The insolubility of graphene nanosheets in aqueous media has been a limitation for the practical applications of this unique material. The non-covalent functionalization of graphene with mixed surfactants is an effective procedure for preparation of stable graphene dispersions. Physical adsorption of surfactants onto graphene surfaces is a significant stage in the dispersion of graphene nanosheets in the aqueous environment. Studies have shown that the presence of electrolyte greatly affects the adsorption process of pure surfactants on solid surfaces. Examination of mixed surfactants adsorption on graphene in the presence of electrolyte will help to better understand the mechanism of molecular interactions between the graphene nanosheets and mixed surfactants. Therefore, in this study, we used molecular dynamics simulations to investigate the adsorption of mixed surfactants on graphene in the presence of electrolyte and to study the morphology of assemblies formed from mixed surfactants on graphene. We investigate the effects of electrolyte concentration and surface coverage of surfactants' mixture on the adsorption process and structural changes in the assemblies formed on graphene nanosheets. We have found that increasing the ionic strength of electrolyte reinforces stretching of surfactants adsorbed on graphene toward the aqueous phase, and this leads to a clear volume expansion in the structure of graphene-surfactant mixture hemi-spherical micelles. In fact, screening effect of electrolyte ions on electrostatic repulsion between charged head-groups made molecules approach each other, leading to a more compact assembly of surfactants on graphene surface. As hemi-spherical micelles of mixed surfactants-graphene expanded, the steric repulsion between these micelles also increased, which in turn, inhibited the re-aggregation of graphene sheets covered with surfactants.

石墨烯纳米片在水性介质中的不溶性已经限制了这种独特材料的实际应用。石墨烯与混合表面活性剂的非共价官能化是制备稳定石墨烯分散体的有效方法。表面活性剂在石墨烯表面上的物理吸附是石墨烯纳米片在水性环境中分散的重要阶段。研究表明，电解质的存在极大地影响了纯表面活性剂在固体表面上的吸附过程。在电解质存在下检查混合表面活性剂在石墨烯上的吸附将有助于更好地理解石墨烯纳米片和混合表面活性剂之间的分子相互作用机理。因此，在这项研究中 我们使用分子动力学模拟研究了存在电解质的情况下混合表面活性剂在石墨烯上的吸附，并研究了混合表面活性剂在石墨烯上形成的组装体的形态。我们研究了电解质浓度和表面活性剂混合物表面覆盖率对石墨烯纳米片上组装过程的吸附过程和结构变化的影响。我们已经发现，增加电解质的离子强度会增强吸附在石墨烯上的表面活性剂向水相的拉伸，这会导致石墨烯-表面活性剂混合物半球形胶束的结构明显体积膨胀。实际上，电解质离子对带电头基之间静电排斥的屏蔽作用使分子彼此接近，导致表面活性剂在石墨烯表面上的组装更紧凑。随着混合的表面活性剂-石墨烯的半球形胶束的扩展，这些胶束之间的空间排斥力也增加，这反过来又抑制了覆盖有表面活性剂的石墨烯片的重新聚集。