Postdoctoral Fellow, 2004-2007
Postdoctoral Fellow, 2002-2003
Ph. D., Physical/Analytical Chemistry, 2001
B. S., Chemistry, 1995
Research Focus: Smart Materials, Novel Structure Assemblies, and Unorthodox Micro- and Nanofabrication Techniques
Reconfigurable Assemblies of Particles by Magnetic Fields
Both magnetic and electric fields are used for polarization-based assembly. Practical applications of this phenomenon are found in electro- and magneto-rheological fluids where the fluid viscosity can be controlled by the strength of the applied field. The assembly of complex, well-defined structures by these methods is recent and has shown promise for programmed assembly. We are exploring several advantages of using magnetic rather than electric fields for the assembly of Janus particles:
a) Magnetic interactions are not screened by common aqueous solutions, whereas electric moments are exponentially screened. As a result, magnetic interactions are much stronger and their magnitudes are much easier to predict on length scales > 100 nm.
b) Common ferromagnetic materials have substantial remnent magnetizations. Combined with the lack screening, such dipoles can be assembled into stable structures in the absence of magnetic fields (without the need for energy input to maintain the structure).
c) Remote demagnetization of the stable structures can be applied remotely, and can be used for recycling structures to their building blocks for further reassembly into different structures.
Figure 1: Uniform latex particles (4.1 µm diameter, half-coated with a thin iron layer) assemble into chains in an applied magnetic field. Their metal coatings are in contact with each other. A) Close-packed “double” chains and B) non-close packed “staggered” chains observed for Janus spheres with low and high magnetic moments, respectively. C) Assemblies persist in the absence of magnetic fields and even moderate agitation. D) Remote demagnetization of the chains can recycle them back to their building blocks.
Nanospinning – A Novel, Scalable Method for the Production of Nanofibers
We have developed a novel method for fabricating nanofibers from solution. It does not use high electric fields to make the fibers but, like electrospinning, it can produce nanofibers from most polymer solutions. It is based on the spontaneous self-assembly of very large numbers of nanofibers in parallel. This patent-pending technology is in the evaluation and scale-up stages as an economical method for the bulk manufacture of nanofibers. It has the potential to achieve production rates similar to well-established techniques, such as melt spinning, while not restricted to only melt-process polymers. The economical spinning of natively hydrophilic and functional nanofibers is of great interest for liquid filtration and protein affinity separation applications where coatings and treatments are necessary to make melt-spun fibers compatible with the application. The technique is also suitable for the fabrication of functional and composite nanofibers with particulate additives. We are continuing the development of nanospinning with support from the National Science Foundation (Grant No. 0927554).
Figure 2: Nanospun fibers in a nonwoven mat produced by our scalable technology.
Encapsulation and Delivery of Pharmaceuticals and Nutraceuticals
Programmed, timed delivery of pharmaceuticals and nutraceuticals is necessary to ensure optimal dosing of drugs, as well as the non-simultaneous release of incompatible drugs that cause adverse interactions. We are developing efficient polymer encapsulation techniques for such programmed release of compounds and a microfluidic platform for the integrated testing of the timed delivery. We are particularly interested in the mechanisms of encapsulation of pharmaceutical and nutraceutical particles. One strategy for the efficient encapsulation is the use of electrostatic charges on the polymer matrix to trap the oppositely charged payload particles. The active compounds are released from the matrix in a programmed fashion by using responsive, biocompatible polymers. The research is in collaboration with Dr. Krassimir Velikov, Unilever R&D, The Netherlands.