Kinetics of Phase Transitions in Multiblock Copolymer Solutions and Gels

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Intellectual Merit of the Proposed Research. Block copolymer solutions in selective solvents exhibit a rich phase behavior forming solutions or gels of spherical or cylindrical micelles. The primary focus of this research is (i) to examine the kinetics of order-disorder and order-order phase transitions between these different states using synchrotron based time-resolved small angle x-ray scattering (SAXS), and (ii) to compare the experimental data with theoretical models and computer simulations to determine structural changes during these transitions and understand the nucleation and growth mechanisms involved in these transitions. The transitions to be investigated include: (i) The transformation kinetics from spherical micelles arranged in various cubic lattices to cylindrical micelles ordered in a hexagonal array and the reverse process.(ii) The effects on the disorder-order kinetics due to the presence of an intermediate metastable or stable phase with a different symmetry than the final ordered state.(iii) Other transitions such as between cubic phases, and between lamellar and gyroid phases.Two novel features of this research are (i) to build a pressure jump apparatus to make almost instantaneous transitions, and (ii) to fabricate nanoscale solid state devices using block copolymer films as templates, e.g. to make a gigahertz nanomechanical resonator. Broader Impacts of the Proposed Research. Solvent mediated interactions are directly relevant to the numerous industrial applications of multiblock copolymer solutions and gels. The research project will also contribute to:1. Enhancement of Infrastructure for Research and Education. (i) The pressure jump apparatus and the data analysis programs will be available to other users at Synchrotron facilities. (ii) The computer simulations will be incorporated into a web-based instructional package being developed for students of Polymer Physics courses at the senior undergraduate and graduate level. 2. Mentoring and Training of Future Scientists and Broadening Representation of Women in Physical Sciences. This research is expected to lead to Ph. D dissertations of two graduate students, as well as to provide research opportunities for undergraduates, both men and women. The students will receive hands-on training in the use of facilities at National Laboratories, participate in local and national meetings, and interact closely with the collaborators from other universities. High school students will participate via BU's Summer Research Program. 3. International collaboration with scientists in Czech Republic is an integral part of this program. The research will be presented at National and International conferences.4. Outreach Activities. The P.I. will continue to give presentations to high school and college students and other general audiences about the broad implications of polymer research via programs such as Freshman Fridays, Science Saturdays and the Pathways Program.