Molecular Dynamics Study on the Mechanism of Graphene Oxide to Destabilize Oil/Water Emulsion

Previous experiments have demonstrated the capability of graphene oxide (GO) to destabilize oil-in-water (O/W) and water-in-oil (W/O) emulsions, although there are debates on the underlying mechanism. Using molecular dynamics simulations, this work targets an atomistic-level understanding of the mechanism for GO to destabilize O/W and W/O emulsions in the presence of violanthrone-79 (VO-79), a model compound for asphaltene. For both types of emulsions, a GO/VO-79 binary film is formed on the oil/water interface, which can stabilize VO-79 on the interface. Detailed structural analysis shows that the majority of GO in the binary film is parallel to the interface and cause VO-79 to align with them, changing the original interface morphology. The results favor the mechanism that GO destabilizes W/O or O/W emulsions by first forming a film around the emulsion droplets and then enhancing the adhesion between droplets, or between a droplet and the macroscopic oil/water interface, through film-film interactions. Additional interfacial tension (IFT) calculations confirm that GO can increase the toluene/water IFT in the presence of VO-79, which is beneficial for emulsion destabilization.

先前的实验已经证明了氧化石墨烯（GO）能够使水包油（O/W）和油包水（W/O）乳液失稳，尽管对于其潜在机制存在争议。通过分子动力学模拟，本研究旨在从原子水平理解在紫蒽酮 - 79（VO - 79，一种沥青质的模型化合物）存在的情况下，氧化石墨烯使水包油和油包水乳液失稳的机制。对于这两种类型的乳液，在油/水界面上形成了氧化石墨烯/紫蒽酮 - 79二元膜，它能够使紫蒽酮 - 79稳定在界面上。详细的结构分析表明，二元膜中的大部分氧化石墨烯与界面平行，并使紫蒽酮 - 79与它们排列对齐，改变了原始的界面形态。研究结果支持这样一种机制：氧化石墨烯通过首先在乳液液滴周围形成一层膜，然后通过膜 - 膜相互作用增强液滴之间，或者液滴与宏观油/水界面之间的附着力，从而使油包水或水包油乳液失稳。额外的界面张力（IFT）计算证实，在紫蒽酮 - 79存在的情况下，氧化石墨烯能够增加甲苯/水的界面张力，这有利于乳液的失稳。