Wearable and implantable devices are the basis of technologies such as human motion monitoring, health monitoring, and human-computer interaction. They have huge application prospects in trillion-scale industries such as smart medical and intelligent robots, and their development trends are flexible and even elastic. And multi-functionalization, the development of flexible and even elastic magnetic and electrical functional materials and devices is the core and key. However, in general, magnetoelectric functional materials are mostly inorganic materials such as metals or oxides, which have poor flexibility; flexible or elastic materials are mostly polymer materials, and generally do not have magnetoelectric functions. How to soften or elasticize magnetoelectric functional materials, or functionalize flexible or elastic materials is a major challenge in this field. To this end, the Key Laboratory of Magnetic Materials and Devices, Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences, conducts research work on the flexibility and elasticity of functional materials such as conductive and magnetic materials. , Conductors and sensors have made a series of progress.
(I) Large-strain elastic conductive materials and elastic heating devices
Stretchable conductive materials are usually nano- or micron-sized conductive fillers (graphene, carbon nanotubes, metal nanowires / nanoparticles, etc.) are incorporated into elastic polymers, and processed by methods such as dispersion and lamination. A multiphase composite system with a conductive function is then obtained. Because the elastic modulus of the solid conductive filler and the elastic matrix are very different (about 1 million times), the gap between the filler particles constituting the conductive path will change significantly during large strains, resulting in unstable conductive properties. In addition, a large number of solid conductive fillers were introduced. Will increase the conductivity of conductive materials, but also deteriorate its elasticity, resulting in limited doping, so its conductivity is generally poor. How to obtain elastic conductors compatible with high electrical conductivity, tensile stability, and large strains remains a challenge.
In order to solve the above problems, doctoral students Yu Zhe, researchers Shang Jie and Li Runwei etc. used liquid metal as the conductive filler, and at the same time built a "gourd string" -like conductive network structure in the conductor to release the strain and further improve its strain stability. The results show that the conductivity of the stretchable conductive material can reach the range of conductors (greater than 1000S / cm), and can achieve a stretch of more than 1000%, and more importantly, the fluctuation of resistance when stretched at 100% is less than 4% Compared with the traditional stretchable conductive material, the change rate of the resistance is reduced by 2-3 orders of magnitude, and the stability of the stretchable conductor under large strain is achieved. As shown in Figure 1a. The work was published as a front cover article on Advanced Electronic Materials (Adv. Electron. Mater. 2018, 4, 1800137). Further, a direct-write printer was constructed by using the above-mentioned stretchable conductive material as ink, and the direct printing and patterning design of this material on an elastic substrate was realized. As shown in FIG. 1b, the printed elastic heating device is designed to have Good thermal stability. This work provides new materials and technologies for the production of flexible wearable electronic devices. The results were published in Advanced Materials Technologies (Adv. Mater. Technol. 2018, 3, 1800435).
(II) Green environmental protection recyclable flexible paper-based circuit
A flexible circuit is a special circuit created on a flexible substrate. At present, there are two major challenges in its application: first, poor fatigue characteristics, easy fracture failure under repeated cyclic strain; second, it cannot be recycled, and traditional recycling methods such as incineration and pickling pollute the environment. In response to the above challenges, PhD student Li Fali, associate researcher Liu Yiwei and researcher Li Runwei prepared liquid metal-based flexible circuits on paper instead of traditional copper, aluminum, and silver circuits, which not only solved the problem of poor bending fatigue, but also Recycling (Figure 2 is a circuit made with liquid metal before and after recycling), which realizes the greening of the entire life cycle of paper-based circuits during manufacturing, use, and recycling. The circuit line width is adjustable between 10μm-200μm, and through up to 10,000 times of folding tests, it is found that the maximum change rate of the circuit resistance is only 4%, which has good strain stability. In addition, the paper-based circuit has a good heat dissipation function. Experiments have shown that the temperature of LED lamps operating on liquid metal-based paper-based circuits is significantly lower than that of pure paper surfaces. This work provides a new method for developing green and recyclable flexible circuits. The results are published in Advanced Materials Technologies (Adv. Mater. Technol. 2018, 1800131).
(3) Digital Flexible Tactile Sensor
Making prosthetics tactile is the dream of many disabled people, and electronic skin is just such a system that can make human prosthetics prosthetic. However, most electronic skins can only convert external force stimuli into analog signals. They cannot convert external force stimuli into physiological pulses like human skin and accurately transmit them to the nervous system to the brain. In response to this problem, Ph.D. student Wu Yuanzhao, associate researcher Liu Yiwei and researcher Li Runwei cleverly used the inductor-capacitor (LC) oscillation mechanism to design the circuit (Figure 3a). When the external stress / strain causes the inductance to change, the LC circuit The frequency will change to obtain the corresponding relationship between the applied stress / strain and the frequency. By further optimizing the LC resonance circuit, it can work within the human body's physiological pulse frequency range. In addition, an "Air gap" structure is also designed (see Figure 3a). The amorphous wire is used as the magnetic core to improve its performance, and a digital flexible haptic with a sensitivity of 4.4kPa -1 and a detection limit of 10μN (equivalent to 0.3Pa) is obtained. The sensor device (see Figure 3b), and by optimizing the sensor's modulus and structure, it can be compatible with a wide detection range, which can sense weak mosquitoes and pulses, and can also sense the pressure when lifting heavy objects. This work provides a new method for developing digital bionic electronic skin.