Characterizing the impact of surfactant structure on interfacial tension: a molecular dynamics study

The effect of sodium branched-alkylbenzene sulfonates on the NaCl solution/oil interface was studied via classical molecular dynamics simulation. The interfacial properties were found to depend on the surfactant concentration and to change dramatically when the concentration exceeded a critical value, the simulated limit area (A _c). When A _c is not close to the theoretical saturated adsorption area (A _min), the surfactant cannot produce ultralow interfacial tension (IFT). When A _c is equal or almost equal to A _min, the effect of the structure of the surfactant must be considered to determine if ultralow IFT is possible: if the sizes of the hydrophobic and hydrophilic groups in the surfactant are similar, the surfactant can produce ultralow interfacial tension (and vice versa). Based on the results of these studies, the effect of surfactant structure on the interfacial properties of the system was investigated, and a method of gauging the IFTs produced by different surfactants was proposed that should prove very useful when designing the optimal surfactant structure to achieve ultralow IFT. Graphical Abstract The interfacial properties of water/surfactant/oil system, such as interfacial thickness and IFT, depending on the surfactant concentration and changing dramatically when the concentration exceed a critical value.