Effect of anionic surfactant and short-chain alcohol mixtures on adsorption at quartz/water and water/air interfaces and the wettability of quartz

Measurements of the advancing contact angles for aqueous solutions of sodium dodecyl sulfate (SDDS) or sodium hexadecyl sulfonate (SHS) in mixtures with methanol, ethanol, or propanol on a quartz surface were carried out. On the basis of the obtained results and Young and Gibbs equations the critical surface tension of quartz wetting, the composition of the surface layer at the quartz–water interface, and the activity coefficients of the anionic surfactants and alcohols in this layer as well as the work of adhesion of aqueous solutions of anionic surfactant and alcohol mixtures to the quartz surface were determined. The analysis of the contact angle data showed that the wettability of quartz changed visibly only in the range of alcohol and anionic surfactant concentration at which these surface-active agents were present in the solution in the monomeric form. The analysis also showed that there was a linear dependence between the adhesion and the surface tension of aqueous solutions of anionic surfactant and alcohol mixtures. This dependence can be described by linear equations for which the constants depend on the anionic surfactant and alcohol concentrations. The slope of all linear dependence between adhesion and surface tension was positive. The critical surface tension of quartz wetting determined from this dependence by extrapolating the adhesion tension to the value equal to the surface tension (for contact angle equal zero) depends on the assumption whether the concentration of anionic surfactant or alcohol was constant. Its average value is equal to 29.95 mN/m and it is considerably lower than the quartz surface tension. The positive slope of the adhesion–surface tension curves was explained by the possibility of the presence of liquid vapor film beyond the solution drop which settled on the quartz surface and the adsorption of surface-active agents at the quartz/monolayer water film–water interface. This conclusion was confirmed by the work of adhesion of aqueous solutions of anionic surfactants and short-chain alcohol mixtures to the quartz surface determined on the basis of the contact angle data and molar fraction of anionic surfactants and alcohols and their activity coefficient in the surface layer.

Influence of alcohol (methanol) and anionic surfactant (SDDS) molar fraction (X2s and X1s) at the water–air and quartz–water interface on the spreading coefficient at the quartz–aqueous solution interface..Figure optionsDownload high-quality image (78 K)Download as PowerPoint slideResearch highlights
► A linear dependence of adhesion and surface tension was seen with a positive slope.
► The critical surface tension of quartz wetting depends on the aqueous solution composition.
► Adhesion work of a solution to quartz can be predicted from the activities of its components.