STRUCTURE OF THE SURFACE OF A SURFACTANT SOLUTION ABOVE THE CRITICAL MICELLE CONCENTRATION

Journal article

The adsorption at the air/solution interface of the surfactant tetradecyltrimethylammonium bromide (C14-TAB) above its critical micelle concentration (cmc = 3.7 mM) has been studied by neutron specular reflection. The amount adsorbed increases with concentration steadily through and above the cmc. Combination of the surface tension and the surface excess, as determined by neutron reflection, has been used to determine the variation of the activity of the surfactant from the cmc up to 0.16 M. The structure of the adsorbed layer at a concentration 50 times the cmc is shown to consist of the usual monolayer of surfactant, an aqueous layer from which surfactant is absent, and a further layer of surfactant with about a 5% excess over the bulk solution. The width and concentration of this lower surfactant layer suggests that it corresponds to an adsorbed layer of micelles and that the center of this layer is located at approximately 90 Å from the center of the monolayer, making the aqueous layer about 55 Å thick. The net positive adsorption of micelles in the region below the monolayer indicates that there is an effective attractive interaction between micelles and the "wall", which may result from the monolayer/micelle interaction being less repulsive than the micelle/bulk solution interaction. There is some, less conclusive, indication that the aqueous layer may also be structured near the monolayer. © 1993 American Chemical Society.

Authors: Lu, J; Simister, E; Thomas, R; Penfold, J

• Publication status: Published
• Journal: JOURNAL OF PHYSICAL CHEMISTRY
• Volume: 97
• Issue: 51
• Pages: 13907-13913
• Publication date: 1993-12-23
• DOI: 10.1021/j100153a074
• EISSN: 1541-5740
• ISSN: 0022-3654