Molecular-Level Insights into the Stability of Aqueous Graphene Oxide Dispersions

We present a comparative experimental and molecular-dynamics (MD) simulation study to elucidate the role of oxygen Anictionalization on aqueous dispersibility of-graphene oxide (GO). Our experiniental results indicated better aqueous dispersibility of hydroxyl-rich GO due to distribution of hydroxyl groups on GO basal. plane covering more GO surface area than the edge carboxyl groups. Photoluminescence and UV absorbance results indicated; that hydroxyl-rich GO consists of modinum number of well-exfoliated, GO layers, which leads to the formation of more stable GO,.dispersions. Further, MD simulations.and thermodynamic calculations dearly indicated that the potential of mean force is most repulsive for hydroxyl-modified GO sheets, in comparison to epoxy-and carboxyl-modified GO sheets. An increase in the number of hydrogen bonds between GO and water molecules :was, observed with increased functionalization. The present experimental study, underpinned by MD simulations, suggests that concentration, distribution,,and chemical nature of individual oxygen functional groups present on GO surface determine the strength and nature of interfacial interactions between GO :and water, which in turn decides the stability of aqueous, GO dispersions. Thus, our results provide a mechanistic insight into the stability of GO dispersions and a guide for, controlling GO aqueous dispersibility by custom functionalization.