Molecular-Level Insights into the Stability of Aqueous Graphene Oxide Dispersions
2017
Bansal, Prerna | Panwar, Ajay Singh | Bahadur, Dhirendra
We present a comparative experimental and molecular dynamics (MD) simulation study to elucidate the role of oxygen functionalization on aqueous dispersibility of graphene oxide (GO). Our experimental 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 maximum number of well-exfoliated GO layers, which leads to the formation of more stable GO dispersions. Further, MD simulations and thermodynamic calculations clearly 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.
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