STUDY OF THE ADSORPTION FROM AQUEOUS-SOLUTION OF MIXTURES OF NONIONIC AND CATIONIC SURFACTANTS ON CRYSTALLINE QUARTZ USING THE TECHNIQUE OF NEUTRON REFLECTION

Neutron reflectivity has been used to determine the surface excesses of hexakis(oxyethylene) monododecyl ether (C-12E6) and hexadecyltrimethylammonium bromide (C16TAB), adsorbed from mixed aqueous solutions onto a quartz substrate. Two compositions were studied with C16TAB mole fractions of 0.55 and 0.92. Surface tension has been used to obtain a value of the interaction parameter, beta = -2.1 +/- 0.3, using regular solution theory. The surface excesses determined from reflection show that in both mixtures, the proportions Of C-12E6 and C16TAB in the adsorbed layer are similar to their proportions in mixed micelles of the bulk solutions calculated from the value of beta above. The adsorbed layer thickness was found to be constant within error and corresponds to a bilayer of mixed surfactant.