Interactions of γ-Cyclodextrin with the Mixed Micelles of Anionic Surfactants and Their Inclusion Complexes Formation

Abstract

Interactions of γ-cyclodextrin (γ-CD) with the single and mixed micelles of sodium dodecyl sulfate (SDS) and sodium lauroyl sarcosine (SLAS) have been studied at different concentrations of γ-CD by using conductivity measurements. From conductivity data, the pure and mixed critical micellar concentration (cmc), the equivalent ionic conductivities of the monomeric species (Λ _m), the associated species (Λ _assc) and the micelle (Λ _mic), the degree of counterion dissociation (χ) in the presence of γ-CD have been evaluated from the slope of the conductivity versus concentration plots for the pure and binary mixture of surfactants. From the dependence of cmc of the surfactantson γ-CD concentration, we have deduced the association constant (K) of surfactant-γ-CD inclusion complexes assuming 2:1 stoichiometry. Theories of Clint, regular solution, and Motomura's have been used for the evaluation of ideality or nonideality of the mixed system. Mixed micelles were found to be rich in SDS content in the presence and the absence of γ-CD. The cmc values have been used to evaluate the transfer of standard free energy of micelles (ΔG⁰ _M,tr) from the aqueous medium to additive medium.

Keywords:

• γ-cyclodextrin
• association constant
• cmc
• mixed micelles
• SDS
• SLAS

P. S. is thankful to the Japan Society for the Promotion of Science (JSPS) for the postdoctoral award. P. S. also has been supported by the Danish Natural Research Council and the Innovation Consortium BIOPRO. D. E. O. is supported by the Danish National Science Foundation and the Villum Kann Rasmussen Foundation.