Monitoring the Discontinuous Dodecamer-Icosamer Transition of a Calix[4]arene-Derived Surfactant by Time-Resolved Small-Angle X-ray Scattering

Non-dependence of dodecamer structures on alkyl chain length in Platonic micelles

When the micellar aggregation number (Nagg) is sufficiently small (Nagg < 30), the micelle shows an abnormal aggregation behavior: monodispersity without any distribution in Nagg, whose values coincide with the vertex number of a regular polyhedral structure, i.e., they are termed Platonic solids. Micelles with these characteristics are named "Platonic micelles". In this study, we investigated the aggregation behavior of calixarene-based micelles bearing primary amines-the first example of Platonic micelles-with increasing alkyl chain length by small-angle X-ray scattering, asymmetrical flow field flow fractionation coupled with multiangle light scattering, and analytical ultracentrifugation measurements. Morphological transition of the micelles from spherical to cylindrical was observed when the alkyl chain length was increased in this calixarene-based micellar system, which is similar to the case of conventional systems and is acceptable in terms of the packing parameter principle. However, although the micellar Nagg normally increases with an increase in the alkyl chain length, the structure of calixarene-based Platonic micelles bearing butyl (C4), heptyl (C5), and hexyl (C6) chains remains at 12-mer. This is presumably due to the relationship between the thermodynamic stability of the Platonic micelles and the coverage ratio defined by the Tammes problem.

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 ( N_agg) have recently been discovered, whose values of N_agg 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 N_agg 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.

Tuning of the aggregation number of Platonic micelles with a binary mixture of calix[4]arene surfactants

The mixture ratios were used as a factor for aggregation number (N_agg) determination in binary mixtures of calix[4]arene surfactants.

Self-Templated Generation of Triggerable and Restorable Nonequilibrium Micelles

Conditional variations can lead to micellar transformations resulting in various (equilibrium) morphologies. However, creating differently shaped assemblies under the same final conditions (same ingredients, composition, temperature, etc.) is challenging. We present a thermoresponsive polyelectrolyte system allowing a pathway-dependent preparation of kinetically stable spherical star-like or cylindrical micelles. In more detail, a temperature-induced structure switch is used to generate equilibrated interpolyelectrolyte complex (IPEC) micelles of different morphologies (templates) below and above the lower critical solution temperature in the presence of plasticizer (salt). Then, lowering the salt concentration at a specific temperature kinetically freezes the formed IPECs, keeping the respective microstructural information encoded in the frozen IPEC also at other temperatures. Hence, different nonequilibrium morphologies at the same final conditions are provided. The salt-triggered transition from nonequilibrium to equilibrium micelles can be repeated for the same sample, highlighting a system with an on-demand changeable and restorable structure.

A tetramer micelle: the smallest aggregation number corresponding to the vertex number of regular polyhedra in platonic micelles

In this paper, we describe the construction of tetramer micelles based on the idea of "Platonic micelles" whose aggregation number (N_agg) matches the vertex number of regular polyhedra and exhibits the monodispersity and discreteness in the N_agg.