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The desorption of C12E8 out of an overcrowded interface due to the sudden shrinkage of a pendant bubble in a quiescent surfactant solution is studied. A video-enhanced pendant bubble tensiometry is utilized for the measurement of the relaxation in surface tension due to the desorption of surfactant. The desorption process is found to be diffusive−kinetic mixed controlled. Rate constants of adsorption/desorption are computed by comparing these tension profiles with numerical solutions, which consider both bulk diffusion and kinetic desorption processes. The values of the kinetic rate constants of C12E8 obtained from the desorption experiment are nearly the same as that obtained from the clean adsorption study (Lin, S. Y., et al., Langmuir 1996, 12, 6530). The concept that there exists a shift in controlling mechanism from diffusion control at dilute concentration to mixed diffusion−kinetic control at more elevated bulk concentration for C12E8 is therefore confirmed.

The adsorption of C12E8 onto a clean air−water interface is studied by using a video-enhanced pendant bubble tensiometry. The controlling mechanism for mass transfer changes as a function of bulk concentration; it shifts from diffusion control at dilute concentration to mixed diffusion−kinetic control at more elevated bulk concentration. The adsorption of C12E8 is found to be anticooperative from the equilibrium surface tension data compared with the prediction of the (generalized) Frumkin model. Relaxation profiles of surface tension for C12E8 molecules absorbing onto a freshly created air−water interface for 21 different bulk concentrations are obtained. Comparison is made for the entire relaxation period of the tension data and the model predictions. Values of the diffusion coefficient and the adsorption/desorption rate constants of C12E8 are calculated from these dynamic surface tension profiles.