Thermodynamics and adsorption behaviour in the quartz/aqueous surfactant system

Experimental results are given for the temperature dependency of the zeta potential and adsorption density in the system of quartz + dodecylammonium acetate solutions. Utilizing the experimental adsorption densities and the Stern-Grahame equation, calculations indicate large entropic effects which are attributed to the phenomenon of hydrophobic bonding. A change in the adsorption mechanism in the temperature range greater than 25°C may be due to a major breakdown of the ordered water structure at the solid surface. The electrokinetic results appear contrary to the prediction of both the simple Gouy-Chapman and the modified Stern theory allowing for a distance of closest approach. It is concluded that the measured effects must be due to changes occurring at, or associated with, both the plane of closest approach and the shear plane.