Preparation of a novel bi-layer modified alumina-based hybrid material and its effect on the thermal conductivity enhancement of polymer composites

In this work, a new kind of double layers modified alumina-based hybrid (silver@copper@alumina (Ag@Cu@Al2O3) hybrid) was successfully synthesized through the two-step layer-by-layer process. First, copper (Cu) nanoparticles were assembled onto alumina (Al2O3) particles by reduction of Cu2+. Second, Ag@Cu@Al2O3 hybrids were assembled via Ag deposition on the surface of Cu@Al2O3 particles. The obtained Ag@Cu@Al2O3 hybrids served as thermally conductive fillers to greatly boost the thermal conductivity of poly (dimethylsiloxane) (PDMS). The thermal conductivity reached 1.465 W m(-1) K-1 at 85 wt% filler loading. The thermal conductivity of PDMS matrix was increased more than 7 times by the addition of Ag@Cu@Al2O3 hybrid, which was much higher than single layer modified alumina-based hybrids (Ag@Al2O3 and Cu@Al2O3 hybrids) and virgin Al2O3 particle. The effect of double layers modified filler, single layer modified filler and virgin filler on the thermal conductivity of PDMS matrix was discussed in detail and the mechanism of these fillers for improving thermal conductivity was studied through Foygel's thermal conduction model. Otherwise, electric, mechanical and thermal properties of Ag@Cu@Al2O3/PDMS composites were also further tested and analyzed.