Investigation of polymer-coated nano silver/polyurethane nanocomposites for electromechanical applications

Composites based on polyurethane (PU) filled with polyninylpyrrolidone (PVP)-coated silver nanoparticles were prepared for electromechanical applications. The polymer coating of the nanosilver led to a better dispersion of the fillers in the polyurethane films and higher values of dielectric permittivity. Different amounts of Ag-PVP were tested up to the percolation threshold close to 45 wt% of fillers. The dielectric, mechanical and electromechanical properties are presented and discussed. Based on laser interferometer measurements and analyses with a cross characterization device, the optimal electromechanical properties were found for the material with 20 wt% of Ag-PVP: a doubling of the dielectric permittivity was obtained as compared to pure polyurethane. In order to explain the difference between experimental and expected results and consequently to achieve a better understanding of the electromechanical behavior of these materials, various hypotheses were discussed and tested. Results pointed at a drop in dielectric permittivities under high electric fields and a decrease in crystallinity as determined by differential scanning calorimetry.