Flexible pressure sensor based on liquid metal composite material and preparation method thereof

Abstract

The present invention discloses a flexible pressure sensor based on a liquid metal composite material, which comprises: a liquid metal composite material layer, a liquid metal electrode layer and a flexible packaging layer arranged in sequence from the inside to the outside; the liquid metal electrode layer is arranged on the upper and lower sides of the liquid metal composite material layer, and the flexible packaging layer is used to encapsulate the liquid metal electrode layer; wherein the liquid metal composite material layer comprises a flexible polymer substrate and a plurality of liquid metal marbles arranged in the flexible polymer substrate, the liquid metal marbles are composed of internal liquid metal droplets and an external wrapping layer, and the external wrapping layer is metal nickel powder. Correspondingly, the present invention also discloses a preparation method, which is used to prepare the above-mentioned flexible pressure sensor of the present invention. The flexible pressure sensor designed by the present invention has the characteristics of good flexibility, strong conductivity, high piezoresistive sensitivity, etc., and has good promotion prospects and application value.

Description

Technical Field

[0001] The present invention relates to the field of flexible electronic technology, and in particular to a flexible pressure sensor based on liquid metal composite materials and a preparation method thereof. Background Art

[0002] In recent years, due to the increasing demand for wearable devices, electronic skin, human-computer interaction and intelligent robots, especially the increasing demand for flexibility and stretchability, flexible sensors have gradually attracted great attention from scholars at home and abroad. Traditional flexible tactile sensors mainly rely on stretchable substrates and flexible conductive materials, including carbon nanotubes, graphene nanosheets, silver nanowires, metal nanoparticles and graphite particles.

[0003] Research has found that traditional flexible conductive materials have problems such as poor conductivity, high hardness, and poor stability. Room temperature gallium-based liquid metal has both metallic conductivity and liquid deformability, and it is also non-volatile, low toxicity, and good bioaffinity. Therefore, gallium-based liquid metal is a natural material choice for studying flexible tactile sensors. Due to its liquid properties, liquid metal can respond sensitively to external pressure, thereby producing resistance changes, which can greatly improve the sensitivity of flexible sensors. However, the huge surface tension of liquid metal makes it very easy for liquid metals to spontaneously fuse, making processing difficult and prone to leakage. In actual use, there are problems such as interface residues.

[0004] For example, the Chinese invention patent with publication number CN111289158A and publication date June 16, 2020, entitled "A Flexible Pressure Sensor and Flexible Pressure Sensing Array", discloses a flexible pressure sensor and a flexible pressure sensing array, in which the electrode layer of the sensor is filled with micron-sized silver flakes, and the sensing layer is filled with nano-carbon black particles. The geometry of the electrode layer and the microstructure of the sensing layer are designed to be stretchable, which effectively improves the flexibility and ductility of the pressure sensor. In this technical solution, the nano-carbon black particles used are susceptible to dispersion, easy to agglomerate, and cause the conductivity of the material to decrease.

[0005] For another example, the Chinese invention patent with publication number CN110823423A and publication date of February 21, 2020, entitled "A Liquid Metal Flexible Pressure Sensor and Its Preparation Method", discloses a liquid metal flexible pressure sensor, which adds conductive nanoparticles to PDMS to form a pressure sensing unit of a preset shape, and the microchannel is infused with an unbroken liquid metal electrode, which is in contact with the pressure sensing unit. In this technical solution, the conductivity of the composite material can be increased by increasing the content of conductive nanoparticles, but this method will also reduce the stretchability of the composite material.

[0006] For another example, the Chinese invention patent with publication number CN115235658A and publication date October 25, 2022, entitled “A method for preparing a flexible porous pressure sensor and a flexible porous pressure sensor” discloses a flexible porous pressure sensor, which injects liquid metal into the interior of the fiber. When the fiber is bent, the volume of the internal liquid metal is compressed, resulting in a change in resistance, thereby effectively improving the ability to accurately measure the change in liquid metal resistance. However, in this technical solution, if Figure 1 As shown, Figure 1 The resistance change characteristic curve of the flexible strain sensor based on the deformation of the liquid metal macrostructure in the prior art is schematically shown. Figure 1 When the flexible strain sensor of the embodiment shown is bent by 5 cm, the resistance change of the flexible strain sensor is less than 4%, and the flexible strain sensor has the problem of poor piezoresistive sensitivity. Summary of the invention

[0007] In order to solve the problems in the background technology, the present invention provides a flexible pressure sensor based on liquid metal composite materials and a preparation method thereof, so as to solve the problems of low stretchability, conductivity and piezoresistive sensitivity existing in the existing flexible pressure sensors. The flexible pressure sensor has the excellent characteristics of good flexibility, strong conductivity and high piezoresistive sensitivity.

[0008] In order to solve the above technical problems, the technical solution adopted by the present invention is: a flexible pressure sensor based on liquid metal composite material, comprising: a liquid metal composite material layer, a liquid metal electrode layer and a flexible packaging layer arranged in sequence from the inside to the outside; the liquid metal electrode layer is arranged on the upper and lower sides of the liquid metal composite material layer, and the flexible packaging layer is used to encapsulate the liquid metal electrode layer; wherein the liquid metal composite material layer includes a flexible polymer substrate and a plurality of liquid metal marbles arranged in the flexible polymer substrate, the liquid metal marbles are composed of internal liquid metal droplets and an external wrapping layer, and the external wrapping layer is metal nickel powder.

[0009] Furthermore, in the flexible pressure sensor described in the present invention, the metal nickel powder is irregular particles with spike-like protrusions, and the irregular particles include star-shaped particles, sea urchin-shaped particles or dendritic particles.

[0010] Furthermore, in the flexible pressure sensor described in the present invention, the metal nickel powder is uniformly coated on the liquid metal droplet.

[0011] In the above technical solution of the present invention, the liquid metal marbles are formed by uniformly wrapping the metal nickel powder on the surface of the liquid metal droplets, which can ensure that the metal nickel powder is concentrated at the interface of the liquid metal droplets in the liquid metal composite material layer.

[0012] Furthermore, in the flexible pressure sensor described in the present invention, a plurality of the liquid metal marbles are densely and evenly filled in the flexible polymer substrate.

[0013] Furthermore, in the flexible pressure sensor described in the present invention, the liquid metal electrode layer includes a mixture of liquid metal and metal powder / non-metal powder, and the flexible packaging layer includes a flexible polymer.

[0014] In the above technical solution of the present invention, during actual preparation, the liquid metal electrode layer can be obtained from a mixture of liquid metal and metal / non-metal powder, which has high viscosity, stretchability and good adhesion to the upper and lower surfaces of the liquid metal composite material layer.

[0015] Furthermore, in the flexible pressure sensor described in the present invention, the liquid metal is pure gallium, gallium-indium alloy or gallium-indium-tin alloy.

[0016] Furthermore, in the flexible pressure sensor described in the present invention, the metal powder is iron powder or copper powder.

[0017] Accordingly, another object of the present invention is to provide a method for preparing a flexible pressure sensor based on a liquid metal composite material, the method being used to prepare the flexible pressure sensor of the present invention, and specifically comprising the following steps S1-S5:

[0018] S1: preparing a plurality of liquid metal droplets, rolling the prepared plurality of liquid metal droplets on the surface of the metal nickel powder layer to form a uniform outer wrapping layer to obtain a plurality of liquid metal marbles, and freezing and solidifying the plurality of liquid metal marbles;

[0019] S2: stacking the plurality of frozen and solidified liquid metal marbles tightly and evenly in a mold to be cast, pouring a flexible polymer material into the mold to be cast, and assisting the flexible polymer material to penetrate into the gaps between the plurality of liquid metal marbles through a vacuum environment, and then performing a heating and curing process to obtain a liquid metal composite material layer;

[0020] S3: fully stirring and mixing the liquid metal and the metal powder / non-metal powder in a concentrated hydrochloric acid environment to obtain a liquid metal mixture electrode material;

[0021] S4: coating the liquid metal mixture electrode material on the upper and lower surfaces of the liquid metal composite material layer to form a liquid metal electrode layer;

[0022] S5: Leading out wires from the liquid metal electrode layer and pouring a flexible polymer material, and then performing a heating and curing process to obtain a flexible packaging layer.

[0023] Furthermore, in the preparation method described in the present invention, in step S1, specifically: ultrasonic dispersion, mechanical shear dispersion or microfluidic method is used to prepare multiple liquid metal droplets with particle sizes ranging from submicron to millimeter level, the prepared multiple liquid metal droplets are rolled on the surface of the metal nickel powder layer to form a uniform outer wrapping layer to obtain a plurality of liquid metal marbles, and the plurality of liquid metal marbles are controlled to be frozen and solidified at -40℃-0℃.

[0024] Furthermore, in the preparation method described in the present invention, in step S2, the heating and curing process is: controlling the heating temperature to 60° C.-80° C., and controlling the heating time to 2-4 hours.

[0025] The beneficial effects of the present invention are as follows: the present invention provides a flexible pressure sensor based on a liquid metal composite material, the flexible pressure sensor is provided with and adopts a new liquid metal composite material, the liquid metal composite material layer thereof includes a flexible polymer substrate and a plurality of liquid metal marbles arranged in the flexible polymer substrate, so as to form a conductive composite material by filling the flexible polymer material with liquid metal marbles, and by increasing the number of liquid metal marbles, the conductivity is improved, so that the liquid metal composite material layer finally obtained has good initial conductivity. At the same time, for the formed liquid metal composite material layer, while increasing the filling ratio of the liquid metal marbles to enhance the conductivity of the composite material, not only will the elastic modulus of the liquid metal composite material not be significantly increased, but also the flexibility of the flexible polymer material will not be destroyed.

[0026] At the same time, the designed liquid metal marbles are composed of an internal liquid metal droplet and an external wrapping layer, and the external wrapping layer is metal nickel powder. The metal nickel powder has a thorn-like protrusion structure and is more concentratedly distributed at the interface of the liquid metal droplet. Under the action of external force, the spikes destroy the polymer layer and build new conductive channels between the liquid metals, significantly changing the resistance characteristics of the liquid metal composite material. Therefore, the flexible pressure sensor can exhibit higher stress-strain sensitivity.

[0027] Correspondingly, the present invention also discloses a method for preparing a flexible pressure sensor based on liquid metal composite materials. The preparation method is used to prepare the above-mentioned flexible pressure sensor of the present invention. The preparation method is simple, the processing difficulty is low, and the time cost can be effectively reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The resistance change characteristic curve of the flexible strain sensor based on the deformation of the liquid metal macrostructure in the prior art is schematically shown.

[0029] Figure 2 It is a schematic structural diagram of the flexible pressure sensor described in the present invention in one embodiment.

[0030] Figure 3 The present invention is a process flow chart of a method for preparing a flexible pressure sensor based on a liquid metal composite material in one embodiment.

[0031] Figure 4 for Figure 2 The working principle diagram of the flexible pressure sensor shown in the figure; wherein, Figure 4 In Figure 4 a is a schematic diagram of the electron tunneling effect between the tips of two adjacent nickel powders. Figure 4 In Figure 4 b is a schematic diagram of the direct conductive connection between the tips of two adjacent nickel powders when pressure P is applied.

[0032] Figure 5 for Figure 2 Equivalent circuit diagram of the piezoresistive effect of the liquid metal composite material of the flexible pressure sensor shown.

[0033] Description of labels:

[0034] 1. Liquid metal composite material layer; 2. Liquid metal electrode layer; 3. Flexible packaging layer; 4. Flexible polymer substrate; 5. Liquid metal marbles; 6. Liquid metal droplets; 7. Metal nickel powder; 8. Wire; 9. Power supply; 10. Switch; 11. Ammeter. DETAILED DESCRIPTION

[0035] In order to explain the technical content, achieved objectives and effects of the present invention in detail, the following is an explanation in combination with the implementation modes and the accompanying drawings.

[0036] Please refer to Figure 2 As shown, the present invention provides a flexible pressure sensor based on liquid metal composite materials, which includes: a liquid metal composite material layer 1, a liquid metal electrode layer 2 and a flexible packaging layer 3 arranged in sequence from the inside to the outside; the above-mentioned liquid metal electrode layer 2 is arranged on the upper and lower sides of the liquid metal composite material layer 1, and the flexible packaging layer 3 is used to encapsulate the liquid metal electrode layer 2; wherein, the liquid metal composite material layer 1 includes a flexible polymer substrate 4 and a plurality of liquid metal marbles 5 arranged in the flexible polymer substrate 4, the above-mentioned plurality of liquid metal marbles 5 are tightly and evenly filled in the flexible polymer substrate 4, and the liquid metal marbles 5 are composed of internal liquid metal droplets 6 and an external wrapping layer, and the external wrapping layer is metal nickel powder 7.

[0037] In specific applications, the metal nickel powder 7 can be evenly coated on the above-mentioned liquid metal droplets 6 to form liquid metal marbles 5, and the liquid metal marbles 5 can roll freely on a general solid surface without leaving any residue on the interface; and the metal nickel powder 7 serving as the outer coating layer of the above-mentioned liquid metal marbles 5 is irregular particles with spike-like protrusions in appearance, and the irregular particles include but are not limited to star-shaped, sea urchin-shaped or tree-shaped structures; the tip of the metal nickel powder 7 and the tip of the adjacent metal nickel powder 7 or other liquid metal droplets 6 can produce an electron tunneling effect (see Figure 4 a) to give the liquid metal composite material basic conductivity.

[0038] Based on this setting, under normal room temperature conditions, the liquid metal has both metallic conductivity and liquid fluidity, and irregular metal nickel powder 7 with a spike-like protrusion structure is evenly wrapped on its surface to form a liquid metal marble 5. In the present invention, the liquid metal composite material layer 1 is filled with liquid metal marbles 5 as a conductive filler. When the above-mentioned liquid metal marbles 5 are arranged in a flexible polymer substrate 4, the liquid metal marbles 5 can be filled with a small spacing and combined with the flexible polymer matrix to form a conductive composite material (i.e., liquid metal composite material). In the initial state, due to the small spacing between the liquid metal marbles 5 and the irregular metal nickel powder 7, a basic conductive path can be constructed under the action of the electron tunneling effect, giving the liquid metal composite material a certain conductivity (see Figure 4 a). If a pressure P is applied to the flexible pressure sensor, as the pressure P is applied, the tip of the irregular nickel powder 7 will pierce the barrier of the flexible polymer, and the adjacent liquid metal marbles will establish a direct and stable conductive connection (see Figure 4 b) outputting a significant resistance change, thereby significantly improving the conductivity of the liquid metal composite material. The present invention is based on the above principle to achieve high-sensitivity measurement of stress and strain.

[0039] Accordingly, when the above-mentioned flexible pressure sensor is actually set up, a mixture of liquid metal and metal powder / non-metal powder can be applied to the upper and lower sides of the liquid metal composite material layer 1 as a flexible electrode, thereby obtaining a liquid metal electrode layer 2. The liquid metal electrode layer 2 as an electrode can also be connected to an external resistance measuring device through a wire 8, for example, Figure 2 As shown, the liquid metal electrode layer 2 can also be connected to an external power supply 9, a switch 10 and an ammeter 11 through a wire 8 to test the resistance value of the sensor. The liquid metal can be specifically selected as pure gallium, gallium-indium alloy or gallium-indium-tin alloy, and the metal powder can be specifically selected as copper powder or iron powder, so that the final mixture has flexible stretchability, conductivity and good adhesion to the upper and lower surfaces of the liquid metal composite material layer 1.

[0040] It should be pointed out that in actual application, the flexible polymer selected for the above-mentioned liquid metal composite material layer 1 and the flexible packaging layer 3 should have good fluidity before curing, and the above-mentioned flexible packaging layer 3 should be consistent with the flexible polymer matrix material used in the liquid metal composite material layer 1, which includes but is not limited to PDMS, Ecoflex, silicone rubber and other materials, so as to achieve a good wrapping and sealing effect on the liquid metal marbles 5 after curing.

[0041] Accordingly, when actually preparing the above-mentioned flexible pressure sensor of the present invention, the following method can be specifically used: Figure 3 The preparation method shown is prepared according to Figure 3 The process flow shown sequentially prepares liquid metal marbles 5, a liquid metal composite material layer 1, a liquid metal motor layer, leads out wires 8 and packages them to obtain a flexible packaging layer 3, and finally connects the flexible pressure sensor to the measurement circuit.

[0042] See also Figure 3 The preparation method designed by the present invention is specifically carried out according to the following steps:

[0043] S1: Use ultrasonic dispersion, mechanical shear dispersion or microfluidics method to prepare multiple liquid metal droplets 6 with particle sizes ranging from submicron to millimeter level, roll the prepared multiple liquid metal droplets 6 on the surface of the metal nickel powder 7 layer to form a uniform outer wrapping layer to obtain multiple liquid metal marbles 5, and control the freezing and solidification of the multiple liquid metal marbles 5.

[0044] S2: Tightly and evenly stack the multiple frozen and solidified liquid metal marbles 5 in the mold to be cast, pour the flexible polymer material into the mold to be cast, and use the vacuum environment to assist the flexible polymer material to penetrate into the gaps between the multiple liquid metal marbles 5, and then perform a heating and curing process to obtain a liquid metal composite material layer 1.

[0045] S3: The liquid metal and the metal powder / non-metal powder are fully stirred and mixed uniformly in a concentrated hydrochloric acid environment to obtain a liquid metal mixture electrode material.

[0046] S4: coating the liquid metal mixture electrode material on the upper and lower surfaces of the liquid metal composite material layer 1 to form a liquid metal electrode layer 2.

[0047] S5 : Leading out the wire 8 from the liquid metal electrode layer 2 and casting the flexible polymer material, and then performing a heating and curing process to obtain the flexible packaging layer 3 .

[0048] The flexible pressure sensor of the present invention can be effectively prepared and obtained through the above steps S1-S5. It should be pointed out that when performing the above step S5, a wire 8 can also be led out from the liquid metal electrode layer 2, and then the flexible polymer material is poured. At this time, after the flexible packaging layer 3 is obtained by solidification, the wire 8 connected to the liquid metal electrode layer 2 can be connected to the resistance measuring device to detect the resistance change of the liquid metal composite material layer 1 of the flexible pressure sensor under the action of external pressure.

[0049] In addition, in the present invention, according to the difference of the selected flexible polymer materials, in order to obtain a better curing effect, in the above steps S2 and S5, the heating curing process performed can be specifically: controlling the heating temperature to 60°C-80°C, and controlling the heating time to 2-4h.

[0050] Accordingly, in order to facilitate the disclosure and explanation of the flexible pressure sensor based on liquid metal composite material and the preparation method thereof according to the present invention, the following embodiments 1 and 2 are also specifically disclosed:

[0051] Embodiment 1:

[0052] In the first embodiment, the flexible pressure sensor is prepared by the following preparation method, which specifically includes the following steps:

[0053] A plurality of liquid metal droplets 6 with an average diameter of 500 microns are prepared by a microfluidic method, and the prepared droplets are rolled on the surface of a metal nickel powder 7 with an average particle size of 20-30 microns to form a uniform outer coating layer, thereby obtaining a plurality of liquid metal marbles 5, and then frozen at -40°C-0°C (determined by the specific composition of the liquid metal droplets 6 and the liquid-solid phase transition point) to obtain a solid marble structure;

[0054] A mold to be cast is prepared by 3D printing or mechanical processing, a plurality of liquid metal marbles 5 are tightly stacked in the mold to be cast, a flexible polymer material is poured into the mold to be cast, and the flexible polymer material is assisted by a vacuum environment to penetrate into the gaps between the plurality of liquid metal marbles 5, the heating temperature is controlled to be 60°C-80°C, and the heating time is controlled to be 2-4h to completely solidify it, thereby obtaining a liquid metal composite material layer 1;

[0055] The liquid metal and metal powders / non-metal powders such as copper powder and iron powder are fully stirred in a concentrated hydrochloric acid environment and mixed evenly to obtain a liquid metal mixture electrode material with high viscosity and good adhesion to PDMS;

[0056] The liquid metal mixture electrode material is coated on the upper and lower surfaces of the liquid metal composite material layer 1 by screen printing technology to form a liquid metal electrode; a wire 8 is led out from the liquid metal electrode, and a flexible polymer material is poured to form a flexible packaging layer 3, and the heating temperature is controlled to 60°C-80°C, and the heating time is controlled to 2-4h to fully solidify it.

[0057] Based on the above steps, the flexible pressure sensor of Example 1 can be obtained. The flexible pressure sensor further connects the wire 8 connecting the liquid metal electrode to a resistance measuring device composed of a power supply 9, a switch 10, and an ammeter 11 to detect the resistance change of the liquid metal composite material layer 1 of the flexible pressure sensor of Example 1 under the action of external pressure.

[0058] In the present invention, the flexible polymer material in Example 1 can be selected from polydimethylsiloxane (PDMS), and the ratio of its A and B components can be adjusted in the range of 10:1 to 30:1, component A is the basic component of PDMS, and component B is the curing agent; accordingly, the elastic modulus of the liquid metal composite material layer 1 after heating and curing is quite different, and can be appropriately adjusted according to the stress and strain detection range in practical applications; in addition, the reason why the curing temperature is controlled between 60°C and 80°C during the heating and curing process is that: too low a temperature will result in too long a curing time and a low elastic modulus of the cured material.

[0059] The working principle of the flexible pressure sensor based on liquid metal composite material in Example 1 of the present invention is as follows: Figure 4 As shown in a, in the initial state, due to the small distance between adjacent liquid metal marbles 5, a basic conductive path can be constructed under the action of electron tunneling effect, giving the composite material a certain conductivity. Figure 4 As shown in b, with the application of pressure P, the tip of the metal nickel powder 7 pierces the barrier of the flexible polymer, and the adjacent liquid metal marbles establish a direct and stable conductive connection, and the conductivity of the liquid metal composite material layer 1 is significantly improved.

[0060] The equivalent circuit of the piezoresistive effect of the liquid metal composite material 1 in the embodiment of the present invention is as follows: Figure 5 As shown, in the initial state, the resistance between electrodes is mainly composed of tunnel resistances Rt1, Rt2, and Rt3 in series, and the specific resistance value is related to the electron tunneling effect and the distance between adjacent conductive fillers; under the action of external force, the tip of the metal nickel powder 7 pierces the barrier of the polymer layer 4 to establish direct conductive contact, that is, the above-mentioned tunnel resistance Rt is connected in parallel to the contact resistance Rc (such as Figure 5 As shown, Rc includes Rc1, Rc 21 ……Rc 2n, Rc3), the contact resistance Rc is related to the tip size of the metal nickel powder 7 and the conductivity of the metal nickel. Obviously, Rc<Rt. At the same time, due to the reduction in the distance between the conductive particles and the participation of more metal nickel powder 7 tips in establishing direct conductive connections, the tunnel resistance Rt and the contact resistance Rc will further decrease. Therefore, the flexible pressure sensor has a very high sensitivity.

[0061] Embodiment 2:

[0062] In this embodiment 2, the embodiment 2 specifically adopts the following preparation method to prepare a flexible pressure sensor, and the preparation method specifically includes the steps of: preparing a plurality of liquid metal droplets 6 with an average diameter of 20 microns by an ultrasonic dispersion method, rolling the prepared plurality of liquid metal droplets 6 on the surface of a metal nickel powder 7 with an average particle size of 2-3 microns to form an external wrapping layer to obtain a plurality of liquid metal marbles 5, and further obtaining a flexible pressure sensor based on a liquid metal composite material according to the preparation process flow of the above-mentioned embodiment 1, which will not be elaborated here.

[0063] In this second embodiment, because the average structural size of the liquid metal marbles 5 is smaller, the overall elastic modulus of the liquid metal composite material layer 1 finally obtained is more than twice higher than that of the first embodiment, and the liquid metal composite material layer 1 has better flexibility. Under the premise of ensuring that the material is not damaged, the stress detection limit of the flexible pressure sensor of this second embodiment can be increased by 2 times, and the strain detection limit can be increased to more than 30%.

[0064] It should be pointed out that in the present embodiment 2, during the actual preparation, the material of the above-mentioned liquid metal droplet 6 can be specifically selected as pure gallium. When the flexible pressure sensor works in an environment below 25°C, the liquid metal droplet 6 can be promoted to transform from liquid to solid through vibration and other influences. The overall elastic modulus of the liquid metal composite material layer 1 is increased by more than 100 times. In this case, the pressure detection range of the flexible pressure sensor can be increased to more than 5MPa, and the strain detection range is reduced to about 5%.

[0065] It should be noted that this second embodiment is intended to demonstrate the scalability of the stress detection capability of the flexible pressure sensor based on liquid metal composite materials designed by the present invention, and while expanding the upper limit of sensor detection, it will not cause obvious loss of sensor sensitivity, thereby ensuring that the flexible pressure sensor of the present invention has the characteristics of good flexibility, strong conductivity, and high piezoresistive sensitivity.

[0066] From the above, it can be seen that the flexible pressure sensor designed by the present invention and the preparation method thereof are not only simple in preparation method and low in processing difficulty, which can effectively reduce time cost, but the flexible pressure sensor finally obtained also has the excellent characteristics of good flexibility, strong conductivity and high piezoresistive sensitivity. The implementation effect is excellent, the applicability is strong, and it has good promotion prospects and application value.

[0067] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent transformations made using the contents of the present invention's specification and drawings, or directly or indirectly applied in related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for preparing a flexible pressure sensor based on liquid metal composite material, characterized in that: Includes steps: S1: preparing a plurality of liquid metal droplets, rolling the prepared plurality of liquid metal droplets on the surface of the metal nickel powder layer to form a uniform outer wrapping layer to obtain a plurality of liquid metal marbles, and freezing and solidifying the plurality of liquid metal marbles; S2: stacking the plurality of frozen and solidified liquid metal marbles tightly and evenly in a mold to be cast, pouring a flexible polymer material into the mold to be cast, and assisting the flexible polymer material to penetrate into the gaps between the plurality of liquid metal marbles through a vacuum environment, and then performing a heating and curing process to obtain a liquid metal composite material layer; S3: fully stirring and mixing the liquid metal and the metal powder / non-metal powder in a concentrated hydrochloric acid environment to obtain a liquid metal mixture electrode material; S4: coating the liquid metal mixture electrode material on the upper and lower surfaces of the liquid metal composite material layer to form a liquid metal electrode layer; S5: Leading out wires from the liquid metal electrode layer and pouring a flexible polymer material, and then performing a heating and curing process to obtain a flexible packaging layer.

2. The preparation method according to claim 1, characterized in that: In step S1, specifically: ultrasonic dispersion, mechanical shear dispersion or microfluidics method is used to prepare multiple liquid metal droplets with particle sizes ranging from submicron to millimeter level, the prepared multiple liquid metal droplets are rolled on the surface of the metal nickel powder layer to form a uniform outer wrapping layer to obtain multiple liquid metal marbles, and the multiple liquid metal marbles are controlled to be frozen and solidified at -40℃-0℃.

3. The preparation method according to claim 2, characterized in that: In step S2, the heating curing process is: controlling the heating temperature to 60°C-80°C, and controlling the heating time to 2-4h.

4. A flexible pressure sensor based on liquid metal composite material, characterized in that: The flexible pressure sensor is made according to the preparation method of the flexible pressure sensor according to any one of claims 1 to 3, comprising: a liquid metal composite material layer, a liquid metal electrode layer and a flexible packaging layer arranged in sequence from the inside to the outside; the liquid metal electrode layer is arranged on the upper and lower sides of the liquid metal composite material layer, and the flexible packaging layer is used to encapsulate the liquid metal electrode layer; wherein the liquid metal composite material layer includes a flexible polymer substrate and a plurality of liquid metal marbles arranged in the flexible polymer substrate, the liquid metal marbles are composed of internal liquid metal droplets and an external wrapping layer, and the external wrapping layer is metal nickel powder; the metal nickel powder is irregular particles with spike-like protrusions.

5. The flexible pressure sensor according to claim 4, characterized in that: The irregular particles include star-shaped particles, sea urchin-shaped particles or dendritic particles.

6. The flexible pressure sensor according to claim 4, characterized in that: The metal nickel powder is uniformly coated on the liquid metal droplets.

7. The flexible pressure sensor according to claim 4, characterized in that: A plurality of the liquid metal marbles are densely and uniformly filled in the flexible polymer substrate.

8. The flexible pressure sensor according to claim 4, characterized in that: The liquid metal electrode layer includes a mixture of liquid metal and metal powder / non-metal powder, and the flexible packaging layer includes a flexible polymer.

9. The flexible pressure sensor according to claim 8, characterized in that: The liquid metal is pure gallium, gallium-indium alloy or gallium-indium-tin alloy.

10. The flexible pressure sensor according to claim 8, characterized in that: The metal powder is iron powder or copper powder.

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