Arrested mobility and thermal fluctuation effects on the mass transfer induced phase separation of ternary polymer solutions*

Many polymer membranes are made by immersion of a polymer solution film in a nonsolvent bath: the mass transfer exchange between the nonsolvent from the bath and the solvent in the film induces phase separation of the film into a polymer-rich phase that becomes the membrane matrix and a polymer-poor phase that becomes the membrane pores. Microstructure formation of these membranes is still not fully understood due to the nature of the physical processes involved: the mass transfer induced phase separation, the coarsening of domains, and the vitrification of the polymer-rich phase that arrests membrane microstructure. In this work, we use phase-field models of the ternary polymer-nonsolvent-solvent system to solve the coupled convection-diffusion and momentum equations that describe membrane formation. We model the glass transition using contrasts in the viscosity and mobility of the polymer-rich and polymer-poor phases. We report how glassy dynamics, and the inclusion of thermal fluctuations, contribute to microstructure formation.