The efficiency and stability of processes requiring rapid surface activity, such as foaming, wetting, and washing, are fundamentally governed by the dynamic behavior of surfactants at the air/liquid interface. While the principles of equilibrium surface tension are well established, the dynamic behavior required for time-sensitive applications presents a greater complexity. Consequently, this study provides a systematic investigation into how specific variations in surfactant molecular architecture dictate both the rate of adsorption at the air/water interface and the kinetics of micellization within the bulk aqueous phase.
We captured the dynamic surface tension on the millisecond-to-second timescale using the maximum bubble pressure method. By varying the alkyl chain length, branching, and type of the hydrophilic head group, we identified the structural features that govern interfacial mobility. The obtained dynamic surface tension data were analyzed with different theoretical models, including the Ward-Tordai model. Because interfacial adsorption is linked to the availability of free monomers in the bulk phase, we complemented our tensiometry data with stopped-flow kinetics that allow us to access information about the release kinetics of surfactants from micellar aggregates. These experiments allowed us to observe micelle dissociation kinetics following rapid dilution from above to below the critical micelle concentration (cmc).
By analyzing both micellar kinetics and adsorption dynamics, we established key structure-property relationships. These insights help explain and predict surfactant performance in time-sensitive applications and can construct a comprehensive molecular picture of the ongoing processes.