Liquid metal used in physics and chemistry and 3D printing to create micro-vehicles

Recently, the Institute of Physics and Chemistry of the Chinese Academy of Sciences and the research group of Tsinghua University have developed a self-driving liquid metal machine coated with a magnetic functional layer and even a miniature vehicle with liquid metal as its wheels. In addition, the research team also reported for the first time the metal wire oscillation effect driven by liquid metal and the liquid metal jumping phenomenon triggered by metal particles. Prior to this, liquid metal machines all appeared in pure liquid form. The discovery of the solid-liquid combined machine effect and technological breakthroughs have enabled liquid metal machines to have functional endo and exoskeletons since then, which will speed up the development of flexible machines.

In the paper Self-Propelled Liquid Metal Motors Steered by Magnetic or Electrical Field for Drug Delivery in Journal of Materials Chemistry B (4, 5349, 2016, cover article), the research team used electroplating The surface of the liquid metal is embedded with a ferromagnetic nickel layer, which realizes the flexible control of the machine under the action of an external magnetic field or electric field, and verifies its potential value in drug delivery. Beyond the random movement of liquid metal machines, the magnetic solid-liquid combined machine can realize complex behaviors such as movement start and stop, steering and acceleration.

The cover story of the journal and the controllable and autonomous movement of a solid-liquid combined magnetic liquid metal machine coated with a nickel shell. Further, the research team also developed a miniature vehicle driven by a flexible and deformable “wheel”, which is composed of metal droplets. It is combined with a 3D printed plastic body. Under the action of an electric field, the liquid metal “wheels” can be rotated and deformed, which in turn drives the vehicle to travel, accelerate and even achieve more complex motions. Using a structure similar to a four-wheel drive vehicle, the research team confirmed that it can move at a speed of 25 mm/s while carrying a weight of 0.4 g. The design concept of this solid-liquid assembled flexible machine can derive more complex and controllable machine structures. The corresponding research was published in RSC Advances (Liquid Metal Wheeled Small Vehicle for Cargo Delivery, 6, 56482-56488, 2016).

In a paper titled Liquid Metal Machine Triggered Violin-like Wire Oscillator (10.1002/advs.201600212, 2016; cover article) published in Advanced Science, the research team reported an unusually unique liquid The self-excited oscillation effect of the metal-solid-liquid combined machine: When the treated copper wire touches the liquid metal containing aluminum, the copper wire will be swallowed by the liquid metal quickly, and then it will shuttle back and forth for a long time on the liquid metal body, like The strings of the violin in playing music are average. In addition, by touching the liquid metal with the stainless steel wire, the oscillation behavior of the copper wire can also be controlled by frequency and amplitude modulation. The mechanism of the above phenomenon is mainly due to the difference in the wetting force between the liquid metal and the copper wire caused by the reaction of aluminum with the alkaline solution. Here, the dynamic coupling of the multiphase interface between the copper wire, liquid metal, electrolyte and hydrogen produces Rhythmic traction. This breakthrough discovery has revolutionized the traditional understanding of interface science and opened up new ideas for the development of flexible intelligent machines. It can also develop control switches for fluid, electrical, mechanical, and optical systems.

In a paper titled Jumping Liquid Metal Droplet in Electrolyte Triggered by Solid Metal Particles (108, 223901, 2016) published in Applied Physics Letters, the authors discovered an interesting class of liquid metals Jumping behavior: After adding solid metal particles (nickel, iron, etc.) to the solution system with metal droplets, the originally static metal droplets begin to jump and leave a series of pie-shaped “footprints” on the bottom of the container. Studies have revealed that when the metal particles are in point contact with the surface of the liquid metal, the electric field strength at the interface is significantly increased, so that hydrogen will be electrolyzed in the solution, and the hydrogen bubbles will continue to adsorb and grow on the substrate to form a “gas spring”, which is a droplet. Jumping provides thrust. One of the factors that cause electric field polarization is the potential difference between the liquid metal and the solid metal particles, that is, the galvanic effect; the other reason is that the microscopic morphology difference between the solid-liquid material interface will lead to the accumulation of electric charge, and then the tip discharge effect.

For more than ten years, the team led by Liu Jing, a researcher from the Institute of Physics and Chemistry, has carried out a large number of original explorations around liquid metal, and has achieved comprehensive breakthroughs in the fields of chip cooling, advanced manufacturing, electronic technology, biomedical and flexible machines. So far, the team has discovered more than 30 types of basic liquid metal phenomena or effects with important scientific significance, developed dozens of practical technologies, and promoted industrialization across the country, including Beijing, Yunnan, Guangdong, etc., and successively contributed to the leading The construction of the production line of liquid metal products, the R&D center and the science and technology museum is completed, and a variety of products have entered the market. The concept of creating a liquid metal valley and even developing a new industrial system for liquid metal is also turning from an ideal into a reality. The results are in the academic circles at home and abroad. And the industry has a major impact. Part of the above research was funded by the President’s Fund of the Chinese Academy of Sciences.

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