Molar volume and conductivity measurements have been carried out at 298.15 K for cetyltrimethylammo-nium chloride (CTAC) + H2O and CTAC +β -cyclodextrin (β-CD) + H2O systems. The apparent critical micelle concentrations, the dissociation degree of the micelle, the transfer free energy for the hydrocarbon chain of CTAC frorn aqueousβ-CD solutions to the micelle, the standard partial molar volumes of CTAC in aqueousβ-CD solutions, the stoichoimetry and the equilibrium constants for the inclusion compounds of CTAC withβ-CD have been determined. The influence ofβ-CD and its complexes on the micellization process of CTAC is analyzed. It is shown thatβ-CD partly screened the hydrophobic hydrocarbon chain of CTAC molecules from contact with the surrounding medium and retarded the formation of CTAC micelles in a certain extent. However, β-CD and its complexes do not participate in the formation of CTAC micelles, and the complexes have no significant effect on the micelle properties once the micelles are formed. The number of CH_2 groups entering the cavity ofβ-CD was calculated based on a simple model. The result suggests thatβ-CD forms inclusion compounds with CTAC, and the stoichoimetry is found to be 2:1 at higher concentrations ofβ-CD.

Key words: CYCLODEXTRIN, CTAB, ELECTRIC CONDUCTANCE, MICELLE, ENVELOPMENT