Diffusion-controlled adsorption kinetics of aqueous micellar solution at air/solution interface

Abstract

For the micellar surfactant solutions, the diffusion equation, in which the effect of the micelles on the monomer diffusion was taken into account, was solved under the initial and boundary conditions by means of Laplace transformation. And a general equation for the dynamic surface adsorption Г(t) as a function of surface lifetime t, critical micelle concentration (cmc), monomer diffusion coefficient D1, and the demicellization constant \( {\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftarrow}$}}{k}} \) was derived. To determine cmc, the equilibrium surface tensions γeq of aqueous hexaethylene glycol monododecyl ether (C12E6) solutions at temperature 25 °C were measured by means of Wilhelmy plate method and the measured cmc is 8.4 × 10−5 mol 1−1. To study adsorption kinetics, the dynamic surface tensions γ(t) of aqueous submicellar and micellar solutions were measured by means of maximal bubble pressure method and analyzed. Both of the monomers diffusion coefficient D1 and the demicellization constant \( {\overset{\lower0.5em\hbox{$\smash{\scriptscriptstyle\leftarrow}$}}{k}} \) were calculated.