Magnetic Field-Induced Self-Assembly of Conjugated Block Copolymers and Nanoparticles at the Air–Water Interface

Abstract

Here, we report the magnetic field-induced selfassembly of a conjugated block copolymer, poly(3-hexylthiopene)block-poly(ethylene glycol) (P3HT-b-PEG), and iron oxide nanoparticles (IONPs) at the air−water interface. Binary selfassembly of P3HT-b-PEG and IONPs at the interface results in nanoparticle-embedded P3HT-b-PEG nanowire arrays with a micrometer-scale domain size. Under the magnetic field, the field-induced magnetic interaction significantly improves the degree of order, generating long-range ordered, direction-controlled nanoarrays of P3HT-b-PEG and IONPs, where IONPs are aligned in the direction of the magnetic field over a sub-millimeter scale. The size of IONPs is an important factor for the formation of an ordered assembly structure at the nanometer scale, as it dictates the magnetic dipole interaction and the entropic interaction between nanoparticles and polymers. The consideration of magnetic dipole interactions suggests that the field-induced self-assembly occurs through the formation of intermediate magnetic subunits composed of short IONP strings along the semirigid P3HT nanowires, which can be aligned through the magnetic interactions, ultimately driving the long-range ordered self-assembly. This study demonstrates for the first time that the magnetic field-induced self-assembly can be used to generate macroscopically ordered polymer films with a nanometer-scale order in low fields.

Conjugated Block Copolymers for Functional Nanostructures

“…(f) Schematic illustration of the magnetic field-induced self-assembly process. Reproduced with permission from refs and . Copyright 2019 and 2022 American Chemical Society.…”

“…Often, incorporation of nanoparticles can induce interesting changes in BCP morphologies by swelling a selective domain or reducing the interfacial energy. − Various types of nanoparticles have been used for binary self-assembly, including metal, semiconductor, silica, and magnetic nanoparticles. Superparamagnetic nanoparticles are of particular interest, as the magnetic field can potentially induce interesting binary assembly structures. , We have adopted the magnetic field-induced alignment of iron oxide nanoparticles (IONPs) for long-range order and direction-controlled self-assembly of P3HT- b -PEG at the air–water interface (Figure a, right) . Without the magnetic field, simultaneous self-assembly of P3HT- b -PEG and IONPs at the air–water interface results in P3HT- b -PEG nanowire arrays embedded with IONPs with a micrometer-scale domain size.…”

“…77,78 We have adopted the magnetic field-induced alignment of iron oxide nanoparticles (IONPs) for long-range order and direction-controlled self-assembly of P3HT-b-PEG at the air−water interface (Figure 5a, right). 79 Without the magnetic field, simultaneous self-assembly of P3HT-b-PEG and IONPs at the air−water interface results in P3HT-b-PEG nanowire arrays embedded with IONPs with a micrometerscale domain size. When self-assembly was carried out under a magnetic field, the field-induced magnetic interaction between IONPs significantly improved the degree of order and generated large-area, direction-controlled nanoarrays of P3HT-b-PEG and IONPs over a sub-millimeter scale, where the nanowire alignment was nearly parallel to the direction of the magnetic field (Figure 5e).…”

Charge-Transfer-Induced Self-Assembly of Doped Conjugated Block Copolymer Nanofibers

“…Molecular doping is gaining increasing attention as a promising avenue for controlling optoelectronic properties of conjugated polymers. − In this approach, small molecule dopants oxidize or reduce host polymers, creating integer charge-transfer (ICT) sites. Ground state charge transfer (CT) gives rise to new or improved functionalities for a number of applications such as field-effect transistors, photovoltaics, ferroelectrics, , thermoelectric devices, − and photopatterning. , An important challenge in this field is the difficulty in controlling the molecular packing and nanoscale morphology of doped organic semiconductors, which exert a significant impact on their functionalities.…”

Air–Water Interfacial Directed Self‐Assembly of Block Copolymer Nanostrand Array

“…On the other hand, Park and co-workers recently reported the direction-controlling methods for the crystallization-induced ISA of rodcoil BCPs using the inclined water surface [13] or using magnetic nanoparticles with a magnetic field. [14] However, these methods are not applicable to align the nanostrands of coil-coil BCP. Despite of many research progresses, the DSA of strand-forming BCP ISA has never been investigated.In this study, we demonstrated the directed ISA of strand-forming BCPs in a more facile and fast way to produce highly aligned transferrable 2D nanopatterns in a large area.…”