Molecular Dynamics study of the effect on the interfacial activity of Alkylamine-Modified graphene oxide

• n-alkylamines causes a synergistic effect on the interfacial properties of GO. • The hydrophobicity of the GO can be tuned by the aliphatic chain length of the n-alkylamines. • aGO behave like a molecular surfactant, decreasing the IFT of the Toluene-Water system as the number of sheets increases. • The GO functionalization with n-alkylamines can change the orientation of the materials at the interface. Several experimental studies have shown that chemical modification of graphene oxide with n-alkylamines allow to control its interfacial activity in oil–water systems, altering its dispersibility and favoring the formation of emulsions. However, due to the complexity of its chemical structure and experimental limitations, the emulsification mechanism and interfacial properties have not been fully understood. In order to understand the behavior at the oil-water interface of alkylamine functionalized Graphene Oxide (GO) based materials, in this research we evaluated the interfacial activity of GO functionalized with different alkylamines (aGO) with different aliphatic chain lengths of 1, 3, 5, 7, 9 and 12 carbon atoms by Molecular Dynamics simulations. The dispersibility of the GO-based materials was analyzed and it was found that the Hydrophilic-Lipophilic Balance (HLB) of the GO can be controlled with the alkylamine chain length, making the GO more hydrophobic as the aliphatic chain length of the alkylamines becomes longer. Alkylamine chains bonded on the GO structure were capable to modifying the orientation relative to the Toluene/Water interface, going from parallel for the GO case to orthogonal for the aGO nanosheets, adopting a “head–tail” configuration due to the hydrophobic effect between the aliphatic chains and the Water molecules. Simulations also revealed that synergistic effect of aGO can decrease the interfacial tension of the Toluene-Water system as the aliphatic chain length and number of sheets increase obeying the Traubés rule, indicating a behavior like molecular surfactant, where the IFT of the system decreases as the amount of surfactant increases.