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Simulations of Polymeric Membrane Formation by Immersion Precipitation: Liquid-Liquid Demixing

Author(s):
Bo Zhou and Adam Powell
Materials Science and Engineering , MIT

The immersion precipitation process makes most commercial microporous membranes, which enjoy widespread use in filtration and purification. This process begins with liquid-liquid demixing of a nonsolvent/solvent/polymer ternary system into polymer-rich and polymer-lean phases. This demixing step determines much of the final morphology. In this work, a ternary Cahn-Hilliard formulation incorporating a Flory-Huggins homogeneous free energy function is used to simulate phase separation during demixing. Then the formulation is coupled with constant-viscosity interface-driven fluid flow. Simulations begin with uniform initial conditions with small random fluctuations, and then with two-layer polymer-solvent/nonsolvent initial conditions to simulate actual membrane fabrication conditions. The results are presented in 2-D and 3-D, which demonstrate the effects of m_{p} (degree of polymerization), K_{ij} (gradient penalty coefficients) and \chi_{ij} (Flory-Huggins interaction parameters) on phase separation behavior.

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Track ID:
Paper #: P7.10
DOI: