Effect of Polymer Molecular Weight on the Viscosity Reduction in Graphene Oxide Suspension

Graphene oxide (GO) has been of particular interest in material science, because it has potential in many applications based on the excellent mechanical and electrical property of the GO. It also exhibits an unique colloidal property based on the high aspect ratio of GO and a noteworthy discovery was that GO can exhibit liquid crystal property in aqueous solution. However, relatively less attention has been paid to GO as two-dimensional colloids. In this study, we examine the detailed microstructure and rheological property of GO dispersions, focusing on their colloidal property. While adding poly(ethylene glycol) (PEG) into GO suspensions can change the state of dispersion and reduce the viscosity of suspension, increasing molecular weight of PEG results in an unexpected viscosity drop. Extensive small angle x-ray scattering and rheology studies were employed to investigate the molecular weight dependent GO dispersions.