CN114150197B - Physical contact rapid reversible color change liquid metal composite material and application thereof - Google Patents

Abstract

The invention belongs to the technical field of functional materials, and in particular relates to a liquid metal composite material with rapid and reversible discoloration in physical contact and a preparation method and application thereof. The liquid metal composite material with rapid and reversible discoloration in physical contact comprises gallium and graphite. The invention does not need an external excitation source, and can realize rapid and reversible color change only through physical contact. The material provides a new and effective technical means for the surface color camouflage of liquid metal robots, and provides a new idea for the development and industrial application of low-power liquid metal color rendering materials. The patent of the present invention uses a simple material synthesis process, has no special condition requirements, is easy to operate, has simple equipment requirements, and is easy to produce on a large scale.

Description

A liquid metal composite material with rapid and reversible discoloration in physical contact and its application

technical field

The invention belongs to the technical field of functional materials, and in particular relates to a metal composite material that can realize rapid and reversible discoloration only through physical contact without an external excitation source, and a preparation method and application thereof.

technical background

Liquid metals, such as gallium (Ga), eutectic gallium indium (GaIn), and gallium indium tin (GaInSn), are becoming increasingly important functional materials in liquid muscles and macroscopic biomimetic liquid robots due to their low melting points and low voltage deformation capabilities . However, in the natural environment, its unique metallic luster makes liquid metal robots particularly easy to detect. Therefore, how to make the liquid robot integrate with the surrounding environment naturally, like the contact discoloration camouflage ability of the liquid metal robot T-1000 in the movie "Terminator 2", has always been the goal of researchers. Inspired by nature, methods such as "electronic paper", "electrochemical" display and plasmonic flipping through metal/organic nanostructures have been developed to camouflage color-changing materials. However, these materials lack flexibility and are easily damaged by external mechanical forces, and they are highly dependent on precise control of voltage/current through a chip, which severely limits the application of these methods to camouflage discoloration in liquid metal robotics. In recent years, some researchers have proposed self-discoloration based on liquid gallium and its alloys, such as reversible discoloration induced by high-temperature oxidation and deformation of gallium-copper/nickel microspheres induced by intense lasers. However, for the former, the discoloration induced by high-temperature oxidation is irreversible, while the latter design is only suitable for small-scale materials, moreover, both designs rely on a higher external energy supply.

According to literature reports, gallium and its room temperature liquid alloys can exhibit a series of mechanical behaviors due to changes in their surface tension, and researchers have developed various liquid robot designs based on this feature. In mechanical behavior, phagocytosis of gallium liquid alloys often results in significant discoloration. Through manipulation, the colored copper particles are spontaneously engulfed by the liquid metal droplets, so that the color of the liquid gallium alloy rapidly changes from red/black to shiny silver. However, this discoloration has been shown to be irreversible, and one of the most important reasons is that the intermetallic compounds formed between copper and gallium prevent the movement of copper particles. But this phenomenon has inspired us a new functional material design strategy that promises to achieve reversible color change through precise control of the motion of chromogenic particles in liquid gallium.

SUMMARY OF THE INVENTION

The present invention provides a liquid metal composite material that is rapidly and reversibly discolored by physical contact, comprising gallium and graphite.

Graphite has properties similar to copper and is often used to reduce the surface tension of gallium in acidic or alkaline environments. With proper control of pH concentration and/or electric field strength, graphite and gallium can be easily converted from wet, partially wet to non-wet. At the same time, graphite is very stable at room temperature, it does not react with acids or bases. More importantly, it cannot react with gallium to form any intermetallic compounds. In addition, graphite also has excellent light absorption ability in the visible spectrum, so graphite becomes an excellent dye for reversible color change of liquid metal gallium. Compared with traditional color-changing functional materials, the present invention does not rely on chip control and external energy supply, and has the advantages of indestructible mechanical force and rapid reversibility. Therefore, the material has the advantages of color camouflage, color rendering and other civil and military fields of liquid robots. greater application prospects.

The liquid metal composite material of gallium and graphite of the present invention can realize the preparation process of the metal material with rapid reversible color change only through physical contact without an external excitation source. The metal gallium-graphite powder composite was prepared by utilizing the autophagy of metal gallium in acid solution due to the removal of the surface oxide layer on the wetted particles. Then, a suitable acid environment is selected, and the graphite paper/graphite block and the metal gallium-graphite powder composite are directly physically contacted/separated to achieve the purpose of rapid discoloration of the surface. The contact surface of the material and the graphite paper will quickly change from metallic silvery white to gray-black, which takes about 3-8 seconds; when the graphite paper is separated from the metal gallium-graphite powder composite material, the color of the composite material will quickly return to its original state. about 6 seconds. The material provides a new effective technical means for the surface color camouflage of liquid metal robots, and provides a new idea for the development and industrial application of low-power liquid metal color rendering materials. The patent of the present invention uses a simple material synthesis process, has no special condition requirements, is easy to operate, has simple equipment requirements, and is easy to produce on a large scale.

The present invention also provides a method for preparing the liquid metal composite material with rapid and reversible discoloration in physical contact, comprising the following steps:

a. Preparation of scaly graphite powder: Cut 50μm thick graphite paper into a 5cm×5cm square shape, put it in a 0.2-1.0mol/L hydrochloric acid solution, and use 4V DC to electrolytically peel off the scaly graphite chips. The electrode spacing is 5cm , the electrolysis time is 10-20min; then the electrolyte is centrifuged, the speed of the centrifuge is 12000r/min, the treatment time is 5min, and the residual liquid is evaporated to dryness to obtain scaly graphite powder;

b. Composite metal gallium and graphite powder: The solid metal gallium with a purity of 99.95wt.% is heated to 90℃ to obtain liquid gallium, and the liquid gallium is taken out with a straw and placed in distilled water at 40-45℃; The scaly graphite powder is added to the surface of the liquid gallium, and the liquid gallium spontaneously devours the scaly graphite powder to obtain a metal gallium-graphite powder composite material. The obtained metal gallium-graphite powder composite material is sucked out of distilled water through a straw and placed in a plastic petri dish Dry in medium.

Preferably, before adding the scaly graphite powder to the surface of the liquid gallium, add 12 mol/L concentrated hydrochloric acid dropwise to the surface of the liquid gallium.

Preferably, the mass proportion of the scaly graphite powder in the metal gallium is 0.001-0.004wt.%.

Preferably, the metal gallium-graphite powder composite material is stored in an environment with a temperature of minus 20 to minus 24°C.

The present invention also claims to protect the application of the liquid metal composite material with rapid and reversible discoloration in physical contact as a camouflage and discoloration material in civil or military fields such as liquid metal robots, toys and entertainment.

Description of drawings

Figure 1 is a diagram of the microstructure of the flake graphite powder.

FIG. 2 is a schematic diagram of the state of metal gallium spontaneously engulfing scaly graphite powder.

Figure 3 is a color gradation diagram caused by the contact/separation of the metal gallium-graphite powder composite material and the graphite paper.

Figure 4. Comparison of the color of metal gallium droplets and the color of metal gallium-graphite powder composites on the surface of graphite paper.

Figure 5 is a diagram of the discoloration mechanism of the present invention.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and embodiments.

Example:

Cut the graphite paper into a 5cm×5cm×50μm (length×width×thickness) square shape, put it in a 0.2-1.0mol/L hydrochloric acid solution, and use 4V DC to electrolyze the scaled graphite chips. The electrode spacing is 5cm. Electrolysis time 10-20min. Centrifuge the electrolyte (centrifuge rotation speed 12000r/min, treatment 5min), and evaporate the residual liquid to obtain scaly graphite chip powder, as shown in Figure 1, put it in a desiccator for use.

The solid metal gallium (purity 99.95wt.%) was heated to 90°C to obtain liquid gallium, and 0.4-0.5mL was taken out through a pipette and placed in distilled water at 40°C. The scaly graphite powder obtained in the previous step was added to the surface of the liquid gallium. Preferably, by directly adding 12 mol/L concentrated hydrochloric acid on the surface of the liquid gallium, the surface oxide layer of the liquid gallium is removed to trigger the spontaneous phagocytosis of the liquid Ga, so that the liquid gallium droplets spontaneously swallow the scaly graphite powder to obtain metallic gallium -Graphite powder composite. At this time, the metal gallium-graphite powder composite material appears as a silver-white liquid sphere on the surface, and the mass proportion of the scale graphite powder in the metal gallium is 0.004wt.%, as shown in Figure 2.

The obtained metal gallium-graphite powder composite material was sucked out of the solution through a pipette, placed in a plastic petri dish to dry, and stored in a refrigerator at a temperature of minus 24°C.

Graphite has properties similar to copper and is often used to reduce the surface tension of gallium in acidic or alkaline environments. With proper pH concentration and/or electric field strength control, graphite and gallium can be easily converted from wet, partially wet to non-wet. At the same time, graphite is very stable at room temperature, it does not react with acids or bases. More importantly, it cannot react with gallium to form any intermetallic compounds. In addition, graphite also has excellent light absorption capabilities in the visible spectrum. Therefore, graphite should be an excellent dye for realizing reversible color change of liquid metals. Hydrochloric acid (HCl) solution has been shown to be an effective solution to trigger the spontaneous phagocytosis of liquid Ga by removing its surface oxide layer. While other commonly used solutions, such as sodium hydroxide (NaOH), sodium carbonate (Na2CO3), cannot support spontaneous phagocytosis without the aid of external electron injection (such as chemical reaction or external electric field). Considering the need to achieve rapid and reversible discoloration through physical contact without introducing an external field or material, the present invention selects a certain concentration of HCl solution environment. Compared with traditional color-changing functional materials, the present invention does not rely on chip control and external energy supply, and has the advantages of indestructible mechanical force and rapid reversibility. Therefore, the material has the advantages of color camouflage, color rendering and other civil and military fields of liquid robots. greater application prospects.

Discoloration test:

A 0.4 mol/L hydrochloric acid solution is prepared, the metal gallium-graphite powder composite material obtained in the embodiment is added to the prepared hydrochloric acid solution, and the temperature of the hydrochloric acid solution is heated to 40-45 °C. Using graphite paper with a size of 5cm×5cm×50μm (length×width×thickness) to directly touch the metal gallium-graphite powder composite material in a hydrochloric acid solution, the surface of the composite material will rapidly change from metallic silver white to gray black, which takes about 8 seconds. ; When the graphite paper is separated from the metal gallium-graphite powder composite material, the color of the composite material will quickly return to its original state, which takes about 6 seconds, as shown in Figure 3.

In the environment of 0.4mol/L hydrochloric acid solution, the metal gallium-graphite powder composite material was directly dropped on the surface of the graphite paper, and the color of the metal gallium-graphite powder composite material rapidly changed to gray-black in only 3 seconds, as shown in Figure 4 shown. The color comparison of the metal gallium droplet and the metal gallium-graphite powder composite on the surface of the graphite paper is shown in Figure 4.

The mechanism of discoloration is shown in Figure 5. Generally speaking, a self-limiting ultra-thin oxide layer will be formed on the surface of liquid gallium in a solution environment. In hydrochloric acid solutions, this oxide layer decreases with increasing acid concentration. However, the electronegativities of gallium and carbon are 1.81 and 2.55, respectively, constituting a galvanic cell reaction in an acidic environment. When the two are not in contact, in an acidic solution of 0.4 mol/L, the formation rate of the oxide layer on the gallium surface is lower than the dissolution rate, so the liquid metal gallium maintains a high surface tension, and the graphite powder is firmly locked in the liquid metal gallium. , so it appears as the metallic luster of gallium itself; but when the two are in contact, due to the potential difference, the electrons of the liquid metal gallium will be quickly transferred to the graphite paper, and the growth rate of the oxide film on the surface of the metal gallium is greatly improved and exceeds its dissolution rate. The surface tension of gallium at this time is not enough to lock the graphite powder inside it. At the same time, due to the polarization produced by the reaction, the upper surface of gallium is positively charged, while the interface with the graphite paper is negatively charged. At this time, the graphite powder inside the liquid metal gallium also retains some electrons, showing electronegativity. Under the action of the electric field, the graphite powder inside the liquid metal gallium migrates toward the upper surface, which results in contact discoloration. When the two are separated, the oxide film on the surface of the metal gallium dissolves rapidly, so the liquid metal gallium has high surface tension again, and the carbon powder is firmly locked in the liquid metal gallium again, thus completing the color recovery.

The invention provides a new effective technical means for the surface color camouflage of the liquid metal robot, and provides a new idea for the development and industrial application of the liquid metal color developing material with low power consumption. The patent of the present invention uses a simple material synthesis process, has no special condition requirements, is easy to operate, has simple equipment requirements, and is easy to produce on a large scale.

Claims (3)

1. A liquid metal composite material capable of rapidly and reversibly changing color by physical contact is characterized by comprising gallium and graphite, and the preparation method comprises the following steps:

a. preparing scaly graphite powder: cutting 50 μm thick graphite paper into 5cm × 5cm square blocks, placing into 0.2-1.0mol/L hydrochloric acid solution, and electrolyzing with 4V direct current to strip scale graphite debris with electrode spacing of 5cm for 10-20 min; centrifuging the electrolyte at the rotation speed of 12000r/min for 5min, and evaporating the dry residual liquid to obtain scaly graphite powder;

b. compounding gallium metal and graphite powder: heating solid gallium with the purity of 99.95wt.% to 90 ℃ to obtain liquid gallium, taking out the liquid gallium by using a suction pipe, and placing the liquid gallium in distilled water at the temperature of 40-45 ℃; b, adding the scaly graphite powder obtained in the step a to the surface of liquid gallium, enabling the liquid gallium to phagocytose the scaly graphite powder spontaneously to obtain a metal gallium-graphite powder composite material, sucking the obtained metal gallium-graphite powder composite material out of distilled water through a suction pipe, and placing the metal gallium-graphite powder composite material in a plastic culture dish for drying;

before adding the scaly graphite powder to the surface of the liquid gallium, dropwise adding 12mol/L concentrated hydrochloric acid to the surface of the liquid gallium;

the mass ratio of the scaly graphite powder in the gallium metal is 0.001-0.004 wt.%.

2. The liquid metal composite material with rapid reversible color change through physical contact as claimed in claim 1, wherein the metal gallium-graphite powder composite material is stored in an environment with a temperature of minus 20 ℃ to minus 24 ℃.

3. The use of the liquid metal composite material with physical contact rapid reversible color change as camouflage and color change material in civil or military fields according to claim 1.

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