Nano-Infiltration for Enhancing Microwave Attenuation in Polystyrene-Nanoparticle Composites

Polymer-based composites have emerged as promising candidates for microwave attenuation. It is now understood that, in order to enhance this attenuation, the amount of functional nanoparticles in the system has to be very high. However, this is limited by the processing challenges because the mixing parameters affect the way the nanoparticles are dispersed in a polymer nanocomposite. Although it is possible to achieve good mixing with the help of current state-of-art technology, the maximum amount of nanoparticles that can be incorporated is limited by several factors. Herein, a unique strategy (nanoinfiltration) is described to increase the filler concentration based on the dynamics of polymer chains in the presence of a solvent that is reported for increasing the filler concentration. Upon spin coating of a polymer solution containing well-dispersed nanoparticles, the solvent causes the polymer to swell, thereby increasing the available free volume where the nanoparticles can get trapped. Interesting morphologies were observed when nanoparticles of different shapes [spherelike Fe3O4, rodlike multiwalled carbon nanotubes (MWCNTs), and sheetlike graphene oxide (GO) and also hybrid structures like reduced graphene oxide, rGO–Fe3O4 and rGO–MoS2 were spin-coated. This establishes a strong correlation between the morphology of the nanoparticles and the free volume and characteristic length of the polymer chain. This approach was extended to design conducting nanocomposites in order to explore them for EMI shielding applications. Herein, we have employed nanoinfiltration to embed different nanoparticles into a composite of recycled polystyrene with multiwalled carbon nanotube (PS–MWCNT). It was observed that the shielding effectiveness of PS–MWCNT was enhanced up to −35 dB after being subjected to nanoinfiltration with rGO–MoS2. In order to evaluate the efficacy of this strategy, PS–MWCNT was sandwiched between two sheets of porous poly­(vinylidene fluoride) containing rGO–MoS2. In doing so, a sharp decrease in the value of the EMI shielding effectiveness was observed. This hence suggests that nanoinfiltration proves to be a useful tool to enhance the radiation shielding property of conducting nanocomposites.