(24f) Measuring the Adsorption Dynamics of a Switchable Tertiary Amine Surfactant Using QCM

The adsorption of switchable amine surfactant, Duomeen TTM, is measured via the quartz crystal microbalance with dissipation (QCM-D). This real time adsorption measurement allows us to probe both equilibrium and kinetics of surfactant adsorption. Duomeen TTM is nonionic under neutral or basic conditions but becomes protonated under acidic conditions. We find that the equilibrium adsorption is highly affected by the pH and salinity of surfactant solution, by modifying the surface charge of both silica substrate and the surfactant head group in opposing ways. Also, the implicit adsorption mechanism can be studied by fitting the experimental data with analytical models. We find that a two-step kinetic model fits the adsorption data well, which is characteristic of consecutive adsorption steps. We hypothesize that the sequential adsorption is mainly due to the competitive adsorption between surfactant micelles and monomers to the silica surface.