Morphology of crystalline nylon-610 membranes prepared by the immersion-precipitation process: competition between crystallization and liquid-liquid phase separation

Nylon-610 membranes were prepared at 25 degrees C by direct immersion of va rious dope solutions into either formic acid/water or 1-octanol bath. Depen ding on the dope and bath conditions, the precipitated membranes demonstrat ed characteristics derived from crystallization and/or liquid-liquid phase separation during the precipitation process. As a good dope solution was im mersed in a harsh bath, e.g., water, precipitation occurred initiated by li quid-liquid phase separation. The formed membrane exhibited a cellular stru cture similar to that commonly observed in amorphous membranes. Alternative ly, when a metastable dope (with respect to crystallization) was immersed i n a soft bath containing a substantial amount of formic acid, crystallizati on dictated the precipitation process to yield bi-continuous, particulate m embranes. Membranes with extensive macrovoids were observed, in the event t hat the dope contained a large amount of solvent. In the latter case, preci pitation took place immediately after immersion, consistent with Strathmann and Smolder's results for several membrane forming systems. In addition, s kinless microporous membranes were prepared by precipitation of the dope so lutions in a 1-octanol bath, in which precipitation occurred slowly and the formed membrane was composed of "sheaf-like" crystallites that interlocked into a homogeneous bi-continuous network (C) 1999 Elsevier Science Ltd. Al l rights reserved.