Syntheses of Silver Nanowires Ink and Printable Flexible Transparent Conductive Film: A Review

In Situ Growth of Nanosilver on Fabric for Flexible Stretchable Electrodes

Flexible sensing can disruptively change the physical form of traditional electronic devices to achieve flexibility in information acquisition, processing, transmission, display, and even energy, and it is a core technology for a new generation of the industrial internet. Fabric is naturally flexible and stretchable, and its knitted ability makes it flexibility and stretchability even more adjustable. However, fabric needs to be electrically conductive to be used for flexible sensing, which allows it to carry a variety of circuits. The dip-coating technique is a common method for preparing conductive fabrics, which are made conductive by attaching conductive fillers to the fabrics. However, the adhesion of the conductive fillers on the surface of such conductive fabrics is weak, and the conductive property will decay rapidly because the conductive filler falls off after repeated stretching, limiting the lifespan of flexible electronic devices based on conductive fabric. We chose multifunctional nanosilver as a conductive filler, and we increased the adhesion of nanosilver to fabric fiber by making nanosilver grow in situ and cover the fiber, so as to obtain conductive fabric with good conductivity. This conductive fabric has a minimum square resistance of 9 Ω/sq and has better electrical conductivity and more stable electrical properties than the conductive fabric prepared using the dip-coating process, and its square resistance did not increase significantlyafter 60 stretches.

Advances in constructing silver nanowire-based conductive pathways for flexible and stretchable electronics

With their soaring technological demand, flexible and stretchable electronics have attracted many researchers' attention for a variety of applications. The challenge which was identified a decade ago and still remains, however, is that the conventional electrodes based on indium tin oxide (ITO) are not suitable for ultra-flexible electronic devices. The main reason is that ITO is brittle and expensive, limiting device performance and application. Thus, it is crucial to develop new materials and processes to construct flexible and stretchable electrodes with superior quality for next-generation soft devices. Herein, various types of conductive nanomaterials as candidates for flexible and stretchable electrodes are briefly reviewed. Among them, silver nanowire (AgNW) is selected as the focus of this review, on account of its excellent conductivity, superior flexibility, high technological maturity, and significant presence in the research community. To fabricate a reliable AgNW-based conductive network for electrodes, different processing technologies are introduced, and the corresponding characteristics are compared and discussed. Furthermore, this review summarizes strategies and the latest progress in enhancing the conductive pathway. Finally, we showcase some exemplary applications and provide some perspectives about the remaining technical challenges for future research.

Metal-Oxide Nanomaterials Synthesis and Applications in Flexible and Wearable Sensors

Metal-oxide nanomaterials (MONs) have gained considerable interest in the construction of flexible/wearable sensors due to their tunable band gap, low cost, large specific area, and ease of manufacturing. Furthermore, MONs are in high demand for applications, such as gas leakage alarms, environmental protection, health tracking, and smart devices integrated with another system. In this Review, we introduce a comprehensive investigation of factors to boost the sensitivity of MON-based sensors in environmental indicators and health monitoring. Finally, the challenges and perspectives of MON-based flexible/wearable sensors are considered.

A wireless optoelectronic skin patch for light delivery and thermal monitoring

Wearable optoelectronic devices can interface with the skin for applications in continuous health monitoring and light-based therapy. Measurement of the thermal effect of light on skin is often critical to track physiological parameters and control light delivery. However, accurate measurement of light-induced thermal effects is challenging because conventional sensors cannot be placed on the skin without obstructing light delivery. Here, we report a wearable optoelectronic patch integrated with a transparent nanowire sensor that provides light delivery and thermal monitoring at the same location. We achieve fabrication of a transparent silver nanowire network with >92% optical transmission that provides thermoresistive sensing of skin temperature. By integrating the sensor in a wireless optoelectronic patch, we demonstrate closed-loop regulation of light delivery as well as thermal characterization of blood flow. This light delivery and thermal monitoring approach may open opportunities for wearable devices in light-based diagnostics and therapies.

Depth mapping of metallic nanowire polymer nanocomposites by scanning dielectric microscopy

Polymer nanocomposite materials based on metallic nanowires are widely investigated as transparent and flexible electrodes or as stretchable conductors and dielectrics for biosensing. Here we show that Scanning Dielectric Microscopy (SDM) can map the depth distribution of metallic nanowires within the nanocomposites in a non-destructive way. This is achieved by a quantitative analysis of sub-surface electrostatic force microscopy measurements with finite-element numerical calculations. As an application we determined the three-dimensional spatial distribution of ∼50 nm diameter silver nanowires in ∼100 nm-250 nm thick gelatin films. The characterization is done both under dry ambient conditions, where gelatin shows a relatively low dielectric constant, ε_r∼ 5, and under humid ambient conditions, where its dielectric constant increases up to ε_r∼ 14. The present results show that SDM can be a valuable non-destructive subsurface characterization technique for nanowire-based nanocomposite materials, which can contribute to the optimization of these materials for applications in fields such as wearable electronics, solar cell technologies or printable electronics.