Adsorption of graphene-oxide nanoparticle at a water-vapour interface: a molecular dynamics investigation

Graphene oxides (GO) is used as a particulate surfactant to change the interfacial properties of drops and bubbles. To get insights into the processes governing GO adsorption, we use molecular simulations to simulate GO nanoparticles at the interface between water and vapour. We first extract the free energy profile normal to the interface for a single particle with varying degree of functionalization at the basal plane and varying particle size using umbrella sampling. We found that the affinity of the particle with the interface decreases for increasing degree of functionalization, and that only particles with a degree of functionalization lower than a threshold are interfacially actives. This is in agreement with experimental observations. We then use molecular dynamics to evaluate the behaviour of a single GO particle at the interface and show that, as a consequence of hydrophilic and hydrophobic patches at the particle surface, a GO particle only partially adsorbs to the interface. Finally we evaluate the role of particle-particle interactions on adsorption as well as on the surface tension by exploring the case of multiple GO particles. Implications of our results for drops/bubbles stabilisation will be discussed.