Solvent Annealing of Striped Ellipsoidal Block Copolymer Particles: Reversible Control over Lamellae Asymmetry, Aspect Ratio, and Particle Surface

Exciton and charge transfer processes within singlet fission micelles

Multiexciton (ME) mechanisms hold great promise for enhancing energy conversion efficiency in optoelectronic and photochemical systems. In singlet fission (SF), the generation of two triplet excitons from a single photon provides a route to circumvent thermal energy losses and organic systems offer opportunities to modulate ME dynamics. However, the practical implementation of SF-based materials is hindered by poor triplet exciton mobility, interfacial recombination losses, and complex dynamics at heterogeneous interfaces. While studies of interfacial SF dynamics have demonstrated the potential for efficient charge and exciton transfer, experimental conditions and design of interfaces vary widely. To address this, we explore polymer-based self-assembled architectures as a tunable platform for studying mesoscale SF interfacial dynamics of (multi)exciton transfer, as well as electron and hole transfer. Specifically, we design amphiphilic block copolymers (BCPs) incorporating pendent tetracene moieties that self-assemble into micellar nanoparticles, placing the tetracenes in the amorphous core. These micelles provide a controlled environment to systematically introduce "dopants" to investigate interfacial dynamics. Importantly, the use of solvents within the micelle core can be also applied to impart polymer chain mobility.

Recent Progress on Preparation of Anisotropic Block Copolymer Particles Self-Assembled in 3D Emulsion Droplets

Self-assembly of block copolymers (BCPs) into anisotropic colloidal particles within 3D emulsion droplets has attracted considerable interest since the confined assembly in deformable geometries offers significant potential for designing and constructing specific anisotropic polymer materials for various applications. By precisely controlling the deformation of emulsion droplets, nucleation, and deposition sequence of BCP segments at the oil/water interface, various anisotropic polymer assembly particles with tunable shapes and internal structures can be generated. This review summarizes the recent advancements in the design and formation of anisotropic polymer assembly particles via confined assembly of BCPs, including an overview of emulsification techniques and methods, the regulation of particle shapes and internal structures, as well as the diverse applications of resulting anisotropic particles. Typically, the regulation of anisotropic shapes can be achieved through experimental approaches, such as the volume ratio and interactions between blocks, surfactant selectivity, crystallization-induced deformation, stimuli-responsive additives, evaporation rate, post-annealing, confinement degree, and disassembly of prepared polymer colloids. Finally, the further perspectives and challenges in the construction anisotropic functional polymer materials are discussed.

Bifunctional additive-driven shape transitions of block copolymer particles through synergistic quaternization and protonation

Block copolymer (BCP) particles with tailored shapes and nanostructures hold promise for applications in cell adhesion, photonic system, and energy storage due to their unique optical and rheological properties. Conventional approaches relying on surfactant-mediated self-assembly often limit particle geometries to simple structures. Herein, we present a versatile approach to expand the morphology of poly(styrene-block-2-vinylpyridine) (PS-b-P2VP) BCP particles through the incorporation of 9-bromononanoic acid (BNA), a bifunctional additive that facilitates synergistic quaternization and protonation. Increasing the BNA-to-2VP molar ratio enhances P2VP hydrophilicity and decreases the pH value, driving dramatic shape transitions from onion-like spheres to tulip bulbs, ellipsoids, discs, and Janus cups. This morphological diversity is attributed to synergetic interfacial instability-driven water infiltration and pH-induced repulsion of protonated P2VP chains. Additives with a single functional group, however, yield limited morphologies, such as tulip bulbs or onion-like spheres. Notably, Janus cups fabricated via this strategy exhibit selective cargo-loading capabilities, highlighting the importance of precise control over the internal composition and structure of BCP particles.

Light-induced charge transfer from a fullerene to a zeolitic imidazolate framework enhances alkaline electrocatalytic hydrogen production

In the process of water electrolysis, the oxygen evolution reaction (OER) suffers from a high energy barrier, which has become a key factor restricting the large-scale commercial application of renewable energy technology. Therefore, it is necessary to develop a durable, efficient, low-cost and environmentally friendly OER electrocatalyst. In the present work, a photo-responsive fullerene (C60) was encapsulated in the cavity of cobalt-containing flake-like zeolitic imidazolate framework-67 (C60@F-ZIF-67). Benefiting from the light-induced charge/energy transfer from the fullerene carbon cage to the metal Co active sites, the as-synthesized C60@F-ZIF-67 exhibited remarkably enhanced OER activity under UV light irradiation. Specifically, the overpotential of 10 mA cm-2 for C60@F-ZIF-67 decreased from 465 mV in the dark to 324 mV under light in 1 M KOH, amounting to an activity improvement of approximately 30.32%. This work provides a new route for the design and construction of photo-assisted efficient electrocatalysts for water splitting.

Organic/inorganic heterostructures templated by interfacial instability-driven BCP colloids in deformable emulsion droplets

Hybrid heterostructure materials have received considerable attention due to the integration of each component and abundant functional applications in micromotors, catalysis, photothermal therapy, drug delivery, and bioimaging. However, the preparation of organic/inorganic heterostructure nanoparticles (HSNPs) with high quality still remains a remarkable challenge since thermodynamically metastable structures usually coexist, resulting in a lack of organic scaffolds with extreme uniformity both in shape and size distribution. Here, we prepared polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymer (BCP) core-shell spherical colloids driven by interfacial instability of soft and deformable emulsion droplets. Ultra-low interfacial tension was achieved through the co-adsorption of BCP segments and sodium dodecyl sulfate (SDS) surfactant, which had a strong affinity with the P4VP segment at the interface of the emulsified droplets. The excellent and homogeneous BCP colloids were further utilized as organic scaffolds to selectively grow a functional SiO2 layer on the surface of the BCP spherical colloids, producing BCP/SiO2 HSNPs with highly uniform shape and size distribution originating from the PS-b-P4VP scaffolds, thus providing an efficient and general strategy to construct and design organic/inorganic HSNPs with diverse applications.

The Process-Directed Self-Assembly of Block Copolymer Particles

The kinetic paths of structural evolution and formation of block copolymer (BCP) particles are explored using dynamic self-consistent field theory (DSCFT). It is shown that the process-directed self-assembly of BCP immersed in a poor solvent leads to the formation of striped ellipsoids, onion-like particles and double-spiral lamellar particles. The theory predicts a reversible path of shape transition between onion-like particles and striped ellipsoidal ones by regulating the temperature (related to the Flory-Huggins parameter between the two components of BCP, χAB ) and the selectivity of solvent toward one of the two BCP components. Furthermore, a kinetic path of shape transition from onion-like particles to double-spiral lamellar particles, and then back to onion-like particles is demonstrated. By investigating the inner-structural evolution of a BCP particle, it is identified that changing the intermediate bi-continuous structure into a layered one is crucial for the formation of striped ellipsoidal particles. Another interesting finding is that the formation of onion-like particles is characterized by a two-stage microphase separation. The first is induced by the solvent preference, and the second is controlled by the thermodynamics. The findings lead to an effective way of tailoring nanostructure of BCP particles for various industrial applications.

Optically active polymer particles with programmable surface microstructures constructed using chiral helical polyacetylene

Micro/nanoparticles with surface microstructures have attracted tremendous attention due to their fascinating structures and properties. Herein, we present the first strategy for producing optically active polymer particles with varying surface microstructures via a template surface modification process in which achiral particles act as the template and helical substituted polyacetylene acts as the chiral component. To prepare the designed chiral-functionalized particles, template particles were first reacted with propargylamine to produce alkynylated template particles. The alkynylated templates further participated in the polymerization of chiral alkyne monomers through a surface grafting precipitation polymerization approach, resulting in achiral particles with surface microstructures covalently bonded with a chiral helical polymer. SEM images ascertain the production of chiral-functionalized particles showing various shapes (jar-like, golf ball-like, and raspberry-like particles). Furthermore, CD and UV-vis absorption spectra demonstrate that the grafted polyacetylene chains adopt a predominantly single-handed helical conformation, thereby affording composite particles with optical activity. Using the established protocol, numerous advanced chiral-functionalized micro/nanostructures are expected to be designed and constructed.

Regioselective Seeded Polymerization in Block Copolymer Nanoparticles: Post-Assembly Control of Colloidal Features

Post-assembly modifications are efficient tools to adjust colloidal features of block copolymer (BCP) particles. However, existing methods often address particle shape, morphology, and chemical functionality individually. For simultaneous control, we transferred the concept of seeded polymerization to phase separated BCP particles. Key to our approach is the regioselective polymerization of (functional) monomers inside specific BCP domains. This was demonstrated in striped PS-b-P2VP ellipsoids. Here, polymerization of styrene preferably occurs in PS domains and increases PS lamellar thickness up to 5-fold. The resulting asymmetric lamellar morphology also changes the particle shape, i.e., increases the aspect ratio. Using 4-vinylbenzyl azide as co-monomer, azides as chemical functionalities can be added selectively to the PS domains. Overall, our simple and versatile method gives access to various multifunctional BCP colloids from a single batch of pre-formed particles.