Control of Photopolymerization Kinetics and Thermodynamics in Self-assembled Surfactant Systems to Direct Polymer Nanostructure

University Of Iowa, Iowa City IA

Investigators

Abstract

Title: Control of Photopolymerization Kinetics and Thermodynamics in Self-assembled Surfactant Systems to Direct Polymer Nanostructure Proposal #1438486 PI: C. Allan Guymon Institution: University of Iowa Recent research has shown that nanotechnology, or the ability to control material structures at very small size scales, can provide unique and useful properties not accessible in traditional materials. Controlling organic polymer structure in materials similar to plastics and contact lenses at the nanometer scale has shown great promise in improving performance. There have been recent advances in developing nanoscale structure in polymer networks using surfactant, or soap, have involved self-assemblies, which are of particular interest. These surfactant (soap) molecules form lyotropic liquid crystals (LLC) in the presence of water that organize into ordered nanometer scale features which can be used to direct, or template, polymer structures. Materials made up of polymers templated by LLC phases have shown great potential in their response to temperature. They can be used as membranes and scaffolds to regenerate biological tissue. Controlling the structure during the polymerization is still difficult with structures typically being much different than the original template, and thus less useful. For this project the PI will use the speed of polymerization in systems with optimized stability to direct polymer structure evolution within LLC templates. The overall goal is to control photopolymerization kinetics and thermodynamics before and during polymerization, and surfactant/monomer chemistry to understand and direct the structural evolution of polymers formed using LLC media. The PI will modulate surfactant and monomer chemical structure and reactivity to reinforce thermodynamic stability of the LLC-self-assembly to improve interactions between the growing polymer network and the template. These systems will be modeled using computational methods to evaluate the thermodynamic stability of the templating mixtures. It is believed that the use of radical photopolymerization will play a pivotal role in successful completion of this work. 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. Polymer nanostructures formed from both traditional chain and thiol-ene step growth photopolymerization mechanisms will be investigated. Critical for project success is the connection between the polymerization kinetics and polymer structure evolution. Polymerization rate, conversion, and phase separation will be monitored in real time using photo-differential scanning calorimetry and through infra-red and Raman spectroscopy experiments. Thermodynamics and kinetics will be correlated to nanostructure before, during, and after polymerization using numerous characterization techniques (small angle X-ray scattering, electron microscopy, solid state and solution NMR). The PI believes that this research will outline the kinetic and thermodynamic factors necessary to direct and control the ultimate polymer nanostructure. This project will provide a relatively simple approach to controllably produce nanostructured organic polymeric materials. Polymers with controlled nano-scale geometries will exhibit unique transport properties and size selectivity, which are critical for advances in applications such as water purification, stimuli response, tissue scaffolds, and hydrogels. A prevailing theme for this research will be student education. Extensive involvement of undergraduate and graduate researchers in a discovery learning environment will be emphasized. Minority undergraduate and graduate researchers will be recruited as part of the NSF REU Program in Nanoscience and Nanotechnology. Additionally, the importance of polymers, nanotechnology, and chemical engineering will be brought to high school students as part of two modules presented yearly to chemistry classes at both local and rural high schools.