Strain and temperature induced phase changes inspin‐coated PVDFthin films

Abstract Poly (vinylidene fluoride) (PVDF) is widely utilized for its unique pyro and piezoelectric properties related to its electro‐active β ‐PVDF. In the past few decades, methods of producing β ‐PVDF by mechanical stretching of non‐polar α ‐PVDF have been extensively documented. The aim of the present study is to understand the correlation between phase and mechanical behavior of β‐PVDF obtained directly from spin‐coating, and its stretch‐induced transformation from α‐PVDF. The effect of thermal annealing and in‐plane anisotropy on mechanical properties of spin‐coated PVDF freestanding thin films is investigated, under in‐situ tensile loading, in conjunction with digital image correlation, to measure the full‐field deformation. Stress–strain behavior of spin‐coated β ‐PVDF and α ‐PVDF are correlated with mechanical stretch‐induced phase transformation in α ‐PVDF. The mechanical strength and failure strain exhibited by spin‐coated and annealed α ‐PVDF (~35 MPa and ~5.5) is much higher than spin‐coated β ‐PVDF (~10 MPa and ~0.45). The room temperature mechanical stretching caused α ‐PVDF to β ‐PVDF beyond a stretch ratio of ~1.2, confirmed by both Fourier transform infrared and Raman spectroscopy. Furthermore, mechanical response and spectroscopic analysis confirmed in‐plane anisotropy due to the spin‐coating process in β ‐PVDF.