A hydrophilicity gradient control mechanism for fabricating delamination-free dual-layer membranes

The present research investigates the solution to solve the delamination issue and control the morphology of dual-layer membranes fabricated from polymer/solvent binary systems without additives, post-treatment and other complicated processes. First, Extem (R), Ultem (R), polysulfone (PSf) and polyethersulfone (PES) were used to study the mechanism behind the adhesion/delamination phenomenon. It was found that adhesion of dual-layer membranes has nothing to do with the similar functional group of top and bottom polymers. Dual-layer membranes with excellent adhesion can be obtained by a newly proposed hydrophilicity control mechanism. More specifically, to obtain a delamination-free membrane, bottom layer should be more hydrophilic than top layer. If not, a significant difference in precipitation rate of the two layers or replacing the coagulant with a milder medium was requested. Then, the method was further extended to prepare multi-layer membranes. Finally, desirable morphology of each layer of dual-layer membranes can be obtained by properly adjusting the thickness and solvent types of top and bottom layers.