Molecular dynamics simulations and quantitative calculations on photo-responsive behavior of wormlike micelles constructed by gemini surfactant 12–3-12·2Br− and cinnamates with different ortho-substituents

Abstract

Photo-responsive wormlike micelles constructed by photo-sensitive molecules and surfactants have attracted widespread attention from researchers. The subtle structural changes in photo-sensitive molecules have a significant effect on the photo-responsive behavior of wormlike micelles, while the underlying mechanism of this effect has not been fully investigated. In this work, photo-responsive wormlike micelles were constructed by Gemini surfactant trimethylene-1, 3-bis (dodecyldimethylammonium bromide) and three cinnamates with different ortho-substituents. The effects of ortho-substituents in cinnamates on the photo-responsive behavior of prepared micelles were explored in details by combining the experimental methods with multi-scale modelling. The experimental results have shown that the wormlike micelles containing different cinnamates exhibit different photo-responsive behaviors and the one containing trans-OMCA shows the best photo-responsiveness (viscosity decrease from 1.63 Pa·s to 0.10 Pa·s with morphology transition from wormlike micelles to spherical micelles) due to the highest conversion fraction (0.88) of the trans-OMCA and forward rate constants (1.09) speed under UV irradiation, which have been reconfirmed by quantitative calculation. Furthermore, the effect of UV irradiation time on the morphology of micelles were studied and the conformational transformation behaviors of wormlike micelles under different UV irradiation time were successfully simulated by adjusting the ratio of cis/trans-isomer. The quantitative calculation illustrates that the existence of methoxy and hydroxyl expands the difference in steric hindrance, hydrophilicity and the electrostatic distribution before and after UV irradiation, and increases the reaction equilibrium constant (methoxy is more effective), thereby enhancing photo-responsive ability of wormlike micelles. The present work provides a comprehensive understanding of photo-responsive morphology transition mechanism of wormlike micelles and the effects of structure of photo-sensitive molecule on the photo-responsiveness of wormlike micelles and thus can find a concrete way to optimize the photo-responsive self-assembly system containing surfactants and photo-sensitive molecule, which is of great importance for the design of smart responsive systems and expansion of their applications.