Liquid crystal functionalization of graphene nanoplatelets for improved thermal and mechanical properties of silicone resin composites

Abstract

A liquid crystalline molecule, polyurethane-imide (PUI), was used to functionalize graphene nanoplatelets (GNS) via covalent bond and π–π interactions. The PUI functionalized graphene nanoplatelets (PUI–GNS) were characterized by fluorescence spectroscopy, thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman spectroscopy, and then mixed with silicone resin as fillers to fabricate silicon resin nanocomposites. The drastic quenching of the PUI fluorescence elucidated that the biphenyl anchoring unit of liquid crystalline PUI was strongly interacted with the surface of graphene sheets via π–π interactions. FTIR and Raman spectroscopy proved the existence of a covalent interaction between the PUI and GNS. The mechanical properties testing indicated that the tensile strength of silicon resin nanocomposites increased by 521% over that of a neat silicon resin when the mass fraction of PUI–GNS was 1.0%, and the elastic modulus of the silicon resin nanocomposite increased by 902% over that of the neat silicon resin if it came up to 2.0%. The thermal conductivity of the resin filled with the PUI–GNS was improved to be 1.3822 W (m K)⁻¹ at a mass fraction of 10.0%, which was enhanced more than 16.5 times over that of the neat silicon resin. The resulting thermally conductive and mechanically applicable silicon resin nanocomposites could be significant in a wide variety of electronic packaging applications.