Effect of Surfactant Headgroup, Salts, and Temperature on Interfacial Properties: Dissipative Particle Dynamics and Experiment for the Water/Octane/Surfactant System

Dissipative particle dynamic (DPD) simulations were performed to study the interfacial properties such as interfacial tension, area compressibility, stress profile, and conformation of surfactant at the water/octane interface. Experimental studies of the interfacial tension (IFT) in water/octane/surfactant systems were conducted using the pendant drop method. The IFT results of DPD agree semiquantitatively with experimental measurements. Three surfactants with different head groups and same alkyl tail, sodium dodecyl sulfate (SDS), dodecyltrimethylammonium bromide (DTAB), and dodecyldimethylamine oxide (DDAO), were selected to study the effect of headgroup structure. The efficiency of surfactants from DPD follows the same order of experimental results DDAO > SDS > DTAB. The DDAO surfactant is more ordered at the interface with a high area compressibility which indicates more highly packed monolayer. The effect of salts and temperature at water/octane/SDS surfactant at the interface were investigated. The addition of salts in the systems stretched and ordered the SDS surfactant more at the interface; as a result, the area compressibility increased. Temperature has little effect on the orientation of the SDS surfactant at the interface, and the area compressibility decreased with increasing temperature.