Interfacial Behavior of n-octyl beta-D-glucopyranoside compared to that ofa technical mixture consisting of octylglucosides

The difference in interfacial behavior between a technical mixture consisti ng of n-octyl glucopyranosides, having between 1 and 7 glucose units in the polar headgroup, and n-octyl beta -n-glucopyranoside was investigated usin g a range of methods. The forces acting between two hydrophobic solid surfa ces across surfactant solutions were determined with a surface force appara tus. It was found that adsorption of the technical mixture generated a long -range repulsive force of electrostatic nature. At shorter separations a lo cal minimum in the force curve (located on the repulsive side) was observed . Further in a steric repulsion dominated the interaction. In contrast, ads orption of pure n-octyl beta -D-glucopyranoside did not generate any long-r ange electrostatic double-layer force and an attractive force was present b etween the monolayer-coated surfaces close to contact. Wetting experiments showed that the technical mixture was a better wetting agent of hydrophobic surfaces (lower contact angle and higher wetting tension). The adsorption to air-liquid interfaces was also investigated by surface tension measureme nts and by measuring the forces acting across single foam films. The latter measurements were carried out using a thin film balance employing the poro us frit technique. The technical mixture was more efficient in generating l ong-range electrostatic forces whereas the pure n-octyl beta -D-glucopyrano side was more efficient in generating stable Newton black films. Pyrene flu orescence measurements revealed that the micelles formed by the technical m ixture continuously change its average composition with concentration towar d structures with a more hydrophobic micellar core.