Electric Field Induced Phase Transitions of Polymer Solutions and Mixtures

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9310506 Fuller The morphology and phase behavior of polymer mixtures can be influenced by the application of external fields. This research examines the manipulation of polymer mixture morphology by the use of electric fields. Preliminary results on polymer solutions are offered that demonstrate a variety of new phenomena, such as electric field-induced de-mixing and re- mixing of polymer mixtures. These results suggest the possibility of systematically controlling the interfacial properties of polymer blends, and the manipulation of their domain structure. Such control could be used in the processing of polymer mixtures to arrive at specific bulk material properties and improve interfacial mixing. The research extends these preliminary results to include polymer blends and polymer gels. In addition, both upper and lower critical solution temperature systems will be examined, since the specific shape of the phase boundary is predicted to determine whether application of an electric field will cause either de-mixing (UCST systems) or re-mixing (LCST systems). Finally, the project considers the simultaneous application of electric and hydrodynamic fields, since real processes normally include the presence of flow. Since hydrodynamic forces are also known to affect the phase behavior of polymer liquids, a nonlinear coupling of the effects of electric and flow fields would be expected. The research combines experimentation and theory. Small angle light scattering and scattering dichroism are used to measure the structure of polymer mixtures subject to external flow fields Both experiments methods provide measures of anisotropy in concentration fluctuations and can be used in situ. The theoretical analysis utilizes current mean field approaches whereby the dynamics of concentration fluctuations can be expressed in terms of the relative importance of fluxes due to the external fields and relaxation mechanisms arising from osmotic forces. ***