Shuyuan Lin

Structural engineering of gold thin films with channel cracks for ultrasensitive strain sensing

This work demonstrates that engineering of the connection channels in gold thin films is an effective way to alter its resistivity for improved sensitivity in strain sensors. We investigated the formation of channel cracks and explored the corresponding piezoresistive behavior. The developed strain sensor possessed GFs as high as 200 (e < 0.5%), 1000 (0.5% < e < 0.7%), and even greater than 5000 (0.7% < e < 1%), which are among the highest values reported thus far at such small deformation, and are promising in the applications of electronic skin, wearable sensors and health monitoring platforms.

A Wearable and Highly Sensitive Graphene Strain Sensor for Precise Home-Based Pulse Wave Monitoring

Profuse medical information about cardiovascular properties can be gathered from pulse waveforms. Therefore, it is desirable to design a smart pulse monitoring device to achieve noninvasive and real-time acquisition of cardiovascular parameters. The majority of current pulse sensors are usually bulky or insufficient in sensitivity. In this work, a graphene-based skin-like sensor is explored for pulse wave sensing with features of easy use and wearing comfort. Moreover, the adjustment of the substrate stiffness and interfacial bonding accomplish the optimal balance between sensor linearity and signal sensitivity, as well as measurement of the beat-to-beat radial arterial pulse. Compared with the existing bulky and nonportable clinical instruments, this highly sensitive and soft sensing patch not only provides primary sensor interface to human skin, but also can objectively and accurately detect the subtle pulse signal variations in a real-time fashion, such as pulse waveforms with different ages, pre- and post-exercise, thus presenting a promising solution to home-based pulse monitoring.

Self-Assembled Graphene Film as Low Friction Solid Lubricant in Macroscale Contact

Promoted by the demand for solid lubricants, graphene has been proved to be a promising material for potential applications in reducing friction and wear. Here, a novel lubricating system where graphene sliding against graphene is developed to achieve low friction in macroscale contact. And the large area graphene film used here were prepared by a unique self-assembly technique based on Marangoni effect. Low friction coefficient of about 0.05 is obtained, and it is demonstrated that the film thickness, applied normal load and annealing process all have important influences on the tribological properties of graphene. The expedient fabrication procedure of large-area graphene film with excellent transferability and high-performance friction-reducing behaviors of the developed lubricating system both have a promising perspective in engineering applications.

A Flexible Platform Containing Graphene Mesoporous Structure and Carbon Nanotube for Hydrogen Evolution

It is of great significance to design a platform with large surface area and high electrical conductivity for poorly conductive catalyst for hydrogen evolution reaction (HER), such as molybdenum sulfide (MoSx), a promising and cost‐effective nonprecious material. Here, the design and preparation of a free‐standing and tunable graphene mesoporous structure/single‐walled carbon nanotube (GMS/SWCNT) hybrid membrane is reported. Amorphous MoSx is electrodeposited on this platform through a wet chemical process under mild temperature. For MoSx@GMS/SWCNT hybrid electrode with a low catalyst loading of 32 μg cm−2, the onset potential is near 113 mV versus reversible hydrogen electrode (RHE) and a high current density of ≈71 mA cm−2 is achieved at 250 mV versus RHE. The excellent HER performance can be attributed to the large surface area for MoSx deposition, as well as the efficient electron transport and abundant active sites on the amorphous MoSx surface. This novel catalyst is found to outperform most previously reported MoSx‐based HER catalysts. Moreover, the flexibility of the electrode facilitates its stable catalytic performance even in extremely distorted states.

Synthetic Multifunctional Graphene Composites with Reshaping and Self-Healing Features via a Facile Biomineralization-Inspired Process

Since graphene is a type of 2D carbon material with excellent mechanical, electrical, thermal, and optical properties, the efficient preparation of graphene macroscopic assemblies is significant in the potentially large-scale application of graphene sheets. Conventional preparation methods of graphene macroscopic assemblies need strict conditions, and, once formed, the assemblies cannot be edited, reshaped, or recycled. Herein, inspired by the biomineralization process, a feasible approach of shapeable, multimanipulatable, and recyclable gel-like composite consisting of graphene oxide/poly(acrylic acid)/amorphous calcium carbonate (GO-PAA-ACC) is designed. This GO-PAA-ACC material can be facilely synthesized at room temperature with a cross-linking network structure formed during the preparation process. Remarkably, it is stretchable, malleable, self-healable, and easy to process in the wet state, but tough and rigid in the dried state. In addition, these two states can be readily switched by adjusting the water content, which shows recyclability and can be used for 3D printing to form varied architectures. Furthermore, GO-PAA-ACC can be functionalized or processed to meet a variety of specific application requirements (e.g., energy-storage, actuators). The preparation method of GO-PAA-ACC composite in this work also provides a novel strategy for the versatile macroscopic assembly of other materials, which is low-cost, efficient, and convenient for broad application.

Recent developments in graphene conductive ink: Preparation, printing technology and application

Electronic printing is an interdisciplinary technology of traditional printing technology and microelectronics manu- facturing. The development of electronic printing has mostly benefited from the progress of nanomaterials research. Graphene, a novel two-dimensional carbon nanomaterial, has shown excellent electrical, thermal, optical properties in flexible electrical devices. Graphene with traditional metals or polymer materials together could act as the main conductive components in conductive ink. Printing of graphene ink represents a cost-effective deposition technique to obtain patterned conductive graphene films, and further assemble them into functional electrical devices. Therefore, electronic printing based on graphene conductive ink is one of the recent research hotspots. In this paper, we review recent developments and advances in research of graphene conductive ink. This review begins with an introduction of different preparation strategies for graphene conductive inks. For printing, the three major pathways for producing graphene sheets are oxidation-reduction, solvent exfoliation and electrochemical expansion of graphite. Different preparation strategies for conductive inks are classified into three major methods: Graphene inks stabilized by surfactants or functional groups, and graphene-based composite conductive ink. The detailed review of graphene conductive ink preparation is discussed with specific examples. Preparation of graphene conductive inks of high concentrations, stability and printing adaptability is the key issue in electronic printing. Subsequently, an introduction of common printing methods and principles is given. Five printing methods are discussed in this review, including inkjet printing, gravure printing, transfer printing, direct writing and three- dimensional (3D) printing. Printing is kind of additive manufacturing, by depositing graphene onto substrates of various materials, sizes, flexibility and roughness for conductive pattern. Different printing techniques have unique requirements of ink rheological properties. The inkjet printing is becoming the most common technique employed in both academic research and industrial application. The realization of rapid, accurate, simple and controllable printing has important influence on the application of graphene conductive ink. Finally, applications of printed graphene conductive ink in flexible functional devices, including basic electrical circuits, energy storage devices and mechanical/chemical sensing devices, are envisioned. Basic electrical circuits, like flexible conductive patterns, field-effect transistors and radio-frequency circuits, play an important role in the fabrication of wearable devices. Printing also offers a cheap, scalable method of fabricating energy storage devices, including supercapacitor and lithium battery. The unique structure of graphene makes possible the fabrication of different kinds of sensors, including strain, temperature, chemical, electrochemical, photo-electricity sensors and biosensors. An outlook of potential future trends in printing graphene conductive ink research and technology is followed. In summary, printing graphene conductive ink has made many significant advances in a wide range of applications. However, the industrial-level application is still limited, and the preparation and application of graphene conductive ink still need further study. A number of key issues should be solved, including stability of graphene ink, electronic conductivity of printed circuit, limited printing resolution, etc. Overall, electronic printing technology based on graphene conductive ink is not meant as a replacement for microelectronic manufacturing engineering, but instead provides an opportunity to produce large-area flexible electronic devices at low cost. Electronic printing of graphene conductive ink will result in a diverse range of novel applications in many fields, and it calls for more research in the future.

Water-driven actuation of Ornithoctonus huwena spider silk fibers

Spider silk possesses remarkable mechanical properties and can lift weight effectively. Certain kinds of spider silk have unique response to liquid, especially water, because of their hydrophilic proteins, β-sheet characters, and surface structure. The Ornithoctonus huwena (O. huwena) spider is a unique species because it can be bred artificially and it spins silk whose diameter is in nanometer scale. In this work, we report the “shrink–stretch” behavior of the O. huwena spider silk fibers and show how they can be actuated by water to lift weight over long distance, at a fast speed, and with high efficiency. We further rationalize this behavior by analyzing the mechanical energy of the system. The lifting process is energy-efficient and environmentally friendly, allowing applications in actuators, biomimetic muscles, or hoisting devices.