The magnetic control effect of magnetic composite functional materials has shown great application value in the fields of soft robot, flexible electronics, energy technology and biomedicine, which has aroused great research interest. For example, the magnetic fluid is a kind of stable suspension which is composed of paramagnetic solid particles, interfacial active agent and base carrier liquid. It has both the flow deformation of liquid and the paramagnetism of solid. However, the magnetic field exists only when the external magnetic field is excited, and does not have permanent magnetic characteristics. Water and oil are often used as the base carrier fluid of magnetic fluid, which not only has poor conductivity, but also has a large density difference with magnetic particles, which leads to precipitation. These problems limit the practical application of MHD. Aiming at this problem, he Zhizhu's research group, Institute of technology, China Agricultural University, took gallium based liquid metal at room temperature as the base carrier and neodymium iron boron microparticles as the magnetic carrier to prepare the liquid metal permanent magnet with reconfigurable magnetic pole, which innovated the traditional solid characteristics of permanent magnet and the electrical insulation wire of magnetic fluid, with its unique high conductivity (& gt; 106s / M) and remanence (& gt); 30 EMU / g) and similar to the plasticine like reconfigurability are expected to show new applications in flexible electronics and soft robots. The results were published on advanced materials (DOI: 10.1002/adma.202000827, back cover paper).
The conductivity of liquid metal permanent magnet is due to the high conductivity of the base liquid itself, while its macro permanent magnetism is due to the orientation of NdFeB particles. Through the selection of NdFeB content and magnetization intensity, the interaction between magnetic particles in the base carrier liquid can be regulated, so as to realize the regulation of viscosity and magnetic intensity of liquid metal permanent magnet. When the Nd-Fe-B content reaches 40 wt%, the liquid metal base carrier liquid after saturation magnetization is firmly bound in the three-dimensional porous interconnected magnetic particles, and its overall behavior is similar to that of rubber mud, which can be repeatedly molded into various forms. In the process of remolding, the magnetic pole orientation of NdFeB particles is disturbed, which leads to the disappearance of macroscopic magnetism and the demagnetization of mechanical mechanics. The macroscopic magnetism can be restored by changing the internal magnetic pole of NdFeB particles by pulse magnetization. For the liquid metal permanent magnet film, the local magnetic pole can be reconstructed by the mechanical way of magnetic particle pole orientation induced by external magnetic field. Based on the above unique electromagnetic and mechanical characteristics, the paper also shows the applications of magnetic circuit printing, magnetic control switch and sensor, flexible paper-based magnetic storage, magnetic control software robot, etc. In particular, a paper-based creeping robot with magnetic control is realized by coating the liquid metal permanent magnet on the paper strip and reconstructing its local magnetic pole. Its creeping speed is as high as 29.7 mm / s. This study broadens the connotation of magnetic composite functional materials, and provides new ideas for the development of flexible electronics and software machines.
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