THE EFFECT OF THE 2ND-PHASE INVERSION ON MICROSTRUCTURES IN PHASE INVERSION EVAL MEMBRANES

There were many discussions in the literature describing the membrane formation mechanism for the phase inversion process such as liquid-liq uid demixing or crystallization, but few references described the phen omena after the event of the phase inversion process. The purpose of t his work is to illustrate the effect of the second phase inversion on membrane structures when the first phase inversion has occurred. Analy sis showed the second phase inversion (crystallization or liquid-liqui d demixing) may be preceded by the first phase inversion (liquid-liqui d demixing only) during poly (ethylene-co-vinyl alcohol) (EVAL) membra ne formation. Therefore, we can make membranes combined with macrovoid s (the first phase inversion) and particulate morphology (the second p hase inversion) from experiments in this work. As a result, the concep t the membrane morphology only influenced by the liquid-liquid demixin g is misleading and the second phase inversion must be considered as a possible and important mechanism. (C) 1998 Elsevier Science B,V. All rights reserved.