Electrically conductive foamed polyurethane/silicone rubber/graphite nanocomposites as radio frequency wave absorbing material: The role of foam structure

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Abstract
Radio frequency wave absorber nanocomposites based on a flexible polyurethane (PU) foam has been manufactured by impregnation of the foam in n‐hexane solution of room temperature vulcanizing silicone rubber (SR), hybridized with graphite nanosheets (GNs) called doping solution. After impregnation, dried samples were kept at ambient temperature for the curing of the soaked graphitized SR. To evaluate the influences of the PU foam structural parameters on electrical conductivity, permittivity, and reflection loss characteristics, various foams with different structures were impregnated in the crosslinkable doping solution. Electrical conductivity, real, and imaginary parts of permittivity were measured within the frequency range of 4–6 GHz via performing waveguide measurements. The coarse thick wall PU foam sample exhibited higher conductivity and permittivity than the fine wire mesh sample having similar amounts of conductive SR/GN doping agent. Moreover, nanocomposites based on coarse foam samples showed higher potential for the wave absorption at lower absorber thickness than the fine wire mesh PU foam. The higher conductivity and hence imaginary permittivity of the coarse structure is attributed to the better coincidence of conductive paths in the PU/SR/GN nanocomposite foam with lines of electric field of the incident wave. The higher real permittivity of the coarse nanocomposite is suggested to be related to the more mutual interactions between graphite nanolayers and aggregates which form a network of minicapacitors in the structure of nanocomposites, leading to a higher capacitance and hence more real permittivity. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers

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