Use of graphene nanosheets and barium titanate as fillers in PMMA for dielectric applications

Abstract

A polymer nanocomposite of reduced graphene oxide (rGO) and barium titanate (BaTiO3) with poly (methyl methacrylate) (PMMA) is fabricated. Enhanced dielectric constant hydrothermally synthesized cubic BaTiO3 nanoparticles of 30–65nm size and rGO nanosheets (few layers) are used as fillers, whereas PMMA is used as matrix. rGO is synthesized by improved Hummer’s graphene method i.e., chemical exfoliation of graphitic material using graphite flakes as starting material, graphite flakes are oxidized by KMnO4, H2SO4 and H3PO4, sonicated to achieve graphene oxide (GO), GO is reduced using hydrazine hydrate (NH2NH2·xH2O) to achieve rGO. Results of X-ray diffraction of non-oxidized graphite flakes showed interlayer spacing of 3.2Å. Upon oxidation interlayer spacing increased to 7.5Å indicating incorporation of oxidizing species within graphite layers. The results of Fourier transform infrared spectroscopy (FTIR) indicated presence of carbonyl and hydroxyl groups which confirmed oxidation. Atomic forces microscopy (AFM) analysis showed thickness of 0.9–1.2nm of GO sheets which confirmed exfoliation into few layers. Reduction of GO to rGO is further confirmed with change in interlayer spacing from 7.5Å to 3.2Å with help of X-ray diffraction spectra and by removal of oxidizing species with help of FTIR. Thick films of pure PMMA, PMMA+BaTiO3 (5wt.%) and PMMA+BaTiO3 (5wt.%)+rGO (0.05, 0.1, 0.15 and 0.2wt.%) are casted using Doctor’s Blade method. SEM images showed the uniform distribution of BaTiO3 nanoparticles and rGO nanosheets within polymer matrix. Dielectric properties are measured using precision impedance analyzer. An increase in dielectric constant is observed with the addition of BaTiO3 and rGO. Increase in dielectric constant up to 0.15wt.% of rGO with 5wt.% of BaTiO3 in PMMA matrix is observed; on further increase in rGO concentration a decrease in dielectric constant is observed. It is concluded after achieving a percolation threshold, dielectric constant is reduced. Optimized composition of nanocomposite with 0.15wt.% rGO and 5wt.% BaTiO3 resulted in three fold increase in dielectric constant as compared to pure PMMA.