Molecular structure and stability of the sorbitan monostearate (Span60) monolayers film at the water–air interface: A molecular dynamics simulation study

Abstract

A sorbitan monostearate (Span60) monolayer film at the water–air interface is presented in the first study using molecular dynamics simulation to investigate this system. The models of the Span60 monolayers in a condensed phase were investigated for all temperatures of the film formation ranging from 22°C to 42°C. Monolayer structure and dynamical properties of the Langmuir film were presented and compared with the experimental data. This study provides insight into the molecular level properties of the surfactant assembly including the monolayer structure, surface tension, lateral diffusion and hydrogen bond dynamics which these results are in good agreement with in experimental data. In addition, this study reveals that the hydrogen bond plays an important role to enhance the film stability. The number and lifetime of hydrogen bonds for the Span60/water are reduced with increasing temperature due to higher mobility of water molecules near the interface. Conversely, the strong interaction among the Span60 molecules themselves and slight decrease in the number of the Span60/water hydrogen bonds with increasing temperature. As a result, the Span60 monolayer film remains stable over these temperature ranges.