Combination of graphene microtubule packaged liquid metal magnetofluid and preparation method and application of combination of graphene microtubule packaged liquid metal magnetofluid

Abstract

The invention discloses a graphene microtube packaged liquid metal magnetofluid assembly which is composed of a hollow thin-wall graphene microtube located on the outer portion and a liquid metal magnetofluid packaged in the graphene microtube. The assembly provided by the invention can stabilize a high-quality and continuous graphene microtube structure with the thickness of several nanometers by utilizing the packaging material in the hollow tube and the polymer supporting layer on the tube wall. Meanwhile, the graphene microtubes can accommodate and protect the liquid metal magnetofluid, so that the liquid metal magnetofluid is prevented from being oxidized and split-phase, and the fluid performance is prevented from being lost and degraded. And finally, the conductivity, fluidity and magnetism of the graphene microtube and the liquid metal magnetofluid are cooperatively utilized, the combination can measure parameters such as magnetic induction intensity, movement direction and speed according to the Faraday electromagnetic induction principle, and the combination is applied to a multifunctional sensor.

Description

Technical Field

[0001] The present invention relates to a method for preparing graphene structures and their assemblies, and in particular, to an assembly of graphene microtubes encapsulating liquid metal magnetofluid, a preparation method and an application thereof, belonging to the technical field of graphene. Background Art

[0002] As a two-dimensional material, graphene has many excellent properties. Creating various forms of graphene structures / materials / composites is of great significance for the development and application of graphene. In addition to common forms such as graphene fibers, films, and sponges, there is also a special form of graphene microtubes. The tube diameters of graphene microtubes are concentrated in the range of millimeters to sub-millimeters, and their inner diameters, wall thicknesses, and lengths are controllable. They have the characteristics of low density, high strength, and excellent electrical and thermal conductivity, and are highly malleable / bendable / foldable. They have good application prospects in the fields of microfluidics, microreactors, catalysis, purification, separation, drug delivery systems, sensing, and environmental protection.

[0003] Currently, common methods for preparing graphene microtubes in the field include: chemical vapor deposition template method, template-assisted self-assembly reduction method, coaxial electrospinning method, etc. The latter two methods involve the assembly and reduction of graphene oxide, and the tube walls of the obtained microtubes are formed by stacking reduced graphene oxide (rGO). The thickness is large, and the structural integrity of rGO is poor, resulting in poor electrical and thermal conductivity, which limits the performance and subsequent applications of the microtubes.

[0004] Chemical vapor deposition is a common method for preparing high-quality graphene. Its principle is that the active intermediate products generated by the high-temperature pyrolysis of carbon-containing precursors are controllably deposited or dissolved and precipitated on the surface of a metal substrate with catalytic activity, and then graphene is formed. The most common is to prepare sheet-like graphene on the surface of copper foil or nickel foil. If a metal wire is used to replace the metal foil and the growth conditions are adjusted, a complete and closed graphene can be prepared on the surface of the metal wire. The metal wire can be regarded as a template, and the graphene on its surface forms graphene microtubes. The inner diameter of the graphene microtubes can reach more than one hundred micrometers. Relatively speaking, their tube walls are very thin, only at the nanoscale. If the metal wire template is removed, the microtube structure is difficult to self-support and is prone to deformation or collapse, and other materials or structural designs need to be combined to enhance its stability.

[0005] Traditional magnetic fluids refer to suspensions in which magnetic particles are uniformly dispersed in carrier liquids such as water, oil, or organic solvents. It combines fluidity and magnetism, and has characteristics such as rapid magnetic response, reversible viscosity change, and controllable thermal and optical properties. However, the density and boiling point of the carrier liquid of traditional magnetic fluids are relatively low and volatile, which limits the suspension stability and working temperature range of magnetic fluids. Using liquid metal as the carrier liquid and uniformly dispersing magnetic particles in it can obtain liquid metal magnetic fluids, which can not only overcome the above limitations, but also introduce high electrical conductivity and high thermal conductivity to magnetic fluids. At the same time, combining magnetic and hydrodynamic properties can greatly expand the functions and applications of magnetic fluids. For example, liquid metal magnetic fluids have a large magnetic Reynolds number and are expected to simulate electromagnetic phenomena that are difficult to observe under some common conditions at room temperature, such as the magnetic fluid phenomenon of ferromagnetic substances flowing in the earth's core.

[0006] High-quality graphene microtubes have a complete wall structure, high electrical conductivity and high thermal conductivity. At the same time, the microtubes are hollow, and the tube diameter and tube length can be adjusted. They are very suitable as multifunctional pipes for containing and transporting fluids, and can also be used as an ideal platform to study the interaction between the intrinsic properties of graphene and the contents of the microtubes. Encapsulating liquid metal magnetic fluid into graphene microtubes to form a composite body, the graphene layer on the tube wall can isolate external water vapor and oxygen, thus ensuring that the liquid metal is not oxidized and maintaining its hydrodynamic properties. The composite body can be used to study the interaction and coupling phenomena between graphene and liquid metal magnetic fluid in a complex electromagnetic environment, and can also be used to construct magnetic sensors or motion sensors. Summary of the Invention

[0007] The object of the present invention is to provide a composite body structure formed by encapsulating liquid metal magnetic fluid in graphene microtubes, its preparation method, and the application of such a composite body in view of the above technical analysis.

[0008] The object of the present invention is achieved by the following technical solutions: A combination body using graphene microtubes to encapsulate liquid metal magnetofluid. The combination body consists of two parts. The external part is a hollow thin-walled graphene microtube, which acts as an encapsulation container. Inside the hollow microtube, room-temperature liquid metal magnetofluid is filled. Due to the relatively large surface tension of the liquid metal, it cannot be completely wetted with graphene. Therefore, when a certain amount of liquid metal magnetofluid is encapsulated in the graphene microtube, looking along the radial cross-section of the microtube, the liquid metal magnetofluid will fill the entire inner diameter radial cross-section of the microtube and be in complete contact with the graphene on the inner side of the tube wall. When observing along the axial cross-section of the microtube, both end faces of the encapsulated liquid metal magnetofluid are convex liquid surfaces. When the inner diameter of the graphene microtube is fixed, the volume of the encapsulated liquid metal magnetofluid is proportional to the length of the magnetofluid "liquid column". Therefore, a specific amount of liquid metal magnetofluid can be encapsulated into a graphene microtube as needed, and the microtube can be either fully filled or not. In the case of not being fully filled, the relative position of the magnetofluid liquid column in the microtube can be adjusted by a magnetic field, and the tube wall of the graphene microtube does not affect the magnetic responsiveness of the magnetofluid. At the same time, because the inner layer of the tube wall of the graphene microtube is formed by highly conductive graphene, even if the liquid metal magnetofluid does not completely fill the entire microtube, this section of the magnetofluid liquid column can form an electronic path with the outside through the tube wall, and the resistance is very small.

[0009] The graphene microtube is characterized by a relatively thin tube wall and a relatively large hollow inner diameter.

[0010] The inner diameter of the graphene microtube is the same as the outer diameter of the metal wire used in the preparation of the graphene microtube. The material of the metal wire should be a metal or alloy that can catalyze the growth of graphene through chemical vapor deposition, such as copper, nickel, platinum, ruthenium, iridium, gold, silver, aluminum, etc. Preferably, they are copper and nickel. If the diameter of the metal wire is too small, the surface curvature is too large and the surface metal lattice stress is large. If the diameter of the metal wire is too large, the surface metal is unevenly heated during the annealing process. Both situations may affect the quality of graphene growth on the surface of the metal wire. Therefore, the diameter of the metal wire, that is, the inner diameter of the final graphene microtube, is 0.1 - 3 mm, preferably 0.5 - 1.5 mm.

[0011] The tube wall of the graphene microtube consists of two tightly combined inner and outer layers. The inner layer is the graphene grown on the surface of the metal wire. This graphene layer is prepared by chemical vapor deposition process, with low impurity content, good lattice integrity, and excellent electrical and thermal conductivity. Its number of layers can be controlled by the conditions during the graphene growth process. Preferably, it is mainly controlled by adjusting the concentration of the carbon source component during the growth process. If the number of layers is too large, the excellent intrinsic properties of graphene will deteriorate, such as the conductivity will decrease. If the number of layers is too small, there may be hole defects in the local area of the graphene tube, resulting in damage to the overall conductivity and sealing performance of the microtube, and at the same time, the strength of the tube wall is limited. The number of graphene layers in the tube wall of the graphene microtube is 1 - 10 layers. Considering the graphene layer spacing, the total thickness is 0.3 - 4 nm. Preferably, the number of graphene layers is 2 - 3 layers, at this time, the strength, conductivity, etc. of the tube wall reach a better balance. Considering that the ratio of the inner diameter of the graphene microtube to the thickness of the graphene layer in the tube wall is greater than 25000, if the metal wire template is removed, the mechanical strength of the graphene layer is not sufficient to support such a large hollow structure and may collapse and deform. Therefore, the tube wall of the graphene microtube needs to be combined with a thicker support layer to provide mechanical support for the hollow microtube. The support layer should be on the outside of the graphene layer and have a good bonding force with graphene. Its material should be one or any combination of polymers such as polymethyl methacrylate, polyacrylonitrile, polyvinyl alcohol, polystyrene, polyethylene, polyimide, polycarbonate, etc. Preferably, it should be polymethyl methacrylate or polyacrylonitrile. The thickness of the support layer on the outside of the tube wall is sufficient to keep the hollow structure of the microtube from collapsing. Its thickness depends on the type of polymer used and can be in the range of 0.5 - 3 μm.

[0012] The liquid metal magnetofluid involved in the present invention needs to be in a flowing state at room temperature. The base liquid of the magnetofluid is selected as a metal gallium-based alloy, and more preferably, a GaInSn alloy is selected. According to the relationship between the alloy ratio and its melting point and the requirement of dispersing magnetic particles, the mass percentage of Ga in the GaInSn alloy is 65 - 75%, the mass percentage of In is 18 - 23%, and the mass percentage of Sn is 8 - 12%. The magnetic particles should have good compatibility with the room-temperature liquid metal, be not easily corroded, have an adjustable loading amount and can reach a large value to improve the magnetic responsiveness. The magnetic particles are one of iron, cobalt, nickel, iron oxide, iron-nickel alloy, neodymium iron boron, etc. Preferably, they are iron or neodymium iron boron. The methods of dispersing magnetic particles into the liquid metal include oxidation mixing method, metal interdiffusion method, surface modification method, etc. The selected magnetic particles in the present invention have good compatibility with the liquid metal. During the preparation process of the magnetofluid, mechanical grinding under atmosphere protection is used, and there will be no oxidation. There is no need to coat or chemically modify the magnetic particles, no need to introduce surfactants, and both nano-scale magnetic particles and micro-scale magnetic particles can be dispersed in the liquid metal matrix to form a magnetofluid and stably exist. The particle size range of the magnetic particles is 30 - 5000 nm.

[0013] The present invention also provides a preparation method for a combination of graphene microtubes encapsulating liquid metal magnetic fluid. The preparation of the combination is divided into three parts, namely the preparation of graphene microtubes, the preparation of liquid metal magnetic fluid, and the encapsulation of liquid metal magnetic fluid into graphene microtubes.

[0014] The preparation method of graphene microtubes is as follows: (1) Preparation of the graphene layer on the tube wall: Select a metal wire with a diameter of 0.1 - 3 mm, and use the atmospheric pressure chemical vapor deposition process to grow graphene on the surface of the metal wire to obtain a metal wire completely covered with graphene. The specific parameters of the atmospheric pressure chemical vapor deposition process, such as the temperature, time, carrier gas composition and partial pressure, and carbon source type and concentration in each link during annealing, growth, and cooling, can be adjusted by those skilled in the art according to the process principle and regulation rules, depending on the equipment, raw materials, target number of layers, etc., as long as it can achieve the growth of graphene on the surface of the metal wire that is complete, continuous, with uniform number of layers, and excellent structure. The number of layers of graphene is 1 - 10 layers, preferably 2 - 3 layers. A fixed length of the metal wire can be intercepted and graphene growth can be carried out successively, or a continuous process can be used to continuously grow graphene on the surface of the metal wire, and then the required length of the graphene-coated metal wire can be intercepted; (2) Preparation of the polymer layer on the tube wall: The polymer is selected from one of polymethyl methacrylate, polyacrylonitrile, polyvinyl alcohol, polystyrene, polyethylene, polyimide, polycarbonate, or a specific combination thereof, and this combination needs to be soluble in the same organic solvent or mixed solvent. The concentration of the polymer solution is appropriate, and it has a suitable viscosity to form a film on the surface of the graphene-coated metal wire by the dipping method and dry quickly. After each dipping, it is dried moderately until the polymer layer is basically dry and no longer flows. Repeat this dipping and film-forming process 2 - 5 times, and the last time it needs to be thoroughly dried to completely remove the solvent in the polymer layer. The polymer layer should be complete, continuous, and have a uniform thickness, and its thickness is 0.5 - 3 μm, which can provide sufficient mechanical support to maintain the hollow structure of the microtube; (3) Preparation of the microtube connection section: Take a polytetrafluoroethylene tube with a length of 1 - 1.5 cm and an inner diameter the same as that of the metal wire used in step (1), and put one end of it on the outside of the product obtained in step (2), and insert it about 5 mm. Then use the polymer solution used in step (2), drop it on the interface of the polytetrafluoroethylene tube and dry it thoroughly, so that the polytetrafluoroethylene tube is firmly fixed on the outside of the polymer layer and the joint is sealed without leakage. The strength and elasticity of the polytetrafluoroethylene tube are appropriate, which is convenient for subsequent firm connection of the syringe needle. If only graphene microtubes are to be obtained without encapsulating fluid in the microtubes, this step is not required; (4)Removing the metal wire template by chemical etching: According to the type of metal wire used in the previous steps, select a suitable chemical etchant such as an acid or a strong oxidant to etch and remove the metal wire template. If the preferred metal wire is copper wire, the preferred etchant is ferric chloride solution or ammonium persulfate solution. The concentration of the etching solution generally does not exceed 0.5 mol / L to avoid local collapse of the microtubes due to too fast etching speed or uneven etching with local metal residues. Subsequently, gradually replace the etching solution with clean water to thoroughly wash and remove the graphene microtubes with the metal wire template. Two peristaltic pumps can be used. One slowly pumps out the etching solution, and the other slowly injects clean water to keep the total liquid volume in the container unchanged, with no obvious flow of the liquid and no shaking of the sample. After thorough cleaning, pump out most of the water in the container, leaving only a small amount of water just to cover the graphene microtubes. Subsequently, move the sample and the container as a whole into the vacuum chamber and turn on the vacuum pump to evacuate. Then, a small amount of water will quickly freeze because the temperature decreases due to adiabatic expansion of the system, and the graphene microtubes are fixed in the ice crystals. Continue to evacuate, and the ice directly sublimes and gradually decreases, and the thin-walled hollow self-supporting graphene microtubes are gradually exposed from the ice. After freeze-drying, complete graphene microtubes are obtained; (5)A hollow graphene microtube can be obtained according to the above steps. A 1 - 1.5 cm long polytetrafluoroethylene tube is fixed at one end of the microtube. The graphene microtube is very thin-walled and very soft and easy to fold and deform, while the polytetrafluoroethylene tube is relatively stiffer. Hold the polytetrafluoroethylene tube with tweezers and insert it into a straight stainless steel needle with a diameter matching it. The inserted length is about 5 mm. Subsequently, use hot melt adhesive to seal and fix the joint between the needle and the polytetrafluoroethylene tube.

[0015] The purpose of the following method steps is to prepare liquid metal magnetic fluid: Use water, ethanol, and acetone to ultrasonically clean the magnetic particles in sequence. After thorough drying, transfer them into an inert atmosphere glove box; transfer the liquid metal into the glove box. Preferably, the liquid metal is GaInSn alloy, and the magnetic particles are iron or neodymium iron boron. All the following operations are carried out inside the glove box. Extract a certain amount of liquid metal with good fluidity below the surface oxide layer and place it in a mortar. Take a small amount of magnetic particles and also pour them into the mortar, and then thoroughly grind the mixture of the liquid metal and the magnetic particles. As the grinding progresses, the magnetic particles on the surface of the mixture gradually fuse with the liquid metal and enter the interior of the alloy phase. Subsequently, repeat the above steps to increase the magnetic particle loading. Finally, the magnetic particles will form an approximately continuous film on the surface of the mixture and cannot obtain sufficient fluidity. At this time, the maximum loading of this particle is reached. Use a syringe or a pipette gun to collect the well-mixed part with good fluidity, and then liquid metal magnetic fluid can be obtained; The purpose of the following method steps is to prepare a combination of graphene encapsulated liquid metal magnetic fluid: Load the liquid metal magnetic fluid obtained in the above steps into a syringe, and attach the straight stainless steel needle with the graphene microtubes fixed in step (5). Place the soft hollow graphene microtube and the needle horizontally on the same glass slide, and fix the metal needle part. Slowly push the syringe using a micro-injection pump, and slowly inject the liquid metal magnetic fluid through the metal needle into the graphene microtube. It can be seen that the microtube changes from transparent to a plump tube with a metallic luster. Cut the connection at one end of the syringe needle to obtain a combination of graphene-encapsulated liquid metal magnetic fluid.

[0016] Furthermore, the present invention provides an application of using the combination of graphene-encapsulated liquid metal magnetic fluid to prepare a sensing device.

[0017] This sensing device is based on the Faraday electromagnetic induction principle and makes full use of the electromagnetic properties of the combination. The basic structure of this sensing device is as follows: Fix the combination of graphene-encapsulated liquid metal magnetic fluid on an insulating substrate such as a glass slide, and drop a drop of liquid metal at each end of the combination; Insert one end of a thin and flexible metal wire into the liquid metal to achieve electrical connection with the graphene microtube, and fix the metal wire on the glass slide to prevent it from detaching from the liquid metal and causing an open circuit; Use two metal wires to connect the two ends of the combination and the two electrodes of a voltage detection device such as an oscilloscope / digital source meter, etc.; The combination, the two metal wires, and the voltage detection device form a loop.

[0018] The insulating substrate in this sensing device and the combination move together in a specific magnetic field. The moving speed or one of its components must cut the magnetic induction line, that is, any movement other than completely parallel to the magnetic induction line meets the requirements. The movement will cause an induced electromotive force to be generated in the combination, which can be measured by the voltage detection device in the loop. When the system error such as the loop resistance is constant, the signal intensity of the induced electromotive force is positively correlated with the magnetic induction intensity and the moving speed, and the positive and negative of the signal are related to the moving direction and the loop connection method. Therefore, when the magnetic induction intensity is known, this sensing device can measure the moving speed and direction, that is, act as a motion sensor; when the moving speed is known, this sensor can measure the magnetic induction intensity at a specific position, that is, act as a magnetic sensor.

[0019] The beneficial effects of the present invention are: The composite provided by this method can utilize the encapsulant within the hollow tube and the polymer support layer of the tube wall to stabilize a high-quality, continuous graphene microtube structure with a thickness of only a few nanometers. Meanwhile, the graphene microtube can accommodate and protect the liquid metal ferrofluid, preventing it from oxidation and phase separation, and thus losing and deteriorating its fluid properties. Finally, by synergistically utilizing the electrical conductivity, fluidity, and magnetism of the graphene microtube and the liquid metal ferrofluid, this composite can measure parameters such as magnetic induction intensity, motion direction, and velocity based on the principle of Faraday electromagnetic induction, and be applied as a multifunctional sensor. This composite may also be used to study the more complex coupled interaction between graphene and liquid metal ferrofluid. Description of the Drawings

[0020] Figure 1 In [figure], a is the scanning electron micrograph of the graphene microtube, and b is the optical photograph; Figure 2 In [figure], a is the Raman spectrum of the graphene grown on the surface of the copper wire, b is the Raman spectrum of the hollow graphene microtube, and c is the Raman spectrum of the polymethyl methacrylate microtube; Figure 3 In [figure], a is the scanning electron micrograph of the GaInSn alloy liquid metal, b is the scanning electron micrograph of the iron powder particles with an average particle size of 2000 nm, and c is the scanning electron micrograph of the liquid metal ferrofluid; Figure 4 In [figure], a is the optical photograph of the composite of the graphene microtube encapsulating the liquid metal ferrofluid, and b and c are the schematic diagrams of the sensing device constructed by the composite; Figure 5 It is the typical signal of the induced electromotive force generated by the reciprocating motion obtained by oscilloscope testing when the composite of the graphene microtube encapsulating the liquid metal ferrofluid is applied as a sensing device. Detailed Embodiments

[0021] To better understand the content of the present invention, multiple specific implementation schemes are provided below. Those skilled in the art will make adjustments according to the actual situation for each implementation scheme, and may also combine the technical features of multiple implementation schemes. However, those skilled in the art will understand that the provided embodiments are only used to illustrate the present invention more clearly, and do not limit the scope of the present invention in any way.

[0022] Example 1 The preparation steps of a composite of a graphene microtube encapsulating a liquid metal ferrofluid are as follows: (1) Select a copper wire with a diameter of 0.2 mm, and grow graphene on the surface of the copper wire using the atmospheric pressure chemical vapor deposition process to obtain a copper wire completely covered with graphene. Adjust the process conditions of each link so that the number of layers of the obtained graphene is 5 layers; (2) Immerse the copper wire coated with vinyl in the anisole solution of polymethyl methacrylate. After each immersion, dry it moderately until the polymer layer no longer flows. Repeat the immersion process 3 times and then dry it thoroughly. The thickness of the polymethyl methacrylate layer is 2 μm; (3) Take a 1-cm-long polytetrafluoroethylene tube with an inner diameter of 0.2 mm and put one end of it outside the product obtained in step (2), with about 5 mm inserted. Drop the anisole solution of polymethyl methacrylate at the interface and dry it thoroughly to fix and seal; (4) Put the product obtained in step (3) into the ferric chloride solution to completely etch away the copper wire. Replace the ferric chloride solution with slow-flowing clear water and thoroughly wash the graphene microtube. Leave a small amount of water to just cover the graphene microtube, evacuate to freeze the small amount of water and sublime the ice, and complete freeze-drying to obtain the graphene microtube ( Figure 1 ); (5) Use tweezers to insert the polytetrafluoroethylene tube at one end of the graphene microtube obtained in step (4) into a straight stainless-steel needle with a matching diameter, with the inserted length about 5 mm. Fix and seal the joint between the two with hot melt adhesive; (6) In a glove box with an inert atmosphere, extract the Ga 0.68 In 0.20 Sn 0.12 alloy with good fluidity below the surface oxide layer and place it in a mortar. Also add a small amount of cleaned and dried iron powder with a particle size of 50 nm to the mortar and thoroughly grind the mixture. The iron powder will gradually fuse and disperse into the alloy. Repeat adding iron powder and thoroughly grinding and dispersing until the iron powder forms an approximate film on the surface and cannot be incorporated into the alloy with fluidity, then the maximum loading amount is reached. Collect the uniformly mixed flowing part to obtain the liquid metal magnetic fluid; (7) Load the liquid metal magnetic fluid obtained in step (6) into a syringe. Attach a straight stainless-steel needle connected to the graphene microtube to the syringe and place the needle and the graphene microtube on the same glass slide. Use a micro-injection pump to slowly push the liquid metal magnetic fluid into the graphene microtube and cut off its connection with the needle, then obtain the combination of graphene-encapsulated liquid metal magnetic fluid.

[0023] Through the above steps, a combination of graphene microtubes encapsulating liquid metal magnetofluid is obtained, which consists of a hollow thin-walled graphene microtube on the outside and a liquid metal magnetofluid encapsulated inside the graphene microtube. Among them, the inner diameter of the hollow graphene microtube is 0.2 mm, the inner side of the tube wall is graphene with 5 layers and a total thickness of 1.75 nm, and the outer side of the tube wall is polymethyl methacrylate with a thickness of 2 μm. The liquid metal magnetofluid is composed of a GaInSn alloy and iron nanoparticles dispersed therein. The mass percentage of Ga in the GaInSn alloy is 68%, the mass percentage of In is 20%, and the mass percentage of Sn is 12%; the average particle size of the iron nanoparticles is 50 nm. The liquid metal magnetofluid fills the entire section of the graphene microtube.

[0024] This combination of graphene microtubes encapsulating liquid metal magnetofluid can be used to prepare a sensing device, which can measure the magnetic induction intensity at a known moving speed as a magnetic sensor. The structure of the sensing device is as follows: The combination is fixed on an insulating substrate such as a glass slide. The two ends of the combination are connected to two copper wires through additional GaInSn droplets, and the other two ends of the two copper wires are connected to an oscilloscope. The copper wires are fixed on the glass slide to prevent them from detaching from the liquid metal and causing an open circuit.

[0025] In this sensing device, the combination fixed on the glass slide moves in a magnetic field with a known moving speed. The signal intensity of the induced electromotive force generated by the combination cutting the magnetic induction line is measured by using an oscilloscope. Based on the Faraday electromagnetic induction principle, the magnetic induction intensity of the region where the combination is located can be obtained.

[0026] Example 2 The preparation steps of a combination of graphene microtubes encapsulating liquid metal magnetofluid are as follows: (1) Select a copper wire with a diameter of 0.5 mm, and grow graphene on the surface of the copper wire by atmospheric pressure chemical vapor deposition to obtain a copper wire completely covered with graphene. Adjust the process conditions of each link so that the number of layers of the obtained graphene is 3 layers ( Figure 2 a); (2) Immerse the copper wire covered with graphene in a anisole solution of polymethyl methacrylate. After each immersion, dry it moderately until the polymer layer no longer flows, and repeat the immersion process 5 times, then dry it thoroughly. The thickness of the polymethyl methacrylate layer is 3 μm; (3) Take a 1 cm long and 0.5 mm inner diameter polytetrafluoroethylene tube, and put one end of it on the outside of the product obtained in step (2), and insert it about 5 mm. Drop an anisole solution of polymethyl methacrylate on the interface ( Figure 2 c), and dry it thoroughly to fix and seal; (4) Place the product obtained in step (3) into an ammonium persulfate solution to completely etch away the copper wire. Replace the ammonium persulfate solution with slowly flowing clear water and thoroughly wash the graphene microtubes. Leave a small amount of water to just cover the graphene microtubes, evacuate to freeze the small amount of water and sublime the ice, and complete freeze-drying to obtain graphene microtubes; (5) Use tweezers to insert the polytetrafluoroethylene tube at one end of the graphene microtube obtained in step (4) into a straight stainless steel needle with a matching diameter. The inserted length is about 5 mm. Fix and seal the joint between the two with hot melt adhesive; (6) In a glove box with an inert atmosphere, extract the Ga 0.685 In 0.215 Sn 0.10 alloy with good fluidity below the surface oxide layer and place it in a mortar. Also add a small amount of washed and dried iron powder with a particle size of 800 nm to the mortar and thoroughly grind the mixture. The iron powder will gradually fuse and disperse into the alloy. Repeat adding iron powder and thoroughly grinding and dispersing until the iron powder forms an approximate film on the surface and cannot obtain fluidity to integrate into the alloy, then the maximum loading amount is reached. Collect the uniformly mixed flowing part to obtain a liquid metal ferrofluid; (7) Load the liquid metal ferrofluid obtained in step (6) into a syringe. The syringe is equipped with a straight stainless steel needle connected to the graphene microtube. Place the needle and the graphene microtube on the same glass slide. Use a micro-injection pump to slowly push the liquid metal ferrofluid into the graphene microtube and cut off its connection with the needle, then obtain a combination of graphene-encapsulated liquid metal ferrofluid.

[0027] Through the above steps, a combination of graphene microtube-encapsulated liquid metal ferrofluid is obtained, which consists of a hollow thin-walled graphene microtube on the outside and a liquid metal ferrofluid encapsulated inside the graphene microtube. Among them, the inner diameter of the hollow graphene microtube is 0.5 mm, the inner side of the tube wall is graphene with 3 layers and a total thickness of 1.05 nm, and the outer side of the tube wall is polymethyl methacrylate with a thickness of 3 μm ( Figure 2 b). The liquid metal ferrofluid is composed of a GaInSn alloy and iron nanoparticles dispersed therein. The mass percentage of Ga in the GaInSn alloy is 68.5%, the mass percentage of In is 21.5%, and the mass percentage of Sn is 10%; the average particle size of the iron nanoparticles is 800 nm. The liquid metal ferrofluid fills the entire section of the graphene microtube.

[0028] This combination of graphene microtubes encapsulating liquid metal magnetofluid can be used to prepare a sensing device, which can measure the magnetic induction intensity as a magnetic sensor at a known moving speed. The structure of the sensing device is as follows: Fix the combination on an insulating substrate such as a glass slide. Both ends of the combination are connected to two aluminum wires through additional GaInSn droplets. The other ends of the two aluminum wires are connected to an oscilloscope. Fix the aluminum wires on the glass slide to prevent them from detaching from the liquid metal and causing an open circuit.

[0029] In this sensing device, the combination fixed on the glass slide moves in a magnetic field with a known moving speed. Use an oscilloscope to measure the signal intensity of the induced electromotive force generated by the combination cutting the magnetic induction line. Based on Faraday's law of electromagnetic induction, the magnetic induction intensity of the region where the combination is located can be obtained.

[0030] Example 3 The preparation steps of a combination of graphene microtubes encapsulating liquid metal magnetofluid are as follows: (1) Select a copper wire with a diameter of 1.5 mm. Use the atmospheric pressure chemical vapor deposition process to grow graphene on the surface of the copper wire to obtain a copper wire completely covered with graphene. Adjust the process conditions of each link so that the number of layers of the obtained graphene is 6 layers; (2) Immerse the graphene-coated copper wire in an ethyl acetate solution of polymethyl methacrylate. After each immersion, dry it moderately until the polymer layer no longer flows. Repeat the immersion process 4 times and dry it thoroughly. The thickness of the polymethyl methacrylate layer is 2.5 μm; (3) Take a 1.5 cm long and 1.5 mm inner diameter polytetrafluoroethylene tube, and put one end of it on the outside of the product obtained in step (2), and insert it about 5 mm. Drop an ethyl acetate solution of polymethyl methacrylate at the interface and dry it thoroughly to fix and seal; (4) Put the product obtained in step (3) into an ammonium persulfate solution to completely etch and remove the copper wire. Replace the ammonium persulfate solution with slow-flowing clean water and thoroughly wash the graphene microtubes. Leave a small amount of water to just cover the graphene microtubes, evacuate to freeze the small amount of water and sublime the ice, and complete freeze-drying to obtain graphene microtubes; (5) Use tweezers to insert the polytetrafluoroethylene tube at one end of the graphene microtube obtained in step (4) into a straight stainless steel needle with a matching diameter, and insert it about 5 mm. Fix and seal the joint with hot melt adhesive; (6) In a glove box with an inert atmosphere, extract Ga 0.72 In 0.19 Sn 0.09 alloy ( Figure 3 a) and place it in a mortar. Put a small amount of washed and dried iron powder with a particle size of 2000 nm ( Figure 3b) Also add it to the mortar and thoroughly grind the mixture. The iron powder will gradually fuse and disperse into the alloy. Repeat the addition of iron powder and thorough grinding and dispersion until the iron powder forms an approximate film on the surface and loses its fluidity and cannot be incorporated into the alloy, then the maximum loading amount is reached. Collect the uniformly mixed flowing part to obtain the liquid metal magnetic fluid ( Figure 3 c); (7) Load the liquid metal magnetic fluid obtained in step (6) into a syringe. Attach a straight stainless-steel needle connected to a graphene microtube to the syringe, and place the needle and the graphene microtube on the same glass slide. Use a micro-injection pump to slowly push the liquid metal magnetic fluid into the graphene microtube and cut off its connection with the needle, then a combination of graphene-encapsulated liquid metal magnetic fluid is obtained.

[0031] Through the above steps, a combination of graphene microtube-encapsulated liquid metal magnetic fluid is obtained, which consists of a hollow thin-walled graphene microtube on the outside and a liquid metal magnetic fluid encapsulated inside the graphene microtube. Among them, the inner diameter of the hollow graphene microtube is 1.5 mm, the inner side of the tube wall is graphene with 6 layers and a total thickness of 2.1 nm, and the outer side of the tube wall is polymethyl methacrylate with a thickness of 2.5 μm. The liquid metal magnetic fluid is composed of a GaInSn alloy and iron particles dispersed therein. The mass percentage of Ga in the GaInSn alloy is 72%, the mass percentage of In is 19%, and the mass percentage of Sn is 9%; the average particle size of the iron particles is 2000 nm. The liquid metal magnetic fluid does not fill the entire graphene microtube ( Figure 4 a).

[0032] This combination of graphene microtube-encapsulated liquid metal magnetic fluid can be used to prepare a sensing device, and this device can measure the magnetic induction intensity at a known moving speed as a magnetic sensor. The structure of this sensing device is as follows: Fix the combination on an insulating substrate such as a glass slide, and connect the two ends of the combination to two copper wires through additional GaInSn droplets ( Figure 4 b), and the other two ends of the two copper wires are connected to a digital source meter. Fix the copper wires on the glass slide to prevent them from detaching from the liquid metal and causing an open circuit ( Figure 4 c).

[0033] In this sensing device, the combination fixed on the glass slide moves in a magnetic field with a known moving speed. Use an oscilloscope to measure the signal intensity of the induced electromotive force generated by the combination cutting the magnetic induction line. Based on Faraday's law of electromagnetic induction, the magnetic induction intensity of the region where the combination is located can be obtained.

[0034] Example 4 The preparation steps of a combination of graphene microtube-encapsulated liquid metal magnetic fluid are as follows: (1) Select a nickel wire with a diameter of 2.5 mm, and grow graphene on the surface of the nickel wire using a normal pressure chemical vapor deposition process to obtain a nickel wire completely covered with graphene. Adjust the process conditions of each link so that the number of layers of the obtained graphene is 3; (2) Use a dimethylformamide solution of polyacrylonitrile to impregnate the olefin-coated nickel wire. After each impregnation, dry it appropriately so that the polymer layer no longer flows. Repeat the impregnation process 4 times and dry it thoroughly. The thickness of the polyacrylonitrile layer is 3 μm; (3) Take a 1 cm long, 2.5 mm inner diameter polytetrafluoroethylene tube and put one end of it around the outside of the product obtained in step (2), inserting about 5 mm. Apply a drop of polyacrylonitrile dimethylformamide solution to the interface and dry thoroughly to fix and seal; (4) Place the product obtained in step (3) into a dilute hydrochloric acid solution and completely etch away the copper wire. Replace the dilute hydrochloric acid solution with slowly flowing clean water and thoroughly wash the graphene microtubes. Leave a small amount of water to just cover the graphene microtubes, evacuate to freeze the small amount of water and allow the ice to sublime, and complete freeze drying to obtain the graphene microtubes; (5) Use tweezers to insert the polytetrafluoroethylene tube at one end of the graphene microtube obtained in step (4) into a straight stainless steel needle with a matching diameter, with the inserted length being about 5 mm. Use hot melt adhesive to seal the joint between the two; (6) In an inert atmosphere glove box, extract the Ga with good fluidity below the surface oxide layer. 0.685 In 0.215 Sn 0.10 The alloy is placed in a mortar, and a small amount of washed and dried NdFeB powder with a particle size of 4500nm is also added to the mortar. The mixture is fully ground, and the NdFeB powder will gradually blend and disperse into the alloy. Repeat the addition of NdFeB powder and fully grind and disperse until the NdFeB powder forms a film on the surface and cannot obtain fluidity to blend into the alloy, which means the maximum load is reached. Collect the evenly mixed flowing part to obtain a liquid metal magnetic fluid; (7) The liquid metal magnetic fluid obtained in step (6) is loaded into a syringe, and a straight stainless steel needle connected to a graphene microtube is installed on the syringe, and the needle and the graphene microtube are placed on the same glass slide. The liquid metal magnetic fluid is slowly pushed into the graphene microtube using a micro-injection pump, and the connection between the graphene microtube and the needle is cut off, thereby obtaining a graphene-encapsulated liquid metal magnetic fluid assembly.

[0035] Through the above steps, a combination of graphene microtubes encapsulating liquid metal magnetic fluid is obtained, which consists of a hollow thin-walled graphene microtube on the outside and a liquid metal magnetic fluid encapsulated inside the graphene microtube. Among them, the inner diameter of the hollow graphene microtube is 2.5 mm, the inner side of the tube wall is graphene with 3 layers and a total thickness of 1.1 nm, and the outer side of the tube wall is polyacrylonitrile with a thickness of 3 μm. The liquid metal magnetic fluid is composed of a GaInSn alloy and neodymium iron boron particles dispersed therein. The mass percentage of Ga in the GaInSn alloy is 68.5%, the mass percentage of In is 21.5%, and the mass percentage of Sn is 10%; the average particle size of the neodymium iron boron particles is 4500 nm. The liquid metal magnetic fluid does not fill the entire graphene microtube, and its occupied length is 60% of the total length of the microtube.

[0036] This combination of graphene microtubes encapsulating liquid metal magnetic fluid can be used to prepare a sensing device. As a motion sensor, this device can measure the rate and direction of motion when the magnetic induction intensity is known. The structure of the sensing device is as follows: The combination is fixed on an insulating substrate such as a glass slide. Both ends of the combination are connected to two gold wires through additional GaInSn droplets, and the other ends of the two gold wires are connected to a digital source meter. The gold wires are fixed on the glass slide to prevent them from detaching from the liquid metal and causing an open circuit.

[0037] In this sensing device, as Figure 5 shown, the combination fixed on the glass slide moves in a magnetic field with a known magnetic induction intensity. The oscilloscope is used to measure the signal intensity and signal positive / negative of the induced electromotive force generated by the combination cutting the magnetic induction line. Based on the Faraday electromagnetic induction principle, the rate of motion of the combination can be deduced from the signal intensity, and the direction of motion can be determined from the positive / negative of the signal.

Claims

1. A graphene microtube encapsulated liquid metal magnetic fluid assembly, characterized in that: It consists of a hollow thin-walled graphene microtube on the outside and a liquid metal magnetic fluid encapsulated inside the graphene microtube.

2. The graphene microtube-encapsulated liquid metal magnetic fluid assembly according to claim 1, characterized in that: The graphene microtube is a hollow microtube with an inner diameter of 0.1-3 mm. The inner side of the tube wall is a graphene with 1-10 layers and a total thickness of 0.3-4 nm, and the outer side of the tube wall is a polymer with a thickness of 0.5-3 μm. The polymer is one or more combinations of polymethyl methacrylate, polyacrylonitrile, polyvinyl alcohol, polystyrene, polyethylene, polyimide, and polycarbonate.

3. The graphene microtube-encapsulated liquid metal magnetic fluid assembly according to claim 1, characterized in that: The liquid metal magnetic fluid is composed of a GaInSn alloy matrix and magnetic particles dispersed therein: the mass percentage of Ga in the GaInSn alloy is 65-75%, the mass percentage of In is 18-23%, and the mass percentage of Sn is 8-12%; the magnetic particles are any one of iron, cobalt, nickel, ferroferric oxide, iron-nickel alloy or neodymium iron boron, and the average particle size is 30-5000nm.

4. The graphene microtube-encapsulated liquid metal magnetic fluid assembly according to claim 1, characterized in that: The liquid metal magnetic fluid encapsulated inside the graphene microtube is completely filled, or the liquid metal magnetic fluid occupies a length of 5 to 95% of the axial length of the microtube.

5. The method for preparing the assembly of graphene microtubes encapsulating liquid metal magnetic fluid according to claim 1, characterized in that: Here are the steps: (1) Using a normal pressure chemical vapor deposition process, 1 to 10 layers of graphene are grown on the surface of a metal wire with a diameter of 0.1 to 3 mm to obtain a graphene-covered metal wire, wherein the material of the metal wire is one of copper, nickel, platinum, ruthenium, iridium, gold, silver, aluminum or an alloy thereof; (2) coating the polymer solution on the surface of the olefin-coated metal wire by a dipping method and drying, repeating 2 to 5 times, and finally drying thoroughly to obtain a polymer coating layer with a thickness of 0.5 to 3 μm; (3) A 1-1.5 cm long polytetrafluoroethylene tube with an inner diameter equal to the diameter of the metal wire in step (1) is placed on one end of the product obtained in step (2), and the interface is sealed with the polymer solution in step (2) and thoroughly dried; (4) placing the product obtained in step (3) in a chemical etching solution to completely etch away the metal wire, then slowly but thoroughly washing the product with deionized water, and finally freeze-drying to obtain a self-supporting graphene microtube, wherein the inner diameter of the microtube is the same as the diameter of the metal wire used in step (1), the number and thickness of the graphene layers on the inner side of the tube wall are the same as the graphene grown on the surface of the metal wire in step (1), and the composition and thickness of the polymer on the outer side of the tube wall are the same as the composition and thickness of the polymer coating layer in step (2); (5) Insert the polytetrafluoroethylene tube at one end of the graphene microtube obtained in step (4) into a straight stainless steel needle with matching diameter, and seal and fix the joint with hot melt adhesive; (6) Under the protection of an oxygen-free atmosphere, the cleaned and dried magnetic particles are added to the unoxidized GaInSn alloy in batches, and each batch is fully ground after addition until the magnetic particles completely enter the alloy phase; until the magnetic particles form a film on the alloy surface and cannot enter the liquid metal phase, then the uniformly mixed flowing part is collected to obtain the liquid metal magnetic fluid; (7) The liquid metal magnetic fluid obtained in step (6) is loaded into a syringe, and the liquid metal magnetic fluid is slowly pushed into the graphene microtube connected thereto through the needle in step (5), thereby obtaining a combination of the graphene microtube encapsulating the liquid metal magnetic fluid.

6. Application of the combination of graphene microtubes encapsulating liquid metal magnetic fluid according to claims 1-5 to prepare a sensing device, which can measure the magnetic induction intensity at a known movement speed as a magnetic sensor, and can detect the movement speed and direction in a magnetic field with a known magnetic induction intensity as a motion sensor.

7. The use of the combination of graphene microtubes encapsulating liquid metal magnetic fluid according to claim 6, characterized in that: The sensor device is formed by fixing the assembly on an insulating substrate, connecting two ends of the assembly with two metal wires using additional liquid metal droplets, and the two metal wires are further connected to a voltage detection device to form a complete circuit.

8. The use of the graphene microtube encapsulated liquid metal magnetic fluid assembly according to claim 6, characterized in that: The insulating substrate and the assembly in the sensing device move together in the magnetic field, and the voltage detection device synchronously measures the induced electromotive force generated by the assembly cutting the magnetic flux lines, calculates the magnetic induction intensity or the movement speed by the intensity of the induced electromotive force, and determines the movement direction by the positive or negative value of the induced electromotive force.

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