Flexible polydimethylsiloxane pressure sensor with micro-pyramid structures and embedded silver nanowires:A novel application in urinary flow measurement

Flexible pressure sensors are lightweight and highly sensitive,making them suitable for use in small portable devices to achieve precise measurements of tiny forces.This article introduces a low-cost and easy-fabrication strategy for piezoresistive flexible pressure sensors.By embedding silver nanowires into a polydimethylsiloxane layer with micro-pyramids on its surface,a flexible pressure sensor is created that can detect low pressure (17.3 Pa) with fast response (<20 ms) and high sensitivity (69.6 mA kPa-1).Furthermore,the pressure sensor exhibits a sensitive and stable response to a small amount of water flowing on its surface.On this basis,the flexible pressure sensor is innovatively combined with a micro-rotor to fabricate a novel urinary flow-rate meter (uroflowmeter),and results from a simulated human urination experiment show that the uroflowmeter accurately captured all the essential shape characteristics that were present in the pump-simulated urination curves.Looking ahead,this research provides a new reference for using flexible pressure sensors in urinary flow-rate monitoring.

Precise assembly and joining of silver nanowires in three dimensions for highly conductive composite structures

Three-dimensional(3D)electrically conductive micro/nanostructures are now a key component in a broad range of research and industry fields.In this work,a novel method is developed to realize metallic 3D micro/nanostructures with silver-thiol-acrylate composites via two-photon polymerization followed by femtosecond laser nanojoining.Complex 3D micro/nanoscale conductive structures have been successfully fabricated with∼200 nm resolution.The loading of silver nanowires(AgNWs)and joining of junctions successfully enhance the electrical conductivity of the composites from insulating to 92.9 Sm^−1 at room temperature.Moreover,for the first time,a reversible switching to a higher conductivity is observed,up to∼10^5Sm^−1 at 523 K.The temperature-dependent conductivity of the composite is analyzed following the variable range hopping and thermal activation models.The nanomaterial assembly and joining method demonstrated in this study pave a way towards a wide range of device applications,including 3D electronics,sensors,memristors,micro/nanoelectromechanical systems,and biomedical devices,etc.

Controlled growth of large＇scale silver nanowires

Large-scale silver nanowires with controlled aspect ratio were synthesized via reducing silver nitrate with 1, 2- propanediol in the presence of poly （vinyl pyrrolidone） （PVP）. Scanning electron microscopy, transmission electron microscopy and x-ray powder diffraction were employed to characterize these silver nanowires. The diameter of the silver nanowires can be readily controlled in the range of 100 to 400 nm by varying the experimental conditions. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results show that there exists no chemical bond between the silver and the nitrogen atoms. The interaction between PVP and silver nanowires is mainly through the oxygen atom in the carbonyl group.

Silver Nanowires Contained Nanofluids with Enhanced Optical Absorption and Thermal Transportation Properties

Two kinds of silver nanowires(100 nm in diameter, 20 μm and 100 μm in length) are prepared. The thermo-physical characteristics, viscosity, and photothermal conversion performance of the silver nanowires(AgNWs)contained ethylene glycol nanofluids are investigated in detail. It is found that thermal conductivity of 100 μm AgNWs contained nanofluids is higher than that of 20 μm AgNWs with the same diameters of 100 nm. Viscosity test shows that the nanofluid is a Newtonian fluid, and the longer silver nanowires, the greater viscosity. In addition, photothermal conversion efficiency of silver nanowires contained nanofluid is studied. We can observe that the 100 μm AgNWs contained nanofluid has a higher photothermal conversion efficiency than that containing 20 μm AgNWs. Moreover, we find that there is a certain correlation between heat transfer and photothermal conversion of nanofluid. It demonstrates that the high heat transfer property of nanofluid will benefit for its photothermal conversion efficiency and the mechanism is proposed. This work provides a new idea to improve photothermal conversion efficiency. We can choose materials with high thermal conductivity and strong light absorption ability to enhance the photothermal conversion performance of nanofluids.

Effect of a Magnetic Field on the Preparation of Silver Nanowires Using Solid Electrolyte Thin Films

The effect of an external magnetic field on the preparation of silver nanowires was studied. The silver nanowires were synthesized using solid electrolyte RbAg4I5 thin films by applying both a direct current （DC） electric field and a magnetic field. The RbAg4I5 thin films, which were prepared by deposition at room temperature and atmospheric pressure on a NaCI substrate, were used for the transfer of Ag^＋ ions between two Ag electrodes during the preparation process. When only the DC electric field is applied, the silver ions migrate toward the cathode. On the edge of the silver film at the cathode the Ag^＋ ions congregate to form aligned nanowires. If the magnetic field is also applied perpendicular to the DC electric field, the morphology of the nanowires can be controlled by rotating the sample in the magnetic field. Experimental results show that the growth of the silver nanowires is determined by the Ag^＋ ionic flux.

Fluxless bonding with silver nanowires aerogel in die-attached interconnection

The electronic product has gravitated towards component miniaturization and integration, employment of lead-free materials, and low-temperature soldering processes. Noble-metal aerogels have drawn increasing attention for high conduction and low density. However,the noble metal aerogels with outstanding solderability were rarely studied. This work has successfully synthesized an aerogel derived from silver nanowires(AgNWs) using a liquid phase reduction method. It is found that the noble metal aerogels can be made into diverse aerogel preformed soldering sheets. The influence of bonding temperature(150-300 ℃), time(2-20 min), and pressure(5-20 MPa) on the joint strength of the AgNWs aerogel affixed to electroless nickel/silver copper plates were investigated. Additionally, the AgNWs aerogel displays almost the same shear strength for substrates of various sizes. In a word, this study presents a flux-free, high-strength, and adaptable soldering structural material.

Fabrication of High-Haze Flexible Transparent Conductive PMMA Films Embedded with Silver Nanowires

High-haze flexible transparent conductive polymethyl methacrylate （PMMA） films embedded with silver nanowires （AgNWs） are fabricated by a low-cost and simple process. The volatilization rate of the solvent in PMMA solution affects the surface microstructures and morphologies, which results in different haze factors of the composite films. The areal mass density of AgNW shows a significant influence on the optical and electrical properties of composite films. The AgNW/PMMA transparent conductive films with the sheet resistance of 5.5Ω sq ^-1 exhibit an excellent performance with a high haze factor of 81.0% at 550？nm.

Efficiency-enhanced AlGaInP light-emitting diodes using transparent plasmonic silver nanowires

Silver nanowire（AgNW） networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide（ITO） and have been proposed to replace ITO, which is currently widely used in optoelectronic devices despite the scarcity of indium on Earth. In this paper, the current spreading and enhanced transmittance induced by AgNWs, which are two important factors influencing the light output power, were analyzed. The enhanced transmittance was studied by finite-difference time-domain simulation and verified by cathodoluminescence measurements.The enhancement ratio of the light output power decreased as the Ga P layer thickness increased, with enhancement ratio values of 79%, 52%, and 15% for Ga P layer thicknesses of 0.5 μm, 1 μm, and 8 μm, respectively, when an AgNW network was included in Al Ga In P light-emitting diodes. This was because of the decreased current distribution tunability of the AgNW network with the increase of the Ga P layer thickness. The large enhancement of the light output power was caused by the AgNWs increasing carrier spread out of the electrode and the enhanced transmittance induced by the plasmonic AgNWs. Further decreasing the sheet resistance of AgNW networks could raise their light output power enhancement ratio.

Stretchable and self-healing conductive fibers from hierarchical silver nanowires-assembled network

Conductive fibers(CFs)with features of high conductivity,stretchability,self-healability,and electromechanical stability are key components of the increasingly popular wearable electronics.However,since the lack of structural design of conductive network and interfacial interaction between soft polymer and conductive additives,it is still hard to enable CFs to meet above requirements.Here,we describe a facial drawing method from a hydrogel reservoir which is remolded into ultrathin and stretchable CFs with excellent multi-responsive self-healability.The hydrogel reservoir was fabricated in synergy of an ice-templating method and in situ polymerization using the assembled framework as a crosslinker.Relying on the effective fabrication mechanism,the diameter of CFs could be well-tuned from 90 to 400μm by adjusting the dipping depth of the glass rod,accompanied with conductivity increased from 0.75 to 2.5 S/m.Since the hierarchical network structure was well maintained in the CFs,professional performances have been proved on the stretchability and electromechanical stability.The presence of massive hydrogen bonding and Ag–S bond enabled the CFs with excellent self-healability under the conditions of contact,electric field,and near infrared light,respectively.Excitingly,the CFs with high sensing property could be integrated into an advanced textile sensor through an effective healing-induced integration strategy,demonstrating its great potentials as superior two-dimensional(2D)electronic skins.

Capturing Plateau-Rayleigh instability in silver nanowires via ultrafast electron microscopy

Understanding the structural stability of nanomaterials such as nanowires is imperative for their practical applications.Here,using single-shot ultrafast transmission electron microscopy,we captured the Plateau-Rayleigh instability behavior of silver nanowires decomposing into silver nanoparticles upon laser irradiation on nanosecond time scales.We found that this dynamic process can be accelerated by a factor of 10 through increasing the peak laser fluence from 6.03 to 14.60 mJ/cm^(2).Moreover,by comparing the laser fluence required to initiate the Plateau-Rayleigh instability in silver nanowires on carbon and Formvar membranes,it was found that the main driving force for the Plateau-Rayleigh instability in this study was substrate heating.Finite element analysis and molecular dynamics simulations are also applied to estimate the temperature jump of the nanowires and atomistic behavior,respectively.In addition,the complex motions of silver nanowires under laser irradiation were systematically investigated by combining the results of ultrafast transmission electron microscopy with scanning electron microscopy characterizations and were determined to be related to nanowire-membrane interactions or pre-existing stresses on the nanowires,which in turn demonstrated the potential of ultrafast transmission electron microscopy for the characterization of nanomaterials and devices under extreme conditions.

Low haze transparent electrodes and highly conducting air dried films with ultra-long silver nanowires synthesized by one-step polyol method

Transparent electrodes made of silver nanowires （AgNWs） exhibit higher flexibility when compared to those made of tin doped indium oxide （ITO） and are expected to be applied in plastic electronics. However, these transparent electrodes composed of AgNWs show high haze because the wires cause strong light scattering in the visible range. Reduction of the wire diameter has been proposed as a way to weaken light scattering, although there have seldom been any studies focusing on the haze because of the difficulty involved in controlling the wire diameter. In this report, we show that the haze can be easily reduced by increasing the length of AgNWs with a large diameter. Ultra-long （u-long） AgNWs with lengths in the range of 20-100 μm and a maximum length of 230 μm have been successfully synthesized by adjusting the reaction temperature and the stirring speed of a one-step polyol process. Compared to typical AgNWs （with diameter and length of 70 nm and 10 μm, respectively） and ITO, a transparent electrode consisting of u-long AgNWs 91 nm in diameter demonstrated a low haze of 3.4%-1.6% and a low sheet resistance of 24-109 Ω/sq. at a transmittance of 94%-97%. Even when fabricated at room temperature without any post-treatment, the electrodes composed of u-long AgNWs achieved a sheet resistance of 19 Ω/sq, at a transmittance of 80%, which is six orders of magnitude lower than that of typical AgNWs.

Highly stretchable polymer/silver nanowires composite sensor for human health monitoring

Flexible strain sensors exhibit outstanding advantages in terms of sensitivity and stability by detecting changes in physical signals.It can be easily attached to human skin and clothed to achieve monitoring of human motion and health.However,general sensing material shows low stretchability and cannot respond to signals under large deformation.In this work,a highly stretchable polymer composite was developed by adding small amount(0.17 wt.%)of silver nanowires(AgNWs)in stretchable conductive polymer materials.The conductivity of polymer/AgNWs composite is 1.3 S/m with the stretchability up to 500%.The stretchable strain sensor based on the polymer/AgNWs composite can respond to strain signals in real time,even for 1%strain response,and shows excellent stability over 1,000 loading/unloading cycles.Moreover,the strain sensor can be attached to human skin and clothed to monitor joints,throat and pulse of the human body.The human body electrocardiogram(ECG)signal was detected successfully with the polymer/AgNWs electrode,which is comparable to the signal obtained by the commercial electrode.Overall,the sensors enable monitoring of human movement and health.These advantages make it a potential application in wearable devices and electronic skin.

Progress in application and preparation of silver nanowires

Silver nanowires have attracted wide research attention for their excellent optical, electrical and chemical properties. Many researches were performed toward syn- thesizing and application of silver nanowires. The appli- cation of silver nanowires such as transparent conductive film electrode, conductive silver adhesive and nanowelding technology was introduced herein. Principles and charac- teristics of different synthesizing methods of silver nano- wires were reviewed in this paper, including template method, liquid polyol method, self-assembly method, ultrasonic reduction method and wet chemical method. The liquid polyol method was the most available one to achieve efficient large-scale production.

Large-area chemical vapor deposition-grown monolayer graphene-wrapped silver nanowires for broad-spectrum and robust antimicrobial coating

New types of antimicrobial systems are urgently needed owing to the emergence of pathogenic microbial strains that gain resistance to antibiotics commonly used in daily life and medical care. In this study we developed for the first time a broad-spectrum and robust antimicrobial thin film coating based on large-area chemical vapor deposition （CVD）-grown graphene-wrapped silver nanowires （AgNWs）. The antimicrobial graphene/AgNW hybrid coating can be applied on commerdal flexible transparent ethylene vinyl acetate/polyethylene terephthalate （EVA/PET） plastic films by a full roll-to-roll process. The graphene/AgNW hybrid coating showed broad-spectrum antimicrobial activity against Gram-negative （Escherichia coli） and Gram-positive bacteria （Staphylococcus aureus）, and fungi （Candida albicans）. This effect was attributed to a weaker microbial attachment to the ultra-smooth graphene film and the sterilization capacity of Ag＋, which is sustainably released from the AgNWs and presumably enhanced by the electrochemical corrosion of AgNWs. Moreover, the robust antimicrobial activity of the graphene/AgNW coating was reinforced by AgNW encapsulation by graphene. Furthermore, the antimicrobial efficiency could be enhanced to -100% by water electrolysis by using the conductive graphene/AgNW coating as a cathode. We developed a transparent and flexible antimicrobial cover made of graphene/AgNW/EVA/PET and an antimicrobial denture coated by graphene/ AgNW, to show the potential applications of the antimicrobial materials.

High-resolution and large-size stretchable electrodes based on patterned silver nanowires composites

Electrodes based on composites of silver nanowires(AgNWs)and elastic polymers have been widely studied and applied in various stretchable electronic devices.However,due to the high aspect ratio of nanowires,the patterning of AgNW-based composite electrodes remains a huge challenge,especially for high-resolution complex circuit wiring on large-size elastic substrates.In this paper,we propose a method for preparing large-size stretchable circuit boards with high-resolution electrodes by the combination of screen printing and vacuum filtration of AgNWs/polydimethylsiloxane(PDMS)composite.The as-prepared stretchable electrodes have smooth edges with patterning resolution up to-50 μm.The conductivity of the composite electrode can be precisely controlled by varying deposition densities of AgNWs and have reached to 1.07 x 10^(4) S/cm when the deposition density was 2.0 mg/cm^(2).In addition,the uniformity of conductivity and the resistance-strain characteristics of composite electrodes were systematically evaluated with different AgNWs deposition densities.The composite electrodes have been successfully employed to construct a large-size programmable display system and an 18-channel surface electromyography(EMG)recording,showing great potentials for some strain-insensitive stretchable circuits in wearable and health-related electronic applications.

Silver nanowires with semiconducting ligands for low- temperature transparent conductors

Metal nanowire networks represent a promising candidate for the rapid fabrication of transparent electrodes with high transmission and low sheet-resistance values at very low deposition temperatures. A commonly encountered challenge in the formation of conductive nanowire electrodes is establishing high-quality electronic contact between nanowires to facilitate long-range current transport through the network. A new system involving nanowire ligand removal and replacement with a semiconducting sol-gel tin oxide matrix has enabled the fabrication of high-performance transparent electrodes at dramatically reduced temperatures with minimal need for post-deposition treatment.

Plasmon-enhanced nanosoldering of silver nanoparticles for high-conductive nanowires electrodes

The silver nanowires(Ag NWs)electrodes,which consist of incompact Ag nanoparticles(NPs)formed by multi-photon photoreduction,usually have poor conductivities.An effective strategy for enhancing conductivity of the Ag NWs elec-trodes is plasmon-enhanced nanosoldering(PLNS)by laser irradiation.Here,plasmon-enhanced photothermal effect is used to locally solder Ag NPs and then aggregates of these NPs grow into large irregular particles in PLNS process.Fi-nite element method(FEM)simulations indicate that the soldering process is triggered by localized surface plasmon-in-duced electric field enhancement at“hot-spots”.The effectiveness of PLNS for enhancing conductivity depends on laser power density and irradiation time.By optimizing the conditions of PLNS,the electrical conductivity of Ag NWs is signific-antly enhanced and the conductivityσs is increased to 2.45×107 S/m,which is about 39%of the bulk Ag.This PLNS of Ag NWs provides an efficient and cost-effective technique to rapidly produce large-area metal nanowire electrodes and capacitors with high conductivity,excellent uniformity,and good flexibility.

Preparation of Silver Nanowires via a Rapid,Scalable and Green Pathway

Rapid synthesis of silver nanowires(Ag NWs) with high quality and a broad processing window is challenging because of the low selectivity of the formation of multiply twinned particles at the nucleation stage for subsequent Ag NWs growth.Herein we report a systematic study of the water-involved heterogeneous nucleation of Ag NWs with high rate(less than 20 min) in a simple and scalable preparation method.Using glycerol as a reducing agent and a solvent with a high boiling point,the reaction is rapidly heated to 210 ℃ in air to synthesize Ag NWs with a very high yield in gram level.It is noted that the addition of a small dose of water plays a key role for obtaining highly pure Ag NWs in high yield,and the optimal water/glycerol ratio is0.25%.After investigating a series of forming factors including reaction temperature and dose of catalysts,the formation kinetics and mechanism of the Ag NWs are proposed.Compared to other preparation methods,our strategy is simple and reproducible.These Ag NWs show a strong Raman enhancement effect for organic molecules on their surface.

Large-area, Flexible Polymer Solar Cell Based on Silver Nanowires as Transparent Electrode by Roll-to-Roll Printing

Conventional organic solar cell＇s （OSC） architectures, including rigid transparent substrate （Glass）, conductive electrode （Indium tin oxide, ITO） and small working areas, are widely utilized in organic photovoltaic fields. However, such a structure as well as conventional spin-coating method obviously restrict their industrial application. In this article, we report the deposition of silver nanowires （AgNWs） on the flexible substrate by slot-die printing. The obtained AgNWs films exhibited a high transmittance and a low resistance, and were further used as the transparent conductive electrode ofOSCs. A typical conjugated polymer, poly[（2-5-bis（2-hexyldecyloxy）phenylene）-alt-（5,6-difluoro-4,7-di（thiophen-2-yl）benzo[c] [1,2,5]thiadiazole）] （PPDT2FBT）, was used as the active material to fabricate large-area （7 cm2） solar cells by a slot-die coating process. The power conversion efficiency （PCE） could reach 1.87% initially and further increased to 3.04% by thermal annealing. Compared to the performance of reference cell on ITO substrate, the result indicated that the AgNWs could be developed as an alternative substitute of conductive electrode to fabricate the large-area flexible OSCs by roll-to-roll printing.

Hybrid windshield-glass heater for commercial vehicles fabricated via enhanced electrostatic interactions among a substrate, silver nanowires, and an over-coating layer

We introduce a transparent windshield-glass heater produced via transparent electrodes using silver nanowire （AgNW） networks for conventional use in the automobile industry. A high-quality conducting hybrid film is deposited on a plasma-treated glass substrate by spraying AgNWs, immersing the sprayed product in positively charged adhesive polymer solution, and then spraying negatively charged graphene oxide （GO） and a silane layer as an over-coating layer （OCL）.The results of heating tests conducted after adhesion tests show that the sheet resistance changes with the application of polymer glue. Surprisingly, the transmittance of the film with the GO OCL is higher than that of the film without the GO OCL. Heating and defrosting tests are carefully conducted via infrared （IR） monitoring. Adhesive-polymer-treated and GO-protected AgNW transparent glass heaters exhibit the best performance with low sheet resistance; thus, through strong electrostatic interaction among the substrate, adhesive layer, and OCL, our AgNW hybrid glass heater can reach the target temperature with a standard vehicle voltage of 12 V in a short period of time.