Membrane formation of poly(vinylidene fluoride)/poly(methyl methacrylate)/diluents via thermally induced phase separation

The role of the single diluents and mixed diluents on fhe poly (vinylidene fluoride) (PVDF)/poly (methyl methacrylate) (PMMA) blend membranes via thermally induced phase separation (TIPS) process was investigated. The crystallization behaviors of PVDF in the diluted samples were examined by differential scanning calorimetry. The melting and crystallization temperatures of those diluted PVDF blend were decreased with the enhanced interactions between polymer chains and diluent molecules. The crystalUnity of PVDF in the diluent was always higher than that obtained in PVDF blend sample. This can be explained by the dilution effects, which increased the average spatial separation distances between crystallizable chains. Thus, the PVDF crystallization was favored. Additionally, solid-liquid (S-L) phase separation occurred in the quenched samples. Illustrated by scanning electron microscopy, inter- and intraspherulitic voids were formed in the ultimate membranes, which related to the polymer/diluent interactions, the kinetics of crystallization and diluent rejection from the growing crystal. The porosity of the PVDF blend membranes obtained from the mixed diluents was higher than those obtained from the single diluent samples.