Exploring the Potential of Polymer-Ceramic Nanocomposites for Energy Harvesting: The Role of Particle Functionalization in Enhancing Dielectric and Piezoelectric Properties

The demand for portable and wireless electronic devices, coupled with the need to decrease reliance on non-renewable energy sources, has led to an increased need for energy harvesting and piezoelectric materials. Energy harvesting materials can transform ambient energy into usable electrical energy, but their performance is often limited by their intrinsic properties. To overcome these limitations, nanocomposites have emerged as a promising solution. These composites consist of a polymeric matrix coupled with a high-performance dielectric/piezoelectric phase, which enhances their mechanical and electrical properties. The interface between the polymer matrix and the ceramic filler plays a crucial role in achieving the desired properties and performance of the composite material. Several methods, including surface modification of the ceramic filler and functionalization of the polymer matrix, have been developed to control the interface. This thesis focuses on producing a composite material with high dielectric and piezoelectric properties through a simple and fast production route. Barium titanate (BaTiO3) ceramic nanoparticles are synthesized via wet chemical methods and then embedded into different polymeric matrices to produce nanocomposites. The synthesis parameters for the ceramic nanofillers are optimized to obtain a highly homogeneous final product with a narrow size distribution. The fillers are characterized both structurally and microstructurally through several spectroscopic techniques such as FTIR (Fourier-Transform Infrared Spectroscopy), XRD (X- Ray Diffraction), and SEM (Scanning Electron Microscopy). Then, to enhance their compatibility with the matrix, they are subjected to hydroxylation treatment and functionalized with different organosilanes and characterized. The effectiveness of the functionalization is evaluated through various techniques, proving a successful reaction with high grafting degree for all samples. The particles are then dispersed in epoxy resin and PDMS (polydimethylsiloxane), and nanocomposites are produced with a process that involves the simultaneous application of both heat and electric field and the impact of the presence of surface coupling agents on the particle dispersibility is evaluated through SEM and EDXS (Energy Dispersive X-Ray Spectroscopy). Then, being PDMS the most suitable candidate for the intended applications, an extensive electric and dielectric characterization is carried out on PDMS-based composites through dielectric spectroscopy in a wide range of frequencies and temperatures and measuring the dielectric breakdown strength to evaluate the energy density of the samples and their suitability for energy harvesting applications. To summarize, the incorporation of organosilanes leads to the creation of stronger interfaces, which result in the production of composites with high dielectric constant, good dielectric breakdown, and improved energy density values, even with lower filler content compared to similar studies. These organosilanes are responsible for activating different polarization mechanisms. Despite the challenges that still need to be addressed, the development of energy harvesting, and piezoelectric materials based on nanocomposites has the potential to revolutionize the way we power electronic devices that can be successfully used in applications such as wearables, soft robotics, sensors, and actuators. Overall, this work unveils the significant potential of dielectric nanocomposites in various applications and highlights the need for continued research and development in this field.