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  1. Abstract

    Photonic crystals are extensively explored to replace inorganic pigments and organic dyes as coloring elements in printing, painting, sensing, and anti‐counterfeiting due to their brilliant structural colors, chemical stability, and environmental friendliness. However, most existing photonic‐crystal‐based pigments can only display monochromatic colors once made, and generating multicolors has to start with designing different building blocks. Here, a novel photonic pigment featuring highly tunable structural colors in the entire visible spectrum, made by the magnetic assembly of monodisperse nanorods into body‐centered‐tetragonal photonic crystals, is reported. Their prominent magnetic and crystal anisotropy makes it efficient to generate multicolors using one photonic pigment by magnetically controlling the crystal orientation. Further, the combination of angle‐dependent diffraction and magnetic orientation control enables the design of rotation‐asymmetric photonic films that display distinct patterns and encrypted information in response to rotation. The efficient multicolor generation through precise orientational control makes this novel photonic pigment promising in developing high‐performance structural‐colored materials and optical devices.

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  2. Abstract

    Engineering the nucleation and growth of plasmonic metals (Ag and Au) on their pre‐existing seeds is expected to produce nanostructures with unconventional morphologies and plasmonic properties that may find unique applications in sensing, catalysis, and broadband energy harvesting. Typical seed‐mediated growth processes take advantage of the perfect lattice match between the deposited metal and seeds to induce conformal coating, leading to either simple size increases (e.g., Au on Au) or the formation of core–shell structures (e.g., Ag on Au) with limited morphology change. In this work, we show that the introduction of a thin layer of metal with considerable lattice mismatch can effectively induce the nucleation of well‐defined Au islands on Au nanocrystal seeds. By controlling the interfacial energy between the seed and the deposited material, the oxidative ripening, and the surface diffusion of metal precursors, we can regulate the number of islands on the seeds and produce complex Au nanostructures with morphologies tunable from core‐satellites to tetramers, trimers, and dimers.

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  3. Abstract

    Conventional templating synthesis confines the growth of seeds in rigid spaces to achieve faithful morphological replication. Herein, we explore the use of spherical shape‐deformable polymeric nanoshells to regulate the anisotropic growth of Ag nanoplates. The flexible shells deform adaptively to accommodate the initial overgrowth of the seeds but restrict the growth in the directions where the shells are fully stretched, eventually producing nanoplates with an unconventional circular profile. The diameter of the final Ag nanoplates can be precisely predicted by stretching and flattering the nanoshells into a plate‐like capsule while retaining their original internal surface area. Furthermore, unlike conventional templates, the polymer shells eventually turn themselves into a conformal coating that binds to the surface of the full‐grown Ag nanoplates and significantly enhances their stability against oxidative etching.

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  4. Abstract

    Mechanochromic response is of great importance in designing bionic robot systems and colorimetric devices. Unfortunately, compared to mimicking motions of natural creatures, fabricating mechanochromic systems with programmable colorimetric responses remains challenging. Herein, we report the development of unconventional mechanochromic films based on hybrid nanorods integrated with magnetic and plasmonic anisotropy. Magnetic-plasmonic hybrid nanorods have been synthesized through a unique space-confined seed-mediated process, which represents an open platform for preparing next-generation complex nanostructures. By coupling magnetic and plasmonic anisotropy, the plasmonic excitation of the hybrid nanorods could be collectively regulated using magnetic fields. It facilitates convenient incorporation of the hybrid nanorods into polymer films with a well-controlled orientation and enables sensitive colorimetric changes in response to linear and angular motions. The combination of unique synthesis and convenient magnetic alignment provides an advanced approach for designing programmable mechanochromic devices with the desired precision, flexibility, and scalability.

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  5. Abstract

    Solar steam generation technologies have gained increasing attention due to their great potential for clean water generation with low energy consumption. The rational design of a light absorber that can maximize solar energy utilization is therefore of great importance. Here, the synthesis of Ni@C@SiO2core–shell nanoparticles as promising light absorbers for steam generation by taking advantage of the plasmonic excitation of Ni nanoparticles, the broadband absorption of carbon, and the protective function and hydrophilic property of silica is reported. The nanoparticle‐based evaporator shows an excellent photothermal efficiency of 91.2%, with an evaporation rate of 1.67 kg m−2 h−1. The performance can be further enhanced by incorporating the nanoparticles into a polyvinyl alcohol hydrogel to make a composite film. In addition, utilizing the magnetic property of the core–shell particles allows the creation of surface texture in the film by applying an external magnetic field, which helps increase surface roughness and further boost the evaporation rate to as high as 2.25 kg m−2 h−1.

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  6. Abstract

    Magnetic assembly at the nanoscale level holds great potential for producing smart materials with high functional and structural diversity. Generally, the chemical, physical, and mechanical properties of the resulting materials can be engineered or dynamically tuned by controlling external magnetic fields. This Review analyzes the recent research progress on nanoscale magnetic assembly approaches toward the development of smart materials. The magnetic interactions between nanoparticles (both magnetic and nonmagnetic) and the interactions between nanoparticles and external magnetic fields are fully expatiated based on numerical simulations. In particular, the advancements of nanoscale magnetic assembly in responsive optical nanostructures, shape‐morphing systems, and advanced materials with tunable surface properties are introduced in three subsections. The key roles of magnetic interactions in nanoscale assembly toward customizable physical and chemical properties are highlighted, with focus on how to enable direct manipulation of the positional and orientational orders of the building blocks and orientational control of soft matrices through the incorporation of anisotropic magnetic structures.

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  7. Abstract

    The dynamic optical switch of plasmonic nanostructures is highly desirable due to its promising applications in many smart optical devices. To address the challenges in the reversibility and transmittance contrast of the plasmonic electrochromic devices, here, a strategy is reported to fabricate color switchable electrochromic films through electro‐responsive dissolution and deposition of Ag on predefined hollow shells of Au/Ag alloy. Using the hollow Au/Ag alloy nanostructures as stable seeds for site‐specific deposition of Ag, elimination of the random self‐nucleation events is enabled and optimal reversibility in color switching is allowed. The hollow structure further enables excellent transmittance contrast between the bleached and colored states. With its additional advantages such as the convenience for preparation, high sensitivity, and field‐tunable optical property, it is believed that this new electrochromic film represents a unique platform for designing novel smart optical devices.

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  8. Abstract

    The fast and reversible switching of plasmonic color holds great promise for many applications, while its realization has been mainly limited to solution phases, achieving solid‐state plasmonic color‐switching has remained a significant challenge owing to the lack of strategies in dynamically controlling the nanoparticle separation and their plasmonic coupling. Herein, we report a novel strategy to fabricate plasmonic color‐switchable silver nanoparticle (AgNP) films. Using poly(acrylic acid) (PAA) as the capping ligand and sodium borate as the salt, the borate hydrolyzes rapidly in response to moisture and produces OHions, which subsequently deprotonate the PAA on AgNPs, change the surface charge, and enable reversible tuning of the plasmonic coupling among adjacent AgNPs to exhibit plasmonic color‐switching. Such plasmonic films can be printed as high‐resolution invisible patterns, which can be readily revealed with high contrast by exposure to trace amounts of water vapor.

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  9. Abstract

    Herein, we show that copper nanostructures, if made anisotropic, can exhibit strong surface plasmon resonance comparable to that of gold and silver counterparts in the near‐infrared spectrum. Further, we demonstrate that a robust confined seeded growth strategy allows the production of high‐quality samples with excellent control over their size, morphology, and plasmon resonance frequency. As an example, copper nanorods (CuNRs) are successfully grown in a limited space of preformed rod‐shaped polymer nanocapsules, thereby avoiding the complex nucleation kinetics involved in the conventional synthesis. The method is unique in that it enables the flexible control and fine‐tuning of the aspect ratio and the plasmonic resonance. We also show the high efficiency and stability of the as‐synthesized CuNRs in photothermal conversion and demonstrate their incorporation into nanocomposite polymer films that can be used as active components for constructing light‐responsive actuators and microrobots.

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  10. Abstract

    Great opportunities emerge not only in the generation of anisotropic plasmonic nanostructures but also in controlling their orientation relative to incident light. Herein, a stepwise seeded growth method is reported for the synthesis of rod‐shaped plasmon nanostructures which are vertically self‐aligned with respect to the surface of colloidal substrates. Anisotropic growth of metal nanostructure is achieved by depositing metal seeds onto the surface of colloidal substrates and then selectively passivating the seed surface to induce symmetry breaking in the subsequent seed‐mediated growth process. The versatility of this method is demonstrated by producing nanoparticle dimers and linear trimers of Au, Au–Ag, Au–Pd, and Au–Cu2O. Further, this unique method enables the automatic vertical alignment of the resulting plasmonic nanostructures to the surface of the colloidal substrate, thereby making it possible to design magnetic/plasmonic nanocomposites that allow the dynamic tuning of the plasmon excitation by controlling their orientation using an external magnetic field. The controlled anisotropic growth of colloidal plasmonic nanostructures and their dynamic modulation of plasmon excitation further allow them to be conveniently fixed in a thin polymer film with a well‐controlled orientation to display polarization‐dependent patterns that may find important applications in information encryption.

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