Behavior of Imine-Based Oligomeric Surfactants in Bulk and at Interfaces: Molecular Dynamics Perspective

Molecular dynamics simulations of oligomeric imine bond surfactants in their aqueous solutions were performed to investigate the aggregation behavior, which is known to influence their antimold activity. The model surfactants consist of two or more cationic surfactants linked by imine bonds. In this study, monomeric, dimeric, and trimeric structures have been considered. As the number of monomeric units in the surfactant molecule increases, it is found that the aggregation number decreases and the size and morphology of the aggregates show notable changes. Monomeric surfactants form spherical micelles, whereas dimeric and trimeric surfactants tend to assemble into interconnected structures. These simulation results are consistent with the reported experimental observations. Umbrella sampling results show that larger aggregates allow for easier monomer exchange with bulk water, whereas smaller aggregates and surfactants with multiple tail groups make monomer extraction energetically more difficult. Efficient monomer release and subsequent binding to the negatively charged membrane together explain the experimentally observed antimold behavior. Additionally, stable π-π stacking interactions between the phenylene rings in the surfactant molecules were observed, which contribute to the structural stability of the aggregates.