Kinetic Control of Polymer Nanostructure in Lyotropic Liquid Crystalline Systems

University Of Iowa, Iowa City IA

Investigators

Abstract

ABSTRACT PI: Allan Guymon Institution: University of Iowa Proposal Number: 0626395 Title: Kinetic Control of Polymer Nanostructure in Lyotropic Liquid Crystalline Systems Project Summary: The use of self-organizing liquid crystals is a means of achieving structural and chemical control of organic polymers on the nanometer scale for enhanced performance. One area that has recently received a great deal of interest is the development of functional nanostructured polymer materials based on lyotropic (i.e., amphiphilic) liquid crystals (LLCs) which 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 using polymerized LLC materials is the ability to retain and control this structure throughout the polymerization. Typically, thermodynamically driven phase separation occurs during polymerization, leaving little or no liquid crystalline order. The polymerization kinetics in LLC systems are highly dependent on order, but the direct correlation between the polymerization rate and ultimate polymer nanostructure has not been explored. Intellectual Merit: The goal of this research is to use the speed of photopolymerization to predict and control the nanostructure produced in LLC systems. Research will focus on reactive surfactant monomers that form LLC phases and both polar and non-polar monomers templated by nonreactive LLCs. The photopolymerization of materials spanning a wide range of LLC phases will be monitored to understand changes that occur during polymerization. Factors that may influence polymer morphology including LLC phase structure and stability, cross-link density, monomer polarity, and double bond location will be examined. Radical photopolymerization 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. Polymers 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, and scanning electron microscopy) will be used to elucidate polymer structure. 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 facilitate development of a complete model outlining the factors, both kinetic and thermodynamic, governing the ultimate polymer nanostructure. Broader Impact: One of the most promising advances that could result with the recent emphasis on nanotechnology is the ability to control properties based on nano-scale architectures produced in organic polymers. This work proposes methods to reproducibly produce nanostructures based on LLC geometries using the inherent speed of photopolymerization allowing control of polymer properties based on nanoscale geometries. If such control can be achieved, substantial advances in applications as diverse as separation technology, hydrogels, and tissue engineering could be realized. A prevailing theme 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 proposed 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 by the PI to chemistry classes at both local and rural high schools.