Small-angle x-ray scattering study of aqueous solutions of sulfonated calix[6]arene derivatives

A small-angle x-ray scattering study has been carried out on aqueous solutions of three sulfonated calixarene derivatives (calix[6]arene-p-hexasulfonate (1-H), 5,11,17,23,29,35-hexasulfonato-37,38,39,40,41,42-hexakis-(hexyloxy)calix[6]arene (1-${\mathrm{C}}_6$), and 5,11,17,23,29,35-hexasulfonato-37,38,39,40,41,42-hexakis (dodecyloxy)calix[6]arene) (1-${\mathrm{C}}_{12}$). Except for 1-H, two ditinct peaks were observed. The peak intensity at the lower angles became greater and the peak position shifted toward higher angles when the surfactant concentration was increased. This peak disappeared in high-salt conditions and was decreased in intensity with increasing temperature. These results were taken as implying that the peak reflects the intermicellar interference and that the micelles formed by the calixarene derivatives also form distorted ordered structures in solutions like many other ionic species studied earlier [N. Ise, Angew. Chem. 25, 323 (1986)]. The intensity of the peak at lrger angles became larger with increasing surfactant concentration but the peak position was not affected, indicating that this peak is due to intramicellar interference. From the observed intensity I(Q) the intraparticle scattering function [P(Q)] was estimated with the assumption that I(Q) in high-salt conditions represents P(Q). The P(Q) thus obtained was compared with theoretical values computed for prolate ellipsoid core-shell models. The dimensions of the models were determined from the fitting. The aggregation number estimated from the models and the molecular size was found to be not very far from that obtained from the Bragg spacing.