Transparent and Hydrophobic “Reduced Graphene Oxide–Titanium Dioxide” Nanocomposites for Nonwetting Device Applications

Graphene oxide–titanium dioxide (GO–TiO2) nanocomposite sheets were transferred onto Si and quartz substrates by Langmuir–Blodgett (LB) technique at different subphase TiO2 concentrations and pH values. The effects of subphase and heat treatment conditions on the composition, surface morphology, microstructure, and hydrophobic performance of the composite sheets were investigated by XPS, Raman, AFM, HR-TEM, and contact-angle measurements. The wetting behavior of composite sheets before and after vacuum heat treatment was analyzed in conjunction with the extent of TiO2 uptake, distribution of nanoparticles over GO sheets, and overall surface roughness. The degree of subphase ionization significantly affects the uptake and aggregation behavior of TiO2, which tends to be dominated by the interaction of TiO2 with carboxylic acid functional groups at the edges of the GO sheets. Wettability studies revealed improvement in the hydrophobicity of composite sheets compared to the GO sheets, which is attributed primarily to the larger surface roughness induced by TiO2 nanoparticles. Heat treatment in vacuum causes formation of a reduced graphene oxide (rGO) wrap on the surface of TiO2 nanoparticles, which substantially enhances the hydrophobicity of the composite sheets. UV exposure causes deterioration of the hydrophobicity of as-transferred composite sheets, while the heat-treated composites retain their superior hydrophobicity, owing to the presence of a rGO wrap, which hinders the reconstruction of surface −OH groups on TiO2. The rGO–TiO2 composite sheets exhibit high transmittance in the visible region and undeteriorated hydrophobic behavior even after prolonged UV irradiation, which have potential applications in the development of flexible transparent nonwetting electronic devices.