Lateral structure of a surfactant layer adsorbed at a hydrophilic solid/liquid interface

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

Corresponding author: steitz@hmi.de

Received: 24 May 2004
Accepted: 5 July 2004

Abstract

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.