Aligning Ag Nanowires by a Facile Bioinspired Directional Liquid Transfer: Toward Anisotropic Flexible Conductive Electrodes

Nanotechnology in action: silver nanoparticles for improved eco-friendly remediation

Nanotechnology is an exciting area with great potential for use in biotechnology due to the far-reaching effects of nanoscale materials and their size-dependent characteristics. Silver and other metal nanoparticles have attracted a lot of attention lately because of the exceptional optical, electrical, and antimicrobial characteristics they possess. Silver nanoparticles (AgNPs) stand out due to their cost-effectiveness and abundant presence in the earth's crust, making them a compelling subject for further exploration. The vital efficacy of silver nanoparticles in addressing environmental concerns is emphasized in this thorough overview that dives into their significance in environmental remediation. Leveraging the distinctive properties of AgNPs, such as their antibacterial and catalytic characteristics, innovative solutions for efficient treatment of pollutants are being developed. The review critically examines the transformative potential of silver nanoparticles, exploring their various applications and promising achievements in enhancing environmental remediation techniques. As environmental defenders, this study advocates for intensified investigation and application of silver nanoparticles. Furthermore, this review aims to assist future investigators in developing more cost-effective and efficient innovations involving AgNPs carrying nanoprobes. These nanoprobes have the potential to detect numerous groups of contaminants simultaneously, with a low limit of detection (LOD) and reliable reproducibility. The goal is to utilize these innovations for environmental remediation purposes.

Assembled one-dimensional nanowires for flexible electronic devices via printing and coating: Techniques, applications, and perspectives

The rapid progress in flexible electronic devices has necessitated continual research into nanomaterials, structural design, and fabrication processes. One-dimensional nanowires, characterized by their distinct structures and exceptional properties, are considered essential components for various flexible electronic devices. Considerable attention has been directed toward the assembly of nanowires, which presents significant advantages. Printing and coating techniques can be used to assemble nanowires in a relatively simple, efficient, and cost-competitive manner and exhibit potential for scale-up production in the foreseeable future. This review aims to provide an overview of nanowire assembly using printing and coating techniques, such as bar coating, spray coating, dip coating, blade coating, 3D printing, and so forth. The application of assembled nanowires in flexible electronic devices is subsequently discussed. Finally, further discussion is presented on the potential and challenges of flexible electronic devices based on assembled nanowires via printing and coating.

Flexible Transparent Conductive Electrodes: Unveiling Growth Mechanisms, Material Dimensions, Fabrication Methods, and Design Strategies

Flexible transparent conductive electrodes (FTCEs) constitute an indispensable component in state-of-the-art electronic devices, such as wearable flexible sensors, flexible displays, artificial skin, and biomedical devices, etc. This review paper offers a comprehensive overview of the fabrication techniques, growth modes, material dimensions, design, and their impacts on FTCEs fabrication. The growth modes, such as the "Stranski-Krastanov growth," "Frank-van der Merwe growth," and "Volmer-Weber growth" modes provide flexibility in fabricating FTCEs. Application of different materials including 0D, 1D, 2D, polymer composites, conductive oxides, and hybrid materials in FTCE fabrication, emphasizing their suitability in flexible devices are discussed. This review also delves into the design strategies of FTCEs, including microgrids, nanotroughs, nanomesh, nanowires network, and "kirigami"-inspired patterns, etc. The pros and cons associated with these materials and designs are also addressed appropriately. Considerations such as trade-offs between electrical conductivity and optical transparency or "figure of merit (FoM)," "strain engineering," "work function," and "haze" are also discussed briefly. Finally, this review outlines the challenges and opportunities in the current and future development of FTCEs for flexible electronics, including the improved trade-offs between optoelectronic parameters, novel materials development, mechanical stability, reproducibility, scalability, and durability enhancement, safety, biocompatibility, etc.

Transparent and Stretchable Electromagnetic Interference Shielding Film with Fence-like Aligned Silver Nanowire Conductive Network

Flexible transparent conductive electrodes (TCEs) that can be used as electromagnetic interference (EMI) shielding materials have a great potential for use as electronic components in optical window and display applications. However, development of TCEs that display high shielding effectiveness (SE) and good stretchability for flexible electronic device applications has proven challenging. Herein, this study describes a stretchable polydimethylsiloxane (PDMS)/silver nanowire (AgNW) TCE with a fence-like aligned conductive network that is fabricated via pre-stretching method. The fence-like AgNW network endowed the PDMS/AgNW film with excellent optoelectronic properties, i.e., low sheet resistance of 7.68 Ω sq^-1 at 73.7% optical transmittance, thus causing an effective EMI SE of 32.2 dB at X-band. More importantly, the fence-like aligned AgNW conductive network reveals a high stability toward tensile deformation, thus gives the PDMS/AgNW film stretch-stable conductivity and EMI shielding property in the strain range of 0-100%. Typically, the film can reserve ≈70% or 80% of its initial EMI SE when stretching at 100% strain or stretching/releasing (50% strain) for 128 cycles, respectively. Additionally, the film exhibits a low-voltage driven and stretchable Joule heating performance. With these overall performances, the PDMS/AgNW film should be well suited for use in flexible and stretchable optical electronic devices.

The Role of Silver Nanoparticles in Electrochemical Sensors for Aquatic Environmental Analysis

With rapidly increasing environmental pollution, there is an urgent need for the development of fast, low-cost, and effective sensing devices for the detection of various organic and inorganic substances. Silver nanoparticles (AgNPs) are well known for their superior optoelectronic and physicochemical properties, and have, therefore, attracted a great deal of interest in the sensor arena. The introduction of AgNPs onto the surface of two-dimensional (2D) structures, incorporation into conductive polymers, or within three-dimensional (3D) nanohybrid architectures is a common strategy to fabricate novel platforms with improved chemical and physical properties for analyte sensing. In the first section of this review, the main wet chemical reduction approaches for the successful synthesis of functional AgNPs for electrochemical sensing applications are discussed. Then, a brief section on the sensing principles of voltammetric and amperometric sensors is given. The current utilization of silver nanoparticles and silver-based composite nanomaterials for the fabrication of voltammetric and amperometric sensors as novel platforms for the detection of environmental pollutants in water matrices is summarized. Finally, the current challenges and future directions for the nanosilver-based electrochemical sensing of environmental pollutants are outlined.

Solution-Processed Flexible Transparent Electrodes for Printable Electronics

Flexible transparent electrodes (FTEs) have been widely witnessed in various printable electronic devices, especially those involving light. So far, solution processes have demonstrated increasing advantages in preparing FTEs not only in their mild operation conditions and high-throughput but also in the diversity in micropatterning conductive nanomaterials into networks. For the FTEs, both high transparency and high conductivity are desirable, which therefore create requirements for the conductive network by considering the trade-off relationship between the coverage and the micropatterns of the network. In addition, the conductive networks also affect the flexibility of FTEs due to the deformation during bending/stretching. Consequently, solution processes capable of micropatterning conductive nanomaterials including nanoparticles, nanowires/polymers, and graphene/MXene play a crucial role in determining the performance of FTEs. Here, we reviewed recent research progress on solution-processed FTEs, including the solution processes, the solution-processable conductive nanomaterials and the substrates for making FTEs, and applications of FTEs in flexible electronics. Finally, we proposed several perspective outlooks of the FTEs, which aim at not only the enhanced performance but also the performances in extreme conditions and in integration. We believe that the review would offer inspiration for developing functional FTEs.

Droplets Patterning of Structurally Integrated 3D Conductive Networks-Based Flexible Strain Sensors for Healthcare Monitoring

Flexible strain sensors with significant extensibility, stability, and durability are essential for public healthcare due to their ability to monitor vital health signals noninvasively. However, thus far, the conductive networks have been plagued by the inconsistent interface states of the conductive components, which hampered the ultimate sensitivity performance. Here, we demonstrate structurally integrated 3D conductive networks-based flexible strain sensors of hybrid Ag nanorods/nanoparticles(AgNRs/NPs) by combining a droplet-based aerosol jet printing(AJP) process and a feasible transfer process. Structurally integrated 3D conductive networks have been intentionally developed by tweaking droplets deposition behaviors at multi-scale for efficient hybridization and ordered assembly of AgNRs/NPs. The hybrid AgNRs/NPs enhance interfacial conduction and mechanical properties during stretching. In a strain range of 25%, the developed sensor demonstrates an ideal gauge factor of 23.18. When real-time monitoring of finger bending, arm bending, squatting, and vocalization, the fabricated sensors revealed effective responses to human movements. Our findings demonstrate the efficient droplet-based AJP process is particularly capable of developing advanced flexible devices for optoelectronics and wearable electronics applications.

Self-assembly, alignment, and patterning of metal nanowires

Armed with the merits of one-dimensional nanostructures (flexibility, high aspect ratio, and anisotropy) and metals (high conductivity, plasmonic properties, and catalytic activity), metal nanowires (MNWs) have stood out as a new class of nanomaterials in the last two decades. They are envisaged to expedite significantly and even revolutionize a broad spectrum of applications related to display, sensing, energy, plasmonics, photonics, and catalysis. Compared with disordered MNWs, well-organized MNWs would not only enhance the intrinsic physical and chemical properties, but also create new functions and sophisticated architectures of optoelectronic devices. This paper presents a comprehensive review of assembly strategies of MNWs, including self-assembly for specific structures, alignment for anisotropic constructions, and patterning for precise configurations. The technical processes, underlying mechanisms, performance indicators, and representative applications of these strategies are described and discussed to inspire further innovation in assembly techniques and guide the fabrication of optoelectrical devices. Finally, a perspective on the critical challenges and future opportunities of MNW assembly is provided.

Printing nanoparticle-based isotropic/anisotropic networks for directional electrical circuits

With the demand for integrated nanodevices, anisotropic conductive films are one type of interconnection structure for electronic components, which have been widely used for improving the integration of the system in printed circuit boards. This work presents a template-assisted printing strategy for the fabrication of nanoparticle-based networks with multi electrical properties. By manipulating the microfluid behavior under the guidance of the grid-shaped template, the continuity of liquid bridges can be precisely controlled in two directions. The isotropous circuits with crossbar paths, discrete paths as well as unidirectional paths are obtained, which achieve the switching of on/off states in the circuits. This work demonstrates a new type of directional circuits by the template-assisted printing method, which provides an effective fabrication strategy for electrical components and integrated systems.

Cost-Effective Fabrication of Uniformly Aligned Silver Nanowire Microgrid-Based Transparent Electrodes with Higher than 99% Transmittance

Silver nanowire (Ag NW)-based transparent electrodes (TEs) are promising alternatives to indium tin oxide (ITO) for next-generation flexible optoelectronic devices. Although many different constructs of Ag NW networks and post-treatment methods have been developed for TE applications, trade-offs between optical and electrical performance still remain. Herein, aided by electrohydrodynamic (EHD) printing, we present a cost-effective strategy to fabricate aligned Ag NW microgrids in a large area with excellent uniformity, resulting in superior optoelectronic properties. Guided by the percolation theory and simulation, we demonstrated that by confining aligned Ag NWs into a microgrid arrangement, the percolation threshold can be reduced significantly and adequate electrical conducting pathways can be achieved with an optimized combination of sheet resistance and optical transparency, which surpass conventional random Ag NW networks and random aligned Ag NW networks. The resulting TEs exhibit an ultrahigh transmittance of 99.1% at a sheet resistance of 91 Ω sq^-1 with extremely low nanowire usage, an areal mass density of only 8.3 mg m^-2, and uniform spatial distribution. Based on this TE design, we demonstrated transparent heaters exhibiting rapid thermal response and superior uniformity in heat generation. Using UV-curable epoxy, highly flexible Ag NW-embedded TEs were fabricated with superior mechanical stabilities and low surface roughness of 2.6 nm. Bendable organic light-emitting diodes (OLEDs) are directly fabricated on these flexible Ag NW electrodes, with higher current efficiency (27.7 cd A^-1) than ITO devices (24.8 cd A^-1).

Self-Assembly of Nanowires: From Dynamic Monitoring to Precision Control

ConspectusNatural biomaterials often show ordered nanowire structures (ONWS) which display unique structural color or superior mechanical performance. Meanwhile, plenty of modern nanodevices with ONWS have flourished with activities focused on both basic and applied research. Manipulating synthetic nanowire (NW) from a disordered state to a hierarchically ordered structure via various assembly strategies brings about intriguing and exotic chemical/physical properties. In the past decades, many methods have been developed to assemble NWs and fabricate organized architectures, such as Langmuir-Blodgett interfacial assembly, spin-coating assembly, fluid-flow-induced assembly, and ice-template assembly. Nevertheless, for practical applications, large-scale and high-efficiency assembly strategies toward precise controlled architectures are largely limited by the lack understanding of assembly mechanisms. Especially, the manipulation principles and driving forces behind the state-of-art assembly strategies are still unclear. Besides, the lesser research attention on dynamic kinetics also impedes the revelation of the NW self-assembly mechanism. With the emergence of advanced in situ techniques, such as synchrotron-based X-ray techniques and in situ transmission electron microscopy (TEM), the dynamic monitoring of NW behavior in many practical environments becomes possible. In addition, the alignment direction and the stacking manner of NW film are of significance to the final performance. There is a lack of connection between the properties of one-dimensional nanoscale building blocks and the functionalities of the macro-assembly structures. To this end, dynamic monitoring is highly desired, which enables the precision modulation of NW assembly structure, leading to the discovery or prediction of new structures, novel properties, and performance optimization.In this Account, we aim to uncover the underlying kinetics of NW assembly or local reaction and mass transportation processes, as well as to build a solid connection from individual NWs to NW assembly structures with enhanced properties and eventually to macroscopic materials application. We first review the recent progress in state-of-art NW assembly strategies for diverse aligned structures according to the manipulation principle and the driving forces. To systematically review the NW self-assembly strategies, we categorize these strategies into three states: NWs on the liquid interface via surface tension, NW assembly in liquid via solution-shearing flow field, and NW assembly at the solid interval via physical repulsive force. Then, we introduce the existing advanced characterization techniques, including synchrotron-based X-ray scattering and in situ TEM, to dynamically monitor the intermediate states of the NW assembly and transport processes. The comprehensive understanding of this thermodynamic and kinetic mechanism facilitates the rational design, large scale, and high-efficiency fabrication of NW assemblies, thus promoting their applications in tailored optical-electrical electronics, smart electrochromic devices, electrocatalysis, structural materials, and chiral photonic crystals.

Meniscus-Assisted Coating with Optimized Active-Layer Morphology toward Highly Efficient All-Polymer Solar Cells

Morphology control is the key to engineering highly efficient solution-processed solar cells. Focusing on the most promising application-oriented photovoltaic all-polymer solar cells (all-PSCs), herein a facile and effective meniscus-assisted-coating (MAC) strategy is reported for preparing high-quality blend films with enhanced crystallinity and an interpenetrating nanofiber network morphology. The all-PSCs based on MAC exhibit excellent optoelectronic properties with efficiencies exceeding 15%, which is the best performance of solution-printing-based all-PSCs, as well as better stability. The crystallization kinetics of the polymer blend film is investigated by in situ UV-vis absorption spectroscopy, and the result explains the linear relationship between the meniscus advance speed and the crystallinity (crystallization rate) of the polymer. To verify the compatibility and universality of this strategy, the MAC strategy is applied to the other three binary systems. By precisely controlling the meniscus advancing speed, 1 cm² all-PSC devices whose efficiencies exceed 12% are fabricated. Such progress demonstrates that the application of the MAC strategy is a promising approach for the fabrication of high-efficiency all-PSCs.

Alignment of organic conjugated molecules for high-performance device applications

High-performance organic semiconductor materials as the electroactive components of optoelectronic devices have attracted much attention and made them ideal candidates for solution-processable, large-area, and low-cost flexible electronics. Especially, organic field-effect transistors (OFETs) based on conjugated semiconductor materials have experienced stunning progress in device performance. To make these materials economically viable, comprehensive knowledge of charge transport mechanisms is required. The alignment of organic conjugated molecules in the active layer is vital to charge transport properties of devices. The present review highlights the recent progress of processing-structure-transport correlations that allow the precise and uniform alignment of organic conjugated molecules over large areas for multiple electronic applications, including OFETs, organic thermoelectric devices (OTEs), and organic phototransistors (OPTs). Different strategies for regulating crystallinity and macroscopic orientation of conjugated molecules are introduced to correlate the molecular packing, the device performance and charge transport anisotropy in multiple organic electronic devices. This article is protected by copyright. All rights reserved.

Microscale Curling and Alignment of Ti3C2T x MXene by Confining Aerosol Droplets for Planar Micro-Supercapacitors

Additive manufacturing techniques have revolutionized the field of fabricating micro-supercapacitors (MSCs) with a high degree of pattern and geometry flexibility. However, traditional additive manufacturing processes are based on the functionality of microstructural modulation, which is essential for device performance. Herein, Ti₃C₂T _x MXene was chosen to report a convenient aerosol jet printing (AJP) process for the in situ curling and alignment of MXene nanosheets. The aerosol droplet provides a microscale regime for curling MXene monolayers while their alignment is performed by the as-generated directional stress derived from the quasi-conical fiber array (CFA)-guided parallel droplet flow. Interdigital microelectrodes were further developed with the curled MXene and a satisfying areal capacitance performance has been demonstrated. Importantly, the AJP technique holds promise for revolutionizing additive manufacturing techniques for fabricating future smart microelectronics and devices not only in the microscale but also in the nanoscale.

Direct Printed Silver Nanowire Strain Sensor for Early Extravasation Detection

In this study, we presented a wearable sensor patch for the early detection of extravasation by using a simple, direct printing process. Silver nanowire (AgNW) ink was first formulated to provide necessary rheological properties to print patterns on flexible plastic sheets. By adjusting printing parameters, alignments of AgNWs in the printed patterns were controlled to enhance the resistance change under stretching conditions. A resistive strain-sensing device was then fabricated by printing patterned electrodes on a stretchable film for skin attachment. The designed sensor pattern was able to detect forces from a specific direction from the resistance change. Moreover, the sensor showed excellent sensitivity (gauge factor (GF) = 100 at 50% strain) and could be printed in small dimensions. Sensors of millimeter size were printed in an array and were used for multiple detection points in a large area to detect extravasation at small volumes (<0.5 mL) at accurate bump location.

Recent progress in post treatment of silver nanowire electrodes for optoelectronic device applications

Owing to the economical and practical solution synthesis and coating strategies, silver nanowires (AgNWs) have been considered as one of the most suitable alternative materials to replace commercial indium tin oxide (ITO) transparent electrodes. The primitive AgNW electrode cannot meet the requirements for preparing high performance optoelectronic devices due to its high contact resistance, large surface roughness and poor stability. Thus, various post-treatments for AgNW film optimization are needed before its actual applications, such as welding treatment to decrease contact resistance and passivation to increase film stability. This review investigates recent progress on the preparation and optimization of AgNWs. Moreover, some unique fabrication strategies to produce highly oriented AgNW films with unique anisotropic properties have also been carried out with detailed analysis. The representative devices based on the AgNW electrode have been summarized and discussed at the end of this review.

Molecular Dynamics of Janus Nanodimers Dispersed in Lamellar Phases of a Block Copolymer

We investigate structural and dynamical properties of Janus nanodimers (NDs) dispersed in lamellar phases of a diblock copolymer. By performing molecular dynamics simulations, we show that an accurate tuning of the interactions between NDs and copolymer blocks can lead to a close control of NDs' space distribution and orientation. In particular, NDs are preferentially found within the lamellae if enthalpy-driven forces offset their entropic counterpart. By contrast, when enthalpy-driven forces are not significant, the distribution of NDs, preferentially observed within the inter-lamellar spacing, is mostly driven by excluded-volume effects. Not only does the degree of affinity between host and guest species drive the NDs' distribution in the polymer matrix, but it also determines their space orientation. In turn, these key structural properties influence the long-time dynamics and the ability of NDs to diffuse through the polymer matrix.

Mechanical design of brush coating technology for the alignment of one-dimension nanomaterials

Widespread approaches to fabricate surfaces with aligned nanostructured topographies have been stimulated by opportunities to enhance interface performance by combing physical and chemical effects, in which brush-coating technology (BCT) is a cost-effective and feasible method for aligned film and large-scale production. Here, we reported a BCT process to realize the alignment of various 1D nanostructures through mechanical design that provides a more precise and higher shear force. By regulating the viscosity of dispersion, shear force is proved to be 24 and 20.3 times larger (when the volume ratio of water and glycerol is 1:3) according to the theoretical calculation and ANSYS simulating calculation results respectively, which plays a vital role in brush coating process. The universality was demonstrated by the alignment of one-dimension nanomaterials with different diameters, including silver nanowires (~80 nm), molybdenum trioxide nanobelts (~150 nm), vanadium pentoxide nanobelts (~150 nm) and bismuth sulfide nanobelts (~200 nm), et al., which in consequence have different alignment ratios. Meanwhile, anisotropic and flexible electrical conductors (the resistance anisotropic ratio was 2) and thermoelectric films (Seebeck coefficient was calculated to be 56.7 µV/K) were demonstrated.

Microscopic Deformation Modes and Impact of Network Anisotropy on the Mechanical and Electrical Performance of Five-fold Twinned Silver Nanowire Electrodes

Silver nanowire (AgNW) networks show excellent optical, electrical, and mechanical properties, which make them ideal candidates for transparent electrodes in flexible and stretchable devices. Various coating strategies and testing setups have been developed to further improve their stretchability and to evaluate their performance. Still, a comprehensive microscopic understanding of the relationship between mechanical and electrical failure is missing. In this work, the fundamental deformation modes of five-fold twinned AgNWs in anisotropic networks are studied by large-scale SEM straining tests that are directly correlated with corresponding changes in the resistance. A pronounced effect of the network anisotropy on the electrical performance is observed, which manifests itself in a one order of magnitude lower increase in resistance for networks strained perpendicular to the preferred wire orientation. Using a scale-bridging microscopy approach spanning from NW networks to single NWs to atomic-scale defects, we were able to identify three fundamental deformation modes of NWs, which together can explain this behavior: (i) correlated tensile fracture of NWs, (ii) kink formation due to compression of NWs in transverse direction, and (iii) NW bending caused by the interaction of NWs in the strained network. A key observation is the extreme deformability of AgNWs in compression. Considering HRTEM and MD simulations, this behavior can be attributed to specific defect processes in the five-fold twinned NW structure leading to the formation of NW kinks with grain boundaries combined with V-shaped surface reconstructions, both counteracting NW fracture. The detailed insights from this microscopic study can further improve fabrication and design strategies for transparent NW network electrodes.

Direct Writing Large-Area Multi-Layer Ultrasmooth Films by an All-Solution Process: Toward High-Performance QLEDs

With increasing the film area/layer, deteriorating in both smoothness and uniformity of thin-films frequently happen, which remains a barrier for making large-area quantum dot light-emitting diodes (QLEDs) by solution processes. Here, we demonstrated a facile all-solution process guided by the conical fiber array to write multi-layer ultrasmooth thin-films directly in centimeter scale. The side-by-side fibrous array helps to align surface tensions at the tri-phase contact line to facilitate large-area homogeneous deposition, which was verified by theoretical simulation. The Laplace pressure along individual conical fiber contributes to the steady liquid transfer. Thin-films with small roughness (<2.03 nm) and large-area (2×2 cm² ) uniformity were prepared sequentially on the target substrate, leading to large-area high-performance QLEDs. The result offers new insights for fabricating large-area high-performance thin-film devices.

Reversible Structure Engineering of Bioinspired Anisotropic Surface for Droplet Recognition and Transportation

Surfaces with tunable liquid adhesion have aroused great attention in past years. However, it remains challenging to endow a surface with the capability of droplet recognition and transportation. Here, a bioinspired surface, termed as TMAS, is presented that is inspired by isotropic lotus leaves and anisotropic butterfly wings. The surface is prepared by simply growing a triangular micropillar array on the pre-stretched thin poly(dimethylsiloxane) (PDMS) film. The regulation of mechanical stress in the PDMS film allows the fine tuning of structural parameters of the micropillar array reversibly, which results in the instantaneous, in situ switching between isotropic and various degrees of anisotropic droplet adhesions, and between strong adhesion and directional sliding of water droplets. TMAS can thus be used for robust droplet transportation and recognition of acids, bases, and their pH strengths. The results here could inspire the design of robust sensor techniques.

Langmuir-Scheaffer Technique as a Method for Controlled Alignment of 1D Materials

A widely applicable method for aligning 1D materials, and in particular carbon nanotubes (CNTs), independent of their preparation would be very useful as the growth methods for these materials are substance-specific. Langmuir-Schaefer (LS) deposition could be such an approach for alignment, as it aligns a large number of 1D materials independently of the desired substrate. However, the mechanism and required conditions for alignment of 1D nanomaterials in a Langmuir trough are still unclear. Here we show, relying on numerical simulations of the Langmuir film compression, that the LS method is a powerful tool to achieve maximal alignment of 1D material in a controllable manner. In particular, 1D materials terminated with a suitable surfactant can align only if the velocity induced by the attraction between individual 1D entities is low enough relative to the flow speed. To validate this model, we achieved an efficient LS alignment of single-walled carbon nanotubes covered with a suitable surfactant relying on the numerical simulations. In situ polarized Raman microspectroscopy during the compression of Langmuir film revealed good quantitative agreement between the numerical simulations and the experiment. This suggests the applicability of the LS technique as a versatile method for the controlled alignment of 1D materials.

Highly conductive and transparent coatings from flow-aligned silver nanowires with large electrical and optical anisotropy

Conductive and transparent coatings consisting of silver nanowires (AgNWs) are promising candidates for emerging flexible electronics applications. Coatings of aligned AgNWs offer unusual electronic and optical anisotropies, with potential for use in micro-circuits, antennas, and polarization sensors. Here we explore a microfluidics setup and flow-induced alignment mechanisms to create centimeter-scale highly conductive coatings of aligned AgNWs with order parameters reaching 0.84, leading to large electrical and optical anisotropies. By varying flow rates, we establish the relationship between the shear rate and the alignment and investigate possible alignment mechanisms. The angle-dependent sheet resistance of the aligned AgNW networks exhibits an electronic transport anisotropy of ∼10× while maintaining low resistivity (<50 Ω sq^-1) in all directions. When illuminated, the aligned AgNW coatings exhibit angle- and polarization-dependent colors, and the polarized reflection anisotropy can be as large as 25. This large optical anisotropy is due to a combination of alignment, polarization response, and angle-dependent scattering of the aligned AgNWs.

Millimeters long super flexible Mn5Si3@SiO2 electrical nanocables applicable in harsh environments

Providing high performance electrical nano-interconnects for micro-nano electronics that are robust in harsh environments is highly demanded. Today, electrical nano-interconnects based on metallic nanowires, e.g. Ag and Cu, are limited by their positive physicochemical reactivity and ductility under large strain (i.e. irreversible dislocations and local necking-down elongation) at high temperatures or in strong oxidizing and acidic environments. Herein, to overcome these limitations, high-quality millimetre-sized soft manganese-based silicide (Mn₅Si₃@SiO₂) nanowire nanocables are designed via a glassy Si–Mn–O matrix assisted growth. The proposed nanocables exhibit good electrical performance (resistivity of 1.28 to 3.84×10^-6 Ωm and maximum current density 1.22 to 3.54×10⁷ A cm⁻²) at temperatures higher than 317°C in air atmosphere, strongly acidic (HCl, PH=1.0) and oxidizing (H₂O₂, 10%) ambient, and under complex electric field. The proposed Mn₅Si₃@SiO₂ nanocables, which withstand a strain of 16.7% free of failure, could be exploited for diverse applications in flexible electronics and complex wiring configurations.

Though high performance electrical interconnects are required for micro/nano electronics, existing metallic nanowires lack structural and electrical stability. Here, the authors report soft manganese-based silicide nanowires with high electrical and structural performance in harsh environments.

In-plane aligned assemblies of 1D-nanoobjects: recent approaches and applications

One-dimensional (1D) nanoobjects have strongly anisotropic physical properties which are averaged out and cannot be exploited in disordered systems. We reviewed the in plane alignment approaches and potential applications with perspectives shared.

Intrinsically Stretchable and Shape Memory Conducting Nanofiber for Programmable Flexible Electronic Films

Recently, flexible and stretchable electronic films have been drawing increasing attention but are limited by the nature of elastomeric materials and the embedded structure; thus, these films cannot achieve long-term and stable electrical performance at certain deformation states in practical applications. Here, we report intrinsically stretchable and shape memory polycaprolactone/polyethylene glycol/silver nanowires films (PPAFs) based on a dual-layer network structure of nanofibers that can achieve both shape-fixable and deformation-reversible conductivity in the elongation range. We also demonstrate the resistance characteristic of PPAFs at the same/different deformation rates, which shows the unique memorable resistance and the variable conversion of a "conductive-insulation-conductive" state. Importantly, the change in sheet resistance of the PPAFs fixed at any rate of deformation could sustainably recover the initial sheet resistance even after cyclic thermal responses. Furthermore, we successfully develop the programmable conductivity of PPAFs as a monitoring, switching, and alarming device for shape memory cycles through the ingenious design of a microcircuit and simulation analysis using Proteus software. PPAFs show great potential for changeable characteristics in both shape and resistance for use in flexible electronic films.

Self-assembled structures of halloysite nanotubes: towards the development of high-performance biomedical materials

Halloysite nanotubes (HNTs), 1D natural tubular nanoparticles, exhibit a high aspect ratio, empty lumen, high adsorption ability, good biocompatibility, and high biosafety, which have attracted researchers' attention in applications of the biomedical area. HNTs can be readily dispersed in water due to their negatively charged surface and good hydrophilicity. The unique rod-like structure and surface properties give HNTs assembly ability into ordered hierarchical structures. In this review, the self-assembly approaches of HNTs including evaporation induced self-assembly by a "coffee-ring" mechanism, shear force induced self-assembly, and electric field force induced self-assembly were introduced. In addition, HNT self-assembly on polymeric substrates and biological substrates including hair, cells, and zebrafish embryos was discussed. These assembly processes are related to noncovalent interactions such as electrostatic, hydrogen bonding, and van der Waals forces or electron-transfer reactions. Moreover, the applications of self-assembled HNT patterns in biomedical areas such as capture of circulating tumor cells, guiding oriented cell growth, controlling cell germination, and delivery of drugs or nutrients were discussed and highlighted. Finally, challenges and future directions of assembly of HNTs were introduced. This review will inspire researchers in the design and fabrication of functional biodevices based on HNTs for tissue engineering, cancer diagnosis/therapy, and personal healthcare products.

Skin-Friendly Electronics for Acquiring Human Physiological Signatures

Epidermal sensing devices offer great potential for real-time health and fitness monitoring via continuous characterization of the skin for vital morphological, physiological, and metabolic parameters. However, peeling them off can be difficult and sometimes painful especially when these skin-mounted devices are applied on sensitive or wounded regions of skin due to their strong adhesion. A set of biocompatible and water-decomposable "skin-friendly" epidermal electronic devices fabricated on flexible, stretchable, and degradable protein-based substrates are reported. Strong adhesion and easy detachment are achieved concurrently through an environmentally benign, plasticized protein platform offering engineered mechanical properties and water-triggered, on-demand decomposition lifetime (transiency). Human experiments show that multidimensional physiological signals can be measured using these innovative epidermal devices consisting of electro- and biochemical sensing modules and analyzed for important physiological signatures using an artificial neural network. The advances provide unique, versatile capabilities and broader applications for user- and environmentally friendly epidermal devices.

Continuous and Controllable Liquid Transfer Guided by a Fibrous Liquid Bridge: Toward High-Performance QLEDs

Solution processing is widely used for preparing quantum dot (QD) films for fabricating QD light-emitting diode display (QLED) devices. However, current approaches suffer from either the coffee-ring effect or a large amount of wasted solution, leading to low performance and high cost. Here, a facile approach guided by a fibrous liquid bridge is developed for the continuous and controllable transfer of QD solution into ultrasmooth films by using a taut fiber with its two ends placed into capillary tubes. Guided along the fiber, a liquid bridge is formed between the horizontal fiber and the substrate, with a large mass of liquid steadily being held within the vertically placed tubes. Directionally moving the liquid bridge generates a high-quality QD film on the substrate. Particularly, the liquid consumption is quantitative, namely, in proportion to the area of the as-prepared film. Moreover, multilayered ultrasmooth red/green/blue QD films are prepared by multiple transfers of liquid onto the same targeted area in sequence. The as-prepared white QLEDs show a rather high performance with a maximum luminance of 57 190 cd m^-2 and a maximum current efficiency of 15.868 cd A^-1 . It is envisioned that this strategy offers new perspectives for the low-cost fabrication of high-performance QLED devices.

Fine printing method of silver nanowire electrodes with alignment and accumulation

One-dimensional metal nanowires offer great potential in printing transparent electrodes for next-generation optoelectronic devices such as flexible displays and flexible solar cells. Printing fine patterns of metal nanowires with widths <100 μm is critical for their practical use in the devices. However, the fine printing of metal nanowires onto polymer substrates remains a major challenge owing to their unintended alignment. This paper reports on a fine-printing method for transparent silver nanowires (AgNWs) electrodes miniaturized to a width of 50 μm on ultrathin (1 μm) polymer substrate, giving a high yield of >90%. In this method, the AgNW dispersion, which is swept by a glass rod, is spontaneously deposited to the hydrophilic areas patterned on a hydrophobic-coated substrate. The alignment and accumulation of AgNWs at the pattern periphery are enhanced by employing a high sweeping rate of >3.2 mm s^-1, improving electrical conductivity and pattern definition. The more aligned and more accumulated AgNWs lower the sheet resistance by a factor of up to 6.8. In addition, a high pattern accuracy ≤ 3.6 μm, which is the deviation from the pattern designs, is achieved. Quantitative analyses are implemented on the nanowire alignment to understand the nanowire geometry. This fine-printing method of the AgNW electrodes will provide great opportunities for realizing flexible and high-performance optoelectronic devices.

A Facile One-Step Approach for Constructing Multidimensional Ordered Nanowire Micropatterns via Fibrous Elastocapillary Coalescence

Nanowire (NW) based micropatterns have attracted research interests for their applications in electric microdevices. Particularly, aligning NWs represents an important process due to the as-generated integrated physicochemical advantages. Here, a facile and general strategy is developed to align NWs using fibrous elastocapillary coalescence of carbon nanotube arrays (ACNTs), which enables constructing multidimensional ordered NW micropatterns in one step without any external energy input. It is proposed that the liquid film of NW solution is capable of shrinking unidirectionally on the top of ACNTs, driven by the dewetting-induced elastocapillary coalescence of the ACNTs. Consequently, the randomly distributed NWs individually rotate and move into dense alignment. Meanwhile, the aggregating and bundling of ACNTs is helpful to produce carbon nanotube (CNT) yarns connecting neighboring bundles. Thus, a micropatterned NW network composed of a top-layer of horizontally aligned NWs and an under-layer of vertical ACNT bundles connected by CNT yarns is prepared, showing excellent performance in sensing external pressure with a sensitivity of 0.32 kPa^-1 . Moreover, the aligned NWs can be transferred onto various substrates for constructing electronic circuits. The strategy is applicable for aligning various NWs of Ag, ZnO, Al₂ O₃ , and even living microbes. The result may offer new inspiration for fabricating NW-based functional micropatterns.

High-Resolution and Large-Area Patterning of Highly Conductive Silver Nanowire Electrodes by Reverse Offset Printing and Intense Pulsed Light Irradiation

Conventional printing technologies such as inkjet, screen, and gravure printing have been used to fabricate patterns of silver nanowire (AgNW) transparent conducting electrodes (TCEs) for a variety of electronic devices. However, they have critical limitations in achieving micrometer-scale fine line width, uniform thickness, sharp line edge, and pattering of various shapes. Moreover, the optical and electrical properties of printed AgNW patterns do not satisfy the performance required by flexible integrated electronic devices. Here, we report a high-resolution and large-area patterning of highly conductive AgNW TCEs by reverse offset printing and intense pulsed light (IPL) irradiation for flexible integrated electronic devices. A conductive AgNW ink for reverse offset printing is prepared by carefully adjusting the composition of AgNW content, solvents, surface energy modifiers, and organic binders for the first time. High-quality and high-resolution AgNW micropatterns with various shapes and line widths are successfully achieved on a large-area plastic substrate (120 × 100 mm²) by optimizing the process parameters of reverse offset printing. The reverse offset printed AgNW micropatterns exhibit superior fine line widths (up to 6 μm) and excellent pattern quality such as sharp line edge, fine line spacing, effective wire junction connection, and smooth film roughness. They are post-processed with IPL irradiation, thereby realizing excellent optical, electrical, and mechanical properties. Furthermore, flexible OLEDs and heaters based on reverse offset printed AgNW micropatterns are successfully fabricated and characterized, demonstrating the potential use of the reverse offset printing for the conductive AgNW ink.

Conductive Polymer Hydrogel Microfibers from Multiflow Microfluidics

Conductive hydrogels are receiving increasing attention for their utility in electronic area applications requiring flexible conductors. Here, it is presented novel conductive hydrogel microfibers with alginate shells and poly (3, 4-ethylenedioxythiophene): poly (4-styrenesulfonate) (PEDOT: PSS) cores fabricated using a multiflow capillary microfluidic spinning approach. Based on multiflow microfluidics, alginate shells are formed immediately from the fast gelation reaction between sodium alginate (Na-Alg) and sheath laminar calcium chloride flows, while PEDOT: PSS cores are solidified slowly in the hollow alginate hydrogel shell microreactors after their precursor solutions are injected in situ as the center fluids. The resultant PEDOT: PSS-containing microfibers are with features of designed morphology and highly controllable package, because material compositions or the sizes of their shell hydrogels can be tailored by using different concentrations or flow rates of pregel solutions. Moreover, the practical values of these microfibers in stretch sensitivity and bending stability are explored based on various electrical characterizations of the compound materials. Thus, it is believed that these microfluidic spinning PEDOT: PSS conductive microfibers will find important utility in electronic applications requiring flexible electronic systems.

Biological and Engineered Topological Droplet Rectifiers

The power of the directional and spontaneous transport of liquid droplets is revealed through ubiquitous biological processes and numerous practical applications, where droplets are rectified to achieve preferential functions. Despite extensive progress, the fundamental understanding and the ability to exploit new strategies to rectify droplet transport remain elusive. Here, the latest progress in the fundamental understanding as well as the development of engineered droplet rectifiers that impart superior performance in a wide variety of working conditions, ranging from low temperature, ambient temperature, to high temperature, is discussed. For the first time, a phase diagram is formulated that naturally connects the droplet dynamics, including droplet formation modes, length scales, and phase states, with environmental conditions. Parallel approaches are then taken to discuss the basic physical mechanisms underlying biological droplet rectifiers, and a variety of strategies and manufacturing routes for the development of robust artificial droplet rectifiers. Finally, perspectives on how to create novel man-made rectifiers with functionalities beyond natural counterparts are presented.

Water super-repellent behavior of semicircular micro/nanostructured surfaces

In this article, we report the construction of semicircular micro/nanostructured surfaces. Based on thermodynamic analysis, free energy (FE) and free energy barrier (FEB) as well as equilibrium contact angle (ECA) and contact angle hysteresis (CAH) for four exact wetting states of semicircular micro/nanostructured surfaces are theoretically discussed in detail. Notably, the wetting behavior is closely related to the exact wetting state and the base radius or space of semicircular micro/nanostructure. Furthermore, it is demonstrated that the stable wetting state of the semicircular micro/nanostructured surfaces depends on the microscale and nanoscale ratio of base space and radius. A suitable semicircular micro/nanostructure of the surface may lead to a droplet in the stable Cassie-Cassie (Cc) state. Moreover, an important role of the nanoscale semicircular surfaces in determining water super-repellence is effective in decreasing or increasing the ratio of microscale base space and radius for the Cassie or Wenzel state. Additionally, wetting behaviour of single semicircular micro- and nano-structured surfaces are comparatively investigated. The FE and ECA of micro/nanostructured surfaces are lower or higher than those of the single microstructured surfaces. However, the effects of nanoscale semicircular surfaces on the FEB and CAH mainly rely on the microscale wetting state. Finally, the related experimental results were used to verify our investigation. These results are in good agreement with the experiment, which are helpful in designing the wetting behavior of hierarchical semicircular micro/nano-structured surface.

Aligning One-Dimensional Nanomaterials by Solution Processes

One-dimensional nanomaterials, including both nanowires (NWs) and nanotubes (NTs), have been extensively investigated in the decades because of their unique physicochemical properties. Particularly, aligning NWs/NTs into a network or complex micropatterns has been a key issue for its unique integrated functionalities, which enjoy benefits in versatile applications. So far, solution processes remain the most effective strategy to align NWs/NTs, which also bear advantages of mild operation condition and large-scale production. In this perspective, particular attention is drawn to the currently widely used solution coating approaches for aligning NWs/NTs, including the Langmuir-Blodgett film technique, solution shearing approaches, and methods of tri-phase contact line manipulation. We also proposed several perspectives in this field.

High pairing rate Janus-structured microfibers and array: high-efficiency conjugate electrospinning fabrication, structure analysis and co-instantaneous multifunctionality of anisotropic conduction, magnetism and enhanced red fluorescence

A highly efficient and convenient conjugate electrospinning technique is employed to obtain high pairing rate Janus-structured microfibers in electrospun products by optimizing the spinning conditions. In addition, a Janus-structured microfiber array rendering tri-functional performance of tunable magnetism, electrically anisotropic conduction and increased fluorescence is prepared via the same technique using a rotating device as a fiber collector. The array is composed of an ordered arrangement of Janus-structured microfibers. The extraordinary Janus structure and oriented arrangement endow the Janus-structured microfibers with excellent fluorescence. The fluorescence intensity of the Janus-structured microfiber array is, respectively, 1.21, 14.3 and 20.3 times higher than that of the Janus-structured microfiber non-array, the composite microfiber array and the composite microfiber non-array. The Janus-structured microfiber array has a similar saturation magnetization to the contradistinctive specimens. Additionally, the magnetism of the Janus-structured microfiber array can be modulated with different mass ratios of Fe₃O₄ nanoparticles (NPs), and the conductance ratio between the length direction and diameter direction of the Janus-structured microfibers for the array can be tuned from 10³ to 10⁶ by adding a higher percentage of polyaniline (PANI). Our new findings have established a highly efficient conjugate electrospinning technique to prepare Janus-structured microfibers of high pairing rate, and complete isolation of fluorescent material from magnetic nanoparticles and conductive material is accomplished in the Janus-structured microfibers to ensure high fluorescence intensity without a notably disadvantageous influence of dark-colored substances. More importantly, the fabrication technique for the Janus-structured microfibers can be generalized to manufacture other Janus-structured multifunctional materials.

High pairing rate Janus-structured microfibers and their arrays, rendering simultaneous anisotropic conduction, magnetism and fluorescence, are successfully fabricated via conjugate electrospinning.

In Situ Characterization of the Triphase Contact Line in a Brush-Coating Process: Toward the Enhanced Efficiency of Polymer Solar Cells

Solution processes have been widely used for making polymer films in organic photoelectric devices but suffer from difficulties in controlling the film formation. Here, by in situ characterization triphase contact lines (TCLs) in a brush-coating process, we clarify how TCLs affect the quality of as-prepared films. By fine-tuning the dewetting of a binary polymer solution (P3HT:PCBM) via different directions, TCLs with different patterns lead to films with different morphologies. High-quality nanothin films with larger crystallized sizes and higher orientations were enabled when TCLs were parallel to the brush edge, based on which the polymer solar cell shows higher power conversion efficiency (2.665%) compared with that of the spin-coated film.

Self-Adapting Wettability of ReS2 under a Constant Stimulus

Responsive materials (RMs) are attracting intense interest for their critical roles in intelligent designs. So far, only by means of applying complicated and multiple stimuli can physical properties of the solid surface realize a transition, limiting their practical applications. Here, the smart self-adapting wettability (SAW) of ReS₂ under sustaining light irradiation, which breaks the stereotype that a single stimulus leads to a monotonic change in properties or structures, is presented. The additional valence electron and defects ensure ReS₂ has a stronger gas adsorption and better hydrolysis capability. Combining theoretical calculations and experimental results, its mechanism, including three stages, namely, hydroxyl substitution, formation of hydrogen bonds, and water desorption, is confirmed. Notably, other transition metal dichalcogenides covering MoS₂ and WS₂ exhibit a similar automatic transition of hydrophobic-hydrophilic-hydrophobic state. This unique SAW provides a brand-new insight to broaden the applications of RMs, which will undoubtedly pave a novel way in RMs design and further devices optimization.

Biocompatible Meshes with Appropriate Wettabilities for Underwater Oil Transportation/Collection and Highly Effective Oil/Water Separation

In this study, we prepared biocompatible superhydrophilic and underwater superoleophobic tannic acid (TA)/polyvinylpyrrolidone (PVP)-coated stainless-steel meshes that mediated extremely efficient separations of mixtures of oil and water. These TA/PVP-coated stainless-steel meshes displayed excellent antifouling properties and could be used to separate oil/water mixtures continuously for up to 24 h. Moreover, a funnel-like TA/PVP-coated stainless-steel mesh device could be used for underwater oil transportation and collection. In conjunction with our continuous oil removal system, this device allowed for the continuous collection and removal of oil pollutants from underwater environments. The high performance of these TA/PVP-coated stainless-steel meshes and their green, low-energy, cost-effective preparation suggests great potential for practical applications.

Bioinspired Controllable Liquid Manipulation by Fibrous Array Driven by Elasticity

Fibers exhibit excellent performance in liquid manipulation that is normally aroused by either the structural or the chemical gradient. Here, we developed radially arranged fiber arrays with different fibrous elasticities that exhibited distinctly different performances in liquid manipulation in terms of the fibrous elastocapillary coalescence, the high-efficiency water encapsulation, and the inability to manipulate liquid. It is proposed that the fiber elasticity acts as a driving force when interacting with liquid, equivalent with the structural and chemical gradient. We revealed the fundamental premise of how fiber elasticity affects its dynamic wetting behaviors, which sheds new light on the design of fiber systems with different liquid-manipulation abilities.

Biomimetic twisted plywood structural materials

Biomimetic designs based on micro/nanoscale manipulation and scalable fabrication are expected to develop new-style strong, tough structural materials. Although the mimicking of nacre-like ‘brick-and-mortar’ structure is well studied, many highly ordered natural architectures comprising 1D micro/nanoscale building blocks still elude imitation owing to the scarcity of efficient manipulation techniques for micro/nanostructural control in practical bulk counterparts. Herein, inspired by natural twisted plywood structures with fascinating damage tolerance, biomimetic bulk materials that closely resemble natural hierarchical structures and toughening mechanisms are successfully fabricated through a programmed and scalable bottom-up assembly strategy. By accurately engineering the arrangement of 1D mineral micro/nanofibers in biopolymer matrix on the multiscale, the resultant composites display optimal mechanical performance, superior to many natural, biomimetic and engineering materials. The design strategy allows for precise micro/nanostructural control at the macroscopic 3D level and can be easily extended to other materials systems, opening up an avenue for many more micro/nanofiber-based biomimetic designs.