Kinetics of thermally induced phase separation in the PVDF blend/methyl salicylate system and its effect on membrane structures

Microporous membranes were prepared via thermally induced phase separation of a poly(vinylidene fluoride) (PVDF)/poly(methyl methacrylate) (PMMA) blend (with mass ratio = 70/30)/methyl salicylate system. The differential scanning calorimetry results revealed that the observation of double melting phenomenon in quenched samples was a result of a variation in the morphology (different crystal size or perfection of crystals), which formed during the sample preparation. When the samples were quenched at 118C, 110C, and 100C, a spherulitic structure was present in the membranes due to the crystallization of PVDF. As the holding time period increased, the crystallization of PVDF was enhanced owing to the aggregation of a polymer-rich phase (PVDF/PMMA blend) during the phase separation. The structure of the resulting PVDF blend membranes, detected by scanning electron microscopy, was greatly affected by liquid-liquid phase separation and the crystallization of PVDF in the mixture.