Molecular dynamic simulation study on effect of anionic–nonionic surfactants on decane desorption from SiO2 surface

•The appropriate number of EO chains can ensure the peeling effect of extended surfactant on oil phase molecules.•The interface properties of surfactants have a significant effect on the desorption behavior of oil on the SiO2.•The diffusion behavior of surfactant affects the desorption effect of the oil phase on the solid surface. During oil production, some amount of crude oil is adsorbed on the rock layer. Therefore, surfactants are needed to detach the residual crude oil from this layer, thereby improving the overall oil recovery rate. In this study, five kinds of anionic–nonionic surfactants were designed by changing the length of ethylene oxide (EO) chains based on the structure of saturated cardanol. 8PO8EOSO3 exhibited good oil-detachment effectiveness, and this was assessed by studying the energy of interface interaction between the solid phase (SiO2) and the liquid phase (oil phase molecules, surfactants, and water). The density distribution data further elucidated that the good interface properties of 8PO8EOSO3 affected the degree of aggregation of the oil phase molecules on the SiO2 surface. This was mainly because the appropriate length of EO chains could realize optimal diffusion coefficients at the oil–water interface. Thus, in the 8PO8EOSO3 system, the oil phase molecules exhibited greater intermolecular distance and weak interactions with SiO2 (radial distribution function). Further, the study of the solid–liquid interface properties and effect of different chain lengths of EO chains on desorption showed that the appropriate number of and EO chains was an important factor in designing the structure of the extended surfactant to ensure that the surfactant realizes a high degree of detachment of the oil phase from SiO2.