Monoliths of Semiconducting Block Copolymers by Magnetic Alignment

Abstract

Achieving highly ordered and aligned assemblies of organic semiconductors is a persistent challenge for improving the performance of organic electronics. This is an acute problem in macromolecular systems where slow kinetics and long-range disorder prevail, thus making the fabrication of high-performance large-area semiconducting polymer films a nontrivial venture. Here, we demonstrate that the anisotropic nature of semiconducting chromophores can be effectively leveraged to yield hierarchically ordered materials that can be readily macroscopically aligned. An n-type mesogen was synthesized based on a perylene diimide (PDI) rigid core coupled to an imidazole headgroup via an alkyl spacer. Supramolecular assembly between the imidazole and acrylic acid units on a poly(styrene-b-acrylic acid) block copolymer yielded self-assembled hexagonally ordered polystyrene cylinders within a smectic A mesophase of the PDI mesogen and poly(acrylic acid). We show that magnetic fields can be used to control the alignment of the PDI species and the block copolymer superstructure concurrently in a facile manner during cooling from a high-temperature disordered state. The resulting materials are monoliths, with a single well-defined orientation of the semiconducting chromophore and block copolymer microdomains throughout the sample. This synergistic introduction of both functional properties and the means of controlling alignment by supramolecular attachment of mesogenic species to polymer backbones offer new possibilities for the modular design of functional nanostructured materials.

Block copolymer electrolytes for rechargeable lithium batteries

“…Work by Weber et al showed that samples, poly(styrene‐ b −4‐vinylbenzyl alkylimidazolium bis(trifluoromethane sulfonlyl)imide) [PS‐ b ‐PVBn‐(alkyl)ImTFSI]), prepared by solvent‐casting and melt‐pressing strongly affect the copolymer conductivities due to the long‐range ordering of polymer morphologies (well‐ordered solvent‐cast film showed higher conductivity than poorly ordered melt‐pressed film) . Additionally, Osuji and coworkers used magnetic field alignment to control the nanoscale structure in BCPs, and their highly aligned samples demonstrated an order of magnitude improvement of ionic conductivity compared to unaligned counterparts by reducing microstructural tortuosity . Their work showed that the ionic conductivity of BCPs strongly is influenced by both the alignment of block domains and the domain orientation.…”

Microphase‐Separated Morphology and Liquid Crystal Orientation in Block Copolymers Comprising a Main‐Chain Liquid Crystalline Central Segment Connected to Side‐Chain Liquid Crystalline Segments at Both Ends

“…LC orientation affects the microdomain orientation because of the anchoring of mesogenic units on the microdomain interface. Side‐chain (SC) LC segments repel amorphous segments to form microdomains and stretch the backbone perpendicular to the interface accompanied by arrangement of the mesogens in the SCs parallel to the interface . A magnetic field can align amorphous microcylinders as well as the LC director of the matrix along the field direction throughout the specimen .…”

“…Side‐chain (SC) LC segments repel amorphous segments to form microdomains and stretch the backbone perpendicular to the interface accompanied by arrangement of the mesogens in the SCs parallel to the interface . A magnetic field can align amorphous microcylinders as well as the LC director of the matrix along the field direction throughout the specimen . Smectic (Sm) LCs under shear flow arrange the director in either the velocity gradient or in neutral directions; thus, the microcylinders immersed in an Sm LC matrix compromise on their orientation, arranging their long axis in either the velocity‐gradient or neutral directions even though shear flows usually arrange microcylinders parallel to the flow direction .…”

Influence of Smectic Liquid Crystallinity on Lamellar Microdomain Structure in a Main‐Chain Liquid Crystal Block Copolymer Fiber

“…Block copolymers incorporating a liquid crystal (LC) segment are designated as LC block copolymers and have attracted attention because their microdomain orientation correlates to the LC orientation owing to the anchoring of mesogenic units on the microdomain interface. Most LC block copolymers have the side‐chain‐type LC segment, which tends to stretch the backbone perpendicular to the interface and arrange the mesogens in the side chains parallel to the interface . Owing to the homogeneous anchoring of mesogens at the interface, a magnetic field can align the amorphous cylinder as well as the LC director along the field direction throughout the specimen .…”