THE KINETIC-STUDY FOR ASYMMETRIC MEMBRANE FORMATION VIA PHASE-INVERSION PROCESS

The kinetics of membrane formation by phase inversion was studied emph asizing the rate of solvent diffusion from a polymer solution during t he phase separation. Diffusional behavior of the solvent can be consid ered Fickian. Membrane morphologies were shown to be strongly dependen t on the rate of solvent diffusion, indicating that mass-transfer rate s of solvent and nonsolvent during phase separation are crucial for de termining the final membrane structure for the following system: polys ulfone (polymer), dimethyl acetamide (solvent), and ethanol (gelation medium). Specific reference to the mechanism of macrovoid formation wa s explored. Macrovoid formation was found to be proportional to the sq uare root of time, suggesting that it is governed by a diffusion proce ss. In addition, latex particles of coagulated polymer formed by the n ucleation and growth of a concentrated polymer phase was observed insi de the macrovoids. Such a result implies that the macrovoids grow by a diffusive flow which results from the growth of the polymer lean phas e during binodal decomposition. (C) 1996 John Wiley & Sons, Inc.