Prediction of EVAL membrane morphologies using the phase diagram of water-DMSO-EVAL at different temperatures

The effects of precipitation temperature on the structures of the EVAL memb ranes formed in a wet phase inversion process were studied. As the temperat ure was changed, the phase behavior (liquid-liquid demixing and crystalliza tion boundaries) of the membrane formation system changed accordingly. Ther efore, a wide variety of morphologies of the EVAL membranes could be synthe sized at different temperatures. At low temperatures (e.g., 25 degrees C), the membrane solution precipitated into a particulate morphology that was g overned by the polymer crystallization mechanism, whereas at elevated tempe ratures (e.g., 65 degrees C) liquid-liquid demixing process dominated the p recipitation process and the membrane became cellular in its morphology. In the intermediate cases, the membrane exhibited a structure containing feat ures from both types of phase separations. For the current system, it was f ound that there existed a good correlation between the phase behavior and t he morphology of the membranes. (C) 1999 Elsevier Science Ltd. All rights r eserved.