A10. Interaction and Adhesive Forces Between Surfaces in Dioxane:Water:AOT Solutions Measured by AFM

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The atomic force microscope (AFM) is used to measure at the molecular scale the long-range and short-range interaction and adhesive forces between mica and SiO2 surfaces in dioxane–water solutions with and without the surfactant, AOT (=sodium bis(2-ethylhexyl) sulfosuccinate). In the case of AOT-free dioxane–water solutions, the characteristics of interactions in solutions of low dioxane concentration are not too different from those in pure water, but very different features, such as a strong attractive long-range force and a step-like short-range force, are found in solutions of high dioxane concentration. These results are consistent with those for alcohol–water solutions obtained in previous experiments. In the case of dioxane–water–AOT solutions, step-like force curves are observed at dioxane weight fractions of wdiox=0.1 and 0.9, which implies that AOT molecules adsorb vertically directing their polar heads towards the medium at wdiox=0.1 and directing those towards the surface at wdiox=0.9. But the contribution of AOT to the interaction and adhesive forces at wdiox=0.5 is found to be small. © 1999 Elsevier Science B.V. All rights reserved.