Wetting transition of a binary liquid due to suppression of electrostatic forces.

Abstract

When a phase-separated mixture of carbon disulfide and nitromethane is put in contact with borosilicate glass, a thick nitromethane-rich wetting layer generally results. The long-range force responsible for this layer is believed to be electrostatic in nature and caused by ionization of hydroxyl groups on the glass surface. We have used a capillary-rise epxeriment to examine the effect on the state of wetting of suppressing this force through the addition of a soluble salt, tetrabutylammonium iodide. We find that for small salt concentrations (0.1M) the glass appears to remain completely wet to within at least 40 K of ${\mathit{T}}_{\mathit{c}}$, but that for larger concentrations (g0.2M) the glass is incompleely wet for temperatures T(${\mathit{T}}_{\mathit{c}}$-25 K). At T\ensuremath{\approxeq}(${\mathit{T}}_{\mathit{c}}$-25 K) the system undergoes a wetting transition from incomplete to complete wetting. The appearance of this wetting transition seems to result from the complete removal of the long-range electrostatic interaction.