The crystallinity and piezoelectric properties of spray-coated films of P(VDF70-TrFE30): effects of film thickness and spin-crossover nanofillers

Abstract

Spray coating of the ferroelectric polymer P(VDF-TrFE) appears as an attractive approach for the fabrication of electromechanical transducers. However, it is important to elucidate how the crystallinity and the associated piezoelectric properties depend on the coating thickness and additives. To this aim, we have spray-coated various substrates both with pure and nanocomposite films of 70–30% copolymers in a broad thickness range (200 nm–30 μm). Using X-ray diffraction, differential scanning calorimetry, Raman spectroscopy and atomic force microscopy, we show that the obtained films are dense and homogeneous with ca. 50% crystallinity, which consists of a major polar phase, with slight alterations in the sub-micrometer thickness regime. Robust piezoelectricity and ferroelectricity are revealed at room temperature through both local hysteresis loops and lithography experiments using the piezoresponse force microscopy technique. After poling, the piezoelectric d₃₃ coefficient displays values up to −19 and −11 pC N⁻¹ for the pure copolymer and the composite, respectively. For a 33 vol% load of inorganic spin-crossover nanofillers, the switching properties are substantially improved and a coercive voltage of <10 V is demonstrated for micrometric films. Overall, this approach appears as a promising way for the in situ integration of high quality piezopolymer films into complex transducer geometries for sensing, actuating and energy harvesting purposes.