THE COMBINED EFFECTS OF EVAPORATION AND QUENCH STEPS ON ASYMMETRIC MEMBRANE FORMATION BY PHASE INVERSION

An analysis of the effects of combined evaporation and quench periods on the formation of asymmetric membranes by the phase inversion technique is presented. The model for the evaporation period assumes binary diffusion and includes composition dependence in the mutual diffusion coefficient and free convection mass transfer in the gas phase. The quench period model includes the use of 4 composition-dependent diffusion coefficients and incorporates a modified form of the interface jump mass balance which enables efficient numerical analysis of composition gradients in the film at the beginning of the quench period. Results for the effects of evaporation-period variables, including: evaporation time, initial cast film thickness, casting surface dimension, and vapor-phase composition, clearly indicate that significant effects of the evaporation period on membrane structure formation and its reproducibility occur within 20 seconds.