Adsorption Kinetics in Micellar Solutions of Nonionic Surfactants

Abstract

Standard models of the adsorption kinetics of surfactants at the air-water surface assume that micelles break down into monomers in the bulk solution and that only monomers adsorb. We show here that micelles of the nonionic surfactant C14E8 adsorb to the surface of a liquid jet at a diffusion-controlled rate. Micellar adsorption can be switched off by incorporation of a small amount of ionic surfactant into the micelle and switched on again by addition of salt. More sophisticated models of adsorption processes in micellar solutions are required that permit a kinetic flux of micelles to the air-water interface.

On the predictions and limitations of the Becker–Döring model for reaction kinetics in micellar surfactant solutions

“…In reality, micelles will pass through an ellipsoidal shape between spheres and rods that smooths out the distribution.) These predictions are in agreement with experimental techniques such as light-scattering methods or small-angle neutron scattering (SANS) experiments which may be used to determine the optimum aggregation number, and stopped-flow experiments to determine the CMC [10].…”

“…As the bulk surfactant concentration is increased, the amount of adsorbed surfactant increases until it becomes energetically more favourable for monomers to combine within the bulk and form aggregates that orient their hydrophobic components towards the centre of the cluster. These aggregates can have various sizes and shapes but for many simple surfactants with a single hydrocarbon chain the aggregates are approximately spherical and contain of the order of 100 monomers [10]. The distribution of aggregate sizes is localized around this optimum value with a half-width of the order of the square root of the aggregation number.…”

“…Some of the monomers released replenish the monomer concentration to its critical value, while the remainder join those aggregates which have not broken down. The associated relaxation times differ by at least three orders of magnitude, with monomer loss occurring on the µs-ms timescale and complete micelle breakdown on the msminutes timescale [10]. Aniansson et al [3] showed how their model could be used to fit Lang's experimental data and extract information about the aggregate distribution, and the theory has since been applied by numerous experimentalists [8,14,17,23,24,28,39].…”

“…The predictions of our models are compared with experimental data obtained from stopped-flow experiments [10]. Here, surfactant solution is rapidly mixed with water by being forced into a mixing chamber and then into an observation cell.…”

Surfactant Adsorption Kinetics by Total Internal Reflection Raman Spectroscopy. 1. Pure Surfactants on Silica

“…This condition is not useful for monomeric surfactants, but it is useful in solutions above the critical micelle concentration if one makes the conventional (though not necessarily correct 30 ) assumption that micelles do not adsorb.…”