Effects of GNP addition on optical properties and band gap energies of PMMA films

Abstract

In this study the effects of graphene nanoplatelet (GNP) doping on the optical parameters (absorption coefficient alpha and extinction coefficient k) and the optical transition energies (optical band gap and Urbach energies) of poly(methyl methacrylate)/graphene nanoplatelet (PMMA/GNP) composite films were studied. PMMA/GNP composite films with various GNP mass fractions were prepared by spin coating technique. The absorbance (A) changes of the prepared composites were measured by using UV-Vis technique. The alpha and k values of the composites were obtained from UV-Vis data. The observed rapid increase in A values in UV-region were associated with the optical transitions of GNP electrons from valence to conduction band. The direct (E-d) and indirect (E-i) optical band gap energies of the composites were determined by using Tauc method. Both of the band gap energies were decreased when the GNP content in the PMMA matrix is increased. The decrease in the band gap energies was interpreted as evidence of increased conductivity of the composites. Additionally energies of the band tails (Urbach energy) were calculated. It was seen that the Urbach energy levels were increased with GNP content. POLYM. COMPOS. 40:1862-1869 2019. (c) 2018 Society of Plastics Engineers