Program

IRTG 1524 Annual Meeting 2017

Friday, October 6, 2017

All Day Arrivals & Hotel Check-In
 

6:00 PM

 

Dinner at NC Museum of Art
Location Map

Saturday, October 7, 2017

NC State University – College of Textiles, Room 2431

8:45 AM

 

Welcome – Professor Keith E. Gubbins

 

SESSION 1

Chair: Rumiana Dimova

*
9:00 AM Eleanor Ewins
Max Planck Institute of Collids & Interfaces, Potsdam, Germany
A significant number of bio-medical and industrial applications require an understanding of the toxicity and potential impact on health that synthetic nano- and micro-particles may have and thus the processes that occur when a particle interacts with a surface of a bio-membrane. One particularly interesting approach is to develop a mechanistic description of how particles of colloidal size interact with and penetrate cell membranes. Giant unilamellar vesicles (GUVs)1 are used as the model membrane system; these are closed lipid bilayers formed from amphiphilic phospholipids. GUVs mimic the size and curvature of plasma (cell) membranes. These structures have sizes in the micrometer range (1-100 μm) thus offering the possibility to directly visualize the particle-membrane interactions and to measure the bilayer mechanical properties2. We have looked both at the interactions with nano- and micro-sized particles. For the former, we have monitored the membrane stability and particle permeability. For the latter, in particular we are exploring the effects of the geometrical and material parameters in the system. The geometrical parameters are defined by the vesicle and particle sizes and can be modulated by selecting a wide range of particle sizes (80 nm-20 μm). A recent theoretical study suggests that the system geometrical parameters can determine whether a particle will be engulfed by the membrane or not3. The interaction outcome also depends on material properties of the system, such as adhesion strength, membrane bending rigidity and spontaneous curvature. The membrane spontaneous curvature (which is due to asymmetries across the membrane), is a material membrane property and can be varied by using membranes with asymmetrically grafted molecules. The effect of the membrane spontaneous curvature has yet to be considered experimentally in this context. With these goals in mind, one possible approach is to vary membrane composition and particle surface chemistry in order to modulate the adhesion strength and bending rigidity. When varying particle surface chemistry, we will also investigate how different surface chemistries on the same particle affect the interaction mechanisms. This can be done by using Janus particles.

  1. R. Dimova, in Advances in Planar Lipid Bilayers and Liposomes, edited by A. Iglič, 1-50 (2012).
  2. R. Dimova, Adv. Colloid Interface Sci. 208, 225-234 (2014).
  3. J. Agudo-Canalejo, R. Lipowsky, ASC Nano 9, 3704–3720 (2015).

9:30 AM Francesco Bonazzi
Max Planck Institute of Colloids & Interfaces, Potsdam, Germany
Inside cells, organelles such as the endoplasmic reticulum and the Golgi apparatus are made of a single biological membrane which is highly bent. Tubules and double bilayer sheets are recurring structures. Several mechanisms have been suggested to describe the bending, among which is the scaffolding by crescent-like particles, the subject of the present research project. The stabilization of the structures of disks is achieved through a scaffolding of crescent-like particles on its edge, while tubules are stabilized by being surrounded by such particles. Variations in concentration and interaction strength of the crescent-like particles influence the final shape. Further investigation is being performed in order to determine the effect of crescent-like particles interacting on their concave side. Such particles are believed to stabilize the three-way junctions of tubules in the peripheral endoplasmic reticulum.
10:00 AM Marek Sokolowski
Institut für Chemie, Technische Universität Berlin, Berlin, Germany
The interaction of nanoparticles with phospholipid membranes has great relevance to the field of nanotechnology. In particular, nanoparticles are interesting as one may expect strongly size-dependent properties and so they also have great potential for several biological applications.1 This opens a new important field in the context of using nanoparticles in nanomedicine but is also relevant to the related field of nanotoxicology2,3. It is obvious that one needs to understand the fundamental interaction of NPs with membranes, i.e., what are their interactions on simple systems like vesicles or supported lipid bilayers (SLB). The strength of the binding of NPs onto a lipid membrane depends on the stiffness of the membrane, electrostatic and van der Waals interaction and the surface modification of the nanoparticles (NPs)4,5. In this work we studied the nanoparticles membrane interaction with “hard” charged (anionic or cationic) SiO2-NPs or “soft” SiO@PDMAEMA-NPs covered by a grafted cationic brush polymer. One attractive method to study the adsorption can be done via acoustic waves using the quartz crystal microbalance with dissipation (QCM-D) by comparing the amount of adsorbed NPs with visualization techniques like the atomic force microscopy. Several parameters influence the interaction like charge density of the SLB and NPs, polymer grafting density, pH and NP concentration. One interesting observation for SiO2@PDMAEMA-NPs is that the amount of adsorbed NPs is reduced upon increasing the polymer brush grafting density even if electrostatic attraction exists.

Figure 1. a) cartoon of SLB bilayer formation from charged vesicles (I) and subsequent NP adsorption (II), b) frequency shifts of an example QCM-D measurement, the dissipation shifts are not shown, I and II show SLB formation and NP adsorption in the measurement.

  1. M. El-Sayed, Acc. Chem. Res., 37, 326 (2004).
  2. H.C.Fischer, W.C. Chan, Curr. Opin. Biotechnol., 18, 565 (2007).
  3. V. E. Kagan, H. Bayir, A.A. Shvedova. Nanomed. Nanotechnol. Biol. Med., 1, 313 (2005).
  4. R. Michel, T. Plostica, L Abezguaz, D. Danino, M. Gradzielski. Soft Matter, 9, 4167 (2013).
  5. R. Michel, M. Gradzielski. Int. J. Mol. Sci., 13, 11610 (2012).

 

10:30-10:45 AM

 

 

BREAK

 

SESSION 2

Chair: Orlin Velev

*
10:45 AM Esra Oguztürk
Physical Chemistry/Molecular Material Science, Technische Universität Berlin, Berlin, Germany
In this project, hybrid supraparticles of microfibrillated cellulose (MFC) and fumed silica (FS) were prepared on superhydrophobic surfaces by means of evaporation induces self-assembly (EISA). By being biocompatible and highly porous, MFC is a promising component to be used in active particles for biomedical or catalytic applications. The other component FS has also wide variety of applications due to its properties such as large surface area, functionality and stability. By changing the ionic strength of the initial solutions, it was possible to control the anisometry of the particles in a systematic fashion, going from spherical to elongated supraparticles2. Our motivation was to use these sub-millimeter anisometric particles to obtain tunable self-propulsion. The self-propelling properties were imparted by adding Pt-covered magnetite (Pt@Fe3O4) nanoparticles to the colloidal suspension and concentrate them on a pre-determined location as a patch, which was possible by doing the preparation on an indented surface which allows controlling the elongation direction of the supraparticles. In this way, supraparticles were obtained with both, magnetic and catalytic properties, which enable self-propulsion with a suitable fuel and the steerability by a magnetic field. The trajectories of these boat-like supraparticles were studied by means of video-microscopy as a function the shape of the supraparticles, the position of the catalytically active patch, and the concentration of the fuel. From these studies systematic correlations between these parameters and the observed trajectories could be deduced, where in particular the extent of anisometry of the supraparticles has a profound effect.

Figure 1: Trajectories of 3 particles. Figure 2: SEM micrographs of freeze-dried MFC based patchy particle (Magnification a: 120x, b: 2000x).

  1. V. Rastogi, S. Melle, O.G. Calderon, A.A. Garcia, M. Marquez, O.D. Velev, Advanced Materials 20, 4263 (2008).
  2. M. Sperling, O.D. Velev, M. Gradzielski, Angew. Chem. Int. Ed. 53, 586 (2014).
11:15 AM Koohee Han
Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA
A new class of dynamically and reversibly reconfigurable colloidal clusters made by magnetic assembly and actuation of metallo-dielectric patchy microcubes will be presented. We describe how magnetically responsive patchy microcubes can be assembled into self-reconfiguring microclusters and employed as microbots and microswimmers. The asymmetrically coated metallic patches on the cubic particles store and release energy through field-induced polarization. Once assembled, the residual magnetic polarization of the metal-coated facets leads to directional dipole-dipole and field-dipole interactions and reconfiguration of the neighboring cubic particles, which is directed by their conformational shape restrictions. Dynamic reconfiguration of assembled clusters can be achieved by on-demand switching between the dipole-field interaction and the residual dipole-dipole interaction by toggling an external magnetic field. The reconfiguration pattern is determined by the sequence of the cube orientation. We will provide examples of assemblies of specific sequences that can be actuated to perform microscale operations such as capturing and transporting live cells, acting as prototypes of microbots. Such reconfigurable clusters can also be designed as self-propelling microswimmers in media with non-Newtonian rheology when actuated with an asymmetric magnetic signal. We will analyze the dynamics of these active structures under different propulsion conditions on the basis of a “coupled scallop” model and will suggest means of controlling the motility in different directions by means of both particle sequence and signal shape.
11:45 AM Guo-Jun Liao
Institut für Theoretische Physik, Technische Universität Berlin, Berlin, Germany
Recent experimental advances in designing “active” colloidal particles with intriguing modes of motion include shape-anisotropic particles1, decorated metallodielectric Janus spheres2, and driven curved polymers3. In the latter example, the active “particles” move in circular paths, yielding novel collective behavior such as vortex states4. Inspired by these research studies, we perform Brownian dynamics simulation to study a more generic model of spherical active Brownian particles, which are driven both by translational and rotational propulsion in two-dimensional space. We investigate how these two different propulsions combine to influence the macroscopic structure of a colloidal system, in which the particle interactions are purely repulsive. Considering a limiting case in which the rotational propulsion is absent, our results reproduce the well-discovered phenomenon where the translational propulsion induces cluster formation, also known as motility-induced phase separation5. Nevertheless, we find that the rotational propulsion generally destabilizes the clusters. Moreover, although the particles are intrinsically assigned to rotate counterclockwise, a novel state of clockwise vortices is found at an optimal value of self-propelled torque. In order to unravel the interplay between active motion and particle alignment, an additional polar interaction is then introduced into the system. We observe orientational ordering and synchronization behavior as the strength and range of the polar interaction increase.

  1. F. Kümmel, B. ten Hagen, R. Wittkowski, I. Buttinoni, R. Eichhorn, G. Volpe, H. Löwen, C. Bechinger, Phys. Rev. Lett., 110, 198302 (2013).
  2. S. Gangwal, O.J. Cayre, M.Z. Bazant, O D. Velev, Phys. Rev. Lett., 100, 058302 (2008).
  3. M. Loose, T.J. Mitchison, Nat. Cell Biol., 16, 38 (2013).
  4. J. Denk, L. Huber, E. Reithmann, E. Frey, Phys. Rev. Lett., 116, 178301 (2016).
  5. 5. M.E. Cates, J. Tailleur, Annu. Rev. Condens. Matter Phys., 6, 219 (2015).
 

12:15-2:00 PM

 

 

LUNCH Room 2427 – Meeting of Project Leaders Room TBD

 

SESSION 3

Chair: Hans Riegler

*
2:00 PM Kaihang Shi
Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA
In this work, we present a flexible conformal sites model based on the statistical mechanics, mapping a real interfacial system with an energetically heterogeneous surface onto a reference system with an energetically homogeneous surface. This model considers the electrostatic forces for site-site interactions and allows for the surface geometric and chemical defects simultaneously. To test this theory, we investigate the adsorption isotherm of Ar at 87.3 K and CO2 at 273 K onto a non-graphitized carbon surface by using grand canonical Monte Carlo simulation. The simulation results show that our conformal sites model is quite successful in reproducing the adsorption behavior in non-polar and in slightly heterogeneous polar systems. Due to its simplicity and accuracy, the conformal sites model can be used for the prediction of adsorption isotherm and other adsorption properties by taking advantage of the corresponding states theory.
2:30 PM Jacek Walkowiak
Helmholtz Zentrum Berlin für Materialien & Energie, Berlin, Germany
Adsorption of Human Serum Albumin (HSA) on spherical polyelectrolyte brushes (SPB) has been characterized by isothermal titration calorimetry (ITC) with respect to temperature to trace thermodynamic driving forces engaged in the interaction of this protein with SPB. SPB’s are a class of functionalized nanoparticles which in this case are composed of a solid polystyrene core onto which surface long chains of poly(acrylic acid) are grafted. Adsorption isotherms were provided from ITC measurements. Nonlinear temperature dependence of the adsorption process is characterized by large positive heat capacity change (∆Cp = 4,315 kJ∙mol-1∙K-1) accompanied by temperature dependent changes in both enthalpy and entropy. As a consequence of the positive ∆Cp in the range of biological temperatures, the adsorption process is entropy-driven and enthalpy-opposed. This finding stands in agreement with counterion release mechanism where proteins acts as multivalent counterions in regard to the polyelectrolyte chains therefore realizing a numbers of monovalent counterions from the charged protein patch and the polyelectrolyte brush. The present analysis demonstrates the importance of counterion release in protein adsorption as well as indicates that SPB’s are a model carrier system that allows us to study this process.
3:00 PM Jason Miles
Department of Chemical & Biomolecular Engineering, North Carolina State University
Surface energy gradients allow for a high-throughput approach to evaluate surface interactions for many biological and chemical processes. We describe the fabrication of surface energy gradients on flat surfaces by a simple, two-step procedure that permits precise tuning of the gradient profile. This process involves the deposition of homogeneous silane SAMs followed by the formation of a surface coverage gradient through the selective removal of silanes from the substrate. Removal of silanes from the surface is achieved using tetrabutylammonium fluoride which cleaves the Si-O bonds at the headgroup of the silane. 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. The effects of degrafting temperature and time are examined in detail and demonstrate the ability to reliably and precisely control the gradient profile on the surface. A relatively homogenous coverage of silane (i.e., without the presence of islands or holes) is observed throughout the degrafting process, providing a much more uniform surface when compared to additive approaches of gradient formation. Linear gradients were formed on the substrates to demonstrate the reproducibility and tunability of this subtractive approach.
3:30 PM Dikran Kesal
Department of Physics, Technical University Darmstadt, Darmstadt, Germany
Polymer brushes are promising candidates for the design of smart surfaces. Exposed to specific stimuli, these systems undergo structural changes. Furthermore, they can be used as a matrix for the uptake of particles. Incorporating gold nanoparticles (AuNPs) in polymer brushes results in nanocomposite materials with interesting nanosensor properties due to the fact that AuNPs exhibit surface plasmon resonance (SPR). Here, the interparticle distance can be used to shift the surface plasmon resonance in a certain way. The distribution of AuNPs within the polymer brush is of great importance with respect to the optical properties. Neutron reflectivity is an excellent method for studying the distribution of AuNPs. Recent observations have shown that the charge of the AuNPs is assumed to drive the uptake and penetration of AuNP into the brush. In the present study the polymer brush consists of the strong polycation PMETAC. 5 nm AuNPs were embedded, which were coated with 3-mercaptopropionic acid. The charge of the AuNP is varied by changing the pH while pH changes have no effect on the brush itself. The focus is on the concentration profile of AuNPs within the polymer brush, which were incubated at different pH values. Neutron reflectivity is used to investigate the impact of electrostatic interaction on the assembly of AuNPs within polymer brush matrices. The sensitivity of the method is enhanced by the use of contrast variation. The reflectivity data are analyzed with a self-written fitting procedure based on volume fraction profiles of all chemical components6. The aim is to correlate the AuNP distribution with optical properties.

  1. S. Christau, J. Genzer, R. v. Klitzing, Z. Phys. Chem. 229, 1089-1117 (2015).
  2. S. Christau, T Möller, F. Brose, J. Genzer, O. Soltwedel, R. v. Klitzing, Polymer 98, 454-463 (2016).
  3. S. Christau, T. Möller, Z. Yenice, J. Genzer, R. v. Klitzing, Langmuir 30, 13033-13041 (2014).
  4. S. Christau, S. Thurandt, Z. Yenice, R. v. Klitzing, Polymers 6, 1877-1896 (2014).
  5. D. Kesal, S. Christau, P. Krause, T. Möller, R. v. Klitzing, Polymers 8, 134 (2016).
  6. E. Schneck, I. Berts, A. Halperin, J. Daillant, G. Fragneto, Biomaterials 46, 95-104 (2015).

 

4:00-4:15 PM

 

 

BREAK

 

SESSION 4

Chair: Richard Spontak

*
4:15 pm Thomas Zemb
Institut de Chimie Séparative de Marcoule, Université de Montpellier
The saga of the “strange” behavior of ternary solutions near the spontaneous WII emulsification phase boundary started with the secret of Eau de Cologne formulation dating back to the 17th century. Then it was noted by enzymologists when studying membrane protein activity without any membrane in the 1950s and finally unexplained analytical centrifuge results in the research of the 1970s about enhanced oil extraction. It has been demonstrated very recently1 by a predictive thermodynamic model that this was not an urban legend, but rather a general property of hydrotropic co-solvents. In 2017, a remarkable result published by Patel and coworkers2 showed that spontaneous formation of microemulsion alias fluid coacervates droplets is important for all cytoplasmic gelled protein coacervates. Due to the increasing importance in several domains of science and technology of these Ultra-flexible microemulsions (UFME), we will attempt to review the understood as well as the not understood properties of hydrotrope-based UFME solutions versus solubilization and separation.

  1. T.N. Zemb, M. Klossek, T. Lopian, J. Marcus, S. Schöettl, D. Horinek, S.F. Prevost, D. Touraud, O. Diat, S. Marčelja, W. Kunz, Proc. Nat. Acad. Sci. USA 113, 4260-4265 (2016).
  2. A. Patel, L. Malinovska, S. Saha, J. Wang, S. Alberti, Y. Krishnan, A.A. Hyman, Science 356, 753-756 (2017).

4:45 PM J. Matthew Mansell
Department of Chemical & Biomolecular Engineering, North Carolina State University
When carbon nanotubes of small diameter are placed in contact with sulfur vapor at high temperature and atmospheric pressure, the formation of stable, nearly one-dimensional, chains of sulfur atoms, adsorbed within the nanotubes, has been observed. In some cases, the chains are electrically conductive. However, at room temperature, bulk sulfur becomes conducting only at pressures in excess of 83 GPa. We use theory and simulation to study the formation mechanisms and properties of these structures, and to develop working definitions of pressure within such systems in order to relate their behavior to pressure in bulk fluids.
 

6:15 PM

 

Dinner at NC Museum of History
Location Map

Sunday, October 8, 2017

NC State University – College of Textiles, Room 2431

SESSION 5

Chair: Stefan Zauscher

*
8:30 AM Qing Tu
Department of Mechanical Engineering & Materials Science, Duke University, Durham, NC, USA, Research Triangle Materials Research Science & Engineering Center, Durham, NC, USA
Interfaces and subsurface layers are critical for the performance of devices made of 2D materials and heterostructures. In this study, advanced scanning probe microscopy (SPM) techniques, including contact resonance atomic force microscopy (CR-AFM) and piezoresponse force microscopy (PFM), are applied to study the interfacial mechanical and piezoelectrical properties of graphene and 2D materials heterostructures. For the first time, CR-AFM is demonstrated with the sensitivity to local stiffness changes that arise from a single atomic layer of a van-der-Waals-adhered material1. A new approach, combining CR-AFM with first-principles calculations and continuum mechanics modeling, is introduced, which can yield a quantitative subsurface atomic structure fingerprint for 2D materials and heterostructures, as demonstrated on an ideal model system – epitaxial graphene on SiC (0001)1. CR-AFM is further used to study the non-ideal interface in mechanical exfoliated graphene on self-assembled monolayers (SAMs), where we found the surface chemistry of the SAM layer can affect the out-of-plane mechanical property of graphene-SAM heterostructure2. The model system of epitaxial graphene on SiC is further investigated with PFM, which revealed a new source of piezoelectricity in graphene layers that arises from the presence of interfacial dipole moments induced by the polarization in the substrate. The SPM methods used here can provide rich structure-property information about interfaces and surfaces, and can be used to understand other interfacial problems of fundamental and practical interest in 2D materials and heterostructures, such as nanoconfined water and 2D layered hybrid organic-inorganic perovskites3.

  1. Q. Tu, B. Lange, Z. Parlak, J. Marcelo Lopes, V. Blum, S. Zauscher, ACS Nano, 10, 6491–6500 (2016).
  2. Q. Tu, H. Kim, T. Oweida, Z. Parlak, Y. Yingling, S. Zauscher, ACS Applied Materials & Interfaces, 9, 10203-10213 (2017).
  3. K. Du, Q. Tu, X. Zhang, Q. Han, J. Liu, S. Zauscher, D. Mitzi, Inorganic Chemistry, 56, 9291-9302 (2017).

9:00 AM Abdul Rauf
Department of Physics & IRIS Adlershof, Humboldt-Universität zu Berlin, Germany
Graphene deposited onto atomically flat muscovite mica makes a flexible, yet impermeable slit pore with lateral dimensions on the scale of several microns. Water molecules can diffuse in and out of the slit pore through the edges, with the graphene conforming to the water layer. Its topography can be detected with sub-Angstrom vertical resolution using scanning force microscopy (SFM) in tapping mode1-3. In this work, we show that mechanically probing the slit pores reveals additional information about the water layers as they grow underneath the flexible graphene cover. Topography images of partially wetted slit pores acquired at different constant forces reveal water islands of different deformability. Since the islands contain a mono-molecularly thick layer of water, the difference in deformability may be attributed to different lateral packing densities of the molecules within the islands. Additionally, we show that a SFM based dynamic nano-mechanical probing method at ultrasonic frequencies4 is more sensitive to the presence of a sub-surface water layer of monomolecular thickness.

Figure 1: (A) SFM topography image of a partially filled graphene-mica slit pore acquired at 5±2nN normal force. Layers of monomolecularly thick water under a single graphene layer are visible as irregularly shaped domains separated by thin channels. Right half of the image shows domains of lower heights compared to domains in left half. (B) A schematic diagram of the water domains covered by graphene. At constant indentation force the tip indents the low density domains more than the high density domains. Low density domains thus appear to be lower in the topography image.
  1. N. Severin, P. Lange, I.M. Sokolov, J.P. Rabe, Nano Lett. 12, 774 (2012).
  2. N. Severin, J. Gienger, V. Scenev, P. Lange, I.M. Sokolov, J.P. Rabe, Nano Lett. 15, 1171 (2015).
  3. H. Lin, A. Schilo, A.R. Kamoka, N. Severin, I.M. Sokolov, J.P. Rabe, Phys. Rev. B 95, 195414 (2017).
  4. S. Zauscher, Z. Parlak, Q. Tu, In: B. Bhushan, ed., Mapping the Stiffness of Nanomaterials and Thin Films by Acoustic AFM Techniques. Berlin: Springer-Verlag, 1023-1051 (2014).

9:30 AM José Danglad-Flores
Max-Planck-Institute of Colloids & Interfaces, Potsdam, Germany
The deposition of thin polymer films on planar solid substrates via spin casting is studied experimentally and theoretically1,2. The polymers are deposited from mixtures of non-volatile polymers with volatile solvents. We investigate for various combinations of different polymers (PMMA, PS, and PS-b-PMMA) and different solvents (toluene, ethyl-acetate), for a wide range of polymer concentrations and spin cast conditions: 1) the final polymer film thickness, 2) the time-resolved film thinning, 3) the time-resolved solvent evaporation, and 4) the evolution of the polymer concentration within the thinning film. The comprehensive experimental data reveal a detailed, time-resolved picture of the spin cast process, which is cast into a rather straightforward, concise theoretical scenario. It is found that easily available bulk properties of the solvent/solute mixture plus a single “calibration” experiment are sufficient for a quantitative description of the spin cast process including even cases of rather high polymer concentrations leading to final film thicknesses of more than micrometers. We also address the structure of molecularly thin polymer films deposited by spin casting on planar substrates pre-coated with nanoparticles of different composition (SiO2, Pt, Au) and sizes between 20 and 200 nm. Real-time optical imaging during the evaporative thinning of the polymer-solvent film reveals the position and the size of the nanoparticles. The nanoparticles cannot be imaged optically because their size is much smaller than the optical resolution limit. However, their position can be visualized optically through their distortion of the film/air interface3. This is confirmed by the surface morphology of dry polymer films with embedded nanoparticles imaged by AFM.

  1. S. Karpitschka, C. Weber, H. Riegler, Chemical Engineering Science, 129, 243 (2015).
  2. J. Danglad-Flores, S. Eickelmann, H. Riegler, Journal of Applied Physics, submitted.
  3. G. Chen, J. Danglad-Flores, S. Eickelmann, H. Riegler J, to be submitted.

10:00 AM Hans Riegler
Technical University of Berlin, Institute for Chemistry, Berlin, Germany
The impact of convex and concave nano size surface modifications on nucleation and growth is investigated experimentally. It is studied which modifications serve as active nucleation sites and demonstrated how they can be used for spatially controlled self-assembly of aggregates precipitated from supersaturated solutions.
 

10:30-10:45 AM

 

 

BREAK

 

SESSION 6

Chair: Martin Schoen

*
10:45 AM Ryan Maloney
Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA
We present a phase diagram of a mixture of two-dimensional rods and spheres with dipole-like short-ranged interactions calculated using discontinuous molecular dynamics simulations. The system undergoes a transition from isotropic fluid phase to a string fluid characterized by an association of the rods into short strings. A second transition from a string fluid to a percolated network occurs as the spheres begin to associate and act as junction points connecting chains of rods. The percolated phase consists of a large network of dipolar rods with smaller clusters of dipolar discs spread throughout the system. We also compare the mixture properties and phase transitions to those of systems of only dipolar discs or dipolar rods to investigate the effects of mixing these two simple systems.
11:15 AM Gerhard H. Findenegg
Stranski Laboratory, Department of Chemistry, TU Berlin, Germany
Adsorption and aggregation of nonionic surfactants at oxide surfaces has been studied extensively in the past, but only for concentrations below and near the critical micelle concentration. Here we report an adsorption study of a short-chain surfactant (C6E3) in porous silica glass materials of different pore sizes (7.5 to 50 nm), covering a wide composition range up to 50 wt.-% of the surfactant in a temperature range from 20°C to the lower critical solution temperature (LCST ≈ 44°C)1,2. Aggregative adsorption of the surfactant is observed at low concentrations, but the excess concentration of C6E3 in the pores decreases and a surface azeotropic point is reached at higher bulk concentrations. Strong depletion of surfactant (corresponding to enrichment of water in the pores) is observed in materials with wide pores at high bulk concentrations. Mesoscale simulations based on dissipative particle dynamics (DPD) were performed to reveal the structural origin of this transition from the adsorption to the depletion regime. The simulated adsorption isotherms reproduce the behavior found in the 7.5 nm pores. The calculated bead density profiles indicate that the repulsive interaction of surfactant head groups causes a depletion of surfactant in the region around the corona of the surface micelles.

  1. G. Rother, D. Müter, H. Bock, M. Schoen, G.H. Findenegg, Mol. Phys. 115, 1408 (2017).
  2. D. Müter, G. Rother, H. Bock, M. Schoen, G.H. Findenegg, DOI:10.1021/acs.langmuir.7b02262.

11:45 AM Irem Altan
Department of Chemistry, Duke University, Durham, NC, USA
Water occupies typically 50% of a protein crystal, and thus significantly contributes to the diffraction signal in crystallography experiments. Separating its contribution from that of the protein is challenging because almost all water molecules are delocalized as a result of the probabilistic nature of solvation, and it is thus difficult to assign them to specific density peaks. The intricate protein-water interface compounds this difficulty. We here compare the solvent structure obtained from diffraction data, for which experimental phasing is available, to that obtained from constrained molecular dynamics (MD) simulations. The resulting spatial density maps show that commonly used MD water models are only partially successful at capturing biomolecular solvation. In general, their radial distribution is captured with only slightly higher accuracy than their angular distribution, and only a fraction of the water molecules assigned with high reliability to the crystal structure are recovered. These differences are likely due to the shortcomings of both the water models and the protein force fields. Despite this difficulty, we nevertheless attempt to infer protonation states of side chains utilizing MD-derived densities, and make some assignments with reasonably high confidence.
 

12:15-2:00 PM

 

 

LUNCH Room 2427

 

SESSION 7

Chair: Jan Genzer

*
2:00 PM Stefanie M. Wandrei
Institut für Chemie, Technische Universität Berlin, Berlin, Germany
We employ classical density functional theory (DFT) to investigate the phase behavior and composition of binary mixtures; each compound consists of hard spheres of different sizes with superimposed dispersion attraction. In addition to the dispersion attraction, molecules of one component carry an additional three-dimensional magnetic “spin” where the orientation-dependent spin−spin interaction is accounted for by the Heisenberg model. We are treating the excess free energy using a modified mean-field approximation (second virial coefficient) for the orientation-dependent pair correlation function. Depending on the concentration of the magnetic particles, the strength of the spin−spin coupling, and the size ratio of the particles, the model predicts the formation of ordered (polar) phases in addition to the more conventional gas and isotropic liquid phases. Key features of our model are a particle-size dependent shift of the gas-liquid critical point (critical temperature and density) and a change in the width of the phase diagram. In the near-critical region, the latter can be analyzed quantitatively in terms of an effective critical exponent βeff that may differ from the classical critical exponent β = ½; the classical value is attained in the immediate vicinity of the critical point as it must. The deviation between βeff and β can be linked to nontrivial composition effects along the phase boundaries.

  1. S.M. Wandrei, D.G. McCarthy, M. Schoen, Langmuir, Article ASAP (2017).
  2. S.M. Cattes, S.H.L. Klapp, M. Schoen, Phys. Rev. E 91, 052127 (2015).

2:30 PM Yiliang Lin
Department of Chemical & Biomolecular Engineering, North Carolina State University, Raleigh, NC, USA; Research Triangle Materials Research Science & Engineering Center, Durham, NC, USA
Metals that are liquid at room temperature are attractive due to their unique combination of fluidic and metallic properties. Gallium-based liquid metal, such as eutectic gallium-indium (EGaIn), are promising alternative for mercury due to their low melting point (m.p. ~15.5°C for EGaIn) and low toxicity. More interestingly, the passivating oxide skin (~3 nm) on gallium-based liquid metal enable non-conventional patterning methods, such as microfluidic injection, to fabricate various kinds of soft electronics, including ultra-stretchable fibers, soft circuit boards, soft antennas and so on. Here, 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. Yet, mechanical pressure sinters locally the liquid metal nanoparticles into conductive paths simply using a writing stylus. Based on this strategy, we fabricated soft circuit boards and flexible antennas with frequency-shifting properties on demand at room temperature. We also demonstrate that it is possible to surface modify the liquid metal nanoparticles as nanomedicine for drug delivery. The transformable liquid metal nanoparticles loaded with drugs can fuse together under low pH in vivo, which facilitates the drug releasing locally to achieve better anti-cancer therapy. In addition to forming liquid metal nanoparticles, we demonstrate the possibility to transform gallium-based liquid metal nanoparticles into nanorods structures in aqueous solution by either moderate heating or light treatment. The transformation phenomenon is well studied and also further utilized as a novel way to remotely control the drug delivery of liquid metal nanomedicine in-vivo through external light source. Surprisingly, the shape changing behavior of the nanomedicine can help achieve better cancer treatment not only through facilitating the drug releasing, but also help break the endosomal membrane due to the aspect ratio change from nanospheres to nanorods.
3:00 PM Josua Grawitter
Institut für Theoretische Physik, Technische Universität Berlin, Berlin, Germany
We study ways to manipulate the surface tension of planar fluid-fluid interfaces using light-switchable surfactants. Light-switchable surfactants are molecules, like AzoTAB, which attach to interfaces and reversibly change their shape under illumination, a process known as photoisomerization. Understanding how they respond to patterns of light could lead to novel light-driven microfluidic devices. The local mixture of surfactants determines local surface tension; therefore, surfactant transport determines the dynamics of surface tension. Surfactants move by diffusion, ad-/desorption, and surface tension-driven advection (the Marangoni effect). We describe all three modes of transport, and photoisomerization, using advection-diffusion-reaction equations. We solve the equations using numerical methods and study the advection patterns produced by spots of light. Spots with constant intensity attract surfactants initially but repel them later on. In some cases, spots with coupled intensities produce oscillating currents between each other. Our study shows that varying the intensity of light spots is a viable method to pump fluid along an interface.
3:30 PM Jana K. Staffa
Physical Chemistry, Technical University Berlin, Berlin, Germany
Electric fields play a crucial role for a wide range of biological processes. For instance, particularly strong fields arise at the interface of lipid membranes and influence the structure and activity of membrane proteins like potential dependent ion channels1. The ion transport through the channels influence the trans-membrane potential. Therefore, it is of highest importance to quantify these electric fields and provide insight into their impact on mechanisms of biochemical reactions. However, the in-situ quantification of these electrostatic fields is still a challenge. A promising approach is based on the so-called vibrational Stark effect (VSE) in which the strength of the electric field can be determined by the shift of the vibrational frequency of a Stark reporter group2. These reporter groups can be introduced into biomimetic interfaces consist of an electrode covered with a self-assembled monolayer (SAM), so that precise electric fields can be applied via an electrochemical potential. In this project, Stark reporter groups will be incorporated in different ways into biomimetic interfaces to determine the intrinsic electric fields of these constructs and to determine the trans-membrane potential of a model membrane system. A useful biomimetic interface to study membrane proteins are SAM-coated electrodes3 or structured membrane models like tethered bilayer lipid membranes (tBLM)4, which display similar interfacial potential distributions. Therefore, the electrode/SAM system was first studied as the simplest model of a biomimetic interface and to determine the interfacial electric fields within a combined spectro-electrochemical and theoretical approach, using surface enhanced IR absorption (SEIRA), attenuated total reflection (ATR), electrochemical impedance spectroscopy (EIS) and density functional theory (DFT). Second, a tBLM with incorporated Stark reporter groups was studied using the same methods and to determine the intrinsic electric field in a model membrane system as well as determine the trans-membrane potential.

  1. J. Kozuch, C. Weichbrodt, D. Millo, K. Giller, S. Becker, P. Hildebrandt, C. Steinem, Phys. Chem. Chem. Phys. 16, 9546–9555 (2014).
  2. G. Schkolnik, J. Salewski, D. Millo, I. Zebger, S. Franzen, P. Hildebrandt, Int. J. Mol. Sci. 13, 7466–7482 (2012).
  3. H. Khoa Ly, N. Wisitruangsakul, M. Sezer, J.-J. Feng, A. Kranich, I.M. Weidinger, I. Zebger, D.H. Murgida, P. Hildebrandt P., J. Electroanal. Chem. 660, 367–376 (2011).
  4. S. Wiebalck, J. Kozuch, E. Forbrig, C.C. Tzschucke, L. Jeuken, P. Hildebrandt, J. Phys. Chem. B 120, 2249 – 2256 (2016).

 

4:00-4:15 PM

 

 

BREAK

 

SESSION 8

Chair: Carol Hall

*
4:15 pm Ankush Singhal
Max Planck Institute of Colloids & Interfaces, Potsdam, Germany
Oil spills are one of the worst environmental disasters in recent history. They affect the whole marine ecosystem along with the habitat near the coastline. One of the major challenges faced in oil spill is the development of the natural materials, which can be used for oil herding and gelling. Chemical herding of oil offers a powerful approach to manage large scale oil spills. Here we aim to introduce a new class of oil-herding agents using environmentally benign cellulose. Cellulose offers lots of advantage, as oil herding and gelling agents over other potential herders such as natural abundance, low-cost, water dispersibility and the ease of functionalizing the large number of hydroxyl groups. The hydrophobicity of the cellulose can be tuned via acetylation of hydroxyl groups making it a profound candidate for this objective. Here, we have developed a coarse-grained model for cellulose polymer where different hydroxyl sites have been acetylated to study its affinity towards the oil. As crude oil consist of long chain hydrocarbons, in our study dodecane has been used as an oil model. Several chemically modified cellulose chains have been simulated in oil and water. Various properties have been studied to evaluate the prospects of modified cellulose as oil herding and gelling agent.
4:45 PM Lei Tang
Department of Mechanical Engineering & Materials Science, Duke University, Durham, NC, USA; Research Triangle Materials Research Science & Engineering Center, Durham, NC, USA
The synthesis of biologically-inspired macromolecules with defined sequence, narrow dispersity, unique structural, and self-assembly properties has large potential ranging from biomedical applications such as nanocarriers for medical therapeutics, to non-biological nanotechnology applications such as DNA-template scaffolds. Here we report terminal deoxynucleotidyl transferase (TdT) catalyzed enzymatic polymerization (TcEP) for the template-free synthesis of high molecular weight polynucleotides. We show that the polymerization proceeds by a living chain-growth polycondensation mechanism and thus the molecular weight of reaction products can be manipulated by the feed ratio of nucleotide (monomer) to oligonucleotide (initiator)1. The underlining living polymerization mechanism allows us to synthesize block co-polynucleotides by sequentially adding different nucleotides (monomer) to the living chain ends. Furthermore, the TcEP synthesized block co-polynucleotides provide access to amphiphilic polynucleotide architectures that can self-assemble into multifunctional micellar structures in solution or into network structures on surfaces2.

  1. L. Tang, L.A. Navarro, A. Chilkoti, S. Zauscher, Angewandte Chemie International Edition 56, 24, 6778-6782 (2017).
  2. L. Tang, V. Tjong, N. Li, Y. Yingling, A. Chilkoti, S. Zauscher, Advanced Materials 26, 19, 3050-3054 (2014).
5:15 PM Radhika Vaid
Fiber and Polymer Science Program, College of Textiles, North Carolina State University, Raleigh, NC, USA
With the advent of new resorbable polymers and the opportunity to use them in a range of different applications, it is important to understand the degradation mechanism in a particular environment, the reaction pathway and change in properties during the resorption process. In this research project we are evaluating a novel polymer, poly-4-hydroxybutyrate (P4HB), for its use as a surgical suture. P4HB is a thermoplastic, aliphatic polyester produced by bacteria. While previous scientific efforts have enabled us to understand some of the properties of this polymer, there are still gaps in our understanding of its resorption or degradation behavior, particularly as a function of pH, which plays a significant role in the rate of suture resorption. Because it has a high degree of polymerization, superior tensile strength and high flexibility compared to polylactic acid (PLA), it is a suitable candidate as a load bearing surgical implant. Like PLA, P4HB also degrades hydrolytically at the aliphatic ester bonds when placed inside the human body. Our research work focuses on the effect of pH on the degradation behavior of P4HB in different hydrolytic environments using both an experimental study and molecular dynamics simulations. This research will be valuable in generating fundamental information about the resorption mechanism and how it correlates with the mechanical performance of P4HB as a suture material and in other medical applications. By understanding how the chemical environment inside the human body influences the rate, mechanism and by-products of the P4HB degradation process, we can confirm its biocompatibility, and predict how to tune the spinning and drawing processes so as to generate the desired resorption profile.
 

6:15 PM

 

Dinner at Lonnie Poole Golf Course
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