The adsorption of C12E4 onto a fresh air-water interface was investigated by using video-enhanced pendant bubble tensiometry. From the comparison between the equilibrium surface tension data and the theoretical relaxation profiles predicted by the Frumkin adsorption isotherm, the adsorption process was found to be anticooperative. Dynamic surface tension data for C12E4 molecules absorbing onto a freshly created air-water interface for different bulk concentrations were used for the determination of the controlling mechanism and the evaluation of diffusivity. Comparison was made for the entire relaxation period of the surface tension data and the model predictions. It is concluded that the adsorption process is of diffusion control and the diffusion coefficient is 6.4 × 10 -6 cm 2 /s. The lower limit of the adsorption rate constant of C12E4 were obtained from the theoretical simulation. Besides, the pendant bubble, at which the interface had reached the equilibrium state, was expanded rapidly and a relationship between surface tension (γ) and surface area (A) was obtained. A curve relating γ and relative surface concentration Γ/Γref was obtained from the γ-A data and then used to examine the adsorption isotherm utilized in this study.

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Two processes for the mass transport of C12E4 in a quiescent surfactant solution were studied: (i) the desorption of C12E4 out of a suddenly compressed interface; (ii) the adsorption of C12E4 onto a suddenly expanded air-water interface. A video-enhanced pendant bubble tensiometer was used for the measurement of surface tension relaxation due to the adsorption or desorption of surfactant molecules. Both processes were found to be diffusion-controlled at dilute concentration but diffusive-kinetic mixed-controlled at more elevated bulk concentration for C12E4. Rate constants of adsorption/desorption were evaluated from the comparison between the surface tension profiles and the theoretical profiles predicted from the Frumkin model. The values of the kinetic rate constants of C12E4 obtained from these two experiments are nearly the same. A theoretical simulation was also performed to confirm the shifting mechanism (