Kailun Xia

Carbonized Silk Fabric for Ultrastretchable, Highly Sensitive, and Wearable Strain Sensors

A carbonized plain-weave silk fabric is fabricated into wearable and robust strain sensors, which can be stretched up to 500% and show high sensitivity in a wide strain range. This sensor can be assembled into wearable devices for detection of both large and subtle human activities, showing great potential for monitoring human motions and personal health.

Carbonized silk georgette as an ultrasensitive wearable strain sensor for full-range human activity monitoring

The increasing demand of wearable electronic devices has promoted the development of high-performance flexible strain sensors which could monitor various physiological parameters. In this work, using silk georgette, which is a commercially available gauzy and lightweight fabric composed of highly twisted yarns in both warp and weft directions as the raw material, an ultrasensitive strain sensor with a wide workable strain range is fabricated through a facile and large-scale process. The obtained strain sensors exhibit remarkable combined features of ultrahigh sensitivity in a wide sensing range (average gauge factor of 29.7 within 40% strain and of 173.0 for a strain of 60–100%), ultralow detection limit (0.01% strain), high durability and stability (10 000 stretching cycles at 100% strain), fast response (<70 ms) and translucence, which could be ascribed to the unique woven structure of silk georgette. Furthermore, the dependence of the performance of the strain sensors on the woven structures has been demonstrated. Finally, the strain sensors based on silk georgette are demonstrated to show potential for applications in monitoring full-range human activities including both vigorous motions and subtle motions.

Extremely Black Vertically Aligned Carbon Nanotube Arrays for Solar Steam Generation

The unique structure of a vertically aligned carbon nanotube (VACNT) array makes it behave most similarly to a blackbody. It is reported that the optical absorptivity of an extremely black VACNT array is about 0.98-0.99 over a large spectral range of 200 nm-200 μm, inspiring us to explore the performance of VACNT arrays in solar energy harvesting. In this work, we report the highly efficient steam generation simply by laminating a layer of VACNT array on the surface of water to harvest solar energy. It is found that under solar illumination the temperature of upper water can significantly increase with obvious water steam generated, indicating the efficient solar energy harvesting and local temperature rise by the thin layer of VACNTs. We found that the evaporation rate of water assisted by VACNT arrays is 10 times that of bare water, which is the highest ratio for solar-thermal-steam generation ever reported. Remarkably, the solar thermal conversion efficiency reached 90%. The excellent performance could be ascribed to the strong optical absorption and local temperature rise induced by the VACNT layer, as well as the ultrafast water transport through the VACNT layer due to the frictionless wall of CNTs. Based on the above, we further demonstrated the application of VACNT arrays in solar-driven desalination.

Intrinsically Stretchable and Conductive Textile by a Scalable Process for Elastic Wearable Electronics

The prosperous development of stretchable electronics poses a great demand on stretchable conductive materials that could maintain their electrical conductivity under tensile strain. Previously reported strategies to obtain stretchable conductors usually involve complex structure-fabricating processes or utilization of high-cost nanomaterials. It remains a great challenge to produce stretchable and conductive materials via a scalable and cost-effective process. Herein, a large-scalable pyrolysis strategy is developed for the fabrication of intrinsically stretchable and conductive textile in utilizing low-cost and mass-produced weft-knitted textiles as raw materials. Due to the intrinsic stretchability of the weft-knitted structure and the excellent mechanical and electrical properties of the as-obtained carbonized fibers, the obtained flexible and durable textile could sustain tensile strains up to 125% while keeping a stable electrical conductivity (as shown by a Modal-based textile), thus ensuring its applications in elastic electronics. For demonstration purposes, stretchable supercapacitors and wearable thermal-therapy devices that showed stable performance with the loading of tensile strains have been fabricated. Considering the simplicity and large scalability of the process, the low-cost and mass production of the raw materials, and the superior performances of the as-obtained elastic and conductive textile, this strategy would contribute to the development and industrial production of wearable electronics.

Growth of large-area aligned pentagonal graphene domains on high-index copper surfaces

Single-crystal graphene domains grown by chemical vapor deposition (CVD) intrinsically tend to have a six-fold symmetry; however, several factors can influence the growth kinetics, which can in turn lead to the formation of graphene with different shapes. Here we report the growth of oriented large-area pentagonal single-crystal graphene domains on Cu foils by CVD. We found that high-index Cu planes contributed selectively to the formation of pentagonal graphene. Our results indicated that lattice steps present on the crystalline surface of the underlying Cu promoted graphene growth in the direction perpendicular to the steps and finally led to the disappearance of one of the edges forming a pentagon. In addition, hydrogen promoted the formation of pentagonal domains. This work provides new insights into the mechanism of graphene growth.

An All-Silk-Derived Dual-Mode E-skin for Simultaneous Temperature–Pressure Detection

Flexible skin-mimicking electronics are highly desired for development of smart human-machine interfaces and wearable human-health monitors. Human skins are able to simultaneously detect different information, such as touch, friction, temperature, and humidity. However, due to the mutual interferences of sensors with different functions, it is still a big challenge to fabricate multifunctional electronic skins (E-skins). Herein, a combo temperature-pressure E-skin is reported through assembling a temperature sensor and a strain sensor in both of which flexible and transparent silk-nanofiber-derived carbon fiber membranes (SilkCFM) are used as the active material. The temperature sensor presents high temperature sensitivity of 0.81% per centigrade. The strain sensor shows an extremely high sensitivity with a gauge factor of ∼8350 at 50% strain, enabling the detection of subtle pressure stimuli that induce local strain. Importantly, the structure of the SilkCFM in each sensor is designed to be passive to other stimuli, enabling the integrated E-skin to precisely detect temperature and pressure at the same time. It is demonstrated that the E-skin can detect and distinguish exhaling, finger pressing, and spatial distribution of temperature and pressure, which cannot be realized using single mode sensors. The remarkable performance of the silk-based combo temperature-pressure sensor, together with its green and large-scalable fabrication process, promising its applications in human-machine interfaces and soft electronics.

CVD growth of fingerprint-like patterned 3D graphene film for an ultrasensitive pressure sensor

With the rapid development of wearable devices, flexible pressure sensors with high sensitivity and wide workable range are highly desired. In nature, there are many well-adapted structures developed through natural selection, which inspired us for the design of biomimetic materials or devices. Particularly, human fingertip skin, where many epidermal ridges amplify external stimulations, might be a good example to imitate for highly sensitive sensors. In this work, based on unique chemical vapor depositions (CVD)-grown 3D graphene films that mimic the morphology of fingertip skin, we fabricated flexible pressure sensing membranes, which simultaneously showed a high sensitivity of 110 (kPa)−1 for 0–0.2 kPa and wide workable pressure range (up to 75 kPa). Hierarchical structured PDMS films molded from natural leaves were used as the supporting elastic films for the graphene films, which also contribute to the superior performance of the pressure sensors. The pressure sensor showed a low detection limit (0.2 Pa), fast response (< 30 ms), and excellent stability for more than 10,000 loading/unloading cycles. Based on these features, we demonstrated its applications in detecting tiny objects, sound, and human physiological signals, showing its potential in wearable electronics for health monitoring and human/machine interfaces.

Superelastic wire-shaped supercapacitor sustaining 850% tensile strain based on carbon nanotube@graphene fiber

Stretchable and flexible supercapacitors are highly desired due to their many potential applications in wearable devices. However, it is challenging to fabricate supercapacitors that can withstand large tensile strain while maintaining high performance. Herein, we report an ultra-stretchable wire-shaped supercapacitor based on carbon nanotube@graphene@MnO2 fibers wound around a superelastic core fiber. The supercapacitor can sustain tensile strain up to 850%, which is the highest value reported for this type of device to date, while maintaining stable electrochemical performance. The energy density of the supercapacitor is 3.37 mWh·cm–3 at a power density of 54.0 mW·cm–3. The results show that 82% of the specific capacitance is retained after 1,000 stretch–release cycles with strains of 700%, demonstrating the superior durability of the elastic supercapacitor and showcasing its potential application in ultra-stretchable flexible electronics.

Wearable Strain Sensors: Carbonized Silk Fabric for Ultrastretchable, Highly Sensitive, and Wearable Strain Sensors (Adv. Mater. 31/2016).

A novel carbonized plain-weave silk-fabric-based wearable strain sensor is proposed by Y. Y. Zhang and co-workers on page 6640. The sensor can be stretched up to 500% with high sensitivity in a wide strain range and can be assembled into wearable devices for the detection of both large and subtle human activities, showing great potential in human-motion detection and robotics.

Splash-Resistant and Light-Weight Silk-Sheathed Wires for Textile Electronics

Silk has outstanding mechanical properties and biocompatibility. It has been used to fabricate traditional textiles for thousands of years and can be produced in large scale. Silk materials are potentially attractive in modern textile electronics. However, silk is not electrically conductive, thus limiting its applications in electronics. Moreover, regenerated silk is generally rigid and brittle, which hinder post processing. Here we report the fabrication of conductive silk wire in which carbon nanotube (CNT) yarns are wrapped with fluffy and flexible silk nanofiber films. The silk nanofiber film was prepared by electrospinning and then wrapped around a rotating CNT yarn in situ. The obtained silk-sheathed CNT (CNT@Silk) wire has an insulating sheath, which protects the body against electrical shock. In addition, the fabricated wires exhibit a high electrical conductivity (3.1 × 104 S/m), good mechanical strength (16 cN/tex), excellent flexibility, and high durability. More importantly, the wires have an extremely low density (2.0-7.8 × 104 g/m3), which is 2 orders of magnitude lower than that of the traditional metal wire (for example, Cu). Moreover, the wires display a good resistance to humidity, and a simple post treatment can make the wires splash-resistant, thereby expanding its applications. On the basis of these features, we demonstrate the use of the lightweight CNT@Silk wires in smart clothes, including electrochromism and near-field communication.