Decoding Wetting Behavior: Capillary Rise Experiments with Amphiphilic Compounds and Theoretical Aspects

Wetting and dewetting dynamics in aqueous solutions containing amphiphilic compounds involve intricate interactions that influence contact angles and surface tension, with broad implications in materials science and biology. This study explores the dynamics of wetting and dewetting on glass surfaces in aqueous media containing the amphiphilic compound C₁₈OE₈₄, focusing on capillary rise behavior. The dynamics were often characterized by an initial overshoot of the liquid meniscus, followed by relaxation toward equilibrium height. For concentrations either far below or well above the cmc, the observed overshoot in meniscus height is small, whereas near the cmc, it becomes markedly pronounced. The relaxation kinetics toward equilibrium vary with concentration, accelerating for concentrations exceeding the cmc. These observations are attributed to a nonequilibrium surface excess situation of surfactant at the liquid/vapor interface, strongly influenced by transport parameters such as concentration and diffusion constants. Given the low cmc of C₁₈OE₈₄, surfactant depletion due to adsorption on capillary walls may further reduce the effective concentration in the capillary, complicating the dynamics.To quantify adsorption effects, the solid/liquid interface adsorption isotherm was determined using ellipsometry. At high concentrations, the capillary rise height evolves smoothly over time. In contrast, for low to moderate concentrations, particularly below or near the cmc, the system exhibits a more complex dynamic behavior: the rise abruptly halts at a height corresponding to a specific surface tension value. This behavior is analyzed through the interplay between time-dependent contact angles and interfacial tension variations, driven by surfactant adsorption kinetics near the three-phase contact line at the solid/vapor and solid/liquid interfaces. The study also highlights how capillary preparation and pretreatment significantly impact wetting kinetics, underscoring the sensitivity of these systems to interfacial conditions. These findings provide insights into the role of surfactant transport and adsorption in controlling wetting dynamics, with potential applications in designing surfaces and formulations for targeted wetting behaviors.