Nanowire Ink Research Articles

Large-Scale Synthesis of Silver Nanowire Ink Suitable for Flexible and Wearable Printed Electronics

Large-Scale Synthesis of Silver Nanowire Ink Suitable for Flexible and Wearable Printed Electronics

Highly Transparent and Flexible Multiwalled Carbon Nanotube–Polyimide Films with Enhanced Electrical Performance as Promising Electrodes

AbstractTransparent and light films with high electrical conductivity are preferred for flexible electronic applications. Here, a film exhibiting high transparency, electrical conductivity, and flexibility is produced using a polyimide (PI) substrate and multiwalled carbon nanotubes (MWCNTs) through spray coating. Cost‐effective MWCNTs are used instead of other electrically conductive materials, including silver nanowire ink, single‐walled carbon nanotubes (SWCNTs), and other carbon materials. The average sheet resistance of the prepared MWCNT–PI film is 520.2 Ω □−1 (infinite for the bare PI film), which is lower than the sheet resistances of the SWCNT–PI film reported by another group. This can be attributed to the increase in electrical conductivity of the highly transparent PI film due to the use of MWCNTs. The transparency of the MWCNT–PI film is 71.834% at 550 nm. When MWCNTs and PI are combined, MWCNTs protrude from the surface of the PI film, creating networks and increasing electrical conductivity. Atomic force microscopy analysis reveals that MWCNT networks form on the surface of the MWCNT–PI film. This study suggests the possibility that MWCNTs can also be used as carbon materials for flexible and highly transparent films.

Insight into the Types of Alkanolamines on the Properties of Copper(II) Formate-Based Conductive Ink.

Conductive inks are one of the most important functional materials for printed flexible electronic devices, and their properties determine the methods of subsequent patterning and metallization. In comparison with copper nanoparticle or nanowire inks, copper particle-free inks employing copper(II) formate (Cuf) as a precursor have attracted the interest of researchers due to their flexibility in preparation, excellent stability, and lower conversion temperature. Alkanolamines can provide Cuf with excellent solubility in alcohols while being less toxic and having a certain reducibility, making them preferable ligands in comparison with aliphatic amines and pyridine. However, there have been few studies on the effects of the alkanolamine types on the performance of Cuf inks. Also, the decomposition mechanism of copper-alkanolamine complex inks is not clear. In this work, different kinds of alkanolamines were chosen as ligands to formulate Cuf inks to address the mentioned issues. The influences of amine types on the stability, wettability, thermal decomposition behavior, and electrical performance of the formulated Cuf particle-free inks were investigated in detail. The results show that the utilization of alkanolamines could provide Cuf with excellent solubility in alcohols, resulting in an ink with good stability and favorable wetting properties. The thermal decomposition temperature and electrical performance of the formulated copper ink are largely dependent on the amine used. When amines with a longer carbon chain and more branches were utilized to prepare the ink, a decreased decomposition temperature was observed on the derived inks because of the steric hindrance effect. Copper films with good morphology and conductivity could be obtained at low temperatures by selecting the appropriate alkanolamine. Copper particle-free conductive ink from 2-amino-2-methyl-1-propanol demonstrated better morphology and electrical performance (16.09 μΩ·cm) and was successfully used for conductive circuits by direct-writing.

Optically Transparent Dual-Band Metamaterial Absorber Using Ag Nanowire Screen-Printed Second-Order Cross-Fractal Structures

In this paper, we propose an optically transparent dual-band metamaterial absorber (MMA) that uses Ag nanowire screen-printed fractal structures. The proposed MMA exhibits near-perfect absorption in the C- and K-bands. This dual-band absorption property is achieved through two inductive–capacitive (L-C) resonances located at 6.45 and 21.14 GHz, which are generated by the second-order fractal structures. We analyzed the microwave absorbing mechanisms through the distributions of the surface current and electromagnetic field on the top and bottom layers. The MMA demonstrates an optical transmittance of 63.1% at a wavelength of 550 nm. This high optical transmittance is attained by screen printing transparent Ag nanowire ink onto a transparent PET substrate. Since screen printing is a simple and low-cost fabrication method, the proposed MMA offers the advantages of being low cost while having the properties of optical transparency and effective dual-band absorption. Consequently, it holds great potential for the radar stealth application of C- and K-bands in that it can be attached to the windows of stealth aircraft due to its optical transparency and dual-band near-perfect absorption property.

Conductivity enhancement of Ag nanowire ink by decorating in situ formed Ag particles under low-temperature sintering

Silver nanowires (AgNWs) have attractive applications in the fabrication of flexible electronics because of their adequate electrical conductivity, mechanical properties, and oxidation resistance. However, the film produced by AgNW ink needs to be sintered at temperatures above 200 °C to obtain high electrical conductivity, which is incompatible with commonly used flexible substrates such as paper or polymer materials. In this study, the AgNW network was decorated by in situ reduced Ag particles (AgPs) to improve the structural integrity and conductivity of the film. After sintering at 80 °C, the pores and voids within the AgNW network were filled with Ag particles smaller than 200 nm, and the porosity of the film was markedly reduced. The lowest resistivity value was 3.9 × 10–5 Ω cm after sintering at 100 °C, only 10.8% and 8.5% of the resistivity values of the films produced from AgNW and ion inks, respectively. During sintering, Ag nucleated on the surface of AgNWs, and its growth and agglomeration resulted in interconnections between the AgNWs and Ag particles. Thereafter, the bridging and filling effect of the Ag particles facilitated the formation of a compact and firm network, improving the film conductivity. The line film printed from the composite ink with 10 layers exhibited a low resistivity of 7.3 × 10–7 Ω·m. Even after 5000 bending cycles, the resistivity of the line only increased by 4.47 × 10–6 Ω·cm from the initial value. The composite ink reported in this study is a promising candidate for the low-cost printing of ultralow-power-consumption wearable electronic devices.

Wet Film Leveling for Promoting the Uniformity and Conductivity of Silver Nanowire Transparent Electrode.

Wet film leveling can greatly promote film uniformity. However, in the field of metal nanowire, wet film leveling is rarely mentioned. For low-viscosity inks like metal nanowire ink, how to realize wet film leveling is still unclear. Herein, we study the wet film leveling of silver nanowire ink and systematically investigate the relationship between leveling effect and influence factors: (1) there is a uniformity-promotion limit for traditional methods, while wet film leveling can break through this limit and further promote the film uniformity; (2) for wet film leveling, lowering ink's surface tension has no effect, and eliminating surface tension gradient by high-surface-tension leveling agent is the main task; (3) leveling process includes wet film destruction process and ink reflow process; (4) in the destruction process, the leveling-agent solubility and quantity dominate the leveling effect, while the influence of surface tension is little; (5) for solubility and quantity, there is a suitable range to realize optimum leveling effect, and the leveling effect exhibits a contrary relationship with the solubility in a suitable range (2-11%); (6) in the reflow process, the main influence factor is ink viscosity, and the leveling effect exhibits a contrary relationship with ink viscosity. After being leveled by 1.5% n-pentanol, the sheet resistance and sheet-resistance variation coefficient of film decrease from 38.3 Ω/sq/3.83% to 25.7 Ω/sq/1.88%. Further study reveals that the film improvement is not from the ink wettability and drying. Above theoretical results possess certain universality for film preparation by a wet process and can be used by the science and industry field.

Enhancing Conductivity of Silver Nanowire Networks through Surface Engineering Using Bidentate Rigid Ligands.

Solution processable metallic nanomaterials present a convenient way to fabricate conductive structures, which are necessary in all electronic devices. However, they tend to require post-treatments to remove the bulky ligands around them to achieve high conductivity. In this work, we present a method to formulate a post-treatment free conductive silver nanowire ink by controlling the type of ligands around the silver nanowires. We found that bidentate ligands with a rigid molecular structure were effective in improving the conductivity of the silver nanowire networks as they could maximize the number of linkages between neighboring nanowires. In addition, DFT calculations also revealed that ligands with good LUMO to silver energy alignment were more effective. Because of these reasons, fumaric acid was found to be the most effective ligand and achieved a large reduction in sheet resistance of 70% or higher depending on the nanowire network density. The concepts elucidated from this study would also be applicable to other solution processable nanomaterials systems such as quantum dots for photovoltaics or LEDs which also require good charge transport being neighboring nanoparticles.

Perforated PVP encapsulated AgNWs for high mass loading in silver nanowire inks for printed RFID integrated wearable smart bands

A perforated PVP coating on AgNWs produces high-mass loading and low-temperature curing inks. The ink produces prints of high conductivity, and an RFID-assisted smart band for wearable position sensing is developed using the ink.

Continuous flow synthesis of metal nanowires: protocols, engineering aspects of scale-up and applications.

This review comprehensively covers the translation from batch to continuous flow synthesis of metal nanowires (i.e., silver, copper, gold, and platinum nanowires) and their diverse applications across various sectors. Metal nanowires have attracted significant attention owing to their versatility and feasibility for large-scale synthesis. The efficacy of flow chemistry in nanomaterial synthesis has been extensively demonstrated over the past few decades. Continuous flow synthesis offers scalability, high throughput screening, and robust and reproducible synthesis procedures, making it a promising technology. Silver nanowires, widely used in flexible electronics, transparent conductive films, and sensors, have benefited from advancements in continuous flow synthesis aimed at achieving high aspect ratios and uniform diameters, though challenges in preventing agglomeration during large-scale production remain. Copper nanowires, considered as a cost-effective alternative to silver nanowires for conductive materials, have benefited from continuous flow synthesis methods that minimize oxidation and enhance stability, yet scaling up these processes requires precise control of reducing environments and copper ion concentration. A critical evaluation of various metal nanowire ink formulations is conducted, aiming to identify formulations that exhibit superior properties with lower metal solid content. This study delves into the intricacies of continuous flow synthesis methods for metal nanowires, emphasizing the exploration of engineering considerations essential for the design of continuous flow reactors. Furthermore, challenges associated with large-scale synthesis are addressed, highlighting the process-related issues.

Thermoelectric nanowires for dense 3D printed architectures.

The large-scale employment of 3D printed inorganic thermoelectrics is primarily constrained because of their lower efficiencies as compared to those fabricated from conventional methods such as spark plasma sintering and hot-pressing. This originates from the significant challenge in the densification of printed parts, particularly through the direct-ink-writing fabrication process, which demands a high binder content for printability. To achieve high-density printed thermoelectrics, the ink formulation process often involves the addition of substantial filler content and sintering aids, coupled with prolonged sintering periods. Here, we propose a strategy to resolve the low densification issue of 3D printed thermoelectrics through a binder-less and sintering aid-free thermoelectric nanowire ink system that can achieve dense thermoelectric structures (up to 82.5% theoretical density). The increase in density and corresponding enhancement of thermoelectric material efficiency are attained in a more tunable and controlled manner without compromising the material composition. A high filler-derived density index (FDI) of 2.51 is also achieved, implying the potential to obtain high-density parts with minimal filler content, thus unlocking a cascade of profound impacts. Crucially, this advancement enables the possibilities of anisotropic engineering in thermoelectric materials, thereby shattering the limitations that have hindered the widespread adoption of 3D printed inorganic thermoelectrics.

Enhancing and Understanding the High Stretchability of Printable, Conductive Silver Nanowire Ink

Enhancing and Understanding the High Stretchability of Printable, Conductive Silver Nanowire Ink

Adjusting the viscosity of silver nanowire ink for promoting the uniformity and conductivity of transparent electrode

Adjusting the viscosity of silver nanowire ink for promoting the uniformity and conductivity of transparent electrode

Eco-friendly screen printing of silver nanowires for flexible and stretchable electronics.

Screen printing is a promising route towards high throughput printed electronics. Currently, the preparation of nanomaterial based conductive inks involves complex formulations with often toxic surfactants in the ink's composition, making them unsuitable as an eco-friendly printing technology. This work reports the development of a silver nanowire (AgNW) ink with a relatively low conductive particle loading of 7 wt%. The AgNW ink involves simple formulation and comprises a biodegradable binder and a green solvent with no toxic surfactants in the ink formulation, making it an eco-friendly printing process. The formulated ink is suitable for printing on a diverse range of substrates such as polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polyimide (PI) tape, glass, and textiles. By tailoring the rheological behaviour of the ink and developing a one-step post-printing process, a minimum feature size of 50 μm and conductivity as high as 6.70 × 106 S m-1 was achieved. Use of a lower annealing temperature of 150 °C makes the process suitable for plastic substrates. A flexible textile heater and a wearable hydration sensor were fabricated using the reported AgNW ink to demonstrate its potential for wearable electronic applications.

High-conductivity screen-printable silver nanowire Ink for optically transparent flexible radio frequency electronics

Optically transparent conductors have paved the way in various optoelectronic and radio frequency devices where high electrical conductivity and optical transparency with mechanical flexibility, as well as large area fabrication are deemed necessary. Printing techniques are viable for fabricating large-area devices with high mechanical flexibilities. However, the preparation of suitable inks and printing recipes is essential to achieve a high electrical conductivity and transparency. In this study, the best tradeoff between conductivity and optical transmittance was achieved through silver (Ag) nanowires (NWs)-based ink formulation with tuned Ag NW loading, solvent compositions and polymer weight percentages. The ink was deposited through screen-printing, which enabled a large-area and high-resolution patterning of the AgNWs. The washing time of the post-printed films exhibited a decisive effect on the initial conductivity, which was further improved through photonic sintering. During the photonic sintering, the voltages, pulse lengths (μs) and fire rates (Hz) were optimized to obtain the best conductivity of the printed films. Maximum optical transparencies of 78% and 83% were achieved for the conductivities of ∼5.88 × 106 and ∼6.25 × 106 S m−1, respectively. As a proof of concept, a fully printed optically transparent antenna was realized that could operate in a wide frequency band suitable for high-data-rate wireless communication.

Multiscale investigation of the fate of silver during printed paper electronics recycling

ABSTRACT The use of printed paper electronics in consumer goods is expected to experience a mass development in the next future. The ink used in these devices contains silver nanomaterials that may be released into the environment at the product end-of-life. We report here the first evaluation of the fate of silver during a pilot-scale recycling of printed paper electronics, made of paper printed with a cellulose nanofibrils-silver nanowire ink. We show that the released effluents are mainly free from silver, which is retained in the pulp conserved for recycling. We use atomic force microscopy experiments to show that this strong pulp-silver bond is due to the embedding of the silver nanowires in the pulp by coils of cellulose nanofibrils. We propose an estimate of the resulting adhesion stress of the nanowires to the ink, high enough to keep the silver inside the pulp during the recycling procedure.

Direct electrohydrodynamic printing of aqueous silver nanowires ink on hydrophobic substrates for flexible and stretchable electronics

Stretchable conductors based on metal nanowires, such as silver nanowires (AgNWs), are essential for the fabrication of stretchable electronics. Electrohydrodynamic (EHD) printing has been developed as a promising technique for patterning various conductive nanomaterials on stretchable substrates. However, the printing performance is adversely affected by poor wettability of the ink on the surface of the stretchable substrates, which are mostly low-surface-energy elastomeric polymers, like polydimethylsiloxane (PDMS). The surface treatments of the substrate surface could improve the printability of the ink on these substrates, but also impose many limitations, as the surface treatment could unfavorably affect the mechanical properties of the polymer and may cause damage to the underlying layer or other existing features on the substrate. The paper investigates EHD direct printing of aqueous AgNWs ink on untreated PDMS using surfactant (i.e., Capstone FS30) modified ink for the fabrication of stretchable electronics. The static contact angles at the different FS30 ratios were measured to analyze their effect on regulating the ink wettability. A set of printing experiments were performance to select the right ink composition to tailor and optimize the ink printability and printing performance. The morphology and electrical properties of printed AgNWs-based conductors can be controlled by selecting different the EHD printing speed. Furthermore, to illustrate the potential for reliable EHD direct printing of AgNWs for stretchable electronics, a wearable electronic patch with a fractal design of the AgNWs pattern was printed on an untreated PDMS substrate using the surfactant modified AgNWs ink, which provides stable electronic response under the bending, tension and compression.

3D Networks of Silver Nanorod–Nanoparticle Hybrids via Aerosol Jetting Printing for Flexible Electrode

To satisfy the functional requirements for next‐generation electronic and optoelectronic devices, diverse protocols have thus been developed for preparing transparent flexible electrodes (TFEs) of metallic nanowires with high flexibility and conductivity, while flexible electrodes with 3D configuration have become a burgeoning frontier. Herein, an innovative 3D network of silver nanorod–nanoparticle hybrids (Ag NNH) is realized by a facile aerosol jet printing (AJP) technique. A dynamic assembly mechanism based on the AJP of silver nanowires (AgNWs) ink is proposed, suggesting a favorable evaporation‐induced migration and assembly process along with the coalescence of deposited droplets. The initially formed Ag NNH random network optimizes the wettability, spreading, and pinning of the droplets, shaping the consecutive deposition behavior of the aerosol droplets for constructing the 3D Ag NNH networks. Planar micro‐supercapacitor (MSC) devices are developed using the Ag NNH network as flexible microelectrode, and a competitive areal capacitance performance has been demonstrated in comparison with other Ag‐based devices. It is envisioned that the as‐developed approach will provide an optional approach for developing future electronic and optoelectronic devices with fascinating hierarchical features.

Preparation and SERS performance of silver nanowires arrays on paper by automatic writing method

Silver nanowire ink was written on the surface of drawing paper by automatic writing method. Scanning electron microscopy was used to characterize the surface morphologies of the drawing paper before and after writing silver nanowires. The effects of fabrication parameters and measurement parameters on silver nanowires arrays were investigated. Crystal violet was selected as the probe molecule to study the SERS performance of silver nanowires arrays. The detection limit of crystal violet was as low as 10-15 mol/L. The uniformity and repeatability of the arrays were also explored, and the relative standard deviation values were about 10%. Moreover, silver nanowires arrays were also relatively stable that SERS signals were still observed after ten weeks. Detection of the crystal violet residue was further achieved on the substrates by continuously pressing nine times. In addition, silver nanowires arrays were also applied to the quantitative analyses of 2, 2′-bipyridyl.

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.

Novel Insights into Inkjet Printed Silver Nanowires Flexible Transparent Conductive Films.

Silver nanowire (AgNWs) inks for inkjet printing were prepared and the effects of the solvent system, wetting agent, AgNWs suspension on the viscosity, surface tension, contact angle between ink droplet and poly(ethylene) terephthalate (PET) surface, and pH value of AgNWs ink were discussed. Further, AgNWs flexible transparent conductive films were fabricated by using inkjet printing process on the PET substrate, and the effects of the number printing layer, heat treatment temperature, drop frequency, and number of nozzle on the microstructures and photoelectric properties of AgNWs films were investigated in detail. The experimental results demonstrated that the 14-layer AgNWs printed film heated at 60 °C and 70 °C had an average sheet resistance of 13 Ω∙sq−1 and 23 Ω∙sq−1 and average transparency of 81.9% and 83.1%, respectively, and displayed good photoelectric performance when the inkjet printing parameters were set to the voltage of 20 V, number of nozzles of 16, drop frequency of 7000 Hz, droplet spacing of 15 μm, PET substrate temperatures of 40 °C and nozzles of 35 °C during printing, and heat treatment at 60 °C for 20 min. The accumulation and overflow of AgNWs at the edges of the linear pattern were observed, which resulted in a decrease in printing accuracy. We successfully printed the heart-shaped pattern and then demonstrated that it could work well. This showed that the well-defined pattern with good photoelectric properties can be obtained by using an inkjet printing process with silver nanowires ink as inkjet material.