The adsorption mechanism of the branched quaternary ammonium salt Gemini surfactant (Gemini C₃) at the water-surfactant-quartz interfaces for both neutral and negatively charged quartz surfaces was studied by a molecular dynamics (MD) method. Initial and final configurations, distributions of the surfactant and its interaction with surfaces, the radial distribution function (RDF) of water molecules, and the mean square displacement (MSD) of the surfactant in bulk phase have been elucidated at the molecular level. The results showed that the adsorption of Gemini surfactants onto the hydrophilic quartz surface was driven by electrostatic interaction, which increased the hydrophobicity of the solid surface when the surfactant concentration was lower than critical micelle concentration (CMC). However, the contact angle only slightly increased since the surface tension decreased simultaneously with growing concentration. Monolayers were formed during the adsorption process of Gemini C₃ molecules on the quartz surface rather than a double layer when the concentration reached the CMC, indicating a gradual transformation of an extended monolayer adsorption configuration into a more compact one. The solid-liquid interfacial tension increased with the surfactant concentration and led to a significant increase of the contact angle. The simulation results were consistent with the experiments, which further revealed the microscopic adsorption mechanism of the Gemini C₃ surfactant onto the quartz surface, and provided theoretical guidance for controlling the wetting properties and surface modification of the rock.

中文翻译：

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分子动力学方法研究新型Gemini表面活性剂在石英表面的吸附行为

支化季铵盐Gemini表面活性剂（Gemini C _{3 ）的吸附机理}) 通过分子动力学 (MD) 方法研究了中性和带负电石英表面的水-表面活性剂-石英界面。表面活性剂的初始和最终构型、分布及其与表面的相互作用、水分子的径向分布函数 (RDF) 以及表面活性剂在体相中的均方位移 (MSD) 已在分子水平上得到阐明。结果表明，Gemini表面活性剂在亲水性石英表面的吸附是由静电相互作用驱动的，当表面活性剂浓度低于临界胶束浓度（CMC）时，会增加固体表面的疏水性。然而，接触角仅略有增加，因为表面张力随着浓度的增加而降低。_{当浓度达到 CMC 时，石英表面上的3 个}分子而不是双层，表明扩展的单层吸附配置逐渐转变为更紧凑的吸附配置。固-液界面张力随着表面活性剂浓度的增加而增加，并导致接触角显着增加。模拟结果与实验结果一致，进一步揭示了Gemini C ₃表面活性剂在石英表面的微观吸附机理，为控制岩石的润湿性和表面改性提供了理论指导。