HEAT OF IMMERSION OF ALUMINA INTO AGUEOUS SODIUM DODECYL SULFONATE SOLUTIONS

The heat of immersion of α-alumina was measured in water and in aqueous solutions of sodium chloride and sodium dodecyl sulfonate at various pH values. In water, the heat of immersion of alumina was found to be -850 ± 15 ergs/cm.2. In sodium chloride solutions without detergent, the heat of immersion was the same as that in distilled water at the same pH, and nearly independent of pH in the range from 3 to 10. In aqueous solutions of sodium dodecyl sulfonate, only when the detergent ions adsorb appreciably into the Stern plane do they affect the heat of immersion of alumina. As increased adsorption occurs either through increasing the detergent concentration in the bulk solution or by lowering the pH, the sensible heat evolved upon immersing alumina increases, reaching a value of -1100 ergs/cm.2 at monolayer coverage. The results are interpreted in terms of a model in which the detergent does not displace water at the oxide surface. © 1968.