft Matter 11, 7827-7834 (2015).

Sabina Islam 

Background: Aromatic polyesters are one of the most important classes of polymers in textile and packaging industries due to their superior mechanical, optical, and processing properties. In order to comply with the low-VOC movement, such specialty polyesters were rendered water-dispersible by functionalizing the polymer backbone with ionic monomers. As a result of being partially soluble, these polyesters forms self-assembled nanoscale particles in water without the requirement of any additional stabilizer(s). These extremely small sized (~20 nm) nanoparticles are composed of hundreds of polymer molecules and offer various colloidal and morphological properties that are significantly different from the conventional emulsion polymerized latex particles. For instance, their nanometer dimensions can be very useful for developing nanocoatings with interesting optical properties.

Results: We fabricated nanofilms of brilliant colors using these polymer dispersions via facile convective deposition method. The microscale thickness of these nanofilms could be correlated to their macroscale optical properties via the constructive interference theory. Additionally, surface roughness modulation of these nanocoatings allowed us to obtain thin-film interference on both macro- and micro-level. Moreover, we observed coffee-ring effect as the addition of water droplets on such thin-films created multiple colorful ring-patterns where surfactants or electrolytes suppressed this effect.

Conclusions: Structural colors of purely physical origin are gaining a lot of interest in industries and academia due to numerous benefits over pigment-based colors, such as more vibrant color formation, resistance to photobleaching, and environment-friendly as no toxic chemical is required. This research is important in understanding the fundamental mechanism of film formation by these polymer nanoparticles. Moreover, the findings of our study open a new possibility and application of such environment-friendly waterborne dispersions in painting, photonic paper, and optical displays.

Soo Ah Jin Characterization of poly(vinyl alcohol) and nanocellulose composite films

Ishan Joshipura Reversible Actuation of Soft Liquid Metal Plugs in Microfluidic Systems Using Low Voltages

Yeongun Ko 

Background: Polymer brushes comprise densely grafted polymer chains on surfaces, which possess high stability and high concentration of reactive centers per unit area compared to physisorbed polymer film. Polymer brushes are employed in many applications, including anti-fouling surfaces, cell adhesive surfaces, responsive surfaces, low-friction surfaces, etc. Recently, researchers reported that charged (or chargeable) polymer brushes can be degrafted from substrate while incubated in buffer solutions. [1]

Results: Based on previous experiments conducted in our group [2,3] and by others [4], we assume that chain degrafting results from the hydrolysis of Si-O groups in head-group of the initiator and/or the ester groups in main body of the initiator. In this work, we study the stability of poly(2-dimethylaminoethyl methacrylate) (PDMAEMA) brushes in two solvents (ethanol and water) at various pH values in water and under different levels of external salt concentration. Our preliminary results are following: first, it is observed that free polymer chains were removed during the incubation in ethanol. Second, in brushes incubated in aqueous buffer solution, increasing molecular weight of the brush facilitates degrafting polymer chains from the substrate. Third, the critical value dividing two different regimes in terms of degrafting behavior is observed. When the initial dry thickness is less than ~70 nm, degrafting in pH 7.4 is faster than degrafting in pH 4, which means hydroxide ions are more effective than swelling in that regime. For dry thickness greater than ~70 nm the swelling effect is stronger than the hydroxide ion catalytic effect and the induced osmotic swelling leads to degrafting of polymer chains from the substrate. Fourth, significant degrafting is not observed after 3 days. Finally, by increasing the ionic strength of incubation solution, the wet thicknesses decrease and less degrafting is observed.

Conclusions: The kinetic of hydrolysis is affected by mechanical forces acting on the initiator. Those forces depend on the molecular weight and the grafting density of the brush, and the concentration and distribution of charges along the macromolecule (tuned by pH – for weak electrolytes – and concentration of external salt).

References:

  1. Tugulu, Stefano and Klok, harm-Anton (2008). Stability and Nonfouling Properties of Poly(poly(ethylene Glycol) Methacrylate) Brushes under Cell Culture Conditions. Biomacromolecules, 9: 906–912.
  1. Bain, Erich D., Dawes, Keith, Özçam A. Evren, Hu, Xinfang, Gorman, Christopher B., Šrogl, Jiří and Genzer, Jan (2012). Surface-Initiated Polymerization by Means of Novel, Stable, Non-Ester-Based Radical Initiator.Macromolecules, 45: 3802-3815.
  1. Galvin, Casey J., Bain, Erich D., Henke Adam and Genzer Jan (2015). Instability of Surface-Grafted Weak Polyacid Brushes on Flat Substrates. Macromolecules, 48: 5677-5687.
  1. Melzak, Kathryn A., Yu, Kai, Bo Deng, Kizhakkedathu, Jayachandran N. and Toca-Herrera, José L (2015). Chain Length and Grafting Density Dependent Enhancement in the Hydrolysis of Ester-Linked Polymer Brushes. Langmuir, 31: 6463-6470.

Yiliang Lin 

Background: Metal nanoparticles find usage in catalysis, optics, energy harvesting, therapeutics, sensors and electronic inks. Here we focus on liquid metal nanoparticles composed of eutectic gallium indium (EGaIn[1]). Due to the low-melting point (m.p. ~15.5°C) and low-toxicity[2], EGaIn is uniquely suitable for applications in soft electronics, such as stretchable wires[3,4], flexible antennas[5] and self-healing circuits[6].

Results: 1) We report on a facile method to synthesize liquid metal nanoparticles in ethanol via sonochemistry. Casting the liquid metal nanoparticles between two elastomer pads results in non-conductive films. However, mechanical pressure sinters locally the liquid metal nanoparticles into conductive paths simply using a writing stylus. This “mechanical sintering” method is attractive relative to conventional sintering techniques (i.e., light or heat) because it work at room temperature. Based on this strategy, we fabricated soft circuit boards and flexible antennas with frequency-shifting properties on demand. 2) We also demonstrate that it is possible to carry out surface modification on the liquid metal nanoparticles as transformable nanomedicine for drug delivery. The drug is loaded on the nanoparticles using thiol chemistry/guest-host reaction and systematic cell/animal study have been carried out to demonstrate the ability for anticancer therapy, further proving the low-toxicity of EGaIn.

Conclusion: The soft nature of liquid metals endows the EGaIn nanomaterials with unique mechanical properties, such as deformability, which make them compatible as nano-scale inks for soft, stretchable electronics and as promising materials for biomedicine, catalysis, and as conductive components in microsystems.

References

  • D. Dickey, R. C. Chiechi, R. J. Larsen, E. A. Weiss, D. A. Weitz, G. M. Whitesides, Adv. Funct. Mater. 2008, 18, 1097–1104.
  • Lu, Q. Hu, Y. Lin, D. B. Pacardo, C. Wang, W. Sun, F. S. Ligler, M. D. Dickey, Z. Gu, Nat. Commun. 2015, 6, 10066.
  • P. Mineart, Y. Lin, S. C. Desai, A. S. Krishnan, R. J. Spontak, M. D. Dickey, Soft Matter 2013, 9, 7695.
  • Zhu, J.-H. So, R. Mays, S. Desai, W. R. Barnes, B. Pourdeyhimi, M. D. Dickey, Adv. Funct. Mater. 2013, 23, 2308–2314.
  • -H. So, J. Thelen, A. Qusba, G. J. Hayes, G. Lazzi, M. D. Dickey, Adv. Funct. Mater. 2009, 19, 3632– 3637.
  • Palleau, S. Reece, S. C. Desai, M. E. Smith, M. D. Dickey, Adv. Mater. 2013, 25, 1589–1592. 

Charles McGill 

Background: Xylose kinetics are studied here as a window into the elementary reactions of hemicellulose pyrolysis. Xylose is a monosaccharide that is a major monomer in many varieties of the biopolymer hemicellulose. Conversion of plant biomass into biofuels is often carried out through the thermal process of pyrolysis. Chemical mechanisms for the decomposition of biomass and its constituent monomers have been widely studied but are generally presented as lumped models where the individual elementary reaction steps are not known [1]. It is the goal of this work to develop a reaction model with elementary steps for xylose. As one of the major constituents of hemicellulose in biomass, the development of thermal degradation mechanisms for xylose is important to the development of mechanisms for hemicellulose and biomass as a whole. Xylose is also used in the production of furfural, an important chemical feedstock. Understanding of the chemical pathways for furfural formation would enable future refinements of the process.

Results: Pyrolysis was carried out on xylose in the 200-300°C temperature range. Permanent gas and condensable vapor products were analyzed by two-dimensional gas chromatography with time-of-flight mass spectrometry (GCxGC-TOFMS). Key products identified were glycolaldehyde, glyceraldehyde, dihydroxyacetone, and furfural along with many minor products. Quantum chemistry modeling was carried out using the Gaussian 09 software package. Over 200 transition states were found for reactions undergone by xylose, including one novel transition. Products from these initial reactions included precursors of the major products glycolaldehyde, glyceraldehyde, and dihydroxyacetone. Transition states and intermediate structures were modeled for the generation of furfural from xylose, resulting in a web of parallel pathways for the formation of furfural.

Conclusions: Several key products were identified for xylose pyrolysis in the 200-300°C temperature range. Elementary reaction pathways were investigated and modeled for each of the major products. The mechanism for furfural formation included several parallel pathways, including some dependent on the novel ring contraction transition.

References:

  1. Di Blasi, C. Modeling Chemical and Physical Processes of Wood and Biomass Pyrolysis. Prog. Energy Combust. Sci. 2008, 34 (1), 47–90.

Jason Miles 

Background: Many chemical and biological processes, such as wettability or adhesion, rely strongly on surface interactions. The use of chemical and surface energy gradients allows for a wide range of parameters to be evaluated on a single substrate. This high-throughput approach allows for faster screening and discovery of materials and surface phenomena. Molecular gradients on surfaces can be used to direct dynamic phenomena on surfaces, such as the motion of water droplets [1] or cells [2]. These gradient surfaces are most commonly formed through the use of self-assembled monolayers (SAMs) or surface-anchored macromolecules, called polymer brushes [3]. A successful method for this application must result in a gradient, which is easy to prepare, should provide sufficient control over the profile of the gradient, and should allow for specific chemistries to be placed on the surface to be used for the appropriate application [4].

Results: We have fabricated wettability gradients on impenetrable, flat substrates by a simple, two-step procedure. This process involves the deposition of homogeneous silane SAMs from anhydrous toluene followed by the formation of a surface coverage gradient through the selective removal of silanes from the substrate. Removal of silanes was achieved by steadily immersing the SAM-coated specimen into a solution containing tetrabutyl ammonium fluoride (TBAF), which cleaves selectively the Si-O bond at the surface. The kinetics of degrafting have been modeled by using a series of first order rate equations, based on the number of attachment points broken to remove a silane from the surface. Degrafting of mono-functional silanes exhibits a single exponential decay in surface coverage; however, there is a delay in degrafting of tri-functional silanes due to the presence of multiple attachment points.

Conclusions: Wettability and chemical gradients can be achieved by selectively degrafting homogeneous silane SAMs. The gradient profile can be tuned by varying the degrafting temperature and time. Modeling the kinetics of degrafting provides insight into the microstructure of silanes on the surface and can be used to predict the gradient profile for a set of degrafting conditions.

References:

  1. Chaudhury, M. K. & Whitesides, G. M. How to make water run uphill. Science 20, 38–59 (2013).
  1. Lee, E.-J., Chan, E. W. L., Luo, W. & Yousaf, M. N. Ligand slope, density and affinity direct cell polarity and migration on molecular gradient surfaces. Rsc Adv. 4, 31581–31588 (2014).
  1. Genzer, J. & Bhat, R. R. Surface-bound soft matter gradients. Langmuir 24, 2294–2317 (2008).
  1. Bhat, R. R., Fischer, D. a. & Genzer, J. Fabricating planar nanoparticle assemblies with number density gradients. Langmuir 18, 5640–5643 (2002).

Amit Mishra 

Background: Given current energy demands and concerns over global climate change, there is a need for efficient energy production from carbonaceous fuel conversion with facile CO2 capture. Chemical looping combustion (CLC) offers a unique solution to this problem, through a redox material capable of fossil fuel conversion with its lattice oxygen. In this two-step process, a metal oxide based redox material is first reduced with a fuel and subsequently re-oxidized to its original state with air. This process offers two main advantages 1) a pure oxygen source through a metal oxide, acting as an “oxygen carrier” and 2) exergy recuperation as result of chemical looping reactions. The first advantage is particularly promising as it results in facile CO2 capture. From a practical standpoint; however, this process can be challenging for solid fuel conversions due to kinetic limitations for solid-solid reactions. A potential solution to this problem is through a material that possesses chemical looping with oxygen uncoupling (CLOU) properties, i.e. spontaneous release of gaseous oxygen for solid fuel combustion. In this work, the AxA’1-xMnyB1-yO3 class of materials has been identified for screening through first principles calculations of oxygen vacancy formation. In particular, vacancy formation in the dilute limit was determined for CaMnO3-δ, BaMnO3-δ, Ca0.75Sr0.25MnO3-δ, CaMn0.75Fe0.25O3-δ. The presented work will show this parameter is an efficient design parameter for CLOU properties.

Results: The vacancy formation energy in the dilute limit was determined for all materials, showing two main findings: 1) Ca is favorable over Ba in the A site of the perovskite in terms of oxygen vacancy formation and 2) doping of Sr in the A site and Fe in the B site of CaMnO3, lowers the energy of vacancy formation even further. These results correspond well to experimental findings, with both dopants increasing the vacancy concentration below 700oC. In addition, the results provide insight into the nature of the vacancy sites within a doped structure. In Ca0.75Sr0.25MnO3, the vacancy preferentially forms under two conditions: 1) relatively close cation neighbors and 2) the closest cation neighbors consisting of either Ca or Mn. With respect to CaMn0.75Fe0.25O3, the vacancy preferentially formed under the conditions: 1) relatively distant cation neighbors and 2) having Fe seated close to the vacancy.

Conclusions: The results of this study show that vacancy formation energy can be used a screening parameter in determining materials suitable for CLOU. Specifically, the results of this study show the energy of vacancy formation in four materials: CaMnO3, BaMnO3, Ca0.75Sr0.25MnO3, and CaMn0.75Fe0.25O3 correspond to low temperature CLOU properties. Insight into the nature of doping reveals that the doped structures preferentially form vacancies in contrasting fashion; oxygen vacancy formation is favored in locations away from a Sr cation and close to an Fe cation. In addition, vacancies in Ca0.75Sr0.25MnO3 prefer to be close to its neighboring cations and those in CaMn0.75Fe0.25O3 tend to be away from its neighboring cations.

Taylor V. Neumann 

Dishit Parekh 

Background: 3D printing is the process of joining materials to build objects from a computer-aided model (CAD) data, usually layer-upon-layer. Polymers are the most common materials to be printed today due to the simplicity of extruding them in molten form that quickly cools and hence solidifies. Although there is a great demand for printing conductive inks for electronics [1], current methods for 3D printing metals tend to be prohibitively expensive, and use energy-intensive lasers at sintering temperatures in excess of 800°C. Secondly, they need vacuum-like pressures to avoid oxidation while handling metal nanoparticles, leading to porosity in finished parts, low resolution and poor electrical conductivity, apart from having slow printing speeds. Finally, the operating procedures are impossible to integrate them with various polymeric, organic, soft and biological materials. Here, we present an alternate but simple approach that utilizes low melting point gallium-based alloys as complements to existing materials for 3D printing electronics allowing co-printing of these metals with polymers at room temperature.

Results: We have utilized these metals to build mechanically stable structures due to the formation of a thin oxide skin on the surface [2] despite having high surface tension (~10x water). The oxide skin is passivating, forms spontaneously in presence of air or dissolved oxygen and allows us to direct-write planar as well as free-standing, out-of-plane conductive microstructures down to a resolution of ~10 microns [3], on-demand using a shear-driven flow occurring at relatively low pressures (~10s of kPa). We exhibit the patterning of 3D multilayered microchannels with vasculature using these printed liquid metals acting as a sacrificial template at room-temperature [4], that can be employed in numerous lab-on-a-chip devices. We also demonstrate rapid prototyping of functional electronics such as flexible and stretchable antennas for radio-frequency defense communications, as well as consumer-based electronic devices like inductive power coils for wireless charging of smartphones, and wearable thermoelectric generators (TEGs) for energy-harvesting applications.

Conclusions: In summary, we show that a shear-driven flow dispensing approach for printing liquid metals can fabricate 2D & 3D microarchitectures. This mechanism validates that skin forming liquids can be molded into several shapes earlier prohibited by the weakening effects of gravity and surface tension, in order to print soft electronic devices at room temperature.

References:

  1. Parekh, Dishit P., Denis Cormier, and Michael D. Dickey (2015). Multifunctional Printing: Incorporating Electronics into 3D Parts Made by Additive Manufacturing. Additive Manufacturing, CRC Press, 8: 215-258.
  1. Michael D. Dickey (2014). Emerging Applications of Liquid Metals Featuring Surface Oxides. ACS Appl. Mater. Interfaces., 6: 18369-18379.
  1. Trlica, C., Dishit P. Parekh, Laza Panich, Collin Ladd, and Michael D. Dickey (2014). 3-D Printing of Liquid Metals for Stretchable and Flexible Conductors. Proceedings of SPIE, 9083: 1-10.
  1. Parekh, Dishit P., Collin Ladd, Laza Panich, Khalil Moussa, and Michael D. Dickey (2016). 3D Printing of Liquid Metals as Fugitive Inks for Fabrication of 3D Microfluidic Channels. Chip, 16: 1812-1820.

Amulya K. Pervaje 

Background: Polyester polyols are polymers with applications in coatings, adhesives, sealants, foams, and as elastomers. Polyester polyols are usually synthesized in a condensation polymerization between diols and dicarboxylic acids. The diol and diacid chemistries alternate along the polyester polyol backbone with ester bonds linking the diol and diacid groups. Multifunctional monomers can also be introduced in the synthesis, resulting in more branches. Polyester polyols are typically terminated by two or more hydroxyl groups. A wide chemical variety of polyester polyols may be synthesized for different applications depending on the monomers used in the synthesis. For different applications, different demands on polyester polyol properties arise and a better prediction method of the polymer’s properties is needed. Our approach models polyester polyols starting from available thermodynamic data on the monomers to predict properties such as glass transition temperature (Tg) of polyester polyols with a specified backbone composition. The top-down coarse grained models used to represent the polyester polyols in molecular dynamics (MD) simulations are based on the SAFT-γ Mie EoS1 with a corresponding states correlation2 that simplifies the fitting of Mie parameters.

Results: First, four neopentyl glycol (NPG) based polyester polyol experimental resins are modeled and simulated with conventional MD methods. The Tg and heat capacity behavior is compared between the experimental data on the resins and simulation results. The simulation analysis includes calculation of other thermodynamic and structural properties to better characterize the system. Then, simulations are done again with a different method, a parallel tempering (PT) MD implementation, to attempt better/faster equilibration in simulation. The effects of the PT simulations are evaluated with comparisons to the conventional MD simulations as well the experimental data. Finally, the parameter space of SAFT-γ Mie models to represent polyester polyols is systematically used to generate a range of models with different parameters to make a connection between the model parameters used in the models and the arising polymer properties for polyester polyols.

Conclusions: The predictive power of the SAFT-γ Mie models for the four NPG-based polyester polyol resins used in this study is shown to be good, especially considering the ease by which the Mie models are fit from three key pieces of monomer data. The systematic study of model parameters on polymer property results gives dbetter understanding of how these models can be tuned to match desired outputs.

References:

  1. Papaioannou, V. et al. Group contribution methodology based on the statistical associating fluid theory for heteronuclear molecules formed from Mie segments. Chem. Phys. 140, 54107 (2014).
  2. Mejia, A., Herdes, C. & Mueller, E. A. Force Fields for Coarse-Grained Molecular Simulations from a Corresponding States Correlation. Ind. Eng. Chem. Res. 53, 4131–4141 (2014).

Adam Quintanilla 

Background: Continuous liquid interface production (CLIP) is used to fabricate complex three-dimensional objects in a layerless process, thereby avoiding negative aspects of traditional 3D printing associated with the layer-by-layer printing process. Traditional photocurable resins used for 3D printing usually produce brittle thermosets and thus are not suitable for applications beyond prototyping. The goal of this research is to incorporate polybutadiene (PBD), as a rubber toughener, into the matrix of a rigid/brittle photocurable resin used with CLIP. Several PBD oligomer resins were compared to investigate the effect of molecular weight and molecular weight distribution, rubber content, and end group functionality on the mechanical properties of ASTM D638 Type V specimens fabricated using CLIP. Toughness was evaluated via tensile testing and phase separation was investigated via microscopy and thermal analysis.

Results: Initial tests show that higher molecular weight PBD and end-group functionality similar to the bulk resin play a significant role in rubber toughening. Addition of up to 10 pph polybutadiene-dimethacrylate to the polymer matrix resulted in an increase of strain at break and thus toughness of the material. SEM images reveal smooth cross-section surfaces indicating crosslinking of the polybutadiene phase and good interaction with the polymer matrix. TEM images reveal spherical microphases 1-20 microns in size, and fairly well-dispersed within the bulk matrix.

Conclusions: The evidence of well-dispersed microphases and improved toughness, as measured by the area under the stress-strain curve, suggest that structures analogous to microphase separated block copolymers can be produced using blended oligomeric resin formulations with CLIP.

Sangchul Roh 

Background: We present a new type of three dimensionally printable polydimethylsiloxane (PDMS) ink and demonstrate its application in soft actuators. Three-dimensional (3D) printing is an emerging technique for engineering complex architectures. 3D printable materials are limited to polymer melts and new ink for printing in order to broaden the applications. One such materials is PDMS, which is widely used in manufacturing of biomedical devices, microfluidics, electronics and soft robotics. However, 3D printing of PDMS is challenging because of the viscous deformation in uncured PDMS fluid.

Results: Here we introduce a new technique for printing PDMS into 3D architectures. Our 3D printable ink consists of PDMS microspheres, water, and PDMS liquid precursor. The PDMS microspheres provide structural frame, and liquid PDMS forms capillary bridges restricting the free flow of the PDMS microspheres in water medium. The PDMS inks exhibit good 3D structural stability, microporosity, and elasticity after crosslinking at an elevated temperature. Furthermore, 3D printed PDMS with embedded magnetic nanoparticles exhibits magnetically responsive capabilities. Elastin-like printed patterns enable unusual contracting or expanding motions to printed PDMS actuators. Compressive moduli of printed PDMS are controllable by the design of elastin-like patterns.

Conclusions: In summary, we demonstrate a new type of programmable actuators which perform anisotropic or localized contraction on demand. The actuation principle may find applications especially in programmable materials and in soft robotics.

Kaihang Shi 

Background: Molecular simulation and theoretical analysis of thin films adsorbed onto solid surfaces or within narrow pores have usually treated the solid surface as atomically smooth and energetically homogeneous. Most surfaces, however, exhibit more or less roughness through geometric curvature, variations of surface composition or chemical groups attached to the surface. Such oversimplification of the surface thus misses important details of adsorption, especially at low bulk pressure. In this research, a flexible conformal sites model, mapping a real interfacial system with non-spherical molecules and an energetically heterogeneous surface onto a reference system with adsorbate molecules and an energetically homogeneous surface with only one species of interaction sites, will be developed. Grand canonical Monte Carlo simulation is used to explore the limits of applicability of this model to the prediction of adsorption isotherms. We hope our model can help to simplify the theoretical treatments of highly heterogeneous interfacial systems, and thus improve the understanding of adsorption, phase transitions and pressure profiles in small pores.

Results: Conformal sites model has been proved, by molecular simulations, quite successful in reproducing the adsorption behavior in non-polar real system. We expect our model can also reproduce the adsorption behavior in highly heterogeneous polar system.

Conclusions: This work would be the first developing a theoretical surface model allowing for both geometric curvature and chemical heterogeneity. Due to the simplicity and accuracy of our model, we anticipate that the new methods to be developed in this work will be incorporated in the software of experimental instruments to study porous materials.

Bharadwaja Srimat Tirumala Peddinti 

Background: In recent years, increasing reports of drug resistant microbial strains is a subject for serious concern. Hospital acquired infections (HAIs) are a major problem caused by drug resistant microbes. Adherence and proliferation of microbes on surfaces such as counter tops, drapes, linens, door handles, monitory and sanitation equipment in health-care settings contribute to increase in HAIs [1]. As increase in microbial drug resistance causes conventional methods of treatment to fail, researchers are looking at alternative routes to tackle the infections. Photodynamic therapy (PDT) is such a technique that uses a photosensitizer (PS) and a light source, to treat medical conditions such as acne, wet-age macular degeneration and initial stages of skin cancer. Initially, the PS is applied on a target area of cancer cells. Subsequently, the target area is illuminated by visible light (typically of red color), thus, activating the PS [2]. The activated PS, through interactions with ground state triplet oxygen diffusing through the cells, converts it into singlet state oxygen. Being very reactive, singlet oxygen can oxidize various components in the cancerous cells leading to its death [3]. Rather than a cure by intracellular absorption, we intend to incorporate the PS on surfaces that will result in killing of microbes by continuous surface disinfection and serving as a preventive measure.

Results: In this study, we have incorporated a PS, meso-Tetraphenylporphine (meso-TPP), in an olefin block copolymer (OBC), INFUSE 9107. Melt pressed PS/polymer films with various concentrations (0.5-10% w/w meso-TPP/INFUSE 9107) of the PS were prepared. Thermal gravimetric analysis revealed that INFUSE 9107 and meso-TPP were thermally stable up to 300 C and 450 C respectively. Scanning electron microscopy (SEM) and Energy-dispersive x-ray spectroscopy (EDX) analysis showed dispersion of meso-TPP on the surface of the films. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis revealed higher concentration of meso-TPP on surface relative to the bulk concentration. Subsequently, after conducting antimicrobial studies on the films, the results will be duly reported.

Conclusions: INFUSE 9107, typically manufactured for nonwoven applications and meso-TPP being thermally stable up to 450 C, are potential materials to produce melt spun fibers. Higher concentration of PS leads to increased antimicrobial efficacy. Hence, surface migration of meso-TPP, otherwise termed as blooming, is beneficial. Thickness of the films and concentration of the PS can be optimized based on their antimicrobial efficacy.

References:

  1. Kramer, A., Schwebke, I., Kampf, G. (2006) How long do nosocomial pathogens persist on inanimate surfaces? A systematic review. BMC Infect. Dis., 6: 130.
  1. Nicolas Solban, I. R. T. H. (2006) Targeted photodynamic therapy. Lasers Surg. Med., 38: 522-531.
  1. Jori, G., Coppellotti, O. (2007) Inactivation of Pathogenic Microorganisms by Photodynamic Techniques: Mechanistic Aspects and Perspective Applications. Anti-Infect. Agents Med. Chem., 6: 119−131.

Mohammad Tuhin 

Background: Shape memory (SM) materials are attractive materials because of their unique characteristics of changing shape based on external stimuli. Recently, SM polymer fibers (SMPFs) were created that are thermally activated, where the key to the technology is that the switching segments (temporary shape) and net points (permanent shape) are physically separated in the fiber through bicomponent spinning technology, using a melt-spinnable grade of poly [styrene-b-(ethylene-co-butylene)-b-styrene] (SEBS) triblock copolymer in the core and a sheath of linear low density polyethylene (LLDPE). The goal of this work is to add additional sensory functionality into these SMPFs by incorporating an electrically conductive polymer, polyaniline (PANI). In order to obtain the final goal, the polyaniline was therefore, characterized for thermal stability, spatial distribution of polyaniline into SEBS, electrical conductivity, and change in crystallinity at different thermal conditions along developing a polyaniline based nanocomposite to obtain enhanced thermal stability. How the incorporation of PANI impacts the phase morphologies of the polymer components of the SMPFs was also predicted with dissipative particle dynamics (DPD) simulations, particularly as a function of the different size and shape of the incorporated particles.

Results: It was found that polyaniline goes through variable thermal stability above 2000C, which also depicted characteristic changes in crystallinity. Using DPD simulation different morphological as well as network characteristics of multiple block copolymer systems were also obtained and it was found that simulation could successfully produce morphologies analogous to those obtained from experimental approaches. Block copolymers having higher block number of chains was also characterized for networks while they form self-assembled nanostructures and depicted higher quantity of networks.

Conclusions: This information obtained using the computational method as well as the experimental characterizations are expected to benefit the current work on the way to developing the SM fiber’s SM characteristics as well as the sensory functionality.

Wenyi Xie 

Background: Carbon nanofibers are useful materials in many different applications, which includes as electrode materials in energy storage devices, as support for catalysts, and as adsorbent materials in water purification.[1-3] Common thermoplastic polymers, such as polyvinyl alcohol and cellulose derivatives are more abundant and inexpensive precursors for preparing carbon nanofibers. These polymers are soluble in common solvent and can be readily processed to prepare nanofibers with high external surface area. However, thermoplastic polymers undergo melting transition upon heating, therefore results in loss of initial morphology and low carbon yield. In this study, vapor infiltration of diethyl zinc is applied to modify electrospun CDA nanofibers for preparing carbon nanofibers. Our goal is to investigate the effect of inorganic modification on the morphology and structural properties of the carbon product from the CDA nanofibers.

Results: Through IR analysis, we found that DEZ could greatly modify the chemical structure of CDA. DEZ could react with the hydroxyl and ester side groups of CDA, as well as reacting with CDA polymer backbone. As a result of the chemical modifications, the DEZ treated CDA did not show melting transition and the fiber structure could be preserved during carbonization for samples with at least 10 wt. % Zn incorporated. In addition, we found the surface area and pore volume of the CDA based carbon nanofibers can be controlled by the amount of DEZ incorporated. While mesoporosity dominated upon small amount DEZ incorporated (~ 7.0 wt. % of Zn), above which the formation of micropores was favored. However, the carbon yield was progressive lowered as the amount of DEZ incorporated increased due to the catalytic effect of Zn on the oxidation of carbon at high temperatures.

Conclusions: This work demonstrates the use of vapor infiltration of DEZ for the preparation of carbon nanofibers from electrospun CDA nanofibers. Moreover, we have shown that the surface area and pore volume distribution of the CDA nanofiber derived carbon products can be controlled by changing the loading of Zn. Therefore, we believe that inorganic modification by vapor infiltration of DEZ is promising for modifying thermoplastic polymers to produce high performance nanostructured carbon materials that are useful for many applications.

References:

  1. Inagaki, M., Yang, Y. & Kang, F. Carbon nanofibers prepared via electrospinning. Mater. 24, 2547– 2566 (2012).
  1. Zhang, B., Kang, F., Tarascon, J. & Kim, J. Progress in Materials Science Recent advances in electrospun carbon nanofibers and their application in electrochemical energy storage. Mater. Sci. 76, 319–380 (2016).
  1. Zhang, L., Aboagye, A., Kelkar, A., Lai, C. & Fong, H. A review: Carbon nanofibers from electrospun polyacrylonitrile and their applications. Mater. Sci. 49, 463–480 (2014).

Seif M. Yusuf 

Background: Oxidative dehydrogenation (ODH) of ethane represents a promising alternative to steam cracking for the production of ethylene that can result in a higher ethane conversion, lower energy consumption and lower CO2/NOx emissions. Conventional ODH, however, suffers from challenges in process safety, controllability, and high capital cost due to the needs to co-feed gaseous oxygen with ethane. In chemical looping ODH (CL-ODH), ethane is partially oxidized by active lattice oxygen in a redox catalyst, producing ethylene and water. The reduced redox catalyst is subsequently re-oxidized with air in a separate reactor prior to the initiation of another redox cycle. Such a cyclic redox scheme eliminates the needs for cryogenic air separation as well as O2 co-feeding. In this process, it is crucial to suppress deep oxidation without sacrificing ethane conversion. This study focuses on testing and characterization of Mg6MnO8 based redox catalysts for the CL-ODH of ethane.

Results: Mg6MnO8 based redox catalysts were able to improve single pass ethane conversion compared to thermal cracking. When promoted with sodium tungstate, the redox catalyst was able to increase the ethylene single pass yield by 38.9% when compared to thermal cracking[1]. Ethane TPR suggests that the reaction pathway for the sodium tungstate promoted redox catalyst is parallel thermal cracking and selective combustion of hydrogen. X-ray Photoelectron Spectroscopy (XPS) and Low Energy Ion Scattering (LEIS) analyses indicate that the sodium tungstate promoter suppresses the amount of surface manganese and reduces the average manganese oxidation state. These results indicate that the sodium tungstate promoter suppresses the amount of surface Mn4+ which is responsible for the unselective electrophilic oxygen species.

Conclusions: Our study indicates that CL-ODH can reduce the CO2 and NOx emissions for ethylene production by as high as 87%[2]. Design and optimization of effective redox catalysts are crucial for successful development of such a promising process. The current study not only reports a highly effective redox catalyst, but also reveal the underlying mechanism for such a redox catalyst. The findings can be significant for further improvements of redox catalyst performances in CL-ODH.

References:

  1. M. Neal, S. Yusuf, J. A. Sofranko, and F. Li, “Oxidative Dehydrogenation of Ethane: A Chemical Looping Approach,” Energy Technol., vol. 4, no. 10, pp. 1200–1208, Jul. 2016.
  1. Haribal, L. M. Neal, and F. Li, “Oxidative Dehydrogenation of Ethane under cyclic redox scheme- Process Simulation and Analysis,” Energy (Accepted).