Studies on syntheses and permeabilities of special polymer membranes. 25. Effects of membrane preparation method on structure and permeation characteristics of poly(vinylidene fluoride) membranes

The permeation characteristics and the formation mechanisms of poly(vinylidene fluoride) (PVF₂) membranes were investigated by changing the casting solvent and the exposure period in the preparation conditions of the membranes. Changes of the microporous structure of the resulting membranes with the exposure period are dependent on differences in forming coacervated droplets based on phase separation. Changes of the permeation characteristics and the formation of coacervation by changing the combination of the mixed solvents are related to differences of the form of PVF₂ molecules in the casting solution, to differences of the formation of surface layer with the evaporation of a low and a high boiling point solvent, and to differences of the hygroscopicity of the high boiling point solvent.