This award is funded under the American Recovery and Reinvestment Act of 2009 (Public Law 111-5).
The use of self-organizing liquid crystals is a method of enhancing performance of organic polymers through structural and chemical control on the nanometer scale. Functional nanostructured polymer materials based on lyotropic (i.e., amphiphilic) liquid crystals (LLCs) have the ability to self-organize in the presence of water into ordered assemblies with periodic nanometer-scale porous domains. Both polymerized LLC monomers and polymers templated by LLCs have recently shown great promise in applications such as solid-state organic catalysts, size selective membranes, and tissue engineering scaffolds. The major obstacle in forming nanostructured polymers using LLC systems is the difficulty in retaining and controlling the self-assembled structure throughout the polymerization. Typically, thermodynamically driven phase separation occurs during polymerization, leaving little or no liquid crystalline order. The PI plans to control both thermodynamic and kinetic factors to direct specific polymer nanostructures from LLC materials. Intellectual Merit: The goal is to utilize the polymerization reaction to direct organic polymer nanostructures through combination of photopolymerization and optimal LLC self-assembly. Research will focus on developing combinations of non-reactive and reactive surfactant systems that form LLC phases. These systems will then be used to template ordered morphology onto polymer networks. The photopolymerization of materials spanning a wide range of LLC phases will be monitored to understand changes in the order that they occur during polymerization. Factors that may influence polymer morphology including LLC phase structure and stability, cross-link density, and polymerization kinetics will be examined. It is assumed that the use of radical photopolymerization will play a pivotal role in this work. This method provides the ability to polymerize in fractions of a second at a wide range of temperatures, thereby allowing kinetic trapping of otherwise thermodynamically unfavorable polymer nanostructures. Polymer structures formed from both traditional chain and thiol-ene step growth polymerization mechanisms will be investigated. With the importance of nanostructure in this project, a number of powerful characterization tools (polarized light microscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy, solid state NMR, and swelling behavior) will be used to elucidate polymer structure during and after polymerization. Critical for success in this research effort is a thorough understanding of the photopolymerization process, including the unique aspects induced by a nanostructured environment. Therefore, photopolymerization kinetics and double bond conversion will be monitored in real-time using photo-differential scanning calorimetry, infra-red and Raman spectroscopy. The results obtained will outline the factors, both kinetic and thermodynamic, that can be used to govern and direct the ultimate polymer nanostructure. Broader Impact: One of the greatest promises of nanotechnology is the ability to control properties based on nano-scale architectures in organic polymers. This work will produce nanostructures reproducibly and consistently based on LLC geometries. Using the inherent speed of photopolymerization and optimal self-assembly throughout polymerization, control of polymer properties based on nano-scale geometries will be afforded. With such control substantial advances in applications as diverse as separation technology, drug delivery, catalysis, hydrogels, and tissue engineering could be realized. A prevailing theme in the project will be student education. Extensive involvement of undergraduate and graduate researchers in a discovery learning environment will be emphasized. The PI has a strong record of including minority student researchers at both the graduate and undergraduate level. At least one minority graduate student will directly participate in the research, and minority undergraduate researchers will be recruited as part of the AGEP Summer Research Program at the University of Iowa. Additionally, the importance of polymers in nanotechnology will be brought to high school students as part of a module presented yearly by the PI to chemistry classes at both local and rural high schools.
