Interfacial Behaviors of Ionic Liquid Cations and Asphaltenes at Oil–Water Interface: Dynamic Diffusion and Interfacially Competitive Adsorption

The ionic liquids (ILs) are reported to perform well in enhancing the oil–solid separation (in pure state or in solution) and oil–water separation (in solution) processes through interfacial alteration. Herein, the interfacial behaviors of IL ([C₈mim]­[Br], [C₁₀mim]­[Br], and [C₁₂mim]­[Br]) cations and asphaltenes (from Indonesian asphalt) at the oil–water interface have been investigated through dynamic and equilibrium characterizations. The dynamic interfacial tensions (DIFTs) of toluene–water systems with and without the addition of ILs and asphaltenes are measured. It is found that both IL cations and asphaltenes could diffuse from bulk solution to the oil–water interface quickly, resulting in a competitive adsorption and accumulation at the interface. The IL cations show faster diffusion ability and stronger interfacial adsorbability compared with the asphaltenes. The π-A isotherms and atomic force microscopy (AFM) surface probing of the spreading protocol and the diffusion protocol show that the IL cations could protect the formation of a continuous cross-network, destroying the interfacial asphaltene film. There is also evidence that the efficiency of the interfacial alteration by IL cations is highly dependent on IL cation type. The above results are further understood by the COSMOthermX simulation. These findings suggest that the IL cations show stronger dynamic diffusion and interfacial adsorption properties compared with asphaltenes.