The effect of the second 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–liquid demixing or crystallization, but few references described the phenomena after the event of the phase inversion process. The purpose of this work is to illustrate the effect of the second phase inversion on membrane structures when the first phase inversion has occurred. Analysis showed the second phase inversion (crystallization or liquid–liquid demixing) may be preceded by the first phase inversion (liquid–liquid demixing only) during poly (ethylene-co-vinyl alcohol) (EVAL) membrane formation. Therefore, we can make membranes combined with macrovoids (the first phase inversion) and particulate morphology (the second phase inversion) from experiments in this work. As a result, the concept the membrane morphology only influenced by the liquid–liquid demixing is misleading and the second phase inversion must be considered as a possible and important mechanism.