Phase separation in mixtures of poly(vinylidene fluoride) and hydroxypropyl cellulose

Abstract

Phase separation has been studied in a mixture composed of a crystalline polymer, poly (vinylidene fluoride) (PVDF), and a mesomorphic polymer, hydroxypropyl cellulose (HPC). The mixture was first studied in solution in a common solvent of the two polymers: the ternary phase diagrams showed a large incompatibility between the two polymers with different chemical structures. Then the solvent was evaporated, and phase separation was studied in the resulting solid biphasic films. The determination of binary phase diagrams as a function of temperature revealed that each phase was composed mainly of one polymer. We also studied the influence of various parameters on the size of the droplets in these films: the proportions of the two polymers (the size of the droplets was larger when the two polymers were in equal proportions, and decreased when the quantity of polymer in the droplets decreased), the polymer concentration in the initial ternary solutions (the size of the droplets increased with polymer concentration), the evaporation rate of the solvent (the size of the droplets in the solid films decreased when the evaporation rate was increased) and the molecular weight of PVDF (the size of the droplets decreased when the molecular weight of PVDF was increased). We have tried to explain the variations observed using ternary phase diagrams, Binder's theory concerning mixtures of two polymers in the melt and by macromolecular diffusion phenomena.