Aggregation behaviour of n-alkyl-β- d-glucopyranoside + water + alcohol mixtures

Abstract

The formation and properties of aggregates in aqueous n-alkyl-β- d-glucopyranoside (C XG 1) + n-alcohol mixtures are investigated theoretically, with particular emphasis on: (1) micellar size and shape; (2) critical micelle concentration; (3) partition of alcohols between micelles and intermicellar solution. In order to check the theoretical results some critical micelle concentrations were estimated using dynamic surface tension measurements. Utilizing a statistical-thermodynamic mixed micelle formation model, developed by Nagarajan and Ruckenstein, expressions for the chemical potentials of each of the solution components are obtained and used, along with the principle of multiple-chemical equilibrium, to calculate the micellar size distribution and the chemical composition of the mixed micelles. All calculations were performed taking a divariante distribution with respect to the aggregation number and with respect to the chemical composition, completely into account. The model contains no adjustable parameter. For energetic reasons the n-alkyl-β- d-glucopyranoside form in pure water and in presence of alcohol spherical bilayer vesicles. The predicted values of the critical micelle concentration are in satisfactory quantitative agreement with experimental values obtained by dynamic surface tension measurements. The number-average aggregation number of the mixed micelles runs through a minimum as function of the alcohol concentration. The alcohol molecules will be incorporated into the aggregates according their overall concentration. The penetration of the alcohol in the micelles does not depend on the chain length of the surfactant molecules.