In the conventional studies of the surfactant transport from a micellar solution onto an air/water interface, the micelle's contribution to the dynamic surface tension reduction is solely taken as a reservoir which can release monomer when the micelle and monomer equilibrium in the bulk is disturbed by the depletion of monomer from the bulk due to the adsorption of monomer onto the interface. The fact that the highest concentration of the monomer can be replenished by micelle breakup in the bulk is the critical micelle concentration (CMC) imposes a kinetic limit on this route. There is observed contradiction between this kinetic limit and the experimental results obtained by the pendant bubble apparatus showing that highly concentrated micellar solution can relax the surface tension much faster than the kinetic limit can predict.

In this paper, the theory and experimental study of the surfactant transport from the micelle solution includes the novel route that micelle can directly adsorb onto the interface and then break up into monomers which can be incorporated into the surface monolayer later. The depletion of micelle via both routes can lead to a micelle-free zone if the adsorption kinetic time scales of both monomer and micelle, as well as the micelle-monomer bulk exchange kinetic scale are much smaller than the micelle diffusion time scale when the surfactant concentration is below a critical value. Hexaethylene glycol monotetradcyl ether surfactant (C14E6) is chosen to visualize the micelle-free zone utilizing confocal laser scanning microscopy. We confirm the micelle free zone by monitoring the excimer emission change of the pyrene fluorescence. Two or more pyrene molecules trapped in the same micelle will emit excimer emission when excited. When micelle are depleted from the bulk underneath the interface, micelle free zone emerges, thus no excimer emission in this micelle-free zone and only monomer emission will be detected.

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