Effect of difference of dielectric constants between polyvinylidene fluoride and diluents, on the morphology of polyvinylidene fluoride memranes prepared by thermally induced phase separation

The effect of difference of dielectric constants between polyvinylidene fluoride(PVDF) and diluents on morphology of PVDF membranes prepared by thermally induced phase separation(TIPS) was studied. 1,4-Butyrrolactone, dimethyl plithalate, methyl salicylate, glycerol triacetate, carbitol acetate and di-n-butyl phthalate were selected as the diluents, respectively. The results show that the difference in dielectric constants between PVDF and diluents have a certain relationship with the morphology of membrane. The dielectric constant is one of important parameters of interaction among molecules. When the dielectric constant of PVDF is larger than that of the diluent, the attractive interaction among PVDF molecules lead to the aggregation of PVDF and crystallization. The incompact particle structure formed. When PVDF and diluents have a similar dielectric constant, attraction and repulsion exist in the equilibrium. The channel-like structure is formed under the condition of quenching. If the dielectric constant of PVDF is smaller than that of diluent, PVDF molecules crystallize difficultly in the diluent due to the repulsive interaction.