Microcalorimetric study of cetylpyridinium-chloride adsorption onto different oxides

Abstract

The adsorption behavior of cetylpyridinium-chloride (CPC) at different oxide surfaces (Al₂O₃, silicagel, SnO₂, TiO₂) was characterized by means of liquid-flow adsorption microcalorimetry. The corresponding adsorption isotherms were also measured by a flow method. It was found that all the experimental enthalpies of displacement were exothermic. The plot of the enthalpies of displacement against the amount of CPC adsorbed results in straight lines with approx. the same slope for all oxides, although the surface charge of the oxides is different. Electrostatic and lateral interactions seem to contribute only little to the measured enthalpies of displacement. In apparent contradiction to these results, the investigation of the pH and electrolyte concentration dependence of CPC adsorption onto silica gel suggests an electrostatic adsorption mechanism coupled with hemicellization.