Discrete and Discontinuous Increase in the Micellar Aggregation Number: Effects of the Alkyl Chain Length on Platonic Micelles.

Micelles with perfect monodispersity in terms of the aggregation number ( Nagg) have recently been discovered, whose values of Nagg interestingly always coincide with the vertex or face number of regular polyhedral structures (i.e., Platonic solids). Owing to the monodispersity of the micelles, named Platonic micelles, we could expect them to exhibit unprecedented aggregation behavior. In this study, the effects of alkyl chain length on micellar aggregation behavior were characterized using small-angle scattering techniques such as small-angle X-ray scattering and asymmetrical flow field-flow fractionation coupled with multi-angle light scattering, as well as analytical ultracentrifugation measurements. The Nagg of Platonic micelles discretely and discontinuously increased when increasing the alkyl chain length, which differs markedly from the findings for conventional micelles. This aggregation behavior could be reasonably explained by the relationship between the thermodynamic stability of the micelles and the coverage density defined by one of the unsolved mathematical problems: the Tammes problem.