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

• Published in: Europhysics letters Vol. 67; no. 6; pp. 962 - 968
• Main Authors: Steitz, R, Müller-Buschbaum, P, Schemmel, S, Cubitt, R, Findenegg, G. H
• Format: Journal Article
• Language: English
• Published: IOP Publishing 01-09-2004; EDP Sciences
• Subjects: 61.12.Ex; 68.08.De; 68.43.Hn
• ISSN: 0295-5075; 1286-4854
• DOI: 10.1209/epl/i2004-10135-4

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 ($\chem{C_8E_4}$), 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.