SOFT POLYMERIC NANOCOMPOSITES FOR ELECTROMECHANICAL CONVERSION

Soft electro-mechanical transducers are receiving a widespread interest for both sensing and energy harvesting applications. In the last decade the research on novel nanocomposites based on polymeric nanocomposites has been very active, and many materials with diverse and innovative compositions and architectures have been fabricated and reported. Nevertheless, there are still some critical aspects that affect this research field, in particular for what regards their characterization. Despite the widespread interest that these smart materials are attracting, the methods commonly used to characterize them are frequently qualitative and unreliable. Moreover, the description of the testing conditions is often incomplete, so that the data cannot be reproduced by other researchers, and the performances of the various materials cannot be compared. The knowledge of these properties is necessary for a complete understanding of the material working principle, for the prediction of its effective properties aimed at optimization purposes, and for the selection of the right material in device applications. In this framework the development of a quantitative and reliable measurement technique is crucial in order to to assess these materials figure of merit, their reliability and reproducibility. This thesis work is focused on the fabrication and characterization of materials with electro-mechanical conversion capabilities, for applications in both energy harvesting and pressure and strain sensing. Four different kinds of materials were developed and tested, three active materials based on piezoelectric BaTiO3 nanoparticles on different polymeric matrixes, that can be applied both as sensors and as energy harvesters, and a passive material based on a piezoresistive polymer/metal nanocomposite, which can be applied as a strain sensor. For the characterization of such nanocomposites, a custom experimental set-up to measure the piezoelectric coefficients in a wide frequency range was developed and validated.