APPLICATION OF TANFORD MICELLIZATION THEORY TO GEL-FILTRATION CHROMATOGRAPHIC DATA FOR NONIONIC SURFACTANTS

The micelle formation of hepta(ethylene glycol) decyl ether (C10E7) has been investigated by frontal gel filtration chromatographic (GFC) and surface tension methods at 25-degrees-C and explained in the framework of the Tanford theory. From an analysis of the concentration dependence of the centroid volume of the GFC pattern, the monomer concentration and weight- (n(w)) and number- (n(n)) average aggregation numbers of C10E7 micelles are estimated as a function of the total C10E7 concentration. The n(w)) value increases rapidly above the critical micellization concentration (cmc) and levels off at higher concentrations. The ratio n(w)/n(n) has a maximum around the cmc and approaches unity at higher concentrations. The derivative GFC pattern suggests the formation of premicelles. The dimerization constant of C10E7 is smaller than that of C10E8. These experimental results are quantitatively explained on the basis of many micellization models, originally considered by Tanford. These models are different in the configurations of the decyl and hepta(oxyethylene) chains, the penetration of water into the micelle core, the roughness of the micellar surface, and the micelle shape. A most probable C10E7 micelle of n(w) = 60, conforming to the present and literature data, seems to be an oblate ellipsoid whose minor semiaxis is the sum of the length of the fully extended decyl chain and that of the randomly coiled hepta(oxyethylene) chain. The micelle size distribution function is calculated on the basis of several micellization models.