Adsorption Kinetics of C₁₂E₈ at the Air−Water Interface:  Desorption from a Compressed Interface

Abstract

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.

Surface rheology and interface stability.

“…For each set of data, a drop was first formed at the end of the syringe tip and allowed to equilibrate for several thousand seconds. We confirmed our equilibrium surface tension values by utilizing Frumkin equation of state values as reported in the literature [Tsay et al 1997]. When equilibrium was achieved, we then either performed a series of oscillatory tests or a series of single-step compressions and expansions.…”

“…Drop images were post-analyzed using software developed in LabVIEW First, images were passed through a edge detection algorithm, and drop profiles were fit to the Young-Laplace equation as described in Appendix A and demonstrated in several other publications [Tsay et al 1997, Lin et al 1995, Lin et al 1996]. For oscillatory measurements, surface tension and area versus time data were each fit to sine waves, and the phase and amplitude were used to calculate the Gibbs elasticity.…”

“…Appropriate frame rates were used for each step so as to prevent over-sampling and bogging down image analysis. These images were post-processed with an edge detection technique, and drop profiles were fit to the Young-Laplace equation, as in previous papers [Tsay et al 1997, Lin et al 1995, Lin et al 1996, to determine the bubble area and surface tension. Tension data for the first 1000 seconds was used to give information about the dynamics of the system; tension and area data for the oscillations were fit to sine waves and elasticities were calculated according to the equations presented in Monteux et al (2004).…”

“…There already exist several detailed descriptions of the adsorption activity of this and similar systems at an interface [Tsay et al 1997 , and as such, we do not suggest that this work in its current state is finished; much of what we set out to do remains to be completed (with respect to modeling surfactant behavior at the interface). Specifically, it is well known that for a fluid interface coated in surfactant, compression and expansion of the interface will result in surfactant exchange with the bulk coupled with a change in the surface tension [Gottier et al 1986, MacLeod & Radke 1994, Pan et al 1998].…”

Monolayers of Some Poly(oxyethylene)-Based Surfactants at the Air–Water Interface: The Effect of Structural Variations and Salt Concentration

“…[4] can be written as ⌸ ϳ ⌫ y ϳ A Ϫy . [6] To obtain the expression for the compressibility factor Z ϳ ⌸A, we substitute A by Z/⌸ and rearrange:…”