Visualizing Nanoscale Coronal Segregation in Rod-Like Micelles Formed by Co-Assembly of Binary Block Copolymer Blends

A Versatile Platform to Generate Shell-Cross-Linked Uniform Π-Conjugated Nanofibers with Controllable Length, High Morphological Stability, and Facile Surface Tailorability

Living crystallization-driven self-assembly (CDSA) has emerged as an efficient route to generate π-conjugated-polymer-based nanofibers (CPNFs) with promising applications from photocatalysis to biomedicine. However, the lack of efficient tools to endow CPNFs with morphological stability and surface tailorability becomes a frustrating hindrance for expanding application spectrum of CPNFs. Herein, a facile strategy to fabricate length-controllable OPV-based (OPV = oligo(p-phenylenevinylene)) CPNFs containing a cross-linked shell with high morphological stability and facile surface tailorability through the combination of living CDSA and thiol-ene chemistry by using OPV5 -b-PNAAM32 (PNAAM = poly(N-allyl acrylamide)) as a model is reported. Uniform fiber-like micelles with tunable length can be generated by self-seeding of living CDSA. By taking advantage of radical thiol-ene reaction between vinyls of PNAAM corona and four-arm thiols, the shell of micelles can be cross-linked with negligible destruction of structure of vinylene-containing OPV core. The resulting micelles show high morphological stability in NaCl solution and PBS buffer, even upon heating at 80 °C. The introduced extra thiol groups in the cross-linked shell can be further employed to install extra functional moieties via convenient thiol-Michael-type reaction. Given the negligible cytotoxicity of resulting CPNFs, this strategy opens an avenue to fabricate various CPNFs of diverse functionalities for biomedicine.

Well-shaped poly(dimethylsiloxane)-based copolymer nanowires from spherical micelles via kinetic shape evolution

The formation of self-assembled arrays or superstructures from copolymers has attracted intense research interest. Herein, we propose a kinetic approach to form self-assembled nanowires using a PDMS-based block copolymer consisting of poly(dimethylsiloxane)-b-poly[2-(cinnamoyloxy)ethyl methacrylate] (PDMS-b-PCEMA). The copolymer was synthesized by using the macroinitiator PDMS-Br to initiate 2-(trimethylsiloxy)ethyl methacrylate (HEMA-TMS) via ATRP, followed by hydrolysis of the TMS group and gradual esterification with cinnamoyl chloride. PDMS-b-PCEMA presented core-shell spherical micelles in tetrahydrofuran, which transformed into nanowires within 5 days self-assembly via a typical kinetic shape evolution. The diameter of the assembled nanowires with a PCEMA inner core and PDMS shell was about 25-35 nm. The formation of these nanowires reflected a balance between the PDMS and PCEMA components: the PDMS segment was soluble enough to form a corona block, which was beneficial for the transformation of the micellar shape. Meanwhile, the PCEMA segment was able to control the diameter of the nanowire micelles but had no decisive effect on their formation. The effect of solvents on the self-assembled micelles indicated that nanowires were formed in tetrahydrofuran and dichloromethane, while core-shell micelles were formed in acetone. This was due to the different permittivities of these solvents. The nanowires were fixed by cross-linking the PCEMA group under UV irradiation, which enhanced their stability. We believe that this work provides a new strategy for the formation of nanowires and offers a guide for the diversified self-assembly of nanostructures from copolymers.

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

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.

Surface Patterning of Uniform 2D Platelet Block Comicelles via Coronal Chain Collapse

The formation of colloids with anisotropically patterned surfaces is of growing interest for the creation of hierarchical structures and the templating of nanoparticles. We have recently shown that well-defined two-dimensional platelets with low areal dispersities can be formed by the seeded growth of a blend of homopolymers and block copolymers. Herein we form rectangular platelets containing two block copolymers with different coronal chemistries. On addition of a solvent that is only able to solvate the corona of one block, we were able to form colloidally stable micelles with patterned surfaces via coronal collapse. Scanning transmission electron microscopy-energy-dispersive X-ray spectroscopy and atomic force microscopy were employed to provide information on the structure and size of the patches decorating the micelle surfaces.

Formation of 2D and 3D multi-tori mesostructures via crystallization-driven self-assembly

The fabrication of three-dimensional (3D) objects by polymer self-assembly in solution is extremely challenging. Here, multi-tori mesostructures were obtained from the crystallization-driven self-assembly of a coil-crystalline block copolymer (BCP) in mixed solvents. The formation of these structures follows a multistep process. First, the BCP self-assembles into amorphous micrometer-large vesicles. Then, the BCP confined in these mesosized vesicles crystallizes. This second step leads to the formation of objects with shapes ranging from closed 3D multi-tori spherical shells to 2D toroid mesh monolayers, depending on the solvent mixture composition. This approach demonstrates how topological constraints induced by the specific interactions between coil-crystalline BCP and solvents can be used to prepare mesostructures of complex morphologies.

A guide to supramolecular polymerizations

Supramolecular polymers are non-covalent assemblies of unimeric building blocks connected by secondary interactions and hold great promises due to their dynamic nature.