A NEUTRON REFLECTIVITY STUDY OF THE ADSORPTION OF AEROSOL-OT ON SELF-ASSEMBLED MONOLAYERS ON SILICON

The structure and composition of layers of the anionic surfactant sodi um bis-(2-ethyl-1-hexanol) sulphosuccinate (AOT) adsorbed from aqueous solution onto self-assembled monolayers of octadecyltrichlorosilane ( OTS) on silicon oxide have been determined in situ using specular neut ron reflection, At its critical micelle concentration (cmc) AOT forms a monolayer with an area per molecule of 80 +/- 5 Angstrom(2) and a th ickness of 15 +/- 2 Angstrom. These values are similar to those of the monolayer formed at the air/water interface at the cmc, Separate isot opic labeling of two parts of the AOT surfactant shows that the molecu le is oriented with the ethyl hexanol chains toward the hydrophobic OT S surface and that there is some penetration of the OTS layer by the c hains. The adsorption of AOT is found to persist at lower concentratio ns than the nonionic surfactant tetraethylene glycol monododecyl ether (C(12)E(4)) over the concentration range cmc/100 to cmc. (C) 1996 Aca demic Press, Inc.