Preparation of Peapod-Like Nano-Copolymers with Periodic Sequence via Polymerization-Induced Morphology Differentiation and Fusion

Inorganic nanoparticles have so far dominated the field of nanoparticle assembly, and assembly of pure organic nanoparticles (such as block copolymer nanoparticles) has rarely been examined in colloidal systems. Expanding the scope of nanoparticles is of great significance for the study of nanoparticle assembly. Herein, a paradigm for the copolymerization of organic nanoparticles into peapod-like linear nanostructures with periodic sequence is introduced. Vesicles and porous spheres are generated in situ during polymerization-induced self-assembly (PISA) and can be viewed as nanoscale monomers ("nanomers"). The subsequent copolymerization of these nanomers is completed in one-pot, which greatly simplifies the preparation of nanomers and peapod-like nano-copolymers. It is demonstrated that appropriate π-π stacking interactions are crucial to the formation of nanomers and their copolymerization progress. Notably, the research subjects in nano-copolymers with periodic sequence have expanded to organic nanoparticles, which is beneficial to further expand the horizons of nanoparticle assembly. Moreover, the multiple separated compartments in the peapod-like nano-copolymers will open new directions toward development of artificial organelle and on-demand catalysis in different compartments within the same nano-object.

Fabrication of Periodic Arrays of Highly Oriented Plasmonic Heterotrimers via Site-Specific Sequential Colloidal Assembly

Plasmonic nanoarrays show applications in biosensors, nanolasers, and photodetectors, but precisely organizing and orienting nanoparticle (NP) trimers on substrates remains a grand challenge. Here, we present a self-assembly strategy to arrange metallic NPs with distinct diameters into centimeter-scale arrays of highly oriented linear trimers by modulating the balance between capillary forces and coordination-electrostatic interactions. We achieved an 88% yield of plasmonic trimers with ±10° orientation uniformity across 1 cm2 substrates by optimizing the ionic strength of the NP solutions. The high uniformity and sub-3-nm interparticle gaps of trimers in arrays enabled the collective polarization-dependent optical responses and high-order plasmonic coupling. Our strategy offers a versatile platform for creating complex nanostructure arrays with heterogeneous assemblies for use in plasmonic devices.

Mechanically Strong Nanocolloidal Supramolecular Plastics Assembled from Carbonized Polymer Dots with Photoactivated Room-Temperature Phosphorescence

The innovative development of supramolecular plastics (SPs) is recognized as one of the global efforts to address the environmental pollution caused by petroleum-based plastics. Traditional SPs usually show weak mechanical strength because of relatively weak noncovalent bonds and a lack of appropriate functions for practical applications. To overcome these limitations, we herein report nanocolloidal supramolecular plastics (NSPs) assembled from newly emerging nanoparticles, namely, carbonized polymer dots (CPDs) modified with ureido pyrimidinone groups. These NSPs display good mechanical properties, unique photoactivated room-temperature phosphorescence (RTP), and excellent solvent stability. Notably, NSPs are recyclable with maintenance of their original mechanics and photoactivated RTP after several usages. Furthermore, photoactivated RTP with multiple colors is achieved by incorporating organic molecules into NSPs. We show proof-of-concept applications of NSPs in high-level information security. The results in this work pave an avenue toward functional materials assembled from CPDs and will advance the development of innovative nanomaterials for sustainable applications.

Convergence of DNA nanotechnology and polymer chemistry to 'synthesize' nanopolymers with branching architectures: a computational perspective

Polymer-like superstructures termed nanopolymers from the self-assembly of atom-like nanoparticles are an emerging class of structured metamaterials with enhanced functionalities, but the controllable 'synthesis' of nanopolymers with non-linear architecture and spatially defined dimensions remains a challenge. Inspired by synthetic concepts of branched polymers, we propose a hierarchical polymerization-like protocol for the programmable coassembly of DNA-based multicomponent mixtures into non-linear nanopolymers with well-defined branching architecture and predictable spatial dimensions. By employing computational simulations, it is theoretically demonstrated that the synergy of sequence-designed DNA motifs and the proposed protocol enables the precise control over the assembly kinetics of atom-like nanoparticles and the branching architectures of nanopolymers, in agreement with the predictions of the generalized polymerization kinetics model. Furthermore, it is demonstrated that the fundamental correlations between the spatial dimension and branching architecture of nanopolymers satisfy the scaling law acquired in polymer science. These findings will facilitate the programmable coassembly of DNA supramolecules into structured metamaterials with architectural complexity observed in nature.

Directional Self-Assembly of Programmable Atom-like Nanoparticles into Colloidal Molecules

Colloidal molecules, novel nanoparticle clusters with molecular-like structures, can enhance material performance and broaden applications in nanotechnology and materials science. However, constructing them with a precise, controllable architecture remains challenging. Inspired by the concepts of chemical reaction, we theoretically design a novel type of nanoparticles bifunctionalized by DNA strands and polymer chains and propose a stepwise strategy to hierarchically program the assembly of bifunctionalized nanoparticles into well-defined colloidal molecules by virtue of coarse-grained molecular dynamics simulations. This method leverages the synergistic effects of polymers and DNA to create programmable atom-like nanoparticles with various valence domains. By carefully designing strands, these nanoparticles are programmed to coassemble into various colloidal molecules with distinct symmetries and coordination numbers, which can be finely tuned by the molecular design of nanoparticles as well as the composition design of the coassembly system. Our strategy provides a novel protocol for the controlled coassembly of nanoparticles into customized colloidal molecules, expanding nanomaterial manufacturing techniques.

Dynamic and asymmetric colloidal molecules

"Colloidal molecules" represent artificial colloidal clusters replicating the geometries of molecules and exhibiting flexibility and fluctuations similar to macromolecules and proteins. Their dynamic and anisotropic characters make them unique and indispensable building blocks for creating hierarchically organized superstructures. Despite the progress in synthesizing and assembling colloidal molecules, unveiling their dynamic characters is challenging in experiments. Here, we employ real-time three-dimensional imaging and simulations to reveal dynamic colloidal molecule structures in micrometre-sized colloidal-emulsion models with tunable electrostatic interactions. Our findings reveal that colloidal molecules' dynamic structures are inherently asymmetric, with angular symmetry emerging through continuous ordering from a liquid-like configuration. We further develop an effective method to guide the ordering of colloidal molecules towards a desired structure by dynamically adjusting the ionic strength in the solvent during the ordering process. We validate this method using molecular dynamics simulations and propose a practical protocol for its experimental implementation. Our research contributes to a clearer physical understanding of dynamic colloidal molecules and offers potential solutions to the complexities inherent in their formation process.

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.

Polymer-Grafted Gold Colloids and Supracolloids: From Mechanisms of Formation to Dynamic Soft Matter

Gold nanoparticles represent nanosized colloidal entities with high relevance for both basic and applied research. When gold nanoparticles are functionalized with polymer-molecule ligands, hybrid nanoparticles emerge whose interactions with the environment are controlled by the polymer coating layer: Colloidal stability and structure formation on the single particle level as well as at the supracolloidal scale can be enabled and engineered by tailoring the composition and architecture of this polymer coating. These possibilities in controlling structure formation may lead to synergistic and/or emergent functional properties of such hybrid colloidal systems. Eventually, the responsivity of the polymer coating to external triggers also enables the formation of hybrid supracolloidal systems with specific dynamic properties. This review provides an overview of fundamentals and recent developments in this vibrant domain of materials science.

Curvature-guided depletion stabilizes Kagome superlattices of nanocrystals

Shape-anisotropic nanocrystals and patchy particles have been explored to construct complex superstructures, but most studies have focused on convex shapes. We report that nonconvex, dumbbell-shaped nanocrystals (nanodumbbells) exhibit globally interlocking self-assembly behaviors governed by curvature-guided depletion interactions. By tailoring the local curvature of nanodumbbells, we can precisely and flexibly adjust particle bonding directionality, a level of control rarely achievable with conventional convex building blocks. These nanodumbbells can undergo long-range ordered assembly into various intricate two-dimensional superlattices, including the chiral Kagome lattice. Theoretical calculations reveal that the Kagome lattice is a thermodynamically stable phase, with depletion interactions playing a crucial role in stabilizing these non-close-packed structures. The emergence of Kagome lattices and other unusual structures highlights the vast potential of nonconvex nanocrystals for creating sophisticated architectures.

Electromagnetic Functions Modulation of Recycled By-Products by Heterodimensional Structure

One of the significant technological challenges in safeguarding electronic devices pertains to the modulation of electromagnetic (EM) wave jamming and the recycling of defensive shields. The synergistic effect of heterodimensional materials can effectively enable the manipulation of EM waves by altering the nanostructure. Here we propose a novel approach for upcycling by-products of silver nanowires that can fabricate shape-tunable aerogels which enable the modulation of its interaction with microwaves by heterodimensional structure of by-products. By-product heterodimensionality was used to design EM-wave-jamming-dissipation structures and therefore two typical tunable aerogel forms were studied. The first tunable form was aerogel film, which shielded EM interference (EMI shielding effectiveness (EMI SE) > 89 dB) and the second tunable form was foam, which performed dual EM functions (SE > 30 dB& reflective loss (RL) < -35 dB, effective absorption bandwidth (EAB) > 6.7 GHz). We show that secondary recycled aerogels retain nearly all of their EM protection properties, making this type of closed-loop cycle an appealing option. Our findings pave the way for the development of adaptive EM functions with nanoscale regulation in a green and closed-loop cycle, and they shed light on the fundamental understanding of microwave interactions with heterodimensional structures.

Shape-Directed Dynamic Assembly of Active Colloidal Metamachines

Modularly organizing active micromachines into high-grade metamachines makes a great leap for operating the microscopic world in a biomimetic way. However, modulating the nonreciprocal interactions among different colloidal motors through chemical reactions to achieve the controllable construction of active colloidal metamachines with specific dynamic properties remains challenging. Here, we report the phototactic active colloidal metamachines constructed by shape-directed dynamic self-assembly of chemically driven peanut-shaped TiO2 colloidal motors and Janus spherical Pt/SiO2 colloidal motors. The long-range diffusiophoretic attraction generated by the photocatalytic reaction dominates the sensing and collision of peanut TiO2 motors with Janus Pt/SiO2 motors. The coupling of local chemical concentration gradient fields between the two types of motors generates short-range site-selective interactions, promoting the shape-directed assembly toward active colloidal metamachines with well-defined spatial configurations. Metamachines, made of colloidal motors, exhibit configuration-dependent kinematics. The colloidal metamachines can be reversibly reconstructed by adjusting lighting conditions and can move phototactically along a predetermined path under the structured light field. Such chemically driven colloidal metamachines that integrate multiple active agents provide a significant avenue for fabricating active soft matter materials and intelligent robotic systems with advanced applications.

Guided ad infinitum assembly of mixed-metal oxide arrays from a liquid metal

Bottom-up nano- to micro-fabrication is crucial in modern electronics and optics. Conventional multi-scale array fabrication techniques, however, are facing challenges in reconciling the contradiction between the pursuit of better device performance and lowering the fabrication cost and/or energy consumption. Here, we introduce a facile mixed-metal array fabrication method based on guided self-assembly of polymerizing organometallic adducts derived from the passivating oxides of a ternary liquid metal to create mixed metal wires. Driven by capillary action and evaporation-driven Marangoni convection, large-area, high-quality organometallic nano- to micro-wire arrays were fabricated. Calcination converts the organometallics into oxides (semiconductors) without compromising wire continuity or array periodicity. Exploiting capillary bridges on a preceding layer, hierarchical arrays were made. Similarly, exploiting the conformity of the liquid to the mold, arrays with complex geometries were made. Given the periodicity and high refractive index of these arrays, we observe guided mode resonance while their complex band structures enable fabrication of diodes or gates. This work demonstrates a simple, affordable approach to opto-electronics based on self-assembling arrays.

Reversible Nanocomposite by Programming Amorphous Polymer Conformation Under Nanoconfinement

Nanoconfinements are utilized to program how polymers entangle and disentangle as chain clusters to engineer pseudo bonds with tunable strength, multivalency, and directionality. When amorphous polymers are grafted to nanoparticles that are one magnitude larger in size than individual polymers, programming grafted chain conformations can "synthesize" high-performance nanocomposites with moduli of ≈25GPa and a circular lifecycle without forming and/or breaking chemical bonds. These nanocomposites dissipate external stresses by disentangling and stretching grafted polymers up to ≈98% of their contour length, analogous to that of folded proteins; use both polymers and nanoparticles for load bearing; and exhibit a non-linear dependence on composition throughout the microscopic, nanoscopic, and single-particle levels.

Spontaneous Catalytic Reaction of a Surfactant in the Interfacial Microenvironment of Colloidal Gold Nanoparticles

The performance of nanomaterials is significantly determined by the interfacial microenvironment, in which a surfactant plays an essential role as the adsorbent, but its involvement in the interfacial reaction is often overlooked. Here, it was discovered that citrate and ascorbic acid, the two primarily used surfactants for colloidal gold nanoparticles (Au NPs), can spontaneously undergo catalytic reaction with trace-level nitrogenous residue under ambient environment to form oxime, which is subsequently cleaved to generate CN- or a compound containing the -CN group. Such a catalytic reaction shows wide universality in both reactants, including various carbonaceous and nitrogenous sources, and metal catalysts, including Au, Ag, Fe, Cu, Ni, Pt, and Pd NPs. Furthermore, with the removal of this reaction, adsorbed CO with diverse adsorption configurations was observed via surface-enhanced Raman spectroscopy under ambient conditions without an applied potential. Our work highlights the non-negligible significance of surfactants in interfacial microenvironments and provides crucial insights into the fundamental understanding of interfacial chemical reactions.

Effect of the number ratio and size ratio on the formation of binary superlattices assembled from polymer-tethered spherical nanoparticles of two sizes

Binary superlattices (BNSLs) with unique configurations are of great interest, attributed to the interaction between two kinds of nanoparticles, providing potential applications in sensing, electronic and optical fields. Here, polystyrene (PS) tethered spherical gold nanoparticles (AuNPs) with two core diameters spontaneously assembled into BNSLs via emulsion-confined self-assembly. BNSLs with specific stoichiometry and interparticle gaps of the NPs are prepared by tuning the number and size ratios of the two types of NPs. Moreover, after introducing long ligands, binary NPs are separated into macrophase separation or mixed together, depending on the interaction between polymer chains tethered to the AuNPs. Finally, PS-tethered AuNPs provide more possibilities for fabricating multifunctional BNSLs.

Swarm Autonomy: From Agent Functionalization to Machine Intelligence

Swarm behaviors are common in nature, where individual organisms collaborate via perception, communication, and adaptation. Emulating these dynamics, large groups of active agents can self-organize through localized interactions, giving rise to complex swarm behaviors, which exhibit potential for applications across various domains. This review presents a comprehensive summary and perspective of synthetic swarms, to bridge the gap between the microscale individual agents and potential applications of synthetic swarms. It is begun by examining active agents, the fundamental units of synthetic swarms, to understand the origins of their motility and functionality in the presence of external stimuli. Then inter-agent communications and agent-environment communications that contribute to the swarm generation are summarized. Furthermore, the swarm behaviors reported to date and the emergence of machine intelligence within these behaviors are reviewed. Eventually, the applications enabled by distinct synthetic swarms are summarized. By discussing the emergent machine intelligence in swarm behaviors, insights are offered into the design and deployment of autonomous synthetic swarms for real-world applications.

In-situ isomerization and reversible self-assembly of photoresponsive polymeric colloidal molecules enabled by ON and OFF light control

Photocatalytic colloids enable light-triggered nonequilibrium interactions and are emerging as key components for the self-assembly of colloidal molecules (CMs) out of equilibrium. However, the material choices have largely been limited to inorganic substances and the potential for reconfiguring structures through dynamic light control remains underexplored, despite light being a convenient handle for tuning nonequilibrium interactions. Here, we introduce photoresponsive N,O-containing covalent organic polymer (NOCOP) colloids, which display multi-wavelength triggered fluorescence and switchable diffusiophoretic interactions with the addition of triethanolamine. Our system can form various flexible structures, including ABn-type molecules and linear chains. By varying the relative sizes of active to passive colloids, we significantly increase the structural diversity of A2B2-type molecules. Most importantly, we demonstrate in-situ transitions between different isomeric configurations and the reversible assembly of various structures, enabled by on-demand light ON and OFF control of diffusiophoretic interactions. Our work introduces a new photoresponsive colloidal system and a novel strategy for constructing and reconfiguring colloidal assemblies, with promising applications in microrobotics, optical devices, and smart materials.

Ultrasonic Control of Polymer-Capped Plasmonic Molecules

Plasmonic molecules (PMs) composed of polymer-capped nanoparticles represent an emerging material class with precise optical functionalities. However, achieving controlled structural changes in metallic nanoparticle aggregation at the nanoscale, similar to the modification of atomic structures, remains challenging. This study demonstrates the 2D/3D isomerization of such plasmonic molecules induced by a controlled ultrasound process. We used two types of gold nanoparticles, each functionalized with hydrogen bonding (HB) donor or acceptor polymers, to self-assemble into different ABN-type complexes via interparticle polymer bundles acting as molecular bonds. Post-ultrasonication treatment significantly shortens these bonds from approximately 14 to 2 nm by enhancing HB cross-linking within the bundles. This drastic change in the bond length increases the stiffness of the resulting clusters, facilitating the transition from 2D to 3D configurations in 100% yield during drop-casting onto substrates. Our results advance the precise control of PMs' nanoarchitectures and provide insights for their broad applications in sensing, optoelectronics, and metamaterials.

Supercrystal Engineering of Nanoarrows Enabled by Tailored Concavity

Self-assembly of nanoparticles into supercrystals represents a powerful approach to create unique and complex superstructures with fascinating properties and novel functions, but the complexity in spatial configuration, and the tunability in lattice structure are still quite limited compared to the crystals formed by atoms and molecules. Herein, shallowly concave gold nanoarrows with a unique concave-convex geometry are synthesized and employed as novel building blocks for shape-directed self-assembly of a wealth of complex 3D supercrystals with unprecedented configurations. The obtained diverse superstructures including six Interlocking-type supercrystals and three Packing-type supercrystals exhibit four types of Bravais lattices (i.e., tP, oI, tI, and oF) and six types of crystallographic space groups (i.e., Pmmm, I222, Pnnm, Ibam, I4/mmm, and Fmmm), which have not been documented in the mesoscale self-assembled systems. It has been revealed that the relative yield of different supercrystal structures is mainly determined by the packing density and deformability of the supercrystals, which are closely related to the tailored concavity of the nanoparticles and is affected by the particle concentration, thus allowing for programmable self-assembly into specific supercrystals through particle shape modulation. The concavity-enabled supercrystal engineering may open a new avenue toward unconventional nanoparticle superstructures with expanded complexity, tunability, and functionality.

Macroscopic Self-Assembly Realized by Polymer Brush─A Thickness-Dependent Rule for Rapid Wet Adhesion

Macroscopic self-assembly of µm-to-mm components (dimension from 100 µm to millimeters), is meaningful to realize the concept of "self-assembly at all scales" and to understand interfacial phenomena such as adhesion, self-healing, and adsorption. However, self-assembly at this length scale is different from molecular self-assembly due to limited collision chances and binding capacity between components. Long-time contact between components is requisite to realize µm-to-mm assembly. Even though the recent idea of adding a compliant coating to enhance the molecular binding capacity is effective for such self-assembly, a trade-off between coating thickness (several micrometers) and assembly efficiency exists. Here a new compliant coating of surface-initiated polymer brush to address the above paradox by both realizing fast assembly and reducing the coating thickness to ≈40 nm by two magnitudes is demonstrated. Millimeter-sized quartz cubes are used as components and grafted with oppositely charged polyelectrolyte brushes, enabling assembly in water by electrostatic attraction and disassembly in NaCl solutions. A rule of thickness-dependent assembly chance is obtained and understood by in situ force measurements and a multivalent theory. The polymer brush strategy pushes the thickness limit of requisite compliant coating to the nanoscale for fast µm-to-mm self-assembly and provides insights into rapid wet adhesion.

Heterogeneous binding of polymers on curved nanoparticles

Unraveling protracted polymer binding on curved surfaces of nanoparticles (NPs) is important for the fabrication of multifunctional nanostructures in cutting-edge research disciplines such as directional self-assembly and nanomedicine. By using our newly developed Integral of First-passage Times (IFS), we demonstrate a curvature-dependent heterogeneous binding of polymers on curved NPs, not only in terms of the binding dynamics but also in terms of the final adsorption densities. The highly curved surfaces on NPs can adsorb larger density polymers with binding kinetics that are faster than those on less curved areas, which is consistent with recent experimental observations. In particular, the spherical corners on cubic NPs with a radius of R = 3.0 nm can adsorb polymers at a density 4.1 times higher than those on planar surfaces and 1.7 times higher than those on rod edge surfaces. A unified relationship between adsorption densities and surface curvatures is proposed to collapse all the data onto one master curve. The findings demonstrate a heterogeneous binding of polymers on curved NPs, providing effective guidelines for the rational design of functional nanostructures in different applications.

Co-Assembly of Soft and Hard Nanoparticles into Macroscopic Colloidal Composites with Tailored Mechanical Property and Processability

Colloidal composites, translating the great potential of nanoscale building bricks into macroscopic dimensions, have emerged as an appealing candidate for new materials with applications in optics, energy storage, and biomedicines. However, it remains a key challenge to bridge the size regimes from nanoscopic colloidal particles to macroscale composites possessing mechanical robustness. Herein, a bottom-up approach is demonstrated to manufacture colloidal composites with customized macroscopic forms by virtue of the co-assembly of nanosized soft polymeric micelles and hard inorganic nanoparticles. Upon association, the hairy micellar corona can bind with the hard nanoparticles, linking individual hard constituents together in a soft-hard alternating manner to form a collective entity. This permits the integration of block copolymer micelles with controlled amounts of hard nanoparticles into macroscopic colloidal composites featuring diverse internal microstructures. The resultant composites showed tunable microscale mechanical strength in a range of 90-270 MPa and macroscale mechanical strength in a range of 7-42 MPa for compression and 2-24 MPa for bending. Notably, the incorporation of soft polymeric micelles also imparts time- and temperature-dependent dynamic deformability and versatile capacity to the resulting composites, allowing their application in the low-temperature plastic processing for functional fused silica glass.

Predicting protracted binding kinetics of polymers: Integral of first-passage times

Capturing protracted binding kinetics of polymers onto the surface of nanoobjects is crucial for the rational design of multifunctional nanostructures, such as patchy nanoparticles and nanodrug carriers. Recently, we developed a method-integral of first-passage times (IFS)-to successfully predict nonequilibrium, kinetically stable superstructures fabricated by two star polymers. However, whether the protracted binding kinetics predicted by IFS corresponds to the actual polymer adsorption has only been incompletely explored. In this paper, we clarify this issue by using IFS to study polymer adsorption with binding ends onto a planar wall as an example. At low free-energy barriers, the IFS-predicted polymer binding kinetics is consistent with those extracted from direct simulations. At high free-energy barriers, the protracted polymer adsorption predicted by IFS coincides with those measured in experiments. Our findings demonstrate the feasibility of IFS to study long-lived formation kinetics of polymer nanostructures by spanning timescales from picoseconds to macroscopic minutes, which establishes a foundation to use IFS in different applications.

Photocontrolled Reversible Solid-Fluid Transitions of Azopolymer Nanocomposites for Intelligent Nanomaterials

Intelligent polymer nanocomposites are multicomponent and multifunctional materials that show immense potential across diverse applications. However, to exhibit intelligent traits such as adaptability, reconfigurability and dynamic properties, these materials often require a solvent or heating environment to facilitate the mobility of polymer chains and nanoparticles, rendering their applications in everyday settings impractical. Here intelligent azopolymer nanocomposites that function effectively in a solvent-free, room-temperature environment based on photocontrolled reversible solid-fluid transitions via switching flow temperatures (Tfs) are shown. A range of nanocomposites is synthesized through the grafting of Au nanoparticles, Au nanorods, quantum dots, or superparamagnetic nanoparticles with photoresponsive azopolymers. Leveraging the reversible cis-trans photoisomerization of azo groups, the azopolymer nanocomposites transition between solid (Tf above room temperature) and fluid (Tf below room temperature) states. Such photocontrolled reversible solid-fluid transitions empower the rewriting of nanopatterns, correction of nanoscale defects, reconfiguration of complex multiscale structures, and design of intelligent optical devices. These findings highlight Tf-switchable polymer nanocomposites as promising candidates for the development of intelligent nanomaterials operative in solvent-free, room-temperature conditions.

Rapid formation of gold core-satellite nanostructures using Turkevich-synthesized satellites and dithiol linkers: the do's and don'ts for successful assembly

Turkevich syntheses represent a foundational approach for forming colloids of monodisperse gold nanoparticles where the use of these structures as building blocks when forming multicomponent nanoassemblies is pervasive. The core-satellite motif, which is characterized by a central core structure onto which satellite structures are tethered, distinguishes itself in that it can realize numerous plasmonic nanogaps with nanometer scale widths. Established procedures for assembling these multicomponent structures are, to a large extent, empirically driven, time-consuming, difficult to reproduce, and in need of a strong mechanistic underpinning relating to the close-range electrostatic interactions needed to secure satellite structures onto core materials. Described herein is a rapid, repeatable procedure for assembling core-satellite structures using Turkevich-grown satellites and dithiol linkers. With this successful procedure acting as a baseline for benchmarking modified procedures, a rather complex parameter space is understood in terms of timeline requirements for various processing steps and an analysis of the factors that prove consequential to assembly. It is shown that seemingly innocuous procedures realize sparsely populated cores whereas cores initially obstructed with commonly used capping agents lead to few disruptions to satellite attachment. Once these factors are placed under control, then it is the ionic strength imposed by the reaction biproducts of the Turkevich synthesis that is the critical factor in assembly because they decide the spatial extent of the electrical double layer surrounding each colloidal nanoparticle. With this understanding, it is possible to control the ionic strength through the addition or subtraction of various ionic species and assert control over the assembly process. The work, hence, advances the rules for a robust core-satellite assembly process and, in a broader sense, contributes to the knowhow required for the precise, programmable, and controllable assembly of multicomponent systems.

Symmetry-Breaking of Nanoparticle Surface Function Via Conformal DNA Design

Asymmetric surface functionalization of complex nanoparticles to control their directional self-assembly remains a considerable challenge. Here, we demonstrated a conformal DNA design strategy for flexible remodeling of the surface of complex nanoparticles, taking Au nanobipyramids (AuNBPs) as a model. We sheathed one or both tips of AuNBPs into conformal DNA origami with an exceptionally accurate orientation control. Such asymmetrically and symmetrically distributed surface patches possess regioselective, sequence, and site-specific DNA binding capabilities. As a result, we realized a series of prototypical multicomponent "colloidal molecules" made of AuNBPs and Au nanospheres (AuNSs) with defined directionality and number of "bonding valence" as well as 1D and 3D hierarchical assemblies, e.g., inverse core-satellites of AuNBPs and AuNSs, side-by-side and tip-to-tip linear assemblies of AuNBPs, and 3D helical superstructures of AuNBPs with tunable twists. These findings inspire new opportunities for nanoparticle surface engineering and the high-order self-assembly of nanoarchitectures with higher complexity and broadened functionalities.

Spearheading a new era in complex colloid synthesis with TPM and other silanes

Colloid science has recently grown substantially owing to the innovative use of silane coupling agents (SCAs), especially 3-trimethoxysilylpropyl methacrylate (TPM). SCAs were previously used mainly as modifying agents, but their ability to form droplets and condense onto pre-existing structures has enabled their use as a versatile and powerful tool to create novel anisotropic colloids with increasing complexity. In this Review, we highlight the advances in complex colloid synthesis facilitated by the use of TPM and show how this has driven remarkable new applications. The focus is on TPM as the current state-of-the-art in colloid science, but we also discuss other silanes and their potential to make an impact. We outline the remarkable properties of TPM colloids and their synthesis strategies, and discuss areas of soft matter science that have benefited from TPM and other SCAs.

Programmable Colloids with Analogous Hypercoordination Complex Architectures

Colloidal molecule clusters (CMCs) are promising building blocks with molecule-like symmetry, offering exceptional synergistic properties for applications in plasmonics and catalysis. Traditional CMC fabrication has been limited to simple molecule-like structures utilizing isotropic particles. Here, we employ molecular dynamics simulation to investigate the co-assembly of anisotropic nanorods (NRs) and the stimulus-responsive polymer (SRP) via reversible adsorption. The results of the simulation show that it is possible to fabricate hypercoordination complex structures with high symmetry from the co-assembly of NRs and the SRP, even in analogy to the Th(BH4)4 structure. The coordination number of these CMCs can be precisely programmed by adjusting the shape and size of the ends of the NRs and the SRP cohesion energy. Furthermore, a finite-difference time-domain simulation indicates these hypercoordination structures exhibit significantly enhanced optical activity and plasmonic coupling effects. These findings introduce a new design approach for complex molecule-like structures utilizing anisotropic nanoparticles and may expand the applications of CMCs in photonics.

Controlled Self-Assembly of Natural Polyphenols Driven by Multiple Molecular Interactions

Nature has exhibited a high degree of control over the structures and functions. Supramolecules have been utilized to mimic the subtle assembly in nature. However, sophisticated synthesis of molecular skeletons or programmable design of the driving forces raises great challenges in fabricating high-level superstructures in a controlled manner. Natural polyphenols show great promises as building blocks for a diverse of assemblies with controlled structures and functionalities. The intrinsically embedded phenolic groups (i. e., catechol and galloyl groups) are readily forming multiple molecular interactions, including coordination, hydrogen bonding, and π-π interactions with various materials of inorganic particles, organic compounds, synthetic polymers, and biomacromolecules, providing the self-assembled structures or nanocoating on surfaces. Subsequent assembly occurred by further bonding of polyphenols to construct supraparticles. To gain control over the self-assembly, the key lies in the interplay among the molecular interactions with one or two being dominant. In this Perspective, we introduce the representative polyphenol-based assemblies and their derived supraparticles to exhibit the effective harness of the controlled self-assembly by polyphenols.

Molecular-Scale Visualization of Steric Effects of Ligand Binding to Reconstructed Au(111) Surfaces

Direct imaging of single molecules at nanostructured interfaces is a grand challenge with potential to enable new, precise material architectures and technologies. Of particular interest are the structural morphology and spectroscopic signatures of the adsorbed molecule, where modern probes are only now being developed with the necessary spatial and energetic resolution to provide detailed information at the molecule-surface interface. Here, we directly characterize the adsorption of individual m-terphenyl isocyanide ligands on a reconstructed Au(111) surface through scanning tunneling microscopy and inelastic electron tunneling spectroscopy. The site-dependent steric pressure of the various surface features alters the vibrational fingerprints of the m-terphenyl isocyanides, which are characterized with single-molecule precision through joint experimental and theoretical approaches. This study provides molecular-level insights into the steric-pressure-enabled surface binding selectivity as well as its effect on the chemical properties of individual surface-binding ligands.

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.

Enhanced Light-Matter Interaction in Metallic Nanoparticles: A Generic Strategy of Smart Void Filling

The intrinsic properties of materials play a substantial role in light-matter interactions, impacting both bulk metals and nanostructures. While plasmonic nanostructures exhibit strong interactions with photons via plasmon resonances, achieving efficient light absorption/scattering in other transition metals remains a challenge, impeding various applications related to optoelectronics, chemistry, and energy harvesting. Here, we propose a universal strategy to enhance light-matter interaction, through introducing voids onto the surface of metallic nanoparticles. This strategy spans nine metals including those traditionally considered optically inactive. The absorption cross section of void-filled nanoparticles surpasses the value of plasmonic (Ag/Au) counterparts with tunable resonance peaks across a broad spectral range. Notably, this enhancement is achieved under arbitrary polarizations and varied particle sizes and in the presence of geometric disorder, highlighting the universal adaptability. Our strategy holds promise for inspiring emerging devices in photocatalysis, bioimaging, optical sensing, and beyond, particularly when metals other than gold or silver are preferred.

Proton-Assisted Assembly of Colloidal Nanoparticles into Wafer-Scale Monolayers in Seconds

Underwater adhesion processes in nature promise controllable assembly of functional nanoparticles for industrial mass production; However, their artificial strategies have faced challenges to uniformly transfer nanoparticles into a monolayer, particularly those below 100 nm in size, over large areas. Here a scalable "one-shot" self-limiting nanoparticle transfer technique is presented, enabling the efficient transport of nanoparticles from water in microscopic volumes to an entire 2-inch wafer in a remarkably short time of 10 seconds to reach near-maximal surface coverage (≈40%) in a 2D mono-layered fashion. Employing proton engineering in electrostatic assembly accelerates the diffusion of nanoparticles (over 50 µm2/s), resulting in a hundredfold faster coating speed than the previously reported results in the literature. This charge-sensitive process further enables "pick-and-place" nanoparticle patterning at the wafer scale, with large flexibility in surface materials, including flexible metal oxides and 3D-printed polymers. As a result, the fabrication of wafer-scale disordered plasmonic metasurfaces in seconds is successfully demonstrated. These metasurfaces exhibit consistent resonating colors across diverse material and geometrical platforms, showcasing their potential for applications in full-color painting and optical encryption 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.

Colloidal Self-Assembly: From Passive to Active Systems

Self-assembly fundamentally implies the organization of small sub-units into large structures or patterns without the intervention of specific local interactions. This process is commonly observed in nature, occurring at various scales ranging from atomic/molecular assembly to the formation of complex biological structures. Colloidal particles may serve as micrometer-scale surrogates for studying assembly, particularly for the poorly understood kinetic and dynamic processes at the atomic scale. Recent advances in colloidal self-assembly have enabled the programmable creation of novel materials with tailored properties. We here provide an overview and comparison of both passive and active colloidal self-assembly, with a discussion on the energy landscape and interactions governing both types. In the realm of passive colloidal assembly, many impressive and important structures have been realized, including colloidal molecules, one-dimensional chains, two-dimensional lattices, and three-dimensional crystals. In contrast, active colloidal self-assembly, driven by optical, electric, chemical, or other fields, involves more intricate dynamic processes, offering more flexibility and potential new applications. A comparative analysis underscores the critical distinctions between passive and active colloidal assemblies, highlighting the unique collective behaviors emerging in active systems. These behaviors encompass collective motion, motility-induced phase segregation, and exotic properties arising from out-of-equilibrium thermodynamics. Through this comparison, we aim to identify the future opportunities in active assembly research, which may suggest new application domains.

Polymer Brushes and Surface Nanostructures: Molecular Design, Precise Synthesis, and Self-Assembly

For over two decades, polymer brushes have found wide applications in industry and scientific research. Now, polymer brush research has been a significant research focus in the community of polymer science. In this review paper, we give an introduction to the synthesis, self-assembly, and applications of one-dimensional (1D) polymer brushes on polymer backbones, two-dimensional (2D) polymer brushes on flat surfaces, and three-dimensional (3D) polymer brushes on spherical particles. Examples of the synthesis of polymer brushes on different substrates are provided. Studies on the formation of the surface nanostructures on solid surfaces are also reviewed in this article. Multicomponent polymer brushes on solid surfaces are able to self-assemble into surface micelles (s-micelles). If the s-micelles are linked to the substrates through cleavable linkages, the s-micelles can be cleaved from the substrates, and the cleaved s-micelles are able to self-assemble into hierarchical structures. The formation of the surface nanostructures by coassembly of polymer brushes and "free" polymer chains (coassembly approach) or polymerization-induced surface self-assembly approach, is discussed. The applications of the polymer brushes in colloid and biomedical science are summarized. Finally, perspectives on the development of polymer brushes are offered in this article.

Kinetically Controlled Site-Specific Self-assembly of Hairy Colloids

The solvophobicity-driven directional self-assembly of polymer-coated gold nanorods is a well-established phenomenon. Yet, the kinetics of this process, the origin of site-selectivity in the self-assembly, and the interplay of (attractive) solvophobic brush interactions and (repulsive) electrostatic forces are not fully understood. Herein, we use a combination of time-resolved (vis/NIR) extinction spectroscopy and finite-difference time-domain (FDTD) simulations to determine conversion profiles for the assembly of gold nanorods with polystyrene shells of distinct thicknesses into their (tip-to-tip) self-assembled structures. In particular, we demonstrate that the assembly process is highly protracted compared with diffusion-controlled rates, and we find that the assembly rate varies for different thickness values of the polymer shell. Our findings were rationalized using coarse-grained molecular dynamics simulations, which also corroborated the tip-to-tip preference in the self-assembly process, albeit with a uniform polymer coating. Utilizing the knowledge of quantified conversion rates for distinct colloidal species, we designed coassembling systems with different brush thicknesses, featuring "narcissistic" self-sorting behavior. This provides new perspectives for high-level supracolloidal self-assembly.

Strongly coupled plasmonic metal nanoparticles with reversible pH-responsiveness and highly reproducible SERS in solution

We report a facile method to prepare polymer-grafted plasmonic metal nanoparticles (NPs) that exhibit pH-responsive surface-enhanced Raman scattering (SERS). The concept is based on the use of pH-responsive polymers, such as poly(acrylic acid) (PAA) and poly(allylamine hydrochloride) (PAH), as multidentate ligands to wrap around the surface of NPs instead of forming polymer brushes. Upon changing the solvent quality, the grafted pH-responsive polymers would drive reversible aggregation of NPs, leading to a decreased interparticle distance. This creates numerous hot spots, resulting in a secondary enhancement of SERS as compared to the SERS from discrete NPs. For negatively charged PAA-grafted NPs, the SERS response at pH 2.5 showed a secondary enhancement of up to 104-fold as compared to the response for discrete NPs at pH 12. Similarly, positively charged PAH-grafted AuNPs showed an opposite response to pH. We demonstrated that enhanced SERS with thiol-containing and charged molecular probes was indeed from the pH-driven solubility change of polymer ligands. Our method is different from the conventional SERS sensors in the solid state. With pH-responsive polymer-grafted NPs, SERS can be performed in solution with high reproducibility and sensitivity but without the need for sample pre-concentration. These findings could pave the way for innovative designs of polymer ligands for metal NPs where polymer ligands do not compromise interparticle plasmon coupling.

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.

Protocol for preparing patterned superlattice structures by printing assembly technology for multi-channel detection

The transformation of superlattice structures into functional devices requires high-quality preparation. Inkjet printing is potentially a cutting-edge technology for nanofabrication. Here, we present a protocol to prepare inks for constructing patterned superlattice structures using print assembly techniques. We describe steps for preparing oleophobic substrates, optimizing ink parameters, and preparing the patterned superlattice array. We then detail procedures for preparing a multichannel surface-enhanced Raman scattering sensor and evaluating its performance. This protocol can potentially facilitate the commercialization of superlattice-related devices. For complete details regarding the use and execution of this protocol, please refer to Zhao et al.1.

Interfacial Behaviors of Giant Amphiphilic Molecules Composed of Hydrophobic Isobutyl POSS and Hydrophilic POSS Bearing Carboxylic Acid Groups at the Air-Water Interface

The behavior of giant amphiphilic molecules at the air-water interface has become a subject of concern to researchers. Small changes in the molecular structure can cause obvious differences in the molecular arrangement and interfacial properties of the monolayer. In this study, we have systematically investigated the interfacial behaviors of the giant amphiphilic molecules with different number of hydrophobic BPOSS blocks and one hydrophilic ACPOSS block ((BPOSS)n-ACPOSS (n = 1-5)) at the air-water interface by the surface pressure-area (π-A) isotherm, Brewster angle microscopy (BAM), compression modulus measurement, and hysteresis measurement. We found that both the number of BPOSS blocks and the compression rate can significantly influence the interfacial behaviors of giant molecules. The π-A isotherms of giant molecules (BPOSS)n-ACPOSS (n = 2-5) exhibit a "cusp" phenomenon which can be attributed to the transition from monolayer to multilayer. However, the cusp is dramatically different from the "collapse" of the monolayer studied in other molecular systems, which is highly dependent on the compression rate of the monolayer. In addition, the compression modulus and hysteresis measurements reveal that the number of BPOSS blocks of (BPOSS)n-ACPOSS plays an important role in the static elasticity, stability, and reversibility of the Langmuir films.

2D Plasmonic Molecules via Hydrogen Bond Interaction between Polymer-Grafted Nanoparticles

The use of macromolecular design features to regulate non-covalent bonding on the nanoscale is a young and emerging fabrication strategy for advanced nanostructures. For the first time, we describe a self-assembly method to create a series of 2D plasmonic molecules (PMs) using hydrogen-bond interaction between a pair of polymer-capped gold nanoparticles (hydrogen-bond donor and acceptor). Due to the nature of hydrogen-bond interaction, we found that polymer interaction and solvation compete with each other during the self-assembly process, which turns out to be the most important condition for controlling the coordination number of PMs. We have conducted an extensive study on the solvent effect, which has helped us to design and fabricate a series of precise PMs with high symmetry.

Controlling Colloidal Crystal Nucleation and Growth with Photolithographically Defined Templates

Colloidal crystallization provides a means to synthesize hierarchical nanostructures by design and to use these complex structures for nanodevice fabrication. In particular, DNA provides a means to program interactions between particles with high specificity, thereby enabling the formation of particle superlattice crystallites with tailored unit cell geometries and surface faceting. However, while DNA provides precise control of particle-particle bonding interactions, it does not inherently present a means of controlling higher-level structural features such as the size, shape, position, or orientation of a colloidal crystallite. While altering assembly parameters such as temperature or concentration can enable limited control of crystallite size and geometry, integrating colloidal assemblies into nanodevices requires better tools to manipulate higher-order structuring and improved understanding of how these tools control the fundamental kinetics and mechanisms of colloidal crystal growth. In this work, photolithography is used to produce patterned substrates that can manipulate the placement, size, dispersity, and orientation of colloidal crystals. By adjusting aspects of the pattern, such as feature size and separation, we reveal a diffusion-limited mechanism governing crystal nucleation and growth. Leveraging this insight, patterns are designed that can produce wafer-scale substrates with arrays of nanoparticle superlattices of uniform size and shape. These design principles therefore bridge a gap between a fundamental understanding of nanoparticle assembly and the fabrication of nanostructures compatible with functional devices.

Recastable assemblies of carbon dots into mechanically robust macroscopic materials

Assembly of nanoparticles into macroscopic materials with mechanical robustness, green processability, and recastable ability is an important and challenging task in materials science and nanotechnology. As an emerging nanoparticle with superior properties, macroscopic materials assembled from carbon dots will inherit their properties and further offer collective properties; however, macroscopic materials assembled from carbon dots solely remain unexplored. Here we report macroscopic films assembled from carbon dots modified by ureido pyrimidinone. These films show tunable fluorescence inherited from carbon dots. More importantly, these films exhibit collective properties including self-healing, re-castability, and superior mechanical properties, with Young's modulus over 490 MPa and breaking strength over 30 MPa. The macroscopic films maintain original mechanical properties after several cycles of recasting. Through scratch healing and welding experiments, these films show good self-healing properties under mild conditions. Moreover, the molecular dynamics simulation reveals that the interplay of interparticle and intraparticle hydrogen bonding controls mechanical properties of macroscopic films. Notably, these films are processed into diverse shapes by an eco-friendly hydrosetting method. The methodology and results in this work shed light on the exploration of functional macroscopic materials assembled from nanoparticles and will accelerate innovative developments of nanomaterials in practical applications.

Heterostructure particles enable omnidispersible in water and oil towards organic dye recycle

Dispersion of colloidal particles in water or oil is extensively desired for industrial and environmental applications. However, it often strongly depends on indispensable assistance of chemical surfactants or introduction of nanoprotrusions onto the particle surface. Here we demonstrate the omnidispersity of hydrophilic-hydrophobic heterostructure particles (HL-HBPs), synthesized by a surface heterogeneous nanostructuring strategy. Photo-induced force microscopy (PiFM) and adhesion force images both indicate the heterogeneous distribution of hydrophilic domains and hydrophobic domains on the particle surface. These alternating domains allow HL-HBPs to be dispersed in various solvents with different polarity and boiling point. The HL-HBPs can efficiently adsorb organic dyes from water and release them into organic solvents within several seconds. The surface heterogeneous nanostructuring strategy provides an unconventional approach to achieve omnidispersion of colloidal particles beyond surface modification, and the omnidispersible HL-HBPs demonstrate superior capability for dye recycle merely by solvent exchange. These omnidispersible HL-HBPs show great potentials in industrial process and environmental protection.

Open and Close-Packed, Shape-Engineered Polygonal Nanoparticle Metamolecules with Tailorable Fano Resonances

A top-down lithographic patterning and deposition process is reported for producing nanoparticles (NPs) with well-defined sizes, shapes, and compositions that are often not accessible by wet-chemical synthetic methods. These NPs are ligated and harvested from the substrate surface to prepare colloidal NP dispersions. Using a template-assisted assembly technique, fabricated NPs are driven by capillary forces to assemble into size- and shape-engineered templates and organize into open or close-packed multi-NP structures or NP metamolecules. The sizes and shapes of the NPs and of the templates control the NP number, coordination, interparticle gap size, disorder, and location of defects such as voids in the NP metamolecules. The plasmonic resonances of polygonal-shaped Au NPs are exploited to correlate the structure and optical properties of assembled NP metamolecules. Comparing open and close-packed architectures highlights that introduction of a center NP to form close-packed assemblies supports collective interactions, altering magnetic optical modes and multipolar interactions in Fano resonances. Decreasing the distance between NPs strengthens the plasmonic coupling, and the structural symmetries of the NP metamolecules determine the orientation-dependent scattering response.

Directional Self-Assembly of Nanoparticles Coated with Thermoresponsive Block Copolymers and Charged Small Molecules

Herein, we report the directional stimuli-responsive self-assembly of gold nanoparticles (AuNPs) coated with a thermoresponsive block copolymer (BCP), poly(ethylene glycol)-b-poly(N-isopropylacrylamide) (PEG-b-PNIPAM) and charged small molecules. AuNPs modified with PEG-b-PNIPAM possessing a AuNP/PNIPAM/PEG core/active/shell structure undergo temperature-induced self-assembly into one-dimensional (1D) or two-dimensional (2D) structures in salt solutions, with the morphology varying with the ionic strength of the medium. Salt-free self-assembly is also realized by modulating the surface charge by the codeposition of positively charged small molecules; 1D or 2D assemblies are formed depending on the ratio between the small molecule and PEG-b-PNIPAM, consistent with the trend observed with the bulk salt concentration. A series of charge-controlled self-assembly at various conditions revealed that the temperature-induced BCP-mediated self-assembly reported here provides an effective means for on-demand directional self-assembly of nanoparticles (NPs) with controlled morphology, interparticle distance, and optical properties, and the fixation of high-temperature structures.

Nanoparticle Self-Assembly: From Design Principles to Complex Matter to Functional Materials

The creation of matter with varying degrees of complexities and desired functions is one of the ultimate targets of self-assembly. The ability to regulate the complex interactions between the individual components is essential in achieving this target. In this direction, the initial success of controlling the pathways and final thermodynamic states of a self-assembly process is promising. Despite the progress made in the field, there has been a growing interest in pushing the limits of self-assembly processes. The main inception of this interest is that the intended self-assembled state, with varying complexities, may not be "at equilibrium (or at global minimum)", rendering free energy minimization unsuitable to form the desired product. Thus, we believe that a thorough understanding of the design principles as well as the ability to predict the outcome of a self-assembly process is essential to form a collection of the next generation of complex matter. The present review highlights the potent role of finely tuned interparticle interactions in nanomaterials to achieve the preferred self-assembled structures with the desired properties. We believe that bringing the design and prediction to nanoparticle self-assembly processes will have a similar effect as retrosynthesis had on the logic of chemical synthesis. Along with the guiding principles, the review gives a summary of the different types of products created from nanoparticle assemblies and the functional properties emerging from them. Finally, we highlight the reasonable expectations from the field and the challenges lying ahead in the creation of complex and evolvable matter.

Molecular Engineering of Colloidal Atoms

Creation of architectures with exquisite hierarchies actuates the germination of revolutionized functions and applications across a wide range of fields. Hierarchical self-assembly of colloidal particles holds the promise for materialized realization of structural programing and customizing. This review outlines the general approaches to organize atom-like micro- and nanoparticles into prescribed colloidal analogs of molecules by exploiting diverse interparticle driving motifs involving confining templates, interactive surface ligands, and flexible shape/surface anisotropy. Furthermore, the self-regulated/adaptive co-assembly of simple unvarnished building blocks is discussed to inspire new designs of colloidal assembly strategies.

Photochromism from wavelength-selective colloidal phase segregation

Phase segregation is ubiquitously observed in immiscible mixtures, such as oil and water, in which the mixing entropy is overcome by the segregation enthalpy1-3. In monodispersed colloidal systems, however, the colloidal-colloidal interactions are usually non-specific and short-ranged, which leads to negligible segregation enthalpy4. The recently developed photoactive colloidal particles show long-range phoretic interactions, which can be readily tuned with incident light, suggesting an ideal model for studying phase behaviour and structure evolution kinetics5,6. In this work, we design a simple spectral selective active colloidal system, in which TiO2 colloidal species were coded with spectral distinctive dyes to form a photochromic colloidal swarm. In this system, the particle-particle interactions can be programmed by combining incident light with various wavelengths and intensities to enable controllable colloidal gelation and segregation. Furthermore, by mixing the cyan, magenta and yellow colloids, a dynamic photochromic colloidal swarm is formulated. On illumination of coloured light, the colloidal swarm adapts the appearance of incident light due to layered phase segregation, presenting a facile approach towards coloured electronic paper and self-powered optical camouflage.