Characterization of the surface layer of integrally skinned polyimide membranes: Relationship with their mechanism of formation

摘要

AbstractA series of dense films and membranes was prepared using different processes; their surface morphology was investigated by transmission electron microscopy using the replication technique. On the basis of TEM results, SEM observations of cross sections of membranes and gas‐separation properties of membranes, two kinds of membrane morphology are evidenced in relation to their preparation conditions and final properties. The first one gives an ultrafiltration‐type membrane. Large nodules are observed on the surface of the membranes. It is suggested that these are formed by liquid–liquid separation that occurs by nucleation and growth of the polymer‐rich phase. The second one yields gas‐separation‐type membranes. No nodules are evident at the surface of these membranes. The skin is formed by a step that concentrates the initial solution. It is followed by the transformation of the solution in the glassy state. Liquid—liquid separation takes place below the first skin layers by nucleation and growth of the polymer‐poor phase. © 1993 John