Molecular Understanding for Motion Modes of Oil Droplets in Aqueous Solutions of Ester- and Amide-Containing Cationic Surfactants

The study of self-propelled motion in soft matter systems has garnered significant interest due to its potential applications in microfluidics, soft robotics, and the design of autonomous systems. Understanding the molecular mechanisms behind such motility is crucial for advancing these applications. This study investigates the self-propelled motion of lauronitrile oil droplets in aqueous surfactant solutions, focusing on the impact of different surfactant molecular structures on droplet dynamics. The research compares surfactants containing ester and amide linkages, which play a critical role in modulating interfacial tension and influencing Marangoni convection—a key factor of droplet movement. surfactants with ester linkages exhibit a higher affinity for lauronitrile and adsorb more rapidly at the oil-water interface, resulting in stronger Marangoni flows and faster droplet motion. In contrast, amide-containing surfactants show slower adsorption and weaker interactions with lauronitrile, leading to reduced or absent motion. These findings provide new insights into the molecular mechanisms underlying self-propelled droplet behavior in non-equilibrium systems, and contribute to a deeper understanding of self-organising phenomena.