Study of the interfacial array behaviour of surfactant at very low concentration by second harmonic generation and molecular dynamic simulation

Abstract The array behaviour of anionic surfactant sodium dodecylbenzenesulfonate (SDBS) on the air/water interface was investigated using non-resonant surface second harmonic generation (SHG) and molecular simulation. It was found that the SHG intensities changed with surfactant concentrations non-monotonously under Critical Micelle Concentration (CMC). The mean orientational angle of SDBS molecule at the air/liquid interface was calculated, and the molecular array behaviour was analyzed by molecular dynamics (MD) simulation. The simulated results agreed with the experimental results very well, which provided the detailed information about the interfacial molecular configuration of surfactant, not only indicating the SHG intensity related to the N s and r(θ) , but also demonstrates that the microscopic information presented by the MD simulation method is reliable. According to the results, the surfactant molecules get clustered even at very low concentration far lower than the CMC.