An effect of ionic liquids on polymorph transformations in polyvinylidenefluoride at its crystallization from solution

According to IR spectroscopy data, crystallization of polyvinylidenefluoride from dimethylformamide and dimethylsulfoxide solutions at 100 °C and 80 °С is accompanied in the last case by the formation of polymorph modification mixtures of γ and β phases. In the presence of a number of ionic liquids, the same crystallization is accompanied by conformation transition in polymer chains from T₃GT₃G⁻ to the conformation of a planar zigzag. We think that it takes place due to ion-dipole interactions between cations of the imidazole ring with fluorine atoms of polymer chains in the amorphous phase. X-ray data show that polar crystals of the β phase of non-doped polymer contain many conformational defects in the form of T₃GT₃G⁻ isomers. At polymer doping with ionic liquid, the number of such defects is lowering. Due to this, the density of crystals formed grows. Conformation changes noted affect the signal of electromechanical response fixed by piezoresponse force microscopy. In particular, it has been shown that in the film under conditions of crystallization chosen process of self-polarization, which is registered by the method of Kelvin mode, takes place.