Contact angles and adsorption in the system quartz-water-dodecane modified by dodecyl ammonium chloride

Abstract

Adsorption of dodecyl ammonium chloride was studied in the system quartz-water-dodecane. The distribution of dodecyl ammonium chloride between water and dodecane was measured as a function of pH; the effect of this surfactant on the water-dodecane interfacial tension was also measured. Adsorption of dodecyl amine at the quartz-dodecane interface approached monomolecular thickness, whereas adsorption of this surfactant was very much smaller at the quartz-water interface. In the pure three-phase system the contact angle was zero. Addition of amine resulted in finite contact angles and hysteresis. The contact angles were sensitive to the method of preparation and cleaning of the quartz surface, and also to the concentration of surfactant and pH. The relationship of the observed contact angles to amine concentration and pH was established. Calculations were made which indicated that adsorption equilibrium was not obtained during measurement of dynamic contact angles. By applying the Young equation to the system and by using the estimated true interfacial tensions rather than the equilibrium values, the observed contact angle behavior was satisfactorily explained.