Ferroelectric elastomers of functionalized polar fillers in polydimethylsiloxane with improved dielectric and ferroelectric properties

Stretchable ferroelectric nanocomposites were prepared by combining the ferroelectric properties of vinylidene fluoride-based homopolymer (PVDF) and its copolymer based on trifluoroethylene (P(VDF-TrFE)) with the elasticity of polydimethylsiloxane (PDMS). To overcome the incompatibility of the polar filler with the non-polar matrix, functionalization of the filler nanoparticles was carried out. A detailed study of the composite films using optical, thermal, mechanical, and dielectric methods was made to find the impact of functionalization and to study the structure-property relationships in the 0–3 composites. Functionalization improved the mechanical properties as inferred from the reduced Mullins effect. It also increased the dielectric breakdown strength, which can allow higher poling fields (Ep). From the scanning electron microscope images and mechanical tests on the composites with 20, 40, and 60 wt % of fillers, 40 wt % was found to be the optimum concentration and was chosen for further measurements. While a 40 wt % PVDF/PDMS composite at room temperature and Ep = 5 V/μm showed a pyroelectric (p) coefficient of 0.06 μC/m2K, its 40 wt % copolymer counterpart for similar conditions showed a higher p (0.4 μC/m2K). However, the corresponding PVDF and P(VDF-TrFE) composites showed similar piezoelectric d31 coefficients. This improved piezoelectric response of the PVDF composite is explained in terms of the additional contribution from Maxwell-Wagner interfacial polarization. A maximum d31 co-efficient of 8.6 pC/N and 10.1 pC/N was measured for the 40 wt % homo- and co-polymer polar composites, respectively, poled with Ep = 20 V/μm and subjected to 50 % strain with a frequency of 0.1 Hz.