Complexation versus micelle formation: α-Cyclodextrin + n-decyltrimethylammonium bromide aqueous solutions

Ultrasonic attenuation spectra as well as dependencies upon surfactant concentration of the specific electric conductivity, the sound velocity, and the density have been measured for aqueous solutions of α-cyclodextrin with different amounts of n-decyltrimethylammonium bromide added. In addition to cyclodextrin isomerization the spectra reveal cyclodextrin–surfactant complexation and, above a critical association concentration, the monomer exchange between surfactant micelles and the suspending liquid. The data are evaluated assuming most α-cyclodextrin to form complexes, predominantly with 1:1 but also with 2:1 cyclodextrin–surfactant stoichiometry.