STUDY OF THE ADSORPTION FROM AQUEOUS-SOLUTION OF MIXTURES OF NONIONICAND CATIONIC SURFACTANTS ON CRYSTALLINE QUARTZ USING THE TECHNIQUE OFNEUTRON REFLECTION

Neutron reflectivity has been used to determine the surface excesses o f hexakis(oxyethylene) monododecyl ether (C-12E6) and hexadecyltrimeth ylammonium bromide (C16TAB), adsorbed from mixed aqueous solutions ont o a quartz substrate. Two compositions were studied with C16TAB mole f ractions of 0.55 and 0.92. Surface tension has been used to obtain a v alue 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 ads orbed layer are similar to their proportions in mixed micelles of the bulk solutions calculated from the value of beta above. The adsorbed l ayer thickness was found to be constant within error and corresponds t o a bilayer of mixed surfactant.