Investigation of the Key Parameters Influencing Crystalline Polymorphism in PVDF Thin Films

This thesis investigates the key processing parameters influencing crystalline polymorphism in poly(vinylidene fluoride) (PVDF) thin films, with particular attention to the formation and stability of the electroactive β and γ phases. Films were prepared using binary DMF/acetone and DMSO/acetone solvent systems with different ratios and deposited by dip and spin coating. The effects of solvent composition, deposition conditions, relative humidity, drying temperature, aging, and annealing were investigated. FTIR was employed as the primary technique for evaluating crystalline phase composition and total crystallinity, complemented by DSC, XRD, and SEM. Solution processing strongly transformed the crystalline structure of PVDF, increasing the electroactive-phase content from approximately 24% in the α-rich starting powder to about 97% in the as-deposited films. Solvent type, solvent ratio, and deposition technique produced comparatively small variations, whereas conditions affecting solvent removal and crystallization, particularly drying temperature and relative humidity, had a stronger influence. Post-deposition annealing produced relatively limited changes until temperatures approaching the melting region, while complete melting and subsequent cooling largely erased the solution-induced electroactive structure and resulted in α-rich recrystallization. Overall, the results show that total crystallinity and crystalline polymorphism are distinct structural parameters and that the crystallization pathway and thermal history play a central role in determining the final crystalline structure of solution-processed PVDF thin films.