Alternating Copolymerization of Inorganic Nanoparticles

Stereospecific supramolecular polymerization of nanoclusters into ultra-long helical chains and enantiomer separation

During the construction of supramolecular polymers of smaller nanoparticles/nanoclusters bearing hierarchy and homochirality, the mechanism understanding via intuitive visualization and precise cross-scale chirality modulation is still challenging. For this goal, a cooperative self-assembly strategy is here proposed by using ionic complexes with uniform chemical composition comprising polyanionic nanocluster cores and surrounded chiral cationic organic components as monomers for supramolecular polymerization. The single helical polymer chains bearing a core-shell structure at utmost length over 20 μm are demonstrated showing comparable flexibility resembling covalent polymers. A nucleation-elongation growth mechanism that is not dealt with in nanoparticle systems is confirmed to be accompanied by strict chiral self-sorting. A permeable membrane prepared by simple suction of such supramolecular polymers displays high enantioselectivity (e.e. 98% after four runs) for separating histidine derivatives, which discloses a benefiting helical chain structure-induced functionalization for macroscopic supramolecular materials in highly efficient racemate separation.

Synthesis of Polymer Brushes on Tannic Acid-Coated Copper Particles and Surface Co-Assembly

The synthesis of polymer brushes on inorganic particles is an effective approach to surface modification. The polymer brushes on the surface endow the substrates with new surface properties. However, the lack of functional groups and the difficulty of surface modification have made it difficult to develop an effective method for the synthesis of polymer brushes on metal surfaces. Herein, a simple and versatile strategy for synthesizing polymer brushes on copper particles is reported. Tannic acid (TA) molecules are adsorbed onto the surfaces of copper particles, forming TA coatings. Quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-polystyrene (qPDMAEMA-b-PS) block copolymer (BCP) chains are grafted on the TA coatings through hydrogen bonding and electrostatic interaction, and PS brushes are grafted on the copper particles. The effects of TA concentration on the adsorption of TA and PS brush synthesis are discussed. The PS brushes are able to form surface nanostructures on the copper particles through co-assembly with PDMAEMA-b-PS BCP chains. The effect of BCP concentration on the surface nanostructures is investigated. It is reasonable to expect that polymer brushes and surface nanostructures can be synthesized on different metal surfaces by using the TA-coating approach reported in this paper.

Hierarchically Responsive Alternating Nano-Copolymers with Tailored Interparticle Bonds

Self-assembly of inorganic nanoparticles (NPs) is an essential tool for constructing structured materials with a wide range of applications. However, achieving ordered assembly structures with externally programmable properties in binary NP systems remains challenging. In this work, we assemble binary inorganic NPs into hierarchically pH-responsive alternating copolymer-like nanostructures in an aqueous medium by engineering the interparticle electrostatic interactions. The polymer-grafted NPs bearing opposite charges are viewed as nanoscale monomers ("nanomers"), and copolymerized into alternating nano-copolymers (ANCPs) driven by the formation of interparticle "bonds" between nanomers. The resulting ANCPs exhibit reversibly responsive "bond" length (i.e., the distance between nanomers) in response to the variation of pH in a range of ~7-10, allowing precise control over the surface plasmon resonance of ANCPs. Moreover, specific interparticle "bonds" can break up at pH≥11, leading to the dis-assembly of ANCPs into molecule-like dimers and trimers. These dimeric and trimeric structures can reassemble to form ANCPs owing to the resuming of interparticle "bonds", when the pH value of the solution changes from 11 to 7. The hierarchically responsive nanostructures may find applications in such as biosensing, optical waveguide, and electronic devices.

Surface Engineering and Programmed Self-Assembly of Silica Nanoparticles with Controllable Polystyrene/Poly(4-vinybenzyl azide) Patches

The programmed self-assembly of patchy nanoparticles (NPs) through a bottom-up approach is an efficient strategy for producing highly organized materials with a predetermined architecture. Herein, we report the preparation of di- and trivalent silica NPs with polystyrene (PS)/poly(4-vinylbenzyl azide) (PVBA) patches and assemble them in a THF mixture by lowering the solvent quality. Silica-PS/PVBA colloidal hybrid clusters were synthesized through the seeded growth emulsion copolymerization of styrene and 4-vinylbenzyl azide (VBA) in varying ratios. Subsequently, macromolecules on silica NPs originating from the copolymerization of growing PS or PVBA chains with the surface-grafted MMS compatibilizer are engineered by fine-tuning of polymer compositions or adjustment of solvent qualities. Moreover, multistage silica regrowth of tripod and tetrapod allowed a fine control of the patch-to-particle size ratio ranging from 0.69 to 1.54. Intriguingly, patchy silica NPs (1-, 2-, 3-PSNs) rather than hybrid clusters are successfully used as templates for multistep regrowth experiments, leading to the formation of silica NPs with a new morphology and size controllable PVBA/PS patches. Last but not least, combined with mesoscale dynamics simulations, the self-assembly kinetics of 2-PSN and 3-PSN into linear colloidal polymers and honeycomb-like lattices are studied. This work paves a new avenue for constructing colloidal polymers with a well-defined sequence and colloidal crystals with a predetermined architecture.

Photo-Induced Self-assembly of Copolymer-Capped Nanoparticles into Colloidal Molecules

Colloidal molecules (CMs) are precisely defined assemblies of nanoparticles (NPs) that mimic the structure of real molecules, but externally programming the precise self-assembly of CMs is still challenging. In this work, we show that the photo-induced self-assembly of complementary copolymer-capped binary NPs can be precisely controlled to form clustered ABx or linear (AB)y CMs at high yield (x is the coordination number of NP-Bs, and y is the repeating unit number of AB clusters). Under UV light irradiation, photolabile p-methoxyphenacyl groups of copolymers on NP-A*s are converted to carboxyl groups (NP-A), which react with tertiary amines of copolymers on NP-B to trigger the directional NP bonding. The x value of ABx can be precisely controlled between 1 and 3 by varying the irradiation duration and hence the amount of carboxyl groups generated on NP-As. Moreover, when NP-A* and NP-B are irradiated after mixing, the assembly process generates AB clusters or linear (AB)y structures with alternating sequence of the binary NPs. This assembly approach offers a simple yet non-invasive way to externally regulate the formation of various CMs on demand without the need of redesigning the surface chemistry of NPs for use in drug delivery, diagnostics, optoelectronics, and plasmonic devices.

On-Demand Assembly of Nanocrystals into a Superstructure Library in Co(OH)2 Single-Walled Nanotubes

The hierarchical self-assembly of colloidal particles facilitates the bottom-up manufacturing of metamaterials with synergistically integrated functionalities. Here, we define a modular assembly methodology that enables multinary co-assembly of nanoparticles in one-dimensional confined space. A series of isotropic and anisotropic nanocrystals such as plasmonic, metallic, visible, and near-infrared responsive nanoparticles as well as transition-metal phosphides can be selectively assembled within the single-walled Co(OH)2 nanotubes to achieve various increasingly sophisticated assembly systems, including unary, binary, ternary, and quaternary superstructures. Moreover, the selective assembly of distinct functional nanoparticles produces different integrated functional superstructures. This generalizable methodology provides predictable pathways to complex architectures with structural programming and customization that are otherwise inaccessible.

Step-growth polymerization of supracolloidal chains from patchy micelles of diblock copolymers

HYPOTHESIS

The formation of supracolloidal chains from the patchy micelles of diblock copolymers bears a close resemblance to traditional step-growth polymerization of difunctional monomers in many aspects, including chain-length evolution, size distribution, and initial-concentration dependence. Thus, understanding the colloidal polymerization based on the step-growth mechanism can offer potential control over the formation of supracolloidal chains in terms of chain structure and reaction rate.

EXPERIMENTS

We analyzed the size evolution of supracolloidal chains of patchy micelles of PS-b-P4VP by investigating a large number of colloidal chains visualized in SEM images. We varied the initial concentration of patchy micelles to achieve a high degree of polymerization and a cyclic chain. To manipulate the polymerization rate, we also changed the ratio of water to DMF and adjusted the patch size by employing PS(25)-b-P4VP(7) and PS(145)-b-P4VP(40).

FINDINGS

We confirmed the step-growth mechanism for the formation supracolloidal chains from patchy micelles of PS-b-P4VP. Based on this mechanism, we were able to achieve a high degree of polymerization early in the reaction by increasing the initial concentration and form cyclic chains by diluting the solution. We also accelerated colloidal polymerization by increasing the ratio of water to DMF in the solution and patch size by using PS-b-P4VP with a larger molecular weight.

Periodic Assembly of Diblock Pt-Au Heteronanowires for the Methanol Oxidation Reaction

Periodic assembly of heterogeneous nanoparticles provides a strategy for integrating distinct nanocatalyst blocks where their synergic effects can be explored for diverse applications. To achieve the synergistic enhancement, an intimate clean interface is preferred which however is usually plagued by the bulky surfactant molecules used in the synthesis and assembly process. Herein, we showed the creation of one-dimensional Pt-Au nanowires (NWs) with periodic alternating Pt and Au nanoblocks, by assembling Pt-Au Janus nanoparticles with the assistance of peptide T7 (Ac-TLTTLTN-CONH₂). It is demonstrated that the Pt-Au NWs showed much-improved performance in the methanol oxidation reaction (MOR), exhibiting 5.3 times higher specific activity and 2.5 times higher mass activity than the current state-of-the-art commercial Pt/C catalyst. In addition, the periodic heterostructure also improves the stability of Pt-Au NWs in the MOR, where the Pt-Au NWs retained 93.9% of their initial mass activity much higher than commercial Pt/C (30.6%).

Supramolecular Polymerization of Polymeric Nanorods Mediated by Block Copolymers

Introducing a second component is an effective way to manipulate polymerization behavior. However, this phenomenon has rarely been observed in colloidal systems, such as polymeric nanoparticles. Here, we report the supramolecular polymerization of polymeric nanorods mediated by block copolymers. Experimental observations and simulation results illustrate that block copolymers surround the polymeric nanorods and mainly concentrate around the two ends, leaving the hydrophobic side regions exposed. These polymeric nanorods connect in a side-by-side manner through hydrophobic interactions to form bundles. As polymerization progresses, the block copolymers gradually deposit onto the bundles and finally assemble into helical nanopatterns on the outermost surface, which terminates the polymerization. It is anticipated that this work could offer inspiration for a general strategy of controllable supramolecular polymerization.

Halogen Bonding-Driven Reversible Self-Assembly of Plasmonic Colloidal Molecules

Colloidal molecules (CMs) assembled from plasmonic nanoparticles are an emerging class of building blocks for creating plasmonic materials and devices, but precise yet reversible assembly of plasmonic CMs remains a challenge. This communication describes the reversible self-assembly of binary plasmonic nanoparticles capped with complementary copolymer ligands into different CMs via halogen bonding interactions at high yield. The coordination number of the CMs is governed by the number ratio of complementary halogen donor and acceptor groups on the interacting nanoparticles. The reversibility of the halogen bonds allows for controlling the repeated formation and disassociation of the plasmonic CMs and hence their optical properties. Furthermore, the CMs can be designed to further self-assemble into complex structures in selective solvents. The precisely engineered reversible nanostructures may find applications in sensing, catalysis, and smart optoelectronic devices.

Solvent-induced assembly of mono- and divalent silica nanoparticles

Particles with attractive patches are appealing candidates to be used as building units to fabricate novel colloidal architectures by self-assembly. Here, we report the synthesis of one-patch silica nanoparticles, which consist of silica half-spheres whose concave face carries in its center a polymeric patch made of grafted polystyrene chains. The multistage synthesis allows for a fine control of the patch-to-particle size ratio from 0.23 to 0.57. The assembly of the patchy nanoparticles can be triggered by reducing the solvent quality for the polystyrene chains. Dimers or trimers can be obtained by tuning the patch-to-particle size ratio. When mixed with two-patch nanoparticles, one-patch nanoparticles control the length of the resulting chains by behaving as colloidal chain stoppers. The present strategy allows for future elaboration of novel colloidal structures by controlled assembly of nanoparticles.

Kinetically Programming Copolymerization-like Coassembly of Multicomponent Nanoparticles with DNA

Programmable coassembly of multicomponent nanoparticles (NPs) into heterostructures has the capability to build upon nanostructured metamaterials with enhanced complexity and diversity. However, a general understanding of how to manipulate the sequence-defined heterostructures using straightforward concepts and quantitatively predict the coassembly process remains unreached. Drawing inspiration from the synthetic concepts of molecular block copolymers is extremely beneficial to achieve controllable coassembly of NPs and access mesoscale structuring mechanisms. We herein report a general paradigm of kinetic pathway guidance for the controllable coassembly of bivalent DNA-functionalized NPs into regular block-copolymer-like heterostructures via the stepwise polymerization strategy. By quantifying the coassembly kinetics and structural statistics, it is demonstrated that the coassembly of multicomponent NPs, through directing the specific pathways of prepolymer intermediates, follows the step-growth copolymerization mechanism. Meanwhile, a quantitative model is developed to predict the growth kinetics and outcomes of heterostructures, all controlled by the designed elements of the coassembly system. Furthermore, the stepwise polymerization strategy can be generalized to build upon a great variety of regular nanopolymers with complex architectures, such as multiblock terpolymers and ladder copolymers. Our theoretical and simulation results provide fundamental insights on quantitative predictions of the coassembly kinetics and coassembled outcomes, which can aid in realizing a diverse set of supramolecular DNA materials by the rational design of kinetic pathways.

Necklace-Like Nanostructures: From Fabrication, Properties to Applications

The shape-controlled synthesis of nanocrystals remains a hot research topic in nanotechnology. Particularly, the fabrication of 1D structures such as wires, rods, belts, and tubes has been an interesting and important subject within nanoscience in the last few decades. 1D necklace-like micro/nanostructures are a sophisticated geometry that has attracted increasing attention due to their anisotropic and periodic structure, intrinsic high surface area, abundant transport channels, exposure of each component to the surface, and multiscale roughness of the surface. These characteristics enable their unique electrical, optical, and catalytic properties. This review provides a comprehensive summary of the advanced research progress on the fabrication strategies, novel properties, and various applications of necklace-like structures. It begins with the main fabrication methods of necklace-like structures and subsequently details a variety of their properties and applications. It concludes with the authors' perspectives on future research and development of the necklace-like structures.

Polymer brush-based nanostructures: from surface self-assembly to surface co-assembly

Surface structures play an important role in the practical applications of materials. The synthesis of polymer brushes on a solid surface has emerged as an effective tool for tuning surface properties. The fabrication of polymer brush-based surface nanostructures has greatly facilitated the development of materials with unique surface properties. In this review article, synthetic methods used in the synthesis of polymer brushes, and self-assembly approaches applied in the fabrication of surface nanostructures including self-assembly of polymer brushes, co-assembly of polymer brushes and "free" block copolymer chains, and polymerization induced surface self-assembly, are reviewed. It is demonstrated that polymer brush-based surface nanostructures, including spherical surface micelles, wormlike surface structures, layered structures and surface vesicles, can be fabricated. Meanwhile, the challenges in the synthesis and applications of the surface nanostructures are discussed. This review is expected to be helpful for understanding the principles, methods and applications of polymer brush-based surface nanostructures.

Polymer-Tethered Nanoparticles: From Surface Engineering to Directional Self-Assembly

ConspectusCurrent interest in nanoparticle ensembles is motivated by their collective synergetic properties that are distinct from or better than those of individual nanoparticles and their bulk counterparts. These new advanced optical, electronic, magnetic, and catalytic properties can find applications in advanced nanomaterials and functional devices, if control is achieved over nanoparticle organization. Self-assembly offers a cost-efficient approach to produce ensembles of nanoparticles with well-defined and predictable structures. Nanoparticles functionalized with polymer molecules are promising building blocks for self-assembled nanostructures, due to the comparable dimensions of macromolecules and nanoparticles, the ability to synthesize polymers with various compositions, degrees of polymerization, and structures, and the ability of polymers to self-assemble in their own right. Moreover, polymer ligands can endow additional functionalities to nanoparticle assemblies, thus broadening the range of their applications.In this Account, we describe recent progress of our research groups in the development of new strategies for the self-assembly of nanoparticles tethered to macromolecules. At the beginning of our journey, we developed a new approach to patchy nanoparticles and their self-assembly. In a thermodynamically driven strategy, we used poor solvency conditions to induce homopolymer surface segregation in pinned micelles (patches). Patchy nanoparticles underwent self-assembly in a well-defined and controlled manner. Following this work, we overcame the limitation of low yield of the generation of patchy nanoparticles, by using block copolymer ligands. For block copolymer-capped nanoparticles, patch formation and self-assembly were "staged" by using distinct stimuli for each process. We expanded this work to the generation of patchy nanoparticles via dynamic exchange of block copolymer molecules between the nanoparticle surface and micelles in the solution. The scope of our work was further extended to a series of strategies that utilized the change in the configuration of block copolymer ligands during nanoparticle interactions. To this end, we explored the amphiphilicity of block copolymer-tethered nanoparticles and complementary interactions between reactive block copolymer ligands. Both approaches enabled exquisite control over directional and self-limiting self-assembly of complex hierarchical nanostructures. Next, we focused on the self-assembly of chiral nanostructures. To enable this goal, we attached chiral molecules to the surface of nanoparticles and organized these hybrid building blocks in ensembles with excellent chiroptical properties. In summary, our work enables surface engineering of polymer-capped nanoparticles and their controllable and predictable self-assembly. Future research in the field of nanoparticle self-assembly will include the development of effective characterization techniques, the synthesis of new functional polymers, and the development of environmentally responsive self-assembly of polymer-capped nanoparticles for the fabrication of nanomaterials with tailored functionalities.

Patchy metal nanoparticles with polymers: controllable growth and two-way self-assembly

We report a new design of polymer-patched gold nanoparticles (AuNPs) with controllable interparticle interactions in terms of their direction and strength. Patchy AuNPs (pAuNPs) are prepared through hydrophobicity-driven surface dewetting under deficient ligand exchange conditions. Using the exposed surface on pAuNPs as seeds, a highly controllable growth of AuNPs is carried out via seed-mediated growth while retaining the size of polymer domains. As guided by ligands, these pAuNPs can self-assemble directionally in two ways along the exposed surface (head-to-head) or the polymer-patched surface of pAuNPs (tail-to-tail). Control of the surface asymmetry/coverage on pAuNPs provides an important tool in balancing interparticle interactions (attraction vs. repulsion) that further tunes assembled nanostructures as clusters and nanochains. The self-assembly pathway plays a key role in determining the interparticle distance and therefore plasmon coupling of pAuNPs. Our results demonstrate a new paradigm in the directional self-assembly of anisotropic building blocks for hierarchical nanomaterials with interesting optical properties.

"Self-Adaptive" Coassembly of Colloidal "Saturn-like" Host-Guest Complexes Enabled by Toroidal Micellar Rubber Bands

The creation of inclusion complexes with "Saturn-like" geometries has attracted increasing attention for supramolecular systems, but expansion of the concept to nanoscale colloidal systems remains a challenge. Here, we report a strategy to assemble toroidal polyisoprene-b-poly(2-vinylpyridine) (PI-b-P2VP) block copolymer micelles with a PI core and a P2VP corona and inorganic (e.g., silica) nanoparticles of variable shape and dimensions into "Saturn-like" constructs with high fidelity and yield. The precise nesting of the nanoparticles between the toroidal building units is realized by virtue of hydrogen bonding and self-adaptive expansion of the flexible toroidal units enabled by a flexible, low T_g PI core. Once the toroidal units are cross-linked, the self-adaptive feature is lost and coassembly yields instead out-of-cavity bound nanoparticles. "Saturn-like" assemblies can also be formed along silica nanosphere-decorated cylindrical micelles or, alternatively, at the hydroxyl-functionalized termini of cylindrical micelles to yield colloidal [3]rotaxanes.

Linear Assembly of Two-Patch Silica Nanoparticles and Control of Chain Length by Coassembly with Colloidal Chain Stoppers

The self-assembly of patchy nanosized building blocks is an efficient strategy for producing highly organized materials. Herein we report the chaining of divalent silica nanoparticles with polystyrene patches dispersed in tetrahydrofuran triggered by lowering the solvent quality. We study the influence of the patch-to-particle size ratio and show that the nature of the added nonsolvent, for example, ethanol, water, or salty water, and its volume fraction should be carefully adjusted. We demonstrate that colloidal assembly initially obeys the kinetic model of step-growth polymerization and that beyond a certain length, the chains have the possibility to cyclize. We also show that the length of the chains can be controlled by the addition of one-patch silica nanoparticles, which act as colloidal analogues of chain stoppers.

Real-time imaging of metallic supraparticle assembly during nanoparticle synthesis

Observations of nanoparticle superlattice formation over minutes during colloidal nanoparticle synthesis elude description by conventional understanding of self-assembly, which theorizes superlattices require extended formation times to allow for diffusively driven annealing of packing defects. It remains unclear how nanoparticle position annealing occurs on such short time scales despite the rapid superlattice growth kinetics. Here we utilize liquid phase transmission electron microscopy to directly image the self-assembly of platinum nanoparticles into close packed supraparticles over tens of seconds during nanoparticle synthesis. Electron-beam induced reduction of an aqueous platinum precursor formed monodisperse 2-3 nm platinum nanoparticles that simultaneously self-assembled over tens of seconds into 3D supraparticles, some of which showed crystalline ordered domains. Experimentally varying the interparticle interactions (e.g., electrostatic, steric interactions) by changing precursor chemistry revealed that supraparticle formation was driven by weak attractive van der Waals forces balanced by short ranged repulsive steric interactions. Growth kinetic measurements and an interparticle interaction model demonstrated that nanoparticle surface diffusion rates on the supraparticles were orders of magnitude faster than nanoparticle attachment, enabling nanoparticles to find high coordination binding sites unimpeded by incoming particles. These results reconcile rapid self-assembly of supraparticles with the conventional self-assembly paradigm in which nanocrystal position annealing by surface diffusion occurs on a significantly shorter time scale than nanocrystal attachment.

Particle-Click-Particle: Colloidal Clusters from Click Seeded Emulsion Polymerization

The self-organization of building blocks in colloidal clusters and their architecture adjustment are crucial for colloid synthesis and design. We report on a click seeded emulsion polymerization via swelling-induced self-assembly...

Customizable nano-sized colloidal tetrahedrons by polymerization-induced particle self-assembly (PIPA)

Colloidal molecules (CMs) are colloidal clusters with molecule-like symmetry and architecture, generated from the self-assembly of nanoparticles with attractive patches. However, large-scale preparation of patchy nanoparticles remains challenging. Here, we...

Divalent Multilinking Bonds Control Growth and Morphology of Nanopolymers

Assembly of nanoscale objects into linear architectures resembling molecular polymers is a basic organization resulting from divalent interactions. Such linear architectures occur for particles with two binding patches on opposite sides, known as Janus particles. However, unlike molecular systems where valence bonds can be envisioned as pointlike interactions nanoscale patches are often realized through multiple molecular linkages. The relationship between the characteristics of these linkages, the resulting interpatch connectivity, and assembly morphology is not well-explored. Here, we investigate assembly behavior of model divalent nanomonomers, DNA nanocuboid with tailorable multilinking bonds. Our study reveals that the characteristics of individual molecular linkages and their collective properties have a profound effect on nanomonomer reactivity and resulting morphologies. Beyond linear nanopolymers, a common signature of divalent nanomonomers, we observe an effective valence increase as linkages lengthened, leading to the nanopolymer bundling. The experimental findings are rationalized by molecular dynamics simulations.

Recent Advances in Synthesis, Properties, and Applications of Metal Halide Perovskite Nanocrystals/Polymer Nanocomposites

Metal halide perovskite nanocrystals (PNCs) have recently garnered tremendous research interest due to their unique optoelectronic properties and promising applications in photovoltaics and optoelectronics. Metal halide PNCs can be combined with polymers to create nanocomposites that carry an array of advantageous characteristics. The polymer matrix can bestow stability, stretchability, and solution-processability while the PNCs maintain their size-, shape- and composition-dependent optoelectronic properties. As such, these nanocomposites possess great promise for next-generation displays, lighting, sensing, biomedical technologies, and energy conversion. The recent advances in metal halide PNC/polymer nanocomposites are summarized here. First, a variety of synthetic strategies for crafting PNC/polymer nanocomposites are discussed. Second, their array of intriguing properties is examined. Third, the broad range of applications of PNC/polymer nanocomposites is highlighted, including light-emitting diodes (LEDs), lasers, and scintillators. Finally, an outlook on future research directions and challenges in this rapidly evolving field are presented.

Colloidal Self-Assembly Approaches to Smart Nanostructured Materials

Colloidal self-assembly refers to a solution-processed assembly of nanometer-/micrometer-sized, well-dispersed particles into secondary structures, whose collective properties are controlled by not only nanoparticle property but also the superstructure symmetry, orientation, phase, and dimension. This combination of characteristics makes colloidal superstructures highly susceptible to remote stimuli or local environmental changes, representing a prominent platform for developing stimuli-responsive materials and smart devices. Chemists are achieving even more delicate control over their active responses to various practical stimuli, setting the stage ready for fully exploiting the potential of this unique set of materials. This review addresses the assembly of colloids into stimuli-responsive or smart nanostructured materials. We first delineate the colloidal self-assembly driven by forces of different length scales. A set of concepts and equations are outlined for controlling the colloidal crystal growth, appreciating the importance of particle connectivity in creating responsive superstructures. We then present working mechanisms and practical strategies for engineering smart colloidal assemblies. The concepts underpinning separation and connectivity control are systematically introduced, allowing active tuning and precise prediction of the colloidal crystal properties in response to external stimuli. Various exciting applications of these unique materials are summarized with a specific focus on the structure-property correlation in smart materials and functional devices. We conclude this review with a summary of existing challenges in colloidal self-assembly of smart materials and provide a perspective on their further advances to the next generation.

Adaptable Multivalent Hairy Inorganic Nanoparticles

We report a polymer brush-based approach for fabricating multivalent patchy nanoparticles (NPs) with the number of nanodomains (valency) from 6 to 10, potentially from 1 to 10, by exploiting the lateral microphase separation of binary mixed homopolymer brushes grafted on NPs with a radius comparable to the polymer sizes. Well-defined mixed brushes were grown on 20.4 nm silica NPs by two-step surface-initiated reversible deactivation radical polymerizations and microphase separated laterally upon casting from a good solvent, producing multivalent NPs on 2D surfaces. A linear relationship between valency and average core size for the corresponding valency was observed. The mixed brush NPs exhibited abilities to form "bonds" through the overlap of nanodomains and to change the valency when interacting with adjacent NPs. This method could open up a new avenue for studying patchy NPs.

Porous self-supporting film of semi-flexible supracolloidal chains of diblock copolymer micelles

Patchy micelles of diblock copolymers can be polymerized into a linear supracolloidal chain. We measure the persistence and contour lengths of supracolloidal chains coated on a solid substrate to evaluate their flexibility. Based on the analysis, the chain is semi-flexible, and the conformation is suitably explained by the worm-like chain model. In addition, utilizing a spin-coating technique with the semi-flexible nature of the chains, we produce a self-supporting film of supracolloidal chains having nanoscale pores essentially from colloidal constituents that tend to form dense packing if there is no prior organization of them into a semi-flexible chain.

Self-regulated co-assembly of soft and hard nanoparticles

Controlled self-assembly of colloidal particles into predetermined organization facilitates the bottom-up manufacture of artificial materials with designated hierarchies and synergistically integrated functionalities. However, it remains a major challenge to assemble individual nanoparticles with minimal building instructions in a programmable fashion due to the lack of directional interactions. Here, we develop a general paradigm for controlled co-assembly of soft block copolymer micelles and simple unvarnished hard nanoparticles through variable noncovalent interactions, including hydrogen bonding and coordination interactions. Upon association, the hairy micelle corona binds with the hard nanoparticles with a specific valence depending exactly on their relative size and feeding ratio. This permits the integration of block copolymer micelles with a diverse array of hard nanoparticles with tunable chemistry into multidimensional colloidal molecules and polymers. Secondary co-assembly of the resulting colloidal molecules further leads to the formation of more complex hierarchical colloidal superstructures. Notably, such colloidal assembly is processible on surface either through initiating the alternating co-assembly from a micelle immobilized on a substrate or directly grafting a colloidal oligomer onto the micellar anchor.

Colloidal self-assembly enables bottom-up manufacture of materials with designed hierarchies and functions. Here the authors develop a facile method to construct multidimensional colloidal architectures via the association of soft block copolymer micelles with simple unvarnished hard nanoparticles.

Symmetry-Broken Patches on Gold Nanoparticles through Deficient Ligand Exchange

Symmetry-broken nanoparticles (NPs) are important building blocks with directional interparticle interaction as a key to access the precise organization of NPs macroscopically. We report a facile, one-pot synthetic approach to prepare high-quality symmetry-broken plasmonic gold NPs (AuNPs). Symmetry-broken patterning is achieved through deficient ligand exchange of isotropic AuNPs with thiol-terminated polystyrene (PS-SH) in the presence of an amphiphilic polymer surfactant. The concentration of PS-SH plays a dominant role in tuning surface patterning and coverage of AuNPs. The formation of asymmetric surface patches arises from the interplay between the conformational entropy of polymer ligands and the interfacial energy between polymer-grafted AuNPs and the solvent. Our method illustrates new paradises to design asymmetric NPs with directional interparticle interactions to access the precise organization of NPs.

Laser-Scanning-Guided Assembly of Quasi-3D Patterned Arrays of Plasmonic Dimers for Information Encryption

The application of plasmonic dimeric nanostructures in color displays, data storage, and especially metamaterials necessitates the patterning of dimers into ordered arrays, but controllable assembly of plasmonic nanoparticles into patterned dimer arrays on substrates still remains a challenge. Here, a facile laser-scanning-based strategy to fabricate quasi-3D patterned arrays of plasmonic nanoparticle dimers with controlled orientation for plasmonic information encryption is reported. Laser scanning of polymer-covered plasmonic nanoparticle (e.g., gold) arrays selectively exposes the surface of irradiated nanoparticle via localized photothermal heating, guiding the assembly of another type of nanoparticles onto the exposure nanoparticle surface to form dimers on substrates. This combined top-down/bottom-up approach is highly flexible in forming high-resolution patterns of plasmonic dimers from nanoparticles of different sizes and shapes. The z-axis orientation, interparticle spacing, and nanoparticle size and shape of plasmonic dimers can be precisely tuned, enabling the modulation of the coupled resonances of the dimer arrays. Moreover, it is demonstrated that the patterned dimer arrays can be used in information encryption where their plasmonic color can be repeatedly displayed and erased. This work provides an important addition to tools for the fabrication of patterned complex plasmonic nanostructures from as-synthesized nanoparticles with broad applications.

Ordered polymer composite materials: challenges and opportunities

Polymer nanocomposites containing nanoscale fillers are an important class of materials due to their ability to access a wide variety of properties as a function of their composition. In order to take full advantage of these properties, it is critical to control the distribution of nanofillers within the parent polymer matrix, as this structural organization affects how the two constituent components interact with one another. In particular, new methods for generating ordered arrays of nanofillers represent a key underexplored research area, as emergent properties arising from nanoscale ordering can be used to introduce novel functionality currently inaccessible in random composites. The knowledge gained from developing such methods will provide important insight into the thermodynamics and kinetics associated with nanomaterial and polymer assembly. These insights will not only benefit researchers working on new composite materials, but will also deepen our understanding of soft matter systems in general. In this review, we summarize contemporary research efforts in manipulating nanofiller organization in polymer nanocomposites and highlight future challenges and opportunities for constructing ordered nanocomposite materials.

Hierarchical self-assembly of miktoarm star copolymers with pathway complexity

The self-assembly of amphiphilic miktoarm star copolymers shows hierarchical pathway complexity from molecular building blocks to miktoarm stars to micellar nano-objects to complex hierarchical assemblies.

Polymeric Ligand-Mediated Regioselective Bonding of Plasmonic Nanoplates and Nanospheres

Nanoparticle (NP) clusters are attractive for many applications, but controllable and regioselective assembly of clusters remains challenging. This communication reports a strategy to precisely assemble Ag nanoplates (NP-As) and Au nanospheres (NP-Bs) grafted with copolymer ligands into defined AB_x clusters with controlled coordination number (x) and orientation of the NPs. The directional bonding of shaped NPs relies on the stoichiometric reaction of complementary reactive groups on copolymer ligands. The x value of NP clusters can be tuned from 1 to 4 by varying the number ratio of reactive groups on single NP-Bs to NP-As. The regioselective bonding of nanospheres to the edge or face of a central nanoplate is governed by the steric hindrance of copolymeric ligands on the nanoplate. The clusters exhibit distinctive plasmonic properties that are dependent on the bonding modes of NPs. This study paves a route to fabricating nanostructures with high precision and complexity for applications in plasmonics, catalysis, and sensing.

Self-assembly of anisotropic nanoparticles into functional superstructures

Self-assembly of colloidal nanoparticles (NPs) into superstructures offers a flexible and promising pathway to manipulate the nanometer-sized particles and thus make full use of their unique properties. This bottom-up strategy builds a bridge between the NP regime and a new class of transformative materials across multiple length scales for technological applications. In this field, anisotropic NPs with size- and shape-dependent physical properties as self-assembly building blocks have long fascinated scientists. Self-assembly of anisotropic NPs not only opens up exciting opportunities to engineer a variety of intriguing and complex superlattice architectures, but also provides access to discover emergent collective properties that stem from their ordered arrangement. Thus, this has stimulated enormous research interests in both fundamental science and technological applications. This present review comprehensively summarizes the latest advances in this area, and highlights their rich packing behaviors from the viewpoint of NP shape. We provide the basics of the experimental techniques to produce NP superstructures and structural characterization tools, and detail the delicate assembled structures. Then the current understanding of the assembly dynamics is discussed with the assistance of in situ studies, followed by emergent collective properties from these NP assemblies. Finally, we end this article with the remaining challenges and outlook, hoping to encourage further research in this field.

Selective Coupling and Polymerization of Folded Polymer Micelles to Nanodomain Self-Assemblies

Herein, we developed selective coupling and polymerization systems of folded polymer micelles via physical interaction in water. The polymer micelles serve as nanodomains to provide double core micelles, alternating necklace micelles, and micelle-connected hydrogels. For this, cation- or anion-tail unimer micelles and amine- or carboxy-tail unimer micelles were designed; the unimer micelles consist of folded amphiphilic random copolymers carrying hydrophilic poly(ethylene glycol) and hydrophobic or hydrogen-bonding pendants. Mixing a cation-tail micelle and an anion-tail micelle, and even the combination of a double cation-tail micelle and a double anion-tail micelle, selectively provided double-core micelles in water without forming large aggregates. Double core micelles afforded structural transformation into linear or cyclic polymers and dynamic exchange of the micelle domains. In contrast, mixing amine-tail micelles and carboxy-tail micelles gave an alternating necklace micelle or a hydrogel. The controlled connection of polymer micelles was achieved by designing suitable physical interaction. This technique opened new ways to create various nanodomain self-assemblies with controlled higher-order structure.

Synthesis of AB n -type colloidal molecules by polymerization-induced particle-assembly (PIPA)

Conventional synthesis of colloidal molecules (CMs) mainly depends on particle-based self-assembly of patchy building blocks. However, direct access to CMs by the self-assembly of isotropic colloidal subunits remains challenging. Here, we report the mass production of AB n -type CMs by polymerization-induced particle-assembly (PIPA), using a linear ABC triblock terpolymer system. Starting from diblock copolymer spheres, the association of spheres takes place in situ during the polymerization of the third block. The third blocks aggregate into attractive domains, which connect spheres into CMs. The stability of CMs is ensured, as long as the conversions are limited to ca. 50%, and the pH is low. The valence of AB n -type CMs (n = 2-6) is determined by the volume ratio of the polymer blocks. By tuning the volume ratio, 78.5% linear AB2-type CMs are yielded. We demonstrate that polymerization-induced particle-assembly is successful for the scalable fabrication of AB n -type CMs (50 g L-1), and can be easily extended to vastly different triblock terpolymers, for a wide range of applications.

Strictly sparse surface modification and its application for endowing nanoparticles with an exact “valency”

Strictly sparse modification of a particle surface and its application for endowing smaller nanoparticles with an exact “valency” is reported.

Polymer-guided assembly of inorganic nanoparticles

The self-assembly of inorganic nanoparticles is of great importance in realizing their enormous potentials for broad applications due to the advanced collective properties of nanoparticle ensembles. Various molecular ligands (e.g., small molecules, DNAs, proteins, and polymers) have been used to assist the organization of inorganic nanoparticles into functional structures at different hierarchical levels. Among others, polymers are particularly attractive for use in nanoparticle assembly, because of the complex architectures and rich functionalities of assembled structures enabled by polymers. Polymer-guided assembly of nanoparticles has emerged as a powerful route to fabricate functional materials with desired mechanical, optical, electronic or magnetic properties for a broad range of applications such as sensing, nanomedicine, catalysis, energy storage/conversion, data storage, electronics and photonics. In this review article, we summarize recent advances in the polymer-guided self-assembly of inorganic nanoparticles in both bulk thin films and solution, with an emphasis on the role of polymers in the assembly process and functions of resulting nanostructures. Precise control over the location/arrangement, interparticle interaction, and packing of inorganic nanoparticles at various scales are highlighted.