COADSORPTION OF 2-NAPHTHOL AND CETYLPYRIDINIUM CHLORIDE AT A SILICA WATER INTERFACE IN RELATION WITH THE MICELLAR SOLUBILIZATION EFFECT

The coadsorption of 2-naphthol and a cationic surfactant, cetylpyridinium chloride (CPyCl), at a silica/water interface has been investigated at pH = 4.5 and pH = 6.5. In both cases, the adsorption of 2-naphthol follows closely the surfactant adsorption. However, complete 2-naphthol desorption is observed as a consequence of the preferential solute solubilization at higher surfactant concentration when regular micelles are formed, without surfactant desorption. The partition coefficient of 2-naphthol between the surfactant layers and water is calculated and compared to the micellar solubilization distribution constant as determined by two independent methods. The partition coefficient of 2-naphthol is shown to be systematically larger for the adsorption process than for the micellar solubilization. Thus, contrary to alcohols and dyes, 2-naphthol presents a good case of complete reversible behavior when coadsorbed with a cationic surfactant at a silica/water interface.