Viscous Fluid Dynamics and Characterization of Nano-Structured Polymers

North Carolina State University, Raleigh NC

Investigators

Abstract

Theoretical work over the last years has shown that the dynamics of two-dimensional viscous fluids is a richer phenomenon than hitherto believed and described theoretically. Depending on the hydrodynamic and diffusive time scales, the scaling invariance of phase coarsening can break down and jagged domains can form. In preliminary experiments, the various viscosity regimes considered in the theoretical simulations have been experimentally observed. A detailed quantitative comparison to theory will be made and the phase separation of viscous fluids, such as polymer melts, will be experimentally determined for fluid pairs ranging from highly immiscible to weakly incompatible. The primary model systems will be poly(methylmethacrylate)/polystyrene (PS), PS/brominated PS, and PS/poly(vinyl methyl ether) above their glass transition temperature. It is expected that data is acquired outside the applicability of the present simulations, most notably fluids with asymmetric composition and volume fractions as well as asymmetric viscosities. An interesting extension to binary viscous liquids will be the investigation of systems that contain small particles or beads in one of the phases. Recent theory shows that the addition of hard particles significantly changes both the kinetics and the morphology of the phase separation. In order to generate truly two-dimensional fluids, a special sample preparation method that will sandwich the polymer films between Si3N4 membranes will be developed. The surfaces will be treated to make them neutral or near neutral for the polymers utilized. In the process, control over confinement effects such as changes of viscosity in thin polymer films will be achieved. Near Edge X-ray Absorption Fine Structure (NEXAFS) microscopy will be an important characterization tool, complemented by other microscopies (AMF, VLM, SEM). - Improvements in the theoretical understanding of NEXAFS spectra will be pursued. The accuracy of compositional quantitation will be improved. Students will be trained in executing interdisciplinary research projects situated at the interface of Physics, Chemistry, Materials and Polymer Science. Fundamental understanding of polymer thin films will be advanced, which might improve applications such as coating, adhesives, lubricants, inks and a variety of thin films applications in the semiconductor industry. Part of the effort continues a longstanding collaboration with Dow Chemical.