Poly(vinylidene fluoride): Crystallization from solution and preparation of Langmuir films

Conditions for the crystallization of block PVDF films from solutions in va rious polar solvent's are analyzed. It is concluded that the crystallizatio n process-proceeds predominantly in the ferroelectric beta-phase. In some c ases, a mixture of polar and nonpolar phases can be formed, which is explai ned by the polymer solution being depleted of the ionogenic impurities that can be trapped on deep traps represented by the polar planes of crystals i n the ferroelectric phase. The type of polymorphous PVDF modification can d epend to a certain extent on the initial state of dissolved polymer. The La ngmuir-Blodgett (LB) films of PVDF were been obtained for the first time an d the conformation of macromolecules in these films was characterized. In t he LB films containing 30 monolayers, the crystallization process takes pla ce in the polar beta-phase having a single-crystal texture (as judged from the value of the final pyroelectric response). The polarization switching i n these films requires a tenfold increase in the coercive field strength as compared to that in the block films. A decrease in the number of monolayer s in the LB films is accompanied by deterioration of the crystal perfection . This is explained by the appearance of flat zig-zag chains having conform ation defects in the form of TGTG(-) and T(3)GT(3)G(-) sequences. These def ects break the crystallographic order in the ferroelectric phase as well. T hese structural changes lead to a significant increase in the coercive fiel ds strength necessary for the polarization switching.