281519 Polymer Interfaces and Gradients At Work: Biomaterials and Energy Materials
Materials interfaces often have a critical impact on transport and interfacial properties that play key roles in biological, chemical, and physical processes. For example, successful synthesis of materials for targeted drug delivery or evaluation of cell responses to chemical and mechanical stimuli rely on manipulation of interactions at the cell/material interface. Similarly, the efficiency of conductive membranes, such as those for organic photovoltaic devices, depends on the membrane/electrode interfacial properties as well as materials interfaces within the membrane for multi-component formulations. My research interests are centered on manipulating interfacial interactions to address challenges in two important areas of research: first, to understand and eliminate cancer metastasis, and second, to improve the efficiency of organic photovoltaic devices so that they can become a competitive alternative energy source. A key component of my approach to these problems is the use of gradient surfaces to study interactions in a high-throughput and combinatorial fashion.
During my doctoral work (with Thomas H. Epps, III, Chemical Engineering, University of Delaware), I designed, developed, and implemented new gradient methods for rapidly investigating the effects of substrate and free surface interfacial interactions on block copolymer thin film nanostructure orientation. These methods included: 1) generation of monolayer substrate surface energy/chemistry gradients via a controlled vapor deposition technique that retained the facile implementation of existing vapor diffusion methods while enhancing gradient tunability, and 2) fabrication of a solvent-resistant microfluidic mixing device for gradient solvent vapor annealing (SVA) of thin films that enabled precise control over solvent vapor compositions and concentrations at the free surface of the films. Block copolymers themselves are ideal candidates for the design of interfaces due to the diversity of self-assembled nanostructures (e.g., spheres, cylinders, networks, lamellae). For example, they can be used to lithographically template organic and inorganic nanoscale features, to pattern peptides on surfaces for biological studies, or to fabricate membranes for nanofiltration or organic optoelectronics.
Silicone elastomer networks (SENs) comprising poly(dimethylsiloxane) (PDMS) and/or poly(vinylmethylsiloxane) (PVMS) provide another interesting platform for interface manipulation due to their biocompatibility, tunable mechanical properties, and for PVMS, chemical modifiability via photoinitiated thiol-ene reactions to attach species to the pendent vinyl groups. With this platform for my post-doctoral work (with Jan Genzer, Chemical and Biomolecular Engineering, North Carolina State University), I am developing a scheme that couples chain extension and networking reactions to achieve soft networks (E’ ~ 10 kPa) which mimic the mechanical properties of soft biological tissues, and I am utilizing PVMS networks to direct the assembly of peptides on surfaces.
Future directions for my research will draw upon my experience with block copolymer thin film self-assembly for templating or patterning interfaces, SENs for tuning the mechanical/adhesive component of interfacial interactions, and gradient methods for high-throughput study. PVMS-containing block copolymer systems will provide an excellent foundation for conducting this research. For example, the combined benefits of block copolymer patterning and tunable PVMS mechanical properties could be used to understand cell responses to local mechanical stimuli for cancer metastasis studies, or the PVMS block could be doped with a photosensitive dye and coupled with a conducting block for organic photovoltaic devices. Gradient methods would be used to direct and understand the self-assembly of these copolymers. Considering the plethora of mechanically tough, stimuli-responsive, biocompatible, and conducting polymers that could be incorporated into a PVMS copolymer, my research in this area will provide countless opportunities to contribute to the fields of cancer research and solar energy while simultaneously enriching the polymer physics knowledge base.