Three-dimensional graphene FOAM/CNT/PDMS composites with exceptional microwave and noise shielding

Graphene foams (GFs) with a cellular structure are prepared based on a chemical vapour deposition (CVD) method. They possess unique properties, such as very low densities, excellent electrical conductivities, and high elasticity and flexibility. GF/poly(dimethyl siloxane) (PDMS) composites are fabricated by incorporating solvent-diluted PDMS into the porous GFs. The unique three-dimensional interconnected porous structure of the composites with inherent percolation can find multi-functional applications requiring electromagnetic wave and sound wave absorption. The GF/PDMS composite with a 90.8% porosity shows the highest electrical conductivity of 6.74 S/cm, leading to the highest EMI SE of average 25 dB in the X-band frequency; while the composite containing a 51.5% porosity is the best performer in terms of sound absorption coefficient in the low frequency 100-1000 Hz. These properties are further enhanced by introducing well-dispersed multi-walled carbon nanotubes (MWCNTs) in the PDMS matrix to form a hybrid structure with two different scales of electrically conductive, open channels. The hybrid composites display significant enhancements in both EMI shielding performance and low frequency sound absorption, compared to the GF/PDMS composites. The GF/MWCNT/PDMS composite with 2 wt.% CNTs and 90.8% porosity delivers an excellent electrical conductivity of 31.5 S/cm and a remarkable EMI SE of ~75 dB, equivalent to nearly 200% increment against the GF/PDMS composite with the same porosity. The addition of MWCNTs significantly improves the overall sound energy dissipation by friction between the CNTs and polymer matrix, leading to a commercially viable sound absorption coefficient of more than 0.3 over the frequency range 100-1000Hz.