Enhancement of shape memory properties of polyvinylidene fluoride (PVDF) based nanocomposites for dielectric applications

In order to eliminate the negative properties of traditional materials we use in today's technological conditions such as high cost, thermal instability, poor mechanical strength, low corrosion resistance, low electrical conductivity, and toxicity and to meet the needs, nanocomposite materials are being developed in which new properties are imparted to materials at nanoscales. Polyvinylidene fluoride (PVDF) is one of the most important fluoropolymers with multifunctional properties and has been extensively researched in piezoelectric, pyroelectric, ferroelectric and dielectric fields. However, there are limited studies on the shape memory properties of PVDF. In order to improve the functional properties, chemical functionality and surface properties of PVDF, it is necessary to improve its properties with nanoscale reinforcement elements and increase its usage efficiency. In this thesis, it is aimed to improve the shape memory properties (shape stability (Rf) and shape memory ratios (Rr)) of nanocomposites produced by adding different ratios of nanoparticles (ZnO, TiO2, Fe3O4, HAp, GO) into PVDF matrix in order to overcome the deficiencies of PVDF, which is frequently used in dielectric applications, and to improve its high performance properties. PVDF and PVDF matrix nanocomposites were prepared by solution casting method. The structural, chemical, morphological and thermal properties of the produced polymer nanocomposites were characterized and determined by methods such as XRD, FTIR, UV, SEM/EDX, TGA/DTA and DSC. Dielectric spectroscopy method was used to examine the dielectric properties, and in shape memory tests, shape stability (Rf) and shape memory (Rr) ratios depending on temperature were determined by bending tests. It was observed that PVDF nanocomposites exhibited a phase transition from the α phase to the β phase, and the crystallinity increased with the addition of nanofiller content. Moreover, nanoparticles were found to improve the dielectric properties and AC conductivity of the PVDF matrix. Bending tests demonstrated that PVDF and PVDF composites exhibit shape memory properties (Rf and Rr averaging more than 90%) depending on temperature.