Interactions between Nonpolar Surfaces Coated with the Nonionic Surfactant Hexaoxyethylene Dodecyl Ether C₁₂E₆and the Origin of Surface Charges at the Air/Water Interface

Abstract

The interactions between nonpolar surfaces coated with the nonionic surfactant hexaoxyethylene dodecyl ether C12E6 were investigated using two techniques and three different types of surfaces. As nonpolar surfaces, the air/water interface, silanated negatively charged glass, and thiolated uncharged gold surfaces were chosen. The interactions between the air/water interfaces were measured with a thin film pressure balance in terms of disjoining pressure as a function of film thickness. The interactions between the solid/liquid interfaces were determined using a bimorph surface force apparatus. The influence of the nature of the surface on the interaction forces was investigated at surfactant concentrations below and above the cmc. The adsorption of the nonionic surfactant on the uncharged thiolated surface does not, as expected, lead to any buildup of a surface charge. On the other hand, adsorption of C12E6 on the charged silanated glass and the charged air/water interface results in a lowering of the surface charge density. The reduction of the surface charge density on the silanated glass surfaces is rationalized by changes in the dielectric permittivity around the charged silanol groups. The reason for the surface charge observed at the air/water interface as well as its decrease with increasing surfactant concentration is discussed and a new mechanism for generation of OH- ions at this particular interface is proposed.

Mixtures of n-dodecyl-β-d-maltoside and hexaoxyethylene dodecyl ether — Surface properties, bulk properties, foam films, and foams

“…Comparing the Π-h curves of the single surfactants [51,52] with those of the 1:1 mixture one clearly sees similarities and differences, which will briefly be addressed in the following. A more detailed analysis will be published soon.…”

Polyelectrolyte-mediated surface interactions

“…We have not been able to find any report describing interactions between adsorbed homopolyelectrolyte layers on uncharged surfaces. (Uncharged polar surfaces can for instance be prepared by self-assembly of OH-functionalized thiols on gold [41], whereas non-polar uncharged surfaces can be prepared by self-assembly of methyl terminated alkyl thiols on gold [42]). However, there are a few studies reporting on the adsorption of heterogeneous polyelectrolytes on uncharged non-polar surfaces [43][44][45].…”

Phase diagrams of nonionic foam films: construction by means of disjoining pressure versus thickness curves

“…In the case of ionic surfactants, the location of the charges corresponds to the location of the headgroups, whereas in the case of nonionic surfactants the charges are believed to be located at the water/air surface. Note that this point is still under debate (see discussion in [6,24]). Last but not least, the van der Waals component vdW of the disjoining pressure, i.e., the long-range attractive contribution, is defined as…”