Thermodynamic structural and morphological investigation of poly(vinylidene fluoride)-camphor systems, preparing porous gels from a solid solvent

Abstract

Poly(vinylidene fluoride) (PVF₂)-camphor systems have been investigated in concentrations ranging from W_PVF2 = 0 to 1 (w/w). The temperature-concentration phase diagram suggests the formation of two different polymer-solvent compounds of an incongruently melting type (C₁ and C₂), a eutectic transition, and a metatectic transition. The data related to the melting enthalpy of the different first-order events provide one with stoichiometries of ½ and ¼ for compound C₁ and compound C₂, respectively (number of camphor molecules per PVF₂ monomer). Time-resolved X-ray experiments carried out as a function of temperature also support the existence of two different compounds. The optical microscopy shows an abrupt change of texture with increasing temperature. The morphology as observed from SEM after drying under vacuum shows tubular, porous structures for concentration below the stoichiometric composition of compound C₂ and the appearance of spherulites above.