It has been reported that the dispersing ability of a given surfactant in surfactant-assisted liquid-phase exfoliation of graphite is extremely affected by its adsorption energy on graphene nanosheets. This study employs computational and experimental techniques to analyze the true relationship between adsorption energy and the dispersing ability of a group of surfactants in the surfactant-assisted liquid-phase exfoliation of graphite. In the first section, adsorption energies computed for a group of homologous surfactants with different hydrocarbon tail lengths are used to predict dispersing-ability trends. It is found that the adsorption energy of the surfactants correlates directly with their tail length. In light of the literature, it is therefore expected that the surfactant with the highest adsorption energy is most effective at dispersing. The experimental section examines this expectation and shows that this is not guaranteed as a general rule. Based on the experimental results, this expectation can be met when surfactant concentrations are quite below surfactants’ critical micelle concentrations (CMCs) but fails at concentrations near or exceeding CMCs. Finally, quantum computation and molecular dynamics simulations are employed to justify the dispersing-ability trend observed at higher concentrations. Results demonstrate that the molecular size of the surfactants becomes considerable at these concentrations. In view of this, a new quantity, “adsorption energy per molecular volume”, is proposed to explain the behavior of the surfactants at high concentrations. Using this new quantity, the dispersing-ability trend observed at higher concentrations is explained.

The production of graphene nanosheets from graphite with the assistance of biological molecules in water medium as well as understanding the morphology of the resulting self-assembly are important in fields of drug delivery, cell imaging, and photothermal therapy. Hence, in this contribution, we have applied docosahexaenoic acid (DHA) fatty acid to disperse graphite. The morphology of self-assembly on the graphene surface and the factors tailoring the morphology were surveyed in light of classical molecular dynamic (MD) and symmetry-adapted perturbation theory (SAPT). The factors such as surface density, environment pH, substrate size, and number of layers were taken into account. The results show that the decrease in pH transmutes the nature of the classical electrostatic interaction between the surfactants from repulsion to attraction, leading to a decline in the stability of the colloidal systems. When the lateral size of the graphene sheet is three times larger than the length of DHA, hemicylinder structures with a 3.5−4 nm width are formed, which is in excellent agreement with AFM results. The simulation of the effect of number layer reveals that the LPE cannot be initiated without ultrasonic assistant. An arsenal of experimental methods including HR-TEM, TEM, AFM, XPS, UV−vis, and zeta potential confirms the existence of colloidal systems with graphene sheet. The dispersion of graphene using DHA largely preserves the intrinsic chemical structure of graphene. This combined experimental and computational study will be a valuable contribution to the dispersion of graphene by means of fatty acids, which could be utilized in medical purposes.

The water droplets surrounded by a rigid interfacial asphaltene (ASP) film is one of the major setbacks in the petroleum industry. In this study, the properties of the interfacial ASP films around water droplets exposed to ionic surfactants as demulsifier were investigated. According to molecular dynamics (MD) simulation, the anionic surfactants are more effective than the cationic surfactant in the demulsification process since the anionic surfactants have the exact desire to localize not only near the ASP molecules but also near the water molecules. It has been found that it is likely to cause film changes and ruptures. Also, the MD simulation results for the desired surfactant, anionic surfactant, demonstrated that an increase in the surfactant concentration had an adverse effect on the system by hindering the change in the interfacial film. The increase in the temperature along with the enhancement in the adsorption rate of the surfactant results in the better performance of the demulsifier. Taking the MD and quantum results into account, the film deformation is a decisive factor in demulsification. The quantum computation has indicated that the electrostatic interactions play a significant role in selecting the attraction position and adsorption energy of the surfactant molecules.