ADSORPTION OF CATIONIC SURFACTANTS ON SIL ICA SURFACES WITH DIFFERENTSURFACE-CHARGE

In this work the adsorption of the cationic surfactants hexadecylpyrid inium chloride and dodecylammonium chloride was investigated on silica gel and precipitated silica at varying pH and electrolyte concentrati on, The enthalpy changes cuased by the displacement process were deter mined by means of flow microcalorimetry. The surface thermodynamic pot ential functions were calculated from the adsorption and calorimetric data to characterize the adsorption exchange processes and the structu re of the adsorption layers. The magnitude and sign of the surface cha rge determine the adsorption mechanism (ionic or molecular) of these i onic surfactants on silica surfaces, The adsorption exchange processes and the adsorption layer structure can be influenced by changing the pH and the electrolyte concentration of the bulk liquid phase. Large e xotermic adsorption heats were determined in the case of adsorption of surfactant molecules and micelles explained by the breaking of ,,iceb erg water'' structure at the surface.