Electrical conductivity transformation mechanism of GNPs/CB/SR nanocomposite foams

Highly flexible and electrically conductive graphene nanoparticles/carbon black/silicon rubber (GNPs/CB/SR) based nanocomposite foams were formed by using azodicarbonamide (AC) physical foaming technology. The foaming parameters (foaming agent and foaming time) were analyzed to investigate the influence on the electrical properties and microcellular structure. The electrical percolation threshold of GNPs/CB/SR nanocomposite foams approximately decreases from 25% to 30%, as the volume expansion increases through foaming. Nanocomposite foams with conductive fillers of 3-12 wt %, foaming agent of 12-18 wt %, foaming time of about 150-500 s, relative densities of 1.0-0.4 g/cm 3 were achieved, providing a scheme to evaluate the transformation of electrical properties with different foaming degree. It is worth noting that the product of AC agent concentration and foaming time reaches a certain value, and the highest electrical conductivity of foamed nanocomposites could be achieved. The nonmonotonicity changing of the electrical conductivity was demonstrated. Combined with the microtopography characterization, the cell growth effect was introduced to illustrate the transformation mechanism of the electrical conductivity. The relationship between the microcellular structure and the electrical conductivity of the foamed nanocomposites was established, which is essential for further optimizations of the foaming materials for the targeted application. (C) 2017 Wiley Periodicals, Inc.