Effect of solvents on photonic crystallinity in graphene oxide dispersions

Structural color reflections from graphene oxide (GO) dispersions in binary mixtures of deionized water and organic solvents were obtained, and they were investigated at varying GO concentrations using three organic solvents: 1,4-dioxane, N-methyl-2-pyrrolidone (NMP), and dimethylformamide (DMF). Adding organic solvents in the aqueous GO dispersion changes the peak wavelength of the reflection spectrum and the purity of the reflection color, and in particular, the dependence of the peak wavelength on the GO concentration was more sensitive in the binary organic solvents than in pure water. This phenomenon can be explained by considering both the variations of the reflective index and the electrical screening effect in the binary solvents. However, only weak structural coloration based on the second order Bragg reflection was obtained in GO dispersions in pure DMF solvent, and even no structural coloration was observed in organic GO dispersions prepared using dried GO powder. These phenomena are related to the gelation at low concentration and the geometrical deformation of GO particles. Electrical switching of the structural color reflection was also demonstrated.