Experiments, molecular dynamics simulations, and quantum chemistry calculations on the effect of gemini surfactants' headgroup on the oil-water interfacial tension.

The effect of the Gemini surfactant headgroup on the oil-water interfacial tension has yet to be systematically revealed. In this work, anionic Gemini surfactants with different hydrophilic headgroups (carboxylic, sulfuric, and sulfonic) were designed and synthesized. The oil-water interfacial tension was tested. The essential parameters for evaluating the interface characteristics, including the oil-water interfacial layer thickness, the coordination number, and the diffusion coefficient, were calculated employing molecular dynamics simulation. The surface electrostatic potential explained the quantitative mechanism of the hydrophobicity and lipophilicity of three types of Gemini surfactants through quantum chemical calculations. The oil-water interfacial tension difference of the Gemini surfactants was revealed at the electronic level. This paper will provide theoretical guidance for designing Gemini surfactants with a high-efficiency performance to enhance oil recovery.