Variation of the physicochemical and morphological characteristics of solvent casted poly(vinylidene fluoride) along its binary phase diagram with dimethylformamide

• PVDF membranes have been produced by exploring binary phase diagram with DMF.
• Suitable porous microstructures with large beta-phase contents are obtained.
• Suitable degrees of crystallinity and mechanical properties are obtained.
• The phase diagram of this binary system has been theoretically studied.
• The obtained porous microstructures are suitable for different applications.

Poly(vinylidene fluoride), PVDF, films and membranes were prepared by solvent casting from dimethylformamide, DMF, by systematically varying polymer/solvent ratio and solvent evaporation temperature. The effect of the processing conditions on the morphology, degree of porosity, mechanical and thermal properties and crystalline phase of the polymer was evaluated. The obtained microstructure is explained by the Flory–Huggins theory. For the binary system, the porous membrane formation is attributed to a spinodal decomposition of the liquid–liquid phase separation. The morphological features were simulated through the correlation between the Gibbs total free energy and the Flory–Huggins theory. This correlation allowed the calculation of the PVDF/DMF phase diagram and the evolution of the microstructure in different regions of the phase diagram. Varying preparation conditions allow tailoring polymer microstructure while maintaining a high degree of crystallinity and a large β crystalline phase content. Further, the membranes show adequate mechanical properties for applications in filtration or battery separator membranes.

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