The objective of this proposed project is to create dispersions of polymer microgels with an inverse thermo-reversible gelation. They will be liquids at room temperature but become solids at an elevated temperature. The central idea is to design and synthesize polymer microgels with environmentally responsive hydrophobic or hydrogen bonding that are sufficient to hold the microgel assembly together but not too strong to cause flocculation. In contrast to physically crosslinked gels such as gelatin, the building blocks of proposed dispersions are colloidal microgels. With a temperature tunable interparticle potential, these microgels can self-assemble into various mesoscopic structures. This proposed project consists of five aims. The first is to synthesize microgels with two interpenetrating polymer networks (IPN). One network is responsive to a temperature change and the other is not. The balance between these two networks provides a suitable interparticle potential, resulting in an inverse thermoreversible gelation. The second is to design and synthesize biodegradable IPN microgels for the use in thermally gelling dispersions. The concept of thermally gelling microgel dispersions will be extended to include microgels with core-shell structures (Aim 3) and to a mixture of two different microgels with hydrogen bonding (Aim 4). The last aim is to use the IPN microgel dispersion as a model system to experimentally study dynamics of melting, the jamming phase diagram, and the interparticle forces. Intellectual merit: This proposed project is innovative because its designs combine the balances between different polymers, different structures and different inter-particle interactions. The polymer microgel synthesis will be correlated with accurate characterizations by UV-visible spectroscopy, static and dynamic light scattering and rhelogical methods. If successful, it will lead to a new class of polymer microgel dispersions with an inverse thermoreversible gelation. In contrast to all known dispersions including hard spheres or atomic systems, the newly designed microgel dispersion with a single polymer concentration can change from a liquid to a gel by increasing temperature, or to a crystal or to a glass by decreasing temperature. This microgel dispersion can provide a model system to study the fundamental problems in melting and jamming processes that have not been fully explored due to limitations of current available colloidal systems. The proposed project will open an avenue to the development of injectable drug delivery liquids by synthesizing biodegradable microgels as building blocks in the dispersions. Broader impacts: The basic sciences established in this research will have impacts not only in polymer sciences but also in biomedical applications. This program will integrate its undergraduate educational efforts with two existing programs that promote research experiences: the Texas Academy of Mathematics and Science (TAMS) and the Ronald F. McNair Post- baccalaureate Achievement Program at University of North Texas. From this proposed inter- disciplinary project, both graduate and undergradaue students will gain valuable experimental and analytical skills in the rapidly growing fields of biopolymers and nanostructured materials.
