Ionic liquids as dispersing agents of graphene nanoplatelets in poly(methyl methacrylate) composites with microwave absorbing properties

Graphene nanoplatelets (GNP) is noncovalently functionalized with imidazolium-, pyridinium-, and vinyl-pyridinium-based ionic liquids containing bromide or bis(trifluoromethyl-sulfonyl)imide (TFSI) as the counteranions, and used to prepare poly (methyl methacrylate) (PMMA) nanocomposites by solution casting approach followed by compression molding technique. The PMMA composites loaded with 1.9 and 1.8 wt% of GNP in PMMA/GNP composite and PMMA/GNP/ionic liquids, respectively, were characterized by melting viscosity, thermogravimetric analysis and AC electrical conductivity (sigma(AC)). The microwave absorption properties at the X-band (8.2-12.4 GHz) frequency were measured for systems with 1 mm thickness using the metal-backed configuration. PMMA nanocomposites loaded with GNP/N-dodecyl-4-vinyl-pyridinium.TFSI (C(12)ViPy.TFSI) displayed higher thermal stability and higher sigma(AC). This system also presented the best response in terms of microwave absorbing properties, with minimum reflection loss (RL) of around -6 dB at 8.7 GHz. Triple layered composite structures with layers of different conductivities and different stacking orders were also investigated in terms of reflection loss. Broadband absorption with minimum RL <= -10 dB (90% of electromagnetic attenuation) in the frequency between 10.2 and 12.4 GHz and better absorbing effectiveness were observed for the PMMA/GNP-PMMA/GNP/C(12)ViPy.TFSI-PMMA/GNP/C(12)ViPy.Br triple-layered system with 3 mm thickness.