Surfactant adsorption dynamics

Abstract

Advances in techniques for investigating dynamic adsorption of surfactants at the air± water interface are discussed. Of particular interest are the maximumbubble-pressure method, and the interrogation of adsorption layers on an overowing cylinder (OFC) cell using ellipsometry, surface-light scattering, laser Doppler velocimetry and neutron re¯ection. Recent studies described here, with a model di-chain anionic¯uorocarbon surfactant sodium bis(1H,1H-nona¯uoro-n-pentyl) sulphosuccinate (di-CF4) demonstrate that the OFC presents an ideal exible platform for investigating dynamics of adsorption from solutions. Under certain conditions the behaviour is consistent with an activated-diOE usion mechanism, as has been found previously for simple alcohols and various other non-ionic and ionic surfactants.

Short-time behavior of mixed diffusion-barrier controlled adsorption

“…Interestingly, the experimental DST behavior of many nonionic surfactant systems appears to contradict the theoretical predictions summarized above: the experimental DST behavior of these nonionic surfactant systems exhibits a √ t variation at short times, and this behavior is considered as a fingerprint for the existence of diffusion-controlled adsorption at short times based on the short-time asymptotic prediction of the diffusioncontrolled model [32,33,35,51,[56][57][58][59][60]. Furthermore, based on this interpretation of the experimental observations, it has been proposed that the fundamental physical basis underlying the existence of the energy barrier is associated with high surfactant surface concentrations [32,35,45,57].…”

“…The scale value for the surfactant flux associated with diffusion of the surfactant molecules through a layer of thickness a (q d ) is given by Fick's law as (35) …”

“…(30)), short-time experimental DST data for these surfactant systems have been interpreted in the context of Eq. (29) [32,33,35,51,[56][57][58][59][60]. Indeed, it is typical to plot the short-time experimental DST as a function of √ t , and to extract D values from the resulting slope using Eq.…”

“…Furthermore, based on this interpretation of the experimental observations, it has been proposed that the fundamental physical basis underlying the existence of the energy barrier is associated with high surfactant surface concentrations [32,35,45,57].…”

“…Comprehensive reviews on the applications and the theory related to the dynamic adsorption of surfactants at surfaces can be found in Refs. [1,6,15,[28][29][30][31][32][33][34][35].…”