A New Look at the Structure and Thermal Behavior of Polyvinylidene Fluoride–Camphor Mixtures

Abstract

An experimental quasi-equilibrium phase diagram of the polyvinylidene fluoride (PVDF)–camphor mixture is constructed using an original optical method. For the first time, it contains a boundary curve that describes the dependence of camphor solubility in the amorphous regions of PVDF on temperature. It is argued that this diagram cannot be considered a full analogue of the eutectic phase diagrams of two low-molar-mass crystalline substances. The phase diagram is used to interpret the polarized light hot-stage microscopy data on cooling the above mixtures from a homogeneous state to room temperature and scanning electron microscopy data on the morphology of capillary-porous bodies formed upon camphor removal. Based on our calorimetry and X-ray studies, we put in doubt the possibility of incongruent crystalline complex formation between PVDF and camphor previously suggested by Dasgupta et al. (Macromolecules 2005, 38, 5602–5608). We also describe and discuss the high-temperature crystalline structure of racemic camphor, which is not available in the modern literature.

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“…This phase is responsible for the high electroactive nature, high dielectric properties, mechanical strength, thermal stability, and electrical insulation properties of PVDF, which makes it useful for applications that require polar behavior, such as piezoelectric sensors and energy harvesting devices [ 189 ]. The second one is an amorphous phase in which the dipoles are not aligned due to random arrangement of the polymer chains [ 190 , 191 ]. The proportions of these two phases are controlled through processing conditions such as temperature, heating and cooling rate, and strain, which can affect the crystallinity of the PVDF material [ 192 ].…”