Molecular insight into photoresponsive surfactant regulated reversible emulsification and demulsification processes.

[Display omitted] • The oil/water interface covered with trans -AzoTAB is stable than that with cis isomer. • Each cis -AzoTAB molecule occupies larger area than trans -AzoTAB molecule. • The addition of a small amount of SDS inhibits the desorption of AzoTAB. • cis -AzoTAB possess a faster molecular diffusion than trans -AzoTAB. Photoresponsive emulsions have attracted growing attention and exhibited enormous potential in a wide range of applications related to their green and efficient characteristics. Herein, molecular dynamics simulations were performed to elaborate the reversible emulsification/demulsification processes regulated by a mixture of an anionic surfactant sodium dodecyl sulfate (SDS), and the photoresponsive cationic surfactant 2-(4-(4-butylphenyl)diazenylphenoxy) ethyltrirnethylammonium bromide (AzoTAB). The simulation results indicate that the oil/water interface dominated by trans -AzoTAB molecules was more stable than that dominated by cis -AzoTAB molecules at specific concentrations, during which emulsification/demulsification can be reversibly regulated by the trans – cis isomerization reaction. The van Hove function results suggest that the cis -AzoTAB molecules possessed a faster diffusion rate than the trans isomer, contributing to the mutual dissolution of the oil and water phases. Furthermore, the role of SDS in regulating emulsification/demulsification processes was revealed. The addition of a small amount of SDS inhibited the desorption of AzoTAB from the oil/water interface and highlighted the influence of the structural difference between trans - and cis -AzoTAB molecules on interfacial stability. This work provides a molecular understanding of the interfacial stability and fluidity of photoresponsive emulsions, which are fundamental principles for the rational design of emulsions and other dispersion systems. [ABSTRACT FROM AUTHOR]