(376ai) A Phase Field Method for Mesoscopic Modeling of Porous Polymer Membrane Formation Via Phase Inversion
Phase inversion, a process that occurs when a polymer collapses from solution into a thin film upon quenching or exposure to another phase, is the most widely used process for producing porous polymer membranes. Modeling of this process has been mostly limited to the continuum level and empirically-derived parameters, with little theoretical basis to connect the process conditions and important characteristics of membrane microstructure. We have developed a large scale three-dimensional mesoscopic simulation model to examine the dynamics of the phase inversion process to predict the morphology of pore structures that develop within polymer membranes. The computational approach is a novel phase-field method based on the Cahn Hilliard equation, which incorporates the thermodynamic and transport parameters relevant to phase separation in polymer solutions. The thermodynamics of mixing for phase equilibrium is described by the Flory-Huggins free energy of mixing for binary solutions. The transport processes are assumed to be diffusive in nature and are dependent on the local temperature and polymer concentration. The proposed large scale three-dimensional model explores parameters relevant to industry in order to capture mesoscopic pore formation. A range of polymer volume fractions and quench rates were investigated to verify the modelâs capability of forming bi-continuous to discrete morphologies. Analysis of pore size and continuity quantify the resulting porous structures and allow comparison to experimental results. The modeling tools developed will enable significant speed-up in membrane development. This talk will focus on initial results of the Cahn Hilliard model and compare simulated structures and morphologies to current manufactured polymer membrane filters.