Exploration of the Adsorption Kinetics of Surfactants at the Water–Oil Interface via Grand-Canonical Molecular Dynamics Simulations

Abstract

It is well-known that surfactants tend to aggregate into clusters or micelles in aqueous solutions due to their special structures, and it is difficult for the surfactant molecules involved in the aggregation to move spontaneously to the oil−water interface. In this article, we developed a new grand-canonical molecular dynamics (GCMD) model to predict the saturated adsorption amount of surfactant with constant concentration of surfactant molecules in the bulk phase, which can prevent surfactants aggregating in the bulk phase and get the atomic details of the interfacial structural change with increase of the adsorption amount through a single GCMD run. The adsorption of anionic surfactant sodium dodecyl sulfate (SDS) at the heptane−water interface was studied to validate the model. The saturated adsorption amount obtained from the GCMD simulation is consistent with the experimental results. The adsorption kinetics of SDS molecules during the simulation can be divided into three stages: linear adsorption stage, transition adsorption stage, and dynamic equilibrium stage. We also carried out equilibrium molecular dynamics (EMD) simulations to compare with GCMD simulation. This GCMD model can effectively reduce the simulation time with correct prediction of the interfacial saturation adsorption. We believe the GCMD method could be especially helpful for the computational study of surfactant adsorption under complex environments or emulsion systems with the adsorption of multiple types of surfactants.

Retraction of “Quantitative Study of Gas–Liquid Interface Adsorption Based on Theoretical Modeling and Molecular Dynamics Simulation”

“…Phan et al established a new model without using the Gibbs equation to quantify the adsorption of cationic surfactants (C 14 TAB and C 16 TAB) at the air–water interface and validated this model by MD simulations. Yang et al, via grand canonical MD simulations, investigated the saturated adsorption of SDS at the oil–water interface. During the simulation process, SDS molecules were gradually released to the interface until the adsorption and desorption at the interface reached equilibrium, which indicates that the interface was saturated.…”

Study on the Dual Effects of MgCl2 on the Characteristics of Foams Stabilized by Sodium Dodecyl Sulfate

“…Simulating the behavior of more SDS molecules within a limited simulation system can provide more statistical samples for analysis, favoring the reduction of errors. Therefore, each SDS molecule was set with an initial occupied surface area of 0.49 nm 2 (slightly larger than the minimum occupied surface area of a single SDS molecule) 55 and uniformly aligned perpendicular to the x-y plane. For each surfactant molecular layer, there are 36 SDS molecules.…”

Insights into Zwitterionic Surfactant Interactions at the Oil–Water Interface by Interferometry Experiments and MDS Calculations

“…Besides the experimental investigation, the theoretical calculation of molecular simulations (MS) can be utilized as an available method to provide direct observations for interfacial phenomenon. A series of literature have been reported for oil− water interfacial adsorption investigation of surfactants, 30 polymers, 31 and polycyclic aromatic compounds. 32 These results indicated that the intrinsic characteristics of interfacial adsorption behavior can be deeply interpreted and supplementary explicated from microscopic aspects by molecular simulation.…”