Dependence of electromagnetic interference shielding ability of conductive polymer composite foams with hydrophobic properties on cellular structure

The introduction of cellular structure in conductive polymer composites is supposed to be an effective way to ameliorate the electromagnetic interference (EMI) shielding properties. Moreover, the wetting behavior should be taken into consideration when exposed to a moist environment. Herein, oleophilic conductive poly(vinylidene fluoride) (PVDF)/multiwall nanotube (MWCNT) composite foams were successfully fabricated through a simple and effective batch foaming process. PVDF/MWCNT nanocomposite foams with various microcellular structures were obtained by controlling the foaming parameters (MWCNT content and impregnation temperature). The electrical conductivity (EC) and EMI shielding properties critically depended on their microcellular structure. Interestingly, the EC and EMI shielding properties declined with a higher degree of foaming in the range of 37 %–67 % for PVDF/1 wt% MWCNT (FC1) and PVDF/2 wt% MWCNT (FC2) nanocomposite foams. Conversely, for the PVDF/5 wt% MWCNT (FC5) and PVDF/8 wt% MWCNT (FC8) nanocomposite foams, the EC and EMI shielding properties gradually increased with an increased degree of foaming in the range of 27 wt%–40 wt%. The optimal EMI shielding properties of PVDF based nanocomposite foams containing MWCNT contents of 1 wt%, 2 wt%, 5 wt% and 8 wt%, reached 18.6 dB, 31.5 dB, 88.3 dB and 132.6 dB, respectively, at a sample thickness of 4.0 mm. Analysis of the EMI shielding mechanism found that absorption resulting from multiple reflections and scattering, and strong conduction band polarization loss were the main contributing factors. Moreover, the PVDF/MWCNT foams were hydrophobic, indicating that they could be competitive candidates for EMI shielding and oil/water separation multi-functional applications.