Lateral structure of a surfactant layer adsorbed at a hydrophilic solid/liquid interfaceR. Steitz1, 2, P. Müller-Buschbaum3, S. Schemmel1, R. Cubitt4 and G. H. Findenegg1
1 Stranski-Laboratorium für Physikalische und Theoretische Chemie Technische Universität Berlin, Strasse des 17. Juni 112 D-10623 Berlin, Germany
2 Berlin Neutron Scattering Center, Hahn-Meitner-Institut Glienicker Strasse 100, D-14109 Berlin, Germany
3 TU München, Physik-Department, LS E13 James-Franck-Strasse 1, 85747 Garching, Germany
4 Institut Laue-Langevin - 6 rue Jules Horowitz, BP 156, 38042 Grenoble, France
(Received 24 May 2004; accepted 5 July 2004)
The lateral structure of the adsorbed layer of a nonionic surfactant at a hydrophilic silicon substrate against water was studied over a wide range of surface concentrations of the surfactant by grazing-incidence small-angle neutron scattering (GISANS). For the chosen surfactant, tetraoxyethylene-mono-n-octyl-ether ( ), these changes in surface concentration were brought about by varying the temperature at a constant bulk concentration somewhat below the CMC of the surfactant. The GISANS measurements indicate the existence of transient surfactant aggregates without a preferred lateral structure at half coverage of the surface, and a correlation length of similar magnitude as the diameter of the surfactant micelles. This study shows that the picture of distinct surface aggregates of a characteristic size and separation that emerges from AFM studies of saturated surfactant layers on such substrates cannot be generalized to the situation below complete surface coverage.
61.12.Ex - Neutron scattering (including small-angle scattering).
68.08.De - Structure, measurements and simulations.
68.43.Hn - Structure of assemblies of adsorbates (two- and three-dimensional clustering).
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