tering (QELS) to determine for SDS micelles the polydispersity, Capillary electrophoresis (CE) was used to study the polydisperdefined as
, where sity of TX-100/SDS and C 12 E 8 /SDS micelle systems. Compared N i is the number of particles with diffusion coefficient D i and with other techniques, CE provides more specific and graphically molecular weight M i , and D is the average diffusion coefficient. detailed information on the compositional polydispersity of such The polydispersity decreases with temperature but increases with micellar systems. Clear evidence of the coexistence of micelles rich concentration and ionic strength. Using the same method, in either nonionic or anionic component has been obtained. This Benedek et al. (13) described the polydispersity of SDS in NaCl coexistence is explained by considering that the stability of mixed solutions by means of the variance (V), defined as N z /N w Γ 1 / micelles is affected by several factors, including counterion bind-4V 2 (N z and N w are the z-average and weight-average aggregation ing, and steric shielding of the electrostatic repulsive interaction among the headgroups of SDS by the bulky EO groups of TX-numbers, respectively). Several workers used a fluorescence 100. Due to these two factors, micelles with different compositions quenching method (14-16) in which the fluorescence decay may be energetically equivalent, leading to a broad distribution of curve of the probe was analyzed to obtain surfactant aggregation micelle size and composition. In this study, we observe how the numbers. Using this method, Reekmans et al. ( 16) concluded for pattern of the distribution changes with the mole fraction of SDS. hexadecyltrimethylammonium chloride systems that ''the system Electrophoretographic patterns also showed that broader composiexhibits a rather broad polydispersity in micellar aggregation tional distribution of the original components produces a wider numbers at low surfactant concentration. Increasing the surfacdistribution of mobilities. α§ 1997 Academic Press tant concentration leads to a growth of the smaller micelles and, Key Words: micelle heterogeneity; CE of micelles; mixed mithus, to a more narrow size distribution.'' Gel chromatography celles; micelle composition. may also be applied to evaluate micelle size distributions. Using this method, Funasaki et al. (17) observed that at intermediate concentrations, C 12 E 6 micelle peaks exhibited some broadening