CALORIMETRIC STUDIES OF CATIONIC SURFACTANT ADSORPTION AT LOW SURFACECOVERAGES ON DIFFERENT SILICA SAMPLES

Calorimetric measurements of adsorption for the surfactant (benzyldime thyldodecylammonium bromide) and its polar head-group (benzyltrimethyl ammonium bromide) from aqueous solutions on two different silica surfa ces (hydrophilic and hydrophobic one) allow a more detailed picture of the subsequent stages of the adsorption process to be drawn. It is po ssible to determine more precisely a boundary between the adsorption o f individual molecules and the formation of surface aggregates. The lo cal disruption of the structure of the interfacial water molecules by surfactant cations gives an endothermic contribution to the total enth alpy of displacement. This contribution depends on the length of alkyl chain as well as on the type and the origin of solid surface.