Electric Field Effects on Miscibility of Polymer Blends

摘要

Polymeric blends exhibit limited miscibility because their macromolecular size minimizes the entropy gain on mixing. As such, the phase behavior of polymeric mixtures is extremely sensitive to enthalpic interactions and external perturbations. Methods by which the miscibility of polymeric blends could be tuned or controlled, without changing the underlying chemistry, have great practical benefits for the processing of such blends. One such possible method is the application of electric fields. Although electric fields are extensively used to orient polymer domains in blends and block copolymers, how electric fields alter the underlying miscibility of the system is poorly understood. Available theoretical calculations use thermodynamic arguments for adding an electrostatic free energy term to the total free energy of mixing and predict changes in the phase separation temperature Ts due to external electric fields that are much smaller than what most experimental results report. To date, neither theory or experiments have found a clear consensus on whether uniform electric fields enhance mixing or demixing. As only a few experimental results have been published over the past several decades with typically only small shifts in Ts, more experiments with unambiguously large shifts in Ts are needed to better understand this effect. Using a fluorescence technique we have developed for measuring the phase separation temperature Ts of polystyrene (PS) / poly(vinyl methyl ether) (PVME) blends, we investigate the change in Ts due to the presence of electric fields. We show that electric fields strongly enhance mixing in PS/PVME polymer blends. For example, for a 50/50 PS/PVME blend composition, Ts is increased by over 13 K for electric fields of 17 kV/mm.