| Abstract
| - The adsorption of the mixed cationic and nonionic surfactants of hexadecyltrimethylammonium bromide(C16TAB) and hexaethylene glycol monododecyl ether (C12EO6) at the hydrophilic silicon−solution interfacehas been measured by specular neutron reflection. The effect of solution composition and concentrationon the adsorbed amount, surface structure, and composition has been investigated at pH 2.4. Specularneutron reflection, in combination with H/D isotopic substitution of both the solvent and surfactant, enablesdetailed structural and compositional information about the adsorbed layer to be obtained. The resultsobtained are compared with those reported elsewhere for the adsorption of the same surfactant mixtureat the air−water interface and for surfactant mixing in micelles. Consistent with other studies, the structureof the adsorbed layer is described as a “defective” bilayer or “flattened” micelles. The variation in theadsorbed amount with solution composition is a maximum at an equimolar solution composition. Forsolutions richer in C16TAB, the surface and solution compositions are identical (consistent with idealmixing). Whereas for solutions richer in C12EO6 there is a departure from ideality, and the surface is richerin the cationic surfactant.
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