Patchy Micelles with a Crystalline Core: Self-Assembly Concepts, Properties, and Applications.

Christian Hils,Judith Schöbel,Holger Schmalz,Ian Manners

doi:10.3390/polym13091481

Abstract

Crystallization-driven self-assembly (CDSA) of block copolymers bearing one crystallizable block has emerged to be a powerful and highly relevant method for the production of one- and two-dimensional micellar assemblies with controlled length, shape, and corona chemistries. This gives access to a multitude of potential applications, from hierarchical self-assembly to complex superstructures, catalysis, sensing, nanomedicine, nanoelectronics, and surface functionalization. Related to these applications, patchy crystalline-core micelles, with their unique, nanometer-sized, alternating corona segmentation, are highly interesting, as this feature provides striking advantages concerning interfacial activity, functionalization, and confinement effects. Hence, this review aims to provide an overview of the current state of the art with respect to self-assembly concepts, properties, and applications of patchy micelles with crystalline cores formed by CDSA. We have also included a more general discussion on the CDSA process and highlight block-type co-micelles as a special type of patchy micelle, due to similarities of the corona structure if the size of the blocks is well below 100 nm.

Highlights

From a conceptual point of view, several strategies exist for the production of patchy micelles with crystalline cores, such as crystallization-driven self-assembly (CDSA) of triblock terpolymers with crystallizable middle blocks, miktoarm stars, or the co-assembly of diblock copolymers with a common crystallizable block but different corona-forming blocks
Patchy micelles have been reported only for block copolymers (BCPs) with platelet-like micelles and co-milene (PE) or poly(ferrocenyl dimethylsilane) (PFS) as crystallizable blocks, despite the fact that a large variety of crystallizable polymer blocks has already been utilized in CDSA
Ring-opening polymerization of lactones or lactides, in combination with controlled radical polymerization techniques, might be another promising alternative, as BCPs based on PCL or PLLA as crystallizable blocks are readily accessible

Summary

Introduction

Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. As pointed out in the introduction, the preparation of one-dimensional (1D) cylindrical (or worm-like) micelles with controlled dimensions, low-length dispersities, and tailored corona structures and functionalities still remains a challenge in the self-assembly of fully amorphous BCPs. Besides, the introduction of a crystallizable block, which adds an additional and strong driving force for micelle formation, has turned out to be a highly efficient route to solve these issues. Analogous to the living polymerization of monomers, CDSA can proceed in a living manner, employing small micellar fragments as seeds (Figure 2a: seeded growth) for the addition of unimers (molecularly dissolved BCPs with a crystallizable block) In this approach, the micellar seeds, termed “stub-like” micelles, are produced by vigorous sonication of long, polydisperse cylindrical micelles prepared by conventional CDSA. Arrangement of surface compartments and the precisely adjustable size of the blocks, usually leading to larger corona segments than commonly observed for patchy CCMs

Short Excursion on Block Co-Micelles

Self-Assembly Concepts for Patchy

Interfacial Activity and Blend Compatibilization

Heterogeneous Catalysis

Findings

Conclusions and Outlook