The role of adsorption of sodium bis(2-ethylhexyl) sulfosuccinate in wetting of glass and poly(methyl methacrylate) surface

Abstract

Advancing contact angles, θ, for aqueous solutions of the anionic surfactant, sodium bis(2-ethylhexyl) sulfosuccinate (AOT) were measured on glass and poly(methyl methacrylate) (PMMA) surface. Using the obtained results we determined the properties of aqueous AOT solutions in wetting of these surfaces. It occurs that the wettability of glass and PMMA by these solutions depends on the concentration of AOT in solution. There is almost linear dependence between the contact angle ( θ) and concentration of AOT (log C) in the range from 5 × 10 −4 to 2.5 × 10 −3 M/dm 3 (value of the critical micelle concentration of AOT—CMC) both for glass and PMMA surface. For calculations of AOT adsorption at solid (glass, PMMA)-solution drop–air system interfaces the relationship between the adhesion tension ( γ LV cos θ) and surface tension ( γ LV) and the Gibbs and Young equations were taken into account. From the measurement and calculation results the slope of the γ LV cos θ − γ LV curve was found to be constant and equal 0.7 for glass and −0.1 for PMMA over the whole range of AOT concentration in solution. From this fact it can be concluded that if Γ SV is equal zero then Γ SL > 0 for the PMMA–solution and Γ SL < 0 for glass–solution systems. It means that surfactant concentration excess at PMMA–solution interface is considerably lower than at solution-air interface, but this excess of AOT concentration at glass–solution interface is lower than in the bulk phase. By extrapolating the linear dependence between the adhesion and surface tension the value of the critical surface tension ( γ c) of wetting for glass and PMMA was also determined, that equaled 25.9 and 25.6 mN/m for glass and PMMA, respectively. Using the value of the glass and PMMA surface tension as well as the measured surface tension of aqueous AOT solutions in Young equation, the solid–liquid interface tension ( γ SL) was found. There was a linear dependence between the γ SL and γ LV both for glass and PMMA, but there were different slope values of the curves for glass and PMMA, i.e. −0.7 and 0.1, respectively. The dependence between the work of adhesion ( W A) and surface tension ( γ LV) was also linear of different slopes for glass and for PMMA surface.