Role of dielectric constant, charge, and interfaces on blend thermodynamics
Blending is a cost effective strategy to generate materials with synergistic properties. Recently, theoretical work has predicted that polymers with high dielectric constants or charges along the backbone will exhibit non-trivial deviations in their phase diagrams from neutral polymers. In particular, miscibility can be enhanced by the prescence of salt and/or electric fields. Our group seeks to map out fundamental phase behavior of high dielectric blends. This insight can then be used to engineer low cost membranes with both high ionic conductivity and good mechanical properties, usually a trade-off when dealing with polymer electrolytes.
Over time, immiscible polymer droplets will tend to grow and coarsen leading to a loss of beneficial properties. To control and suppress this phenomena, we will develop ionic surfactants which can compatibilize highly immiscible polymers such as an ionic/non-ionic pair which would be desirable for membrane applications. An understanding of nucleation and growth phenomena in neat and compatibilized systems will be pursued as well as an understanding of 2D vs 3D phase separation. In 2D systems, the role of interfaces and electric field will be examined to form kinetically trapped blend morphologies for applications such as reverse osmosis membranes.
Many aspects of phase separation and blend morphology are impacted by the interfacial tension between components. Model bilayer studies will be undertaken using time-resolved, coherent x-ray scattering at Argonne National Lab. X-ray photon correlation spectroscopy (XPCS) is a powerful tool for measuring surface and interfacial tension as well as the dynamics of concentration fluctuations of phase-separating blends. This work will provide a fundamental insight of the kinetic aspects of thermodynamic phase separation.