Contact line pinning to autonomous drop motion of aqueous 1-Tetradecyl-3-methylimidazolium bromide solutions on hydrophilic surfaces

Wettability dynamics of aqueous surface-active ionic liquid (SAIL) 1-tetradecyl-3-methylimidazolium bromide [C₁₄mim]Br solutions were studied on the complete wetting glass surface. The wetting dynamics were analyzed in terms of contact angle, contact line mobility, elapsed time, and SAIL concentrations. Distinct and surprising dynamic wetting states, such as autophobing, autonomous drop motion, contact line expansion, droplet splitting, and droplet pinning, were observed. These wetting regimes depended on the concentrations of SAIL, and the self-propelled autonomous motion may result from the adsorption of the SAIL molecules. The wetting gradient, due to reactive wetting was responsible for drop motility on contact angle hysteresis-free surface. The movement of the droplet contact line exhibited distinct wetting based on the concentration of SAIL. At a concentration of 0.25 mM, the droplets demonstrated higher speeds. In the concentration range of 0.75 mM to 1.25 mM, an autophobing effect was observed, whereas, at concentrations exceeding 2.5 mM, the droplets displayed pinning behavior. Furthermore, the droplet dynamics were also studied in the presence of polyvinylpyrrolidone (PVP) and polyethylene glycol (PEG-200) polymers. The moving droplets showed pinning behavior at higher polymeric concentrations. The studies of SAIL-water–glass surface interactions demonstrated self-motility drops with solute transfer behavior and self-cleaning ability, that can be used to develop controlled liquid transport structures, and microfluidic devices and to understand the self-cleaning processes.