THE COMPOSITION OF MIXED SURFACTANTS AND CATIONIC POLYMER SURFACTANT MIXTURES ADSORBED AT THE AIR-WATER-INTERFACE/

The use of specular neutron reflection and small-angle neutron scatter ing (SANS) to determine the composition of mixed surfactants and polym er/surfactant mixtures, absorbed at the air-water interface, in micell es and polymer or micellar complexes, is described. For the characteri sation of adsorption at the air-water interface by neutron reflectivit y, the emphasis is predominantly on the concentration regime where the surface is in equilibrium with a bulk aggregated phase; that is, for concentrations greater than the cmc of the mixture. This is a regime t hat is difficult to access by standard experimental techniques. The SA NS measurements of micelle composition are an important complement to the reflectivity measurements in the understanding of mixed surfactant adsorption. Recent results on the anionic/non-ionic surfactant mixtur e of sodium dodecyl sulphate (SDS) and hexaethylene monododecyl ether (C12E6) in the absence and presence of the cationic polymer and on the non-ionic mixture of monododecyl/triethylene glycol (C12E3)/monododec yl octaethylene glycol (C12E8) illustrate the power and advantages of neutron scattering techniques. (C) 1997 Elsevier Science B.V.