Formation Of Ultrafiltration Polymeric Membrane Via Phase-inversion: A Monte Carlo Simulation

Polymeric ultrafiltration membrane formed via phase inversion by immersing polymer solution into the nonsolvent bath was simulated with Monte Carlo method; the diffusion dynamics and the effect of thermodynamics on membrane evolution process are studied. The simulation is performed by using bond fluctuation lattice model for polymer in two dimensional spaces where the exchange algorithm of probability density is employed to simulate open and wide coagulation bath. This paper provides details about the dynamics and membrane evolution during the membrane formation, and would be used as a reference and guidance for the experiments.The diffusion dynamics of membrane formation is studied. The quantitative analysis illustrated that the solvent diffusion during coagulation process obeys Fick law, and the diffusion parameter is fitted by Fick's function on different temperature and concentration conditions. The effects of temperature and solution concentration on nonsolvent apparent coefficient are studied. It is found that the apparent diffusion coefficients obeyed Arrhenius equation, and the diffusion activation energy Ea increases while the coefficient A decreases with the polymer concentration increasing. For the effect of concentration on the nonsolvent apparent diffusion coefficient, it is shown an exponent relationship which conforms to Phillies'model expressed by D=D0exp(-acv). It is found that the parameter a decrease with the increase of temperature, and the value of v is between 0.9~1.0.The effects of solution concentration and temperature on membrane morphology are studied. With the diffusion of nonsolvent, a kind of co-continuous structure is observed on proper concentration and temperature condition. The phase separation mechanism of this process is discussed, and the evolution of pores structure within the mico-layers near the interface is provided as a reference and guidance for the experiments. There is no obvious phase-separation on high temperature condition; and polymer-rich phase disperse in the polymer-lean phase as islands on low concentration condition.