Sustainable fabrication of functionally graded material type Ag/silicone rubber nanocomposite by sonochemical effects

In this study, a composite material consisting of silicone rubber and silver (Ag) nanoparticles was fabricated using a sonochemical approach. By irradiating silver oxide (Ag₂O) and silicone rubber in ethanol, a functionally graded material (FGM) was synthesized, in which Ag nanoparticles were incorporated on the surface and interior of the silicone rubber. The structure of the FGM had a smaller composition of Ag nanoparticles from the surface to the inside of the silicone rubber, which changed continuously. This compositional gradient improved the heat resistance of silicone rubber by about 30°C. Although this gradient material had an extremely small Ag loading amount of about 0.5 mg/cm per unit area of silicone rubber, this material exhibited good conductivity (under 10^-4 Ω･cm). Notably, this material can be easily fabricated using ultrasonic irradiation. Due to cavitation effects, even at room temperature and atmospheric pressure, chemical reactions for this FGM between the solvents and solutes occurred. This reaction requires only Ag₂O, silicone rubber, and ethanol as raw materials, and the only byproduct is O₂. Therefore, this sonochemical process is simple and sustainable, as the product can be obtained cost effectively and environmentally friendly.