Well-Ordered Inorganic Nanoparticle Arrays Directed by Block Copolymer Nanosheets

Well-Ordered Nanoparticles/Block Copolymer Nanosheets with a Controllable Location of Nanoparticles

Precisely controlling the spatial distributions and arrangements of metal nanoparticles (NPs) into block copolymers is of great importance for fabricating novel nanomaterials with the desired optical and electronic properties. Herein, we develop a simple yet versatile strategy to prepare organic/inorganic nanosheets formed by the coassembly of polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) and PS tethered gold nanoparticles (AuNPs@PS) within emulsion droplets. The arrangement of the AuNPs@PS building blocks within the block copolymers (BCP)/AuNPs nanosheets can be adjusted by tuning the effective size ratio (λeff), which can be controlled by the core diameter of the AuNPs and the molecular weight of the PS. Furthermore, the content of the AuNPs is also another essential parameter to manipulate the structures of the nanosheets with the specific λeff. Thus, the BCP/AuNPs hybrid nanosheets with controllable distributions and arrangements of the AuNPs were successfully prepared via tuning of λeff and the content of AuNPs. This study provides a facile way to fabricate well-ordered hybrid nanosheets.

Dynamic Photonic Janus Colloids with Axially Stacked Structural Layers

Diblock copolymer (dBCP) particles capable of dynamic shape and color changes have gained significant attention due to their versatility in programmable shapes and intricate nanostructures. However, their application in photonic systems remains limited due to challenges in achieving a sufficient number of defect-free photonic layers over a tens-of-micrometer scale. In this study, we present a pioneering demonstration of photonic dBCP particles featuring over 300 axially stacked photonic layers with responsive color- and shape-transforming capabilities. Our approach leverages the complex interplay between the macrophase separation of multiple incompatible components and the microphase separation of dBCP from solvent-evaporative microemulsions. Specifically, continuous phase separation of silicone oil from polystyrene-block-poly(2-vinylpyridine) (PS-b-P2VP), triggered by solvent evaporation, promotes the anisotropic growth of PS-b-P2VP layers. This results in the formation of Janus colloids, where an oil droplet merges with a nanostructured polymer cone and lamellar structures align along the long axis of the cone. We highlight the capability to precisely adjust the particle morphology and the corresponding orientation, dispersion, and structural color window by modulating both the molecular weight of PS-b-P2VP and the volume ratio between PS-b-P2VP and silicone oil. Furthermore, reversible swelling/deswelling of photonic colloids is visualized and correlated with their structural colors. Finally, we demonstrate the potential of this study by presenting a multicolor-patterned array of photonic colloids, highlighting the possibilities for applications in smart photonic ink and devices.

Nanoparticle Assembly: From Self-Organization to Controlled Micropatterning for Enhanced Functionalities

Nanoparticles form long-range micropatterns via self-assembly or directed self-assembly with superior mechanical, electrical, optical, magnetic, chemical, and other functional properties for broad applications, such as structural supports, thermal exchangers, optoelectronics, microelectronics, and robotics. The precisely defined particle assembly at the nanoscale with simultaneously scalable patterning at the microscale is indispensable for enabling functionality and improving the performance of devices. This article provides a comprehensive review of nanoparticle assembly formed primarily via the balance of forces at the nanoscale (e.g., van der Waals, colloidal, capillary, convection, and chemical forces) and nanoparticle-template interactions (e.g., physical confinement, chemical functionalization, additive layer-upon-layer). The review commences with a general overview of nanoparticle self-assembly, with the state-of-the-art literature review and motivation. It subsequently reviews the recent progress in nanoparticle assembly without the presence of surface templates. Manufacturing techniques for surface template fabrication and their influence on nanoparticle assembly efficiency and effectiveness are then explored. The primary focus is the spatial organization and orientational preference of nanoparticles on non-templated and pre-templated surfaces in a controlled manner. Moreover, the article discusses broad applications of micropatterned surfaces, encompassing various fields. Finally, the review concludes with a summary of manufacturing methods, their limitations, and future trends in nanoparticle assembly.

Nanosheet Particles with Defect-Free Block Copolymer Structures Driven by Emulsions Containing Crystallizable Surfactants

Highly anisotropic-shaped particles with well-ordered internal nanostructures have received significant attention due to their unique shape-dependent photonic, rheological, and electronic properties and packing structures. In this work, nanosheet particles with cylindrical block copolymer (BCP) arrays are achieved by utilizing collapsed emulsions as a scaffold for BCP self-assembly. Highly elongated structures with large surface areas are formed by employing crystallizable surfactants that significantly reduce the interfacial tension of BCP emulsions. Subsequently, the stabilized elongated emulsion structures lead to the formation of BCP nanosheets. Specifically, when polystyrene-block-polydimethylsiloxane (PS-b-PDMS) and 1-octadecanol (C18-OH) are co-assembled within an emulsion, C18-OH penetrates the surfactant layer at the emulsion interface, lowering the interfacial tension (i.e., below 1 mN m-1 ) and causing emulsion deformation. In addition, C18-OH crystallization allows for kinetic arrest of the collapsed emulsion shape during solvent evaporation. Consequently, PS-b-PDMS BCPs self-assemble into defect-free structures within nanosheet particles, exhibiting an exceptionally high aspect ratio of over 50. The particle formation mechanism is further investigated by controlling the alkyl chain length of the fatty alcohol. Finally, the coating behavior of nanosheet particles is investigated, revealing that the deposition pattern on a substrate is strongly influenced by the particle's shape anisotropy, thus highlighting their potential for advanced coating applications.

2D superlattices via interfacial self-assembly of polymer-grafted Au nanoparticles

Nanoparticle (NP) superlattices are periodic arrays of nanoscale building blocks. Because of the collective effect between functional NPs, NP superlattices can exhibit exciting new properties that are distinct from those of individual NPs or corresponding bulk materials. In particular, two-dimensional (2D) NP superlattices have attracted increasing attention due to their emerging applications in micro/opto-electronics, catalysis, sensing, and other fields. Among various preparation methods, evaporation-induced interfacial self-assembly has become the most popular method for preparing 2D NP superlattices because it is a simple, low-cost, and scalable process that can be widely applied to various NPs. Introducing soft ligands, such as polymers, can not only provide convenience in controlling the self-assembly process and tuning superlattice structures but also improve the properties of 2D NP superlattices. This feature article focuses on the methods of evaporation-induced self-assembly of polymer-grafted Au NPs into free-standing 2D NP superlattice films at air/liquid interfaces and 2D NP superlattice coatings on substrates, followed by studies on in situ tracking of the self-assembly evolution process through small-angle X-ray scattering. Their application in nano-floating gate memory devices is also included. Finally, the challenges and perspectives of this direction are discussed.

A novel theoretical method to determine the effective optical properties of high refractive index nanocomposites

The continuous development of advanced optical devices towards high performance, miniaturization and integration has led to an increasing demand for high refractive index optical materials. Nanocomposites - made from high refractive index inorganic nanoparticles and good processability polymers - combine the advantages of both materials to create a synergistic effect. However, the diversity and complexity of the composites make laboratory preparation less efficient. Therefore, to prepare composites that meet the refractive index requirements, it is essential to predict the effective optical properties at different wavelengths. This study proposes a finite element parametric retrieval (FEPR) method to calculate the effective complex refractive index of nanocomposites (meff). The effects of the ratio of film thickness to particle diameter, particle arrangement, particle volume fraction (fv) and particle diameter (d) on meff are considered. The results demonstrate that changing the spatial arrangement, volume fraction and diameter of the particles can cause changes in the scattering effect of particles or the interaction between the electromagnetic waves and the particles, resulting in changes in the meff. Compared with effective medium theory (EMT), the FEPR method can be used to characterise the meff values in complex cases through finite element parametric modelling. The FEPR method is an efficient and accurate method for predicting the effective optical properties of nanocomposites, and can also be applied to the design and development of materials to discover the factors influencing the properties and variation patterns from large amounts of data, and to obtain predictive models that can guide the design of new materials.

Prismatic Block Copolymer Hexosomes

Cubosomes and hexosomes are recent solution morphologies with an ordered porous structure and are observed for lipids and amphiphilic block copolymers (BCPs) with high hydrophobic fractions. Whereas lipid hexosomes typically exhibit a prismatic shape, BCP hexosomes have so far only been observed as closed microspheres where inner channels are not connected to the surrounding medium. Here, we describe the formation of flat, prismatic BCP hexosomes with pronounced faceting and a highly ordered lattice of hexagonally packed channels. We assemble polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP or SV) into the hexosome framework using polystyrene-block-poly(4-vinylpyridine)-block-poly(tert-butyl methacrylate) (PS-b-P4VP-b-PT or SVT) as a macromolecular surfactant in low-χ solvents. During solvent exchange, SV-rich domains form through liquid-liquid phase separation, followed by solidification and confined assembly within these domains. Since the final solvent (acetone) has a very low χ parameter toward PS and P4VP (equaling low interfacial tension), solidification of the hexosome occurs under confinement conditions that we term "supersoft". The low interfacial tension allows the stabilization of the hexagonal-prismatic shape, which originates from the hexagonal lattice of channels. Increasing the interfacial tension with polar cosolvents at some point dominates the particle shape, resulting in deformation of prismatic BCP hexosomes into spinning-top structures. The use of low-χ solvents for confined assembly of BCPs may allow the formation of unusual particle shapes simply by tuning the polymer-solvent interaction.

Entropically Driven Fabrication of Binary Superlattices Assembled from Polymer-Tethered Nanocubes and Nanospheres

The spontaneous organization of two types of nanoparticles (NPs) with different shapes or properties into binary nanoparticle superlattices (BNSLs) with different configurations has recently attracted significant attention due to the coupling or synergistic effect of the two types of NPs, providing an efficient and general route for designing new functional materials and devices. Here, this work reports the co-assembly of polystyrene (PS) tethered anisotropic gold nanocubes (AuNCs@PS) and isotropic gold NPs (AuNPs@PS) via an emulsion-interface self-assembly strategy. The distributions and arrangements of the AuNCs and spherical AuNPs in the BNSLs can be precisely controlled by adjusting the effective size ratio (λ_eff ) of the effective diameter (d_eff ) of the embedded spherical AuNPs to the polymer gap size (L) between the neighboring AuNCs. λ_eff determines not only the change of the conformational entropy of the grafted polymer chains (∆S_con ) but also the mixing entropy (∆S_mix ) of the two types of NPs. During the co-assembly process, ∆S_mix tends to be as high as possible, and the -∆S_con tends to be as low as possible, leading to free energy minimization. As a result, well-defined BNSLs with controllable distributions of spherical and cubic NPs can be obtained by tuning λ_eff . This strategy can also be applied for other NPs with different shapes and atomic properties, thus largely enriching the BNSL library and enabling the fabrication of multifunctional BNSLs, which have potential applications in photothermal therapy, surface-enhanced Raman scattering, and catalysis.

Sub-micron microparticles with tunable fluorescence emission obtained via co-self-assembly of amidoximed polymeric ligands and lanthanide ions

Lanthanide coordinating polymeric microparticles have witnessed increasing research interests during the past decades due to their versatile morphology and tunable fluorescent properties. Herein, we have synthesized an amidoximed block copolymer containing aromatic backbone and pendent amidoxime as well as carboxyl groups, which has been employed as the ligand to sensitize the intrinsic fluorescence emission of lanthanide ions of Tb³⁺ and Eu³⁺. Furthermore, the lanthanide coordinating polymeric microparticles showing tunable green and red emission fluorescence have been prepared via the emulsion confinement co-self-assembly of amidoximed polymeric ligands with Tb³⁺ and Eu³⁺. It is found that both the fluorescence emission and sizes of obtained fluorescent microparticles can be easily modulated in a wide range by tuning concentration of polymers and lanthanide ions, as well as emulsion evaporation temperature. Thanks to their tunable sizes (250-900 nm), fluorescence emission as well as presence of surface active functional groups, the present fluorescent microparticles would find potential applications in in-vitro detection, optical encoding and devices.

Block Copolymer Enabled Synthesis and Assembly of Chiral Metal Oxide Nanoparticle

Chiral metal oxide nanostructures have received tremendous attention in nanotechnological applications owing to their intriguing chiroptical and magnetic properties. Current synthetic methods mostly rely on the use of amino acids or peptides as chiral inducers. Here, we report a general approach to fabricate chiral metal oxide nanostructures with tunable magneto-chiral effects, using block copolymer (BCP) inverse micelle and R/S-mandelic acid (MA). Diverse chiral metal oxide nanostructures are prepared by the selective incorporation of precursors within micellar cores followed by the oxidation process, exhibiting intense chiroptical properties with a g-factor up to 7.0 × 10^-3 in the visible-NIR range for the Cr₂O₃ nanoparticle multilayer. The BCP inverse micelle is found to inhibit the racemization of MA, allowing MA to act as a chiral dopant that imparts chirality to nanostructures via hierarchical chirality transfer. Notably, for paramagnetic nanostructures, magneto-chiroptical modulation is realized by regulating the direction of the external magnetic field. This BCP-driven approach can be extended to the mass production of chiral nanostructures with tunable architectures and optical activities, which may provide insights into the development of chiroptical functional materials.

Study of the phase-transition behavior of (AB)3 type star polystyrene-block-poly(n-butylacrylate) copolymers by the combination of rheology and SAXS

A series of three-armed star polystyrene-block-poly(n-butylacrylate) copolymers (PS-b-PBA)3 were synthesized to study the phase-transition behavior of the copolymers. The order-to-disorder transition temperature has been determined by oscillatory at different temperatures and dynamic temperature sweep at a fixed frequency. Moreover, the micro-phase separation in the block copolymers has been evaluated by time–temperature superposition, while the free volume and the active energy of the copolymers have been calculated. Interestingly, active energy decreased with the increase in the molecular weight of the PBA components. To further determine the order-to-disorder transition temperature precisely, small angle X-ray scattering was performed at different temperatures. These results confirm that the chain mobility of the star-shaped copolymers is strongly dependent on the arm molecular weight of the star polymers, which will be beneficial for the processing and material preparation of the block copolymers.

Silver Nanocrystal Array with Precise Control via Star-like Copolymer Nanoreactors

Silver nanocrystal arrays had attracted much attention due to the unique plasmonic effect of their ordered nanostructure and the synergy among adjacent nanocrystals. Conventional preparation methods had several limitations, such as high cost, harsh preparation conditions, and complicated influencing factors, which could not be employed to fabricate the nanocrystal arrays in highly controlled fashion. To solve these issues, we reported ordered arrays of different Ag nanocrystals with precise control prepared by utilizing amphiphilic star-like poly(4-vinylpyridine)-block-polystyrene diblock copolymers as nanoreactors synthesized by sequential atom transfer radical polymerization. Moreover, this unimolecular nanoreactor method based on star-like copolymers with stable and predesigned nanostructures was proved to be a universal approach to prepare other nanocrystal arrays. This strategy had low cost, simple process flow, wide applicability, and structural stability that could fabricate nanocrystal array with precise control and continuously prepare more complex nanostructure units in a large scale to meet different functions and applications.

Reaction-Based Scalable Inorganic Patterning on Rigid and Soft Substrates for Photovoltaic Roofs with Minimal Optical Loss and Sustainable Sunlight-Driven-Cleaning Windows

Recently developed fabrication methods for inorganic patterns (such as laser printing and optical lithography) can avoid some patterning processes conducted by conventional etching and lithography (such as substrate etching and modulation) and are thereby useful for applications in which the substrates and materials must not be damaged during patterning. Simultaneously, it is also necessary to develop facile and economical methods producing inorganic patterns on various substrates without requiring a special apparatus while attaining the above-mentioned advantages. The present study proposes a reaction-based method for fabricating inorganic patterns by immersing substrates coated with a colloidal nanosheet into an aqueous solution containing inorganic precursors. Silica and TiO₂ patterns spontaneously developed during the conversion of each inorganic precursor. These patterns were successful on rigid and flexible substrates. We fabricated these patterns on a wafer-sized silicon and large flexible poly(ethylene terephthalate) film, suggesting the scalability. We fabricated a biomimetic pattern on both sides of a glass window, as a photovoltaic roof, for minimal optical losses to maximally present photovoltaic effects of a solar cell. The TiO₂ pattern on glass window exhibits sustainable sunlight-driven-cleaning activity for contaminants. The method could provide a platform for economical high-performance inorganic patterns for energy, environmental, electronics, and other areas.

Self-Assembly of Homo-Polyarylene Ether Into Reactive Matrix for Fabrication of Hybrid Functional Microparticles

Emulsion confinement self-assembly of block copolymer has witnessed increasing research interest in the recent decade, but the post-functionalization and application of the resultant polymeric micro/nano-particles are still in their infancy. In this work, a super-engineering polyarylene ether containing pendent nitrile and carboxyl (PAE-NC) has been synthesized and converted into polymeric microparticles for macromolecular enrichment via emulsion confinement self-assembly and subsequent surface modification. Moreover, the encapsulation capacity of PAE-NC was evaluated using hydrophobic fluorescent quantum dots (QD) as a functional probe. Particularly, we found that both the as-synthesized PAE-NC and its hydrolyzed derivatives could be converted into microparticles via emulsion confinement self-assembly. Furthermore, the co-self-assembly of red-emitting QD and PAE-NC enables the phase transfer of hydrophobic QD into hydrophilic luminescent microparticles with the persisted fluorescence emission. Based on these results, the current PAE-NC would be served as a versatile and robust matrix to fabricate advanced microparticles or microcapsules for various applications.

Self-assembly of anisotropy gold nanocubes into large area two-dimensional monolayer superlattices

The spontaneous self-assembly of metal nanocrystals into two-dimensional (2D) monolayer superlattices with highly ordered symmetry and configuration paves the way towards the fabrication of functional materials. However, there remains great challenge for anisotropic nanocrystals to self-assembly into high quality superlattice because of the orientation and configuration consistency. Here, a facile yet universal solvent annealing driven 2D interfacial assembly of synthetic dried metal nanocrystals is firstly developed to realize the construction of the non-close-packing 2D monolayer gold nanocube (AuNC) superlattice with tunable interparticle distance and internal configurations (i.e. face-to-face and hexagonally-packed arrangement), which is achieved by precisely controlling molecular weight of polymer ligands tethered on AuNCs and the van der Waals forces between the adjacent AuNCs. In addition, the scale of the generated 2D monolayer AuNC superlattice with highly ordered internal arrangement and orientation can reach up to hundreds of micrometers, thus acquiring significant surface-enhanced Raman scattering performance of the large scale superlattice due to the strong plasma coupling effect. This strategy not only provides a robust route to fabricate nanocrystal superlattice structures but also offers a promising platform for preparing diverse functional materials with potential applications in electronics, photonics, detections, and others.

Symmetry-Breaking and Self-Sorting in Block Copolymer-Based Multicomponent Nanocomposites

Co-assembly of inorganic nanoparticles (NPs) and nanostructured polymer matrix represents an intricate interplay of enthalpic or entropic forces. Particle size largely affects the phase behavior of the nanocomposite. Theoretical studies indicate that new morphologies would emerge when the particles become comparable to the soft matrix's size, but this has rarely been supported experimentally. By designing a multicomponent blend composed of NPs, block copolymer-based supramolecules, and small molecules, a 3-D ordered lattice beyond the native BCP's morphology was recently reported when the particle is larger than the microdomain of BCP. The blend can accommodate various formulation variables. In this paper, when the particle size equals the microdomain size, a symmetry-broken phase appears in a narrow range of particle sizes and compositions, which we named the "train track" structure. In this phase, the NPs aligned into a 3-D hexagonal lattice and packed asymmetrically along the c axis, making the projection of the ac and the bc plane resemble train tracks. Computational studies show that the broken symmetry reduces the polymer chain deformation and stabilizes the metastable hexagonally perforated lamellar morphology. Given the mobility of the multicomponent blend, the system shows a self-sorting behavior: segregating into two macroscopic phases with different nanostructures based on only a few nanometers NP size differences. Smaller NPs form "train track" morphology, while larger NPs form a "simple hexagon" structure, where the NPs take a symmetric hexagonal arrangement. Detailed structural evolution and simulation studies confirm the systematic-wide cooperativity across different components, indicating the strong self-regulation of the multicomponent system.

Light-driven sequential shape transformation of block copolymer particles through three-dimensional confined self-assembly

Shape-controlled block copolymer (BCP) particles that respond to light stimulus have drawn great attention due to their promising applications in smart materials, yet polymeric particles with light-triggered controllable sequential shape transformation (SST) are still rarely reported. By confined co-assembly of polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) and azo-containing light-responsive additives within emulsions, herein, we fabricated BCP particles with light-controlled SST behavior. Attributed to the quaternization of P2VP chains with bromoalkyl additives and the trans-cis isomerization of an azo group under UV light, the interfacial interactions between the BCPs and the surrounding aqueous phase are significantly varied; therefore, the particles exhibit three distinct phases in sequence: (1) elongation of ellipsoidal particles with increasing domain spacing; (2) shape transformation of elongated ellipsoidal particles into accordion-like particles; and (3) disassembly of polymer particles into small spheres. In addition, these particles with SST behavior can be used in light-controlled drug release at a high spatial-temporal resolution, demonstrating their potential in clinical settings and biomedicine.

Self-Assembly of Polystyrene-b-poly(2-vinylpyridine)/Chloroauric Acid at the Liquid/Liquid Interface

The self-assembly of polystyrene-block-poly(2-vinylpyridine) at the liquid/liquid interface has been systematically investigated to develop a series of primary morphologies of the aggregates. The block copolymers self-assembled into large areas of nanodot arrays, parallel nanostrands, layered films, parallel nanobelts, honeycomb monolayers, and foams by reacting with chloroauric acid, depending on the molecular structure of the block copolymers and the amount of chloroauric acid. The formation of the first four ordered structures resulted from interfacial adsorption and self-assembly, and nucleation and epitaxial growth. The latter two structures were attributed to the water hole templating effect and spontaneous interfacial emulsification, respectively. This work provides insight into the self-assembly behavior of block copolymers at the interface and provides a facile approach for fabricating functional structures.

Uniform Nanorods with Regioselective Distribution of Inorganic Nanoparticles Templated by 2D Block Copolymer Nanosheets

The inorganic/organic hybrid materials with regioselective distribution of functional inorganic nanoparticles (NPs) have received constant interest attributed to fascinating integrated properties. However, there remains a formidable challenge in realizing the regioselective distribution of NPs for the specific hybrid nanorods. Herein, we report the construction of uniform core-shell hybrid nanorods with the regioselective distribution of inorganic NPs by selectively disassembling the prepared NPs/polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) hybrid nanosheets. Moreover, through precisely adjusting the parameters, such as complexation ability between the metal precursor and P4VP blocks, the protonation degree of P4VP blocks and complexation time, the NPs/polymer core-shell hybrid nanorod with the uniform distribution of NPs, and dumbbell-like hybrid nanorods with selective distribution of NPs at both ends can be obtained. This finding reveals a unique insight into the design of the anisotropic functional hybrid materials with the regioselective distribution of inorganic NPs.

Confinement-Assembly of Terpolymer-based Janus Nanoparticles

While the confinement assembly of block copolymers (BCPs) into functional microparticles has been extensively studied, little is known about the behavior of Janus nanoparticles (JNPs) in spherical confinement. Here, we investigate the confinement self-assembly of JNPs in drying emulsion droplets and compare their behavior to their ABC triblock terpolymer precursor. Emulsions of both materials were prepared using Shirasu Porous Glass (SPG) membranes leading to narrow size distributions of the microparticles with average hydrodynamic radii in the range of R_h = 250 - 500 nm (depending on the pore radius, R_pore ). The internal structure of the microparticles was verified with transmission electron microscopy (TEM) on ultrathin cross-sections and compared to the corresponding bulk morphologies. While the confinement-assembly of terpolymers resulted in microparticles with ordered inner morphologies, order for JNPs diminished when the Janus balance (JB) deviated from parity. This article is protected by copyright. All rights reserved.

A 3D Hierarchical Host with Enhanced Sodiophilicity Enabling Anode-Free Sodium-Metal Batteries

Sodium-metal batteries (SMBs) are considered as a compliment to lithium-metal batteries for next-generation high-energy batteries because of their low cost and the abundance of sodium (Na). Herein, a 3D nanostructured porous carbon particle containing carbon-shell-coated Fe nanoparticles (PC-CFe) is employed as a highly reversible Na-metal host. PC-CFe has a unique 3D hierarchy based on sub-micrometer-sized carbon particles, ordered open channels, and evenly distributed carbon-coated Fe nanoparticles (CFe) on the surface. PC-CFe achieves high reversibility of Na plating/stripping processes over 500 cycles with a Coulombic efficiency of 99.6% at 10 mA cm^-2 with 10 mAh cm^-2 in Na//Cu asymmetric cells, as well as over 14 400 cycles at 60 mA cm^-2 in Na//Na symmetric cells. Density functional theory calculations reveal that the superior cycling performance of PC-CFe stems from the stronger adsorption of Na on the surface of the CFe, providing initial nucleation sites more favorable to Na deposition. Moreover, the full cell with a PC-CFe host without Na metal and a high-loading Na₃ V₂ (PO₄ )₃ cathode (10 mg cm^-2 ) maintains a high capacity of 103 mAh g^-1 at 1 mA cm^-2 even after 100 cycles, demonstrating the operation of anode-free SMBs.

Architecture- and Composition-Controlled Self-Assembly of Block Copolymers and Binary Mixtures With Crosslinkable Components: Chain Exchange Between Block Copolymer Nanoparticles

Chain exchange behaviors in self-assembled block copolymer (BCP) nanoparticles (NPs) at room temperature are investigated through observations of structural differences between parent and binary systems of BCP NPs with and without crosslinked domains. Pairs of linear diblock or triblock, and branched star-like polystyrene-poly(2-vinylpyridine) (PS-PVP) copolymers that self-assemble in a PVP-selective mixed solvent into BCP NPs with definite differences in size and self-assembled morphology are combined by diverse mixing protocols and at different crosslinking densities to reveal the impact of chain exchange between BCP NPs. Clear structural evolution is observed by dynamic light scattering and AFM and TEM imaging, especially in a blend of triblock + star copolymer BCP NPs. The changes are ascribed to the chain motion inherent in the dynamic equilibrium, which drives the system to a new structure, even at room temperature. Chemical crosslinking of PVP corona blocks suppresses chain exchange between the BCP NPs and freezes the nanostructures at a copolymer crosslinking density (CLD) of ∼9%. This investigation of chain exchange behaviors in BCP NPs having architectural and compositional complexity and the ability to moderate chain motion through tailoring the CLD is expected to be valuable for understanding the dynamic nature of BCP self-assemblies and diversifying the self-assembled structures adopted by these systems. These efforts may guide the rational construction of novel polymer NPs for potential use, for example, as drug delivery platforms and nanoreactors.

Lens-Shaped Carbon Particles with Perpendicularly-Oriented Channels for High-Performance Proton Exchange Membrane Fuel Cells

Two-dimensional sheet-like mesoporous carbon particles are promising for maximizing the number of active sites and the mass transport efficiency of proton exchange membrane fuel cells (PEMFCs). Herein, we develop a series of lens-shaped mesoporous carbon (LMC) particles with perpendicularly oriented channels (diameter = 60 nm) and aspect ratios (ARs) varying from 2.1 to 6.2 and apply them for the fabrication of highly efficient PEMFCs. The membrane emulsification affords uniform-sized, lens-shaped block copolymer particles, which are successfully converted into the LMC particles with well-ordered vertical channels through hyper-cross-linking and carbonization steps. Then, an ultralow amount (1 wt %) of platinum (Pt) is loaded into the particles. The LMC particles with higher ARs are packed with a higher density in the cathode and are better aligned on the cathode surface compared to the LMC particles with lower ARs. Thus, the well-ordered channels in the particles facilitate the mass transport of the reactants and products, significantly increasing the PEMFC performance. For example, the LMC particles with the AR of 6.2 show the highest initial single cell performance of 1135 mW cm^-2, and the cell exhibits high durability with 1039 mW cm^-2 even after 30 000 cycles. This cell performance surpasses that of commercial Pt/C catalysts, even at 1/20 of the Pt loading.

Poly(vinylpyridine)-Containing Block Copolymers for Smart, Multicompartment Particles

Multicompartment particles generated by the self-assembly of block copolymers (BCPs) have received considerable attention due to their unique morphologies and functionalities. A class of important building blocks for multicomponent particles...

Polymers as Versatile Players in the Stabilization, Capping, and Design of Inorganic Nanostructures

The integration of simple components to generate sophisticated hybrid materials with fine-tuned properties represents a significant scientific challenge. Herein, we present recent advances in the use of polymers to control the synthesis and properties of three of the most relevant inorganic nanoparticles, namely, quantum dots (QDs), magnetic nanoparticles (MNPs), and noble metal nanoparticles (NMNPs). We show relevant examples of how polymeric structures synthesized by techniques such as ATRP, RAFT, and living cationic polymerization are used to aid in the synthesis and stabilization of the nanostructures to generate nanocomposites with outstanding capabilities. Special emphasis is placed on describing how some of the exceptional physicochemical properties of polymers are used as nanoreactors to facilitate the synthesis of the nanostructure by providing an adequate chemical environment. Additionally, we also describe how polymers are utilized to protect the integrity of the nanostructure from chemical degradation. The integration of polymeric structures and the nanostructures has a strong impact on the dispersion and morphology of the latter and, consequently, endow them with novel and promising features. The advances described here, particularly the use of polymers to modulate and provide new properties to nanoparticles, exemplify the great versatility of polymers and how these may expand the capabilities of inorganic nanostructures that can be used to generate novel and sophisticated hybrid materials.

Morphology and Degradation of Multicompartment Microparticles Based on Semi-Crystalline Polystyrene-block-Polybutadiene-block-Poly(L-lactide) Triblock Terpolymers

The confinement assembly of block copolymers shows great potential regarding the formation of functional microparticles with compartmentalized structure. Although a large variety of block chemistries have already been used, less is known about microdomain degradation, which could lead to mesoporous microparticles with particularly complex morphologies for ABC triblock terpolymers. Here, we report on the formation of triblock terpolymer-based, multicompartment microparticles (MMs) and the selective degradation of domains into mesoporous microparticles. A series of polystyrene-block-polybutadiene-block-poly(L-lactide) (PS-b-PB-b-PLLA, SBL) triblock terpolymers was synthesized by a combination of anionic vinyl and ring-opening polymerization, which were transformed into microparticles through evaporation-induced confinement assembly. Despite different block compositions and the presence of a crystallizable PLLA block, we mainly identified hexagonally packed cylinders with a PLLA core and PB shell embedded in a PS matrix. Emulsions were prepared with Shirasu Porous Glass (SPG) membranes leading to a narrow size distribution of the microparticles and control of the average particle diameter, d ≈ 0.4 µm–1.8 µm. The core–shell cylinders lie parallel to the surface for particle diameters d < 0.5 µm and progressively more perpendicular for larger particles d > 0.8 µm as verified with scanning and transmission electron microscopy and particle cross-sections. Finally, the selective degradation of the PLLA cylinders under basic conditions resulted in mesoporous microparticles with a pronounced surface roughness.

Periodic nanowire arrays with alternating compositions and structures fabricated using a simultaneous nanowire formation step

Arrays of alternating metallic nanostructures present hybrid properties, which are useful for applications in photonics and catalysis. Block copolymer films provide versatile templates for fabricating periodic arrays of nanowires. Yet, creating arrays with alternating compositions or structures requires different modifications of domains of the same kind. By controlling the penetration depth of metal precursors into the film we were able to impregnate different layers of copolymer cylinders with different metals. Capitalizing on the hexagonal packing of the cylinders led to simultaneous formation of nanowires with alternating compositions and periodic arrangement on the substrate after plasma etching. Selective deposition of nanoparticles on the film enabled creating alternating bare and decorated nanowires, as well as trimetallic nanowire arrays.

Hierarchical colloidosomes self-assembled from block copolymer micelles via emulsion interfacial confinement

Hierarchical self-assembly of polymeric building blocks into high-level colloidosomes is desirable to not only design novel nanostructures but also fabricate the complex artificial materials across many length scales with multifunctionality. Although great progress has been made in the designing the hierarchical colloidosomes, the fabrication of polymeric colloidosomes self-assembled from block copolymer (BCP) colloidal nanoparticles still remains challenge. Here, we report the fabrication of the hierarchical polymeric colloidosomes with typical hollow internal structures self-assembled from the polystyrene-block-poly (2-vinyl pyridine) (PS-b-P2VP) BCP spherical micelles through the emulsion interfacial confinement, which is constructed through the water-in-1-butanol emulsion system. Moreover, the hierarchical colloidosomes can disassemble into the original uniform spherical micelles under the acid aqueous solution, indicating that the colloidosomes possess good pH stimuli-responsibility. Finally, the stability of the colloidosomes can be greatly improved by cross-linking the P2VP corona of original spherical micelles, offering the effective templates for construction of the multifunctional materials. This finding provides a simple yet effective method for the fabrication of the hierarchical colloidosomes from the BCP building blocks.

Effect of Ionic Strength, Nanoparticle Surface Charge Density, and Template Diameter on Self-Limiting Single-Particle Placement: A Numerical Study

For the bottom-up approach where functional materials are constructed out of nanoscale building blocks (e.g., nanoparticles), it is essential to have methods that are capable of placing the individual nanoscale building blocks onto exact substrate positions on a large scale and on a large area. One of the promising placement methods is the self-limiting single-particle placement (SPP), in which a single nanoparticle in a colloidal solution is electrostatically guided by electrostatic templates and exactly one single nanoparticle is placed on each target position in a self-limiting way. This paper presents a numerical study on SPP, where the effects of three key parameters, (1) ionic strength (IS), (2) nanoparticle surface charge density (σ_NP), and (3) circular template diameter (d), on SPP are investigated. For 40 different parameter sets of (IS, σ_NP, d), a 30 nm nanoparticle positioned at R⃗ above the substrate was modeled in two configurations (i) without and (ii) with the presence of a 30 nm nanoparticle at the center of a circular template. For each parameter set and each configuration, the electrostatic potentials were calculated by numerically solving the Poisson-Boltzmann equation, from which interaction forces and interaction free energies were subsequently calculated. These have identified realms of parameter sets that enable a successful SPP. A few exemplary parameter sets include (IS, σ_NP, d) = (0.5 mM, -1.5 μC/cm², 100 nm), (0.05 mM, -0.5 μC/cm², 100 nm), (0.5 mM, -1.5 μC/cm², 150 nm), and (0.05 mM, -0.8 μC/cm², 150 nm). This study provides clear guidance toward experimental realizations of large-scale and large-area SPPs, which could lead to bottom-up fabrications of novel electronic, photonic, plasmonic, and spintronic devices and sensors.

Hierarchical superstructures assembled from pH-responsive gold nanoparticles in deformable emulsion droplets

Integrating stimuli-responsive nanoparticles (NPs) into shape-tunable hierarchical superstructures has emerged as a powerful way to fabricate smart materials. Here, we propose a robust strategy for the fabrication of sheet-like superlattices and hollow capsules by precisely tuning the interfacial tension of emulsion droplets containing pH-responsive gold nanoparticle building blocks, providing an efficient route to construct hierarchical superstructures with different applications.

Diversifying Composition Leads to Hierarchical Composites with Design Flexibility and Structural Fidelity

Although significant progress has been made in the self-assembly of nanostructures, present successes heavily rely on precision in building block design, composition, and pair interactions. These requirements fundamentally limit our ability to synthesize macroscopic materials where the likelihood of impurity inclusion escalates and, more importantly, to access molecular-to-nanoscopic-to-microscopic-to-macroscopic hierarchies, since the types and compositions of building blocks vary at each stage. Inspired by biological blends and high-entropy alloys, we hypothesize that diversifying the blend's composition can overcome these limitations. Increasing the number of components increases mixing entropy, leading to the dispersion of different components and, as a result, enhances interphase miscibility, weakens the dependence on specific pair interactions, and enables long-range cooperativity. This hypothesis is validated in complex blends containing small molecules, block copolymer-based supramolecules, and nanoparticles/colloidal particles. Hierarchically structured composites can be obtained with formulation flexibility in the filler selection and blend composition. It is worth noting that, by adding small molecules, we can solve the size constraint that plagues traditional block copolymer/nanoparticle blends. Detailed characterization and simulation further confirm that each component is distributed to locally mediate unfavorable interactions, cooperatively mitigate composition fluctuations, and retain structural fidelity. Furthermore, the blends have sufficient mobility to access tunable microstructures without compromising the order of the nanostructure. Besides establishing a kinetically viable pathway to release current constraints in the composite design and to navigate uncertainties during structure formation over multiple length scales, the present study demonstrates that entropy-driven behaviors can be realized in systems beyond high-entropy alloys despite inherent differences between metal alloys and organic/inorganic hybrids.

Photoswitchable Surfactant-Driven Reversible Shape- and Color-Changing Block Copolymer Particles

Polymer particles that switch their shape and color in response to light are of great interest for the development of programmable smart materials. Herein, we report block copolymer (BCP) particles with reversible shapes and colors activated by irradiation with ultraviolet (UV) and visible lights. This shape transformation of the BCP particles is achieved by a spiropyran-dodecyltrimethylammoium bromide (SP-DTAB) surfactant that changes its amphiphilicity upon photoisomerization. Under UV light (365 nm) irradiation, the hydrophilic ring-opened merocyanine form of the SP-DTAB surfactant affords the formation of spherical, onion-like BCP particles. In contrast, when exposed to visible light, surfactants with the ring-closed form yield prolate or oblate BCP ellipsoids with axially stacked nanostructures. Importantly, the change in BCP particle morphology between spheres and ellipsoids is reversible over multiple UV and visible light irradiation cycles. In addition, the shape- and color-switchable BCP particles are integrated to form a composite hydrogel, demonstrating their potential as high-resolution displays with reversible patterning capabilities.

Fluorescence Switchable Block Copolymer Particles with Doubly Alternate-Layered Nanoparticle Arrays

The precise self-assembly of block copolymers (BCPs) and inorganic nanoparticles (NPs) under 3D confinement offers microparticles with programmable nanostructures and functionalities. Here, fluorescence-switchable hybrid microspheres are developed by forming doubly alternating arrays of Au NPs and CdSe/ZnS quantum dots (QDs) within polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) BCP domains. These doubly alternating arrays afford controlled nonradiative energy transfer (NRET) between the QDs and Au NPs that is dependent on the layer-to-layer distance. Solvent-selective swelling of the hybrid particles tunes the distance between layers, modulating their NRET behavior and affording switchable fluorescence. The particle fluorescence is "OFF" in water through strong NRET from the QDs to Au NPs, but is "ON" in alcohols due to the increased distance between the Au NP and QD arrays in the swollen P4VP domains. The experimentally observed NRET intensity as a function of interparticle distance shows larger quenching efficiencies than those theoretically predicted due to the enhanced quenching within a 3D-confined system. Finally, the robust and reversible fluorescence switching of the hybrid particles in different solvents is demonstrated, highlighting their potentials for bioimaging, sensing, and diagnostic applications.

Unconventional-Phase Crystalline Materials Constructed from Multiscale Building Blocks

Crystal phase, an intrinsic characteristic of crystalline materials, is one of the key parameters to determine their physicochemical properties. Recently, great progress has been made in the synthesis of nanomaterials with unconventional phases that are different from their thermodynamically stable bulk counterparts via various synthetic methods. A nanocrystalline material can also be viewed as an assembly of atoms with long-range order. When larger entities, such as nanoclusters, nanoparticles, and microparticles, are used as building blocks, supercrystalline materials with rich phases are obtained, some of which even have no analogues in the atomic and molecular crystals. The unconventional phases of nanocrystalline and supercrystalline materials endow them with distinctive properties as compared to their conventional counterparts. This Review highlights the state-of-the-art progress of nanocrystalline and supercrystalline materials with unconventional phases constructed from multiscale building blocks, including atoms, nanoclusters, spherical and anisotropic nanoparticles, and microparticles. Emerging strategies for engineering their crystal phases are introduced, with highlights on the governing parameters that are essential for the formation of unconventional phases. Phase-dependent properties and applications of nanocrystalline and supercrystalline materials are summarized. Finally, major challenges and opportunities in future research directions are proposed.

Molecular Weight Dependent Morphological Transitions of Bottlebrush Block Copolymer Particles: Experiments and Simulations

The molecular weights and chain rigidities of block copolymers can strongly influence their self-assembly behavior, particularly when the block copolymers are under confinement. We investigate the self-assembly of bottlebrush block copolymers (BBCPs) confined in evaporative emulsions with varying molecular weights. A series of symmetric BBCPs, where polystyrene (PS) and polylactide (PLA) side-chains are grafted onto a polynorbornene (PNB) backbone, are synthesized with varying degrees of polymerization of the PNB (N_PNB) ranging from 100 to 300. Morphological transitions from onion-like concentric particles to striped ellipsoids occur as the N_PNB of the BBCP increases above 200, which is also predicted from coarse-grained simulations of BBCP-containing droplets by an implicit solvent model. This transition is understood by the combined effects of (i) an elevated entropic penalty associated with bending lamella domains of large molecular weight BBCP particles and (ii) the favorable parallel alignment of the backbone chains at the free surface. Furthermore, the morphological evolutions of onion-like and ellipsoidal particles are compared. Unlike the onion-like BBCP particles, ellipsoidal BBCP particles are formed by the axial development of ring-like lamella domains on the particle surface, followed by the radial propagation into the particle center. Finally, the shape anisotropies of the ellipsoidal BBCP particles are analyzed as a function of particle size. These BBCP particles demonstrate promising potential for various applications that require tunable rheological, optical, and responsive properties.

Dynamic Manipulation of DNA-Programmed Crystals Embedded in a Polyelectrolyte Hydrogel

DNA is a powerful tool for programming the three-dimensional organization of nanomaterials, where the specificity of nucleotide base-pairing can enable precise, complex, and dynamically addressable structures like colloidal crystals. However, because these DNA-programmed materials are often only stable in solution, their organization can be easily disrupted by changes to its local environment. Methods to stabilize these materials have been developed, but often come at the expense of altering or permanently fixing the materials' structures, removing many of the benefits of using DNA interactions to program assembly. Thus, these methods limit the application of DNA-assembled structures as dynamic and programmable material components. Here, a method is presented to resolve these drawbacks for DNA-grafted nanoparticles, also known as Programmable Atom Equivalents (PAEs), by embedding assembled lattices within a hydrogel matrix. The preformed lattices are exposed to polymerizable residues that electrostatically bind to the charged backbone of the DNA ligands and form a continuous, permeating gel network that stabilizes the colloidal crystals upon introduction of a radical initiator. After embedding PAEs in a hydrogel, deformation of the macroscopic matrix results in concomitant deformation of the PAE lattices, allowing superlattice structural changes to be induced by chemical methods (such as changing solute concentration to alter swelling pressure) or by application of mechanical strain. Changes to the structure of the PAE lattices are reversible and repeatable over multiple cycles and can be either isotropic (such as by swelling) or anisotropic (such as by mechanical deformation). This method of embedding nanoparticle crystals inside of a flexible and environmentally responsive hydrogel is therefore a useful tool in extending the utility of PAEs and other micro- and nanostructures assembled with DNA.

Block copolymer-nanodiamond coassembly in solution: towards multifunctional hybrid materials

Polymer-nanodiamond composites are excellent candidates for the fabrication of multifunctional hybrid materials. They integrate polymer flexibility and exceptional properties of nanodiamonds (NDs), such as biocompatibility, mechanical strength, color centers, and chemically-tailored surfaces. However, their development is hindered by the challenge of ensuring that NDs are homogeneously distributed in the composites. Here, we exploit colloidal coassembly between poly(isoprene-b-styrene-b-2-vinyl pyridine) (ISV) block copolymers (BCPs) and NDs to avoid ND self-agglomeration and direct ND spatial distribution. NDs were first air oxidized at 450 °C to obtain stable dispersions in dimethylacetamide (DMAc). By adding ISV into the dispersions, patchy hybrid micelles were formed due to H-bonds between NDs and ISV. The ISV-ND coassembly in DMAc was then used to fabricate nanocomposite films with a uniform sub-50 nm ND distribution, which has never been previously reported for an ND loading (φND) of more than 50 wt%. The films exhibit good transparency due to their well-defined nanostructures and smoothness and also exhibit an improved UV-absorption and hydrophilicity compared to neat ISV. More intriguingly, at a φND of 22 wt%, ISV and NDs coassemble into a network-like superstructure with well-aligned ND strings via a dialysis method. Transmission electron microscopy and dynamic light scattering measurements suggest a complex interplay between polymer-polymer, polymer-solvent, polymer-ND, ND-solvent, and ND-ND interactions during the formation of structures. Our work may provide an important foundation for the development of hierarchically ordered nanocomposites based on BCP-ND coassembly, which is beneficial for a wide spectrum of applications from biotechnology to quantum devices.

Frustrated Microparticle Morphologies of a Semicrystalline Triblock Terpolymer in 3D Soft Confinement

Self-assembly of block copolymers (BCPs) in three-dimensional (3D) confinement of emulsion droplets has emerged as a versatile route for the formation of functional micro- and nanoparticles. While the self-assembly of amorphous coil-coil BCPs is fairly well documented, less is known about the behavior of crystalline-coil BCPs. Here, we demonstrate that confining a linear ABC triblock terpolymer with a crystallizable middle block in oil-in-water (O/W) emulsions results in a range of microparticles with frustrated inner structure originating from the conflict between crystallization and curved interfaces. Polystyrene-block-polyethylene-block-poly(methyl methacrylate) (PS-b-PE-b-PMMA, S₃₂E₃₆M₃₂⁹³) in toluene droplets was subjected to different preparation protocols. If evaporation was performed well above the bulk crystallization temperature of the PE block (T_evap > T_c), S₃₂E₃₆M₃₂⁹³ first microphase-separated into microparticles with lamella morphology followed by crystallization into a variety of frustrated morphologies (e.g., bud-like, double staircase, spherocone). By evaporating at significantly lower temperatures that allow the PE block to crystallize from solution (T_evap < T_c), S₃₂E₃₆M₃₂⁹³ underwent crystallization-driven self-assembly into patchy crystalline-core micelles, followed by confinement assembly into lenticular microparticles with compartmentalized hexagonal cylinder lattices. The frequency of these frustrated morphologies depends on polymer concentration and the evaporation protocol. These results provide a preliminary understanding of the morphological behavior of semicrystalline block copolymers in 3D soft confinement and may provide alternative routes to structure multicompartment microparticles from a broader range of polymer properties.

Encapsulation of inorganic nanoparticles in a block copolymer vesicle wall driven by the interfacial instability of emulsion droplets

We proposed an effective route, i.e., three-dimensional confined co-assembly of block copolymers and inorganic nanoparticles, to efficiently encapsulate high-density and large-size nanoparticles into the wall of polymeric vesicles.

Effect of Site-Specific Functionalization on the Shape of Nonspherical Block Copolymer Particles

Shape-anisotropic polymeric colloids having chemically distinct compartments are promising materials, however, introducing site-specific surface functionality to block copolymer (BCP) particles has not yet been actively investigated. The current contribution demonstrates the selective surface functionalization of nanostructured, ellipsoidal polystyrene-b-polybutadiene (PS-b-PB) particle and investigate their effects on the particle shape. Photo-induced thiol-ene click reaction was used as a selective functionalization chemistry for modifying the PB block, which was achieved by controlling the feed ratio of functional thiols to the double bonds in PB. Importantly, the controlled particle elongation was observed as a function of the degree of PB functionalization. Such an increase in the aspect ratio is attributed to the (i) increased incompatibility of the PS and modified PB block and (ii) the reduced surface tension between the particles and surrounding aqueous medium, both of which contributes to the further elongation of ellipsoids. Further tunability of the elongation behavior of ellipsoids was further demonstrated by controlling the particle size and chemical structure of functional thiols, showing the versatility of this approach for controlling the particle shape. Finally, the utility of surface functionality was demonstrated by the facile complexation of fluorescent dye on the modified surface of the particle via favorable interaction, which showed stable fluorescence and colloidal dispersity.

Self-assembly of gold nanocubes into three-dimensional hollow colloidosomes and two-dimensional superlattices

Self-assembly of metal nanocubes (NCs) into periodic structures has applications in the fabrication of functional materials. Here, we propose a facile yet robust strategy for the fabrication of three-dimensional (3D) hollow colloidosomes and two-dimensional (2D) superlattices with highly ordered face-to-face configuration of gold NCs (AuNCs) via the hierarchical assembly of polymer-tethered AuNCs at the emulsion interface, providing a universal route for the preparation of hierarchical NC superstructures with applications in various fields.