Liquid metal pressure sensing fiber and its preparation method and application

Abstract

The application relates to a liquid metal pressure sensing fiber and a preparation method and application thereof, and belongs to the technical field of sensing fiber preparation. The liquid metal pressure sensing fiber of the application is a pressure sensing fiber sequentially comprising a small-hole elastomer layer, a large-hole elastomer layer and a liquid metal conductive core layer from outside to inside. The liquid metal pressure sensing fiber disclosed by the application has a multi-layer structure, and when two fibers are used to form a capacitive pressure sensor, the pressure sensing fiber exhibits a segmented sensing effect. On the other hand, the multi-layer structure contains a porous structure, and under the same pressure, the distance between the liquid metal cores of the two fibers without the porous structure is reduced more, so that the capacitance changes more, that is, the porous structure improves the sensitivity of the pressure sensing fiber, and therefore the application has a good application prospect in the preparation of flexible wearable electronic products.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of sensing fiber, and relates to a liquid metal pressure sensing fiber and a preparation method and application thereof. BACKGROUND

[0002] With the development of electronic technology, the demand for electronic circuits is no longer limited to traditional rigid substrate circuit boards. To meet the needs, flexible substrate electronic devices have emerged. The biggest difference between flexible substrate electronic devices and rigid substrate electronic devices is their new flexible characteristics such as bending, folding and stretching. There are many kinds of flexible electronic devices, such as flexible sensors, flexible electric heaters, electronic skin, etc.

[0003] An important component of flexible wearable electronic products, flexible pressure sensors, have received extensive attention in various application fields such as medical monitoring, human-machine interface or robotic prosthetics. Conventional flexible wearable pressure sensors lack sufficient deformability and comfort, and their functions are relatively single, so fiber-based pressure sensors have emerged. Flexible pressure sensors are generally divided into capacitive, resistive / pressure resistive, piezoelectric and triboelectric pressure sensors. Capacitive pressure sensors have obvious advantages in flexible pressure sensors due to their stability and fatigue resistance. Current flexible capacitive pressure sensors generally use metals and their alloys, conductive polymers, etc. as electrodes. Most of these materials have problems such as poor deformability and mechanical stability, so it is urgent to find a suitable flexible electrode.

[0004] Liquid metal (LM) has been widely used in the field of flexible pressure sensors due to its excellent properties of high electrical conductivity, fluidity, high deformability and good environmental stability. Liquid metal is a metal or alloy. Unlike the well-known toxic substance mercury, gallium-based liquid metal is not only non-toxic to living organisms, but also has excellent biocompatibility. Direct contact with gallium-based liquid metal will not trigger any immune response and will not cause any harm to living organisms (Chen S, Zhao R, Sun X, Wang H, Li L, Liu J. Toxicity and biocompatibility of liquid metals. Adv Healthc Mater. 2023; 12(3): e2201924). Therefore, LM is an ideal material for preparing flexible pressure sensors.

[0005] Although the emergence of liquid metal to some extent solves the problem of poor deformability and mechanical stability of flexible pressure sensor electrode, the existing flexible pressure sensor cannot generally meet the needs of adapting to complex surfaces due to the limitation of its own structure. The fiber-based flexible pressure sensor has the indispensable advantages of high tensile property, high flexibility and excellent deformability in the field of flexible sensing, so the fiber-based pressure sensor has been widely concerned. The traditional fiber-based pressure sensor is generally simply wrapped by the conductive "core" layer through the protective "sheath" layer, which will cause the problem of low sensitivity of the pressure sensing fiber. There are many methods to improve the sensitivity of the pressure sensor, and changing the geometry of the active layer (the layer that deforms under pressure and determines the change of output signal) is a low-cost and simple manufacturing method.

[0006] In order to make the fiber-based pressure sensor better applicable to the fields of sports, health monitoring and sensing, it is of great significance to start from the modification of the active layer and develop a liquid metal pressure sensing fiber with good linearity and high sensitivity. SUMMARY

[0007] Therefore, one of the purposes of the present application is to provide a liquid metal pressure sensing fiber; the second purpose of the present application is to provide a preparation method of the liquid metal pressure sensing fiber; and the third purpose of the present application is to provide an application of the liquid metal pressure sensing fiber in sports, health monitoring or sensing.

[0008] To achieve the above purposes, the present application provides the following technical solutions:

[0009] 1. A liquid metal pressure sensing fiber, the liquid metal pressure sensing fiber being a pressure sensing fiber sequentially comprising an elastic body layer with small holes, an elastic body layer with large holes and a liquid metal conductive core layer from outside to inside;

[0010] The pore size of the small holes in the elastic body layer with small holes is 1-99 pm, and the pore size of the large holes in the elastic body layer with large holes is 232-200 pm.

[0011] The elastic body is an elastic polymer capable of wet spinning, and the liquid metal includes but is not limited to any one of gallium, gallium alloy, bismuth or bismuth alloy.

[0012] Preferably, the elastic body includes but is not limited to polyester resin, polyamide resin or cellulose and its derivatives.

[0013] Preferably, the diameter of the liquid metal pressure sensing fiber is 100-2000 pm.

[0014] The thickness of the small-pore elastomer layer is 10-1500 μm, the thickness of the large-pore elastomer layer is 101-1500 μm, and the diameter of the liquid metal wire core is 10-1500 μm.

[0015] Preferably, the liquid metal includes any one or several of pure gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, pure bismuth, and bismuth-indium-tin alloy.

[0016] 2. A method for preparing the liquid metal pressure-sensing fiber as described above, comprising the following steps:

[0017] (1) Preparing a hollow fiber: a mixed solution of a porogen and an elastomeric polymer solution capable of wet spinning, a single wet spinning elastomeric polymer solution, and a coagulation bath liquid are sequentially used as an outer layer spinning solution, a middle layer spinning solution, and an inner layer spinning solution, respectively, and coaxial wet spinning is performed at a spinning rate of 0.01-0.5 mL / min, 0.01-0.5 mL / min, and 0.01-0.5 mL / min, respectively; after spinning is completed, the hollow fiber is immersed in the coagulation bath for 1-24 h until complete solidification, and then heated and ultrasonicated to completely dissolve the porogen, thereby obtaining a hollow fiber, from the outside to the inside, a small-pore elastomer layer, a large-pore elastomer layer, and an internal hollow portion.

[0018] (2) Preparing a pressure-sensing fiber: a liquid metal is injected into the internal hollow portion of the hollow fiber prepared in step (1), and after encapsulation, a liquid metal pressure-sensing fiber is obtained.

[0019] Preferably, the mass ratio of the porogen to the elastomeric polymer capable of wet spinning is 99:1-1:1.

[0020] Preferably, the porogen is a particle such as sodium chloride particle that is insoluble in an organic solvent.

[0021] Preferably, the encapsulation method is encapsulation with a conductive copper foil adhesive.

[0022] Preferably, the coagulation bath liquid is deionized water.

[0023] 3. Use of the liquid metal pressure-sensing fiber as described above in the preparation of a flexible wearable electronic product.

[0024] The application has the beneficial effects that the application discloses a liquid metal pressure sensing fiber, which is a pressure sensing fiber with a small-pore elastomer layer, a large-pore elastomer layer and a liquid metal conductive core layer from outside to inside.

[0025] Additional advantages, objects, and features of the application will be set forth in part by the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or can be learned by practice of the application. The objects and other advantages of the application can be realized and attained by the methods and techniques particularly pointed out in the written description. BRIEF DESCRIPTION OF DRAWINGS

[0026] In order to make the purposes, technical solutions and advantages of the application clearer, the preferred detailed description of the application will be given below with reference to the drawings, in which:

[0027] Figure 1 The preparation flow chart of the liquid metal pressure sensing fiber of the application;

[0028] Figure 2 The cross-section scanning electron microscope image of the liquid metal pressure sensing fiber prepared in Example 2, in which the scale is 300 mu m;

[0029] Figure 3 The stress-strain curve comparison result of the product prepared in Example 2 (with a small-pore layer) and the product prepared in Comparative Example 1 (without a small-pore layer);

[0030] Figure 4 The pressure response comparison result of the product prepared in Example 2 (with a small-pore layer) and the product prepared in Comparative Example 1 (without a small-pore layer);

[0031] 1 is deionized water, 2 is polyurethane solution, 3 is the mixture of polyurethane and sodium chloride particles, 4 is a three-layer coaxial spinning needle, 5 is a hollow hollow fiber layer, 6 is a mixed liquid metal, 7 is a liquid metal pressure sensing fiber, 8 is a small hole elastomer layer of a liquid metal pressure sensing fiber, 9 is a large hole elastomer layer of a liquid metal pressure sensing fiber, and 10 is a liquid metal conductive core layer of a liquid metal pressure sensing fiber. DETAILED DESCRIPTION

[0032] The advantages and effects of the present application can be easily understood by those skilled in the art from the above description. The present application can also be implemented or applied in other different specific embodiments, and the details in the specification can be modified or changed based on different views and applications without departing from the spirit of the present application. It should be noted that the drawings provided in the following examples only illustrate the basic concept of the present application in a schematic manner, and the following examples and features in the examples can be combined with each other without conflict.

[0033] Example 1

[0034] A liquid metal pressure sensing fiber, the specific preparation method comprising the following steps:

[0035] 1. A hollow fiber is prepared from the outside to the inside in order of small hole elastomer layer, large hole elastomer layer, and internal hollow part:

[0036] (1) Prepare a polyurethane spinning solution: weigh 20 g of polyurethane (polyurethane) particles and dissolve in 80 g of dimethylformamide, stir for 3 h, then heat at 60°C for 2 h to obtain a 20 wt.% polyurethane spinning solution.

[0037] (2) Mix the above polyurethane solution with sodium chloride particles according to a mass ratio of 2:1 to obtain a mixed spinning solution.

[0038] (3) Preparation of hollow fiber: a, the coagulation bath liquid (deionized water), 20 wt.% polyurethane spinning solution prepared in step (1) and mixed spinning solution prepared in step (2) are coaxially wet spun as inner layer spinning solution, middle layer spinning solution and outer layer spinning solution respectively, and the coaxial wet spinning is carried out at a rate of 0.05 mL / min, 0.1 mL / min and 0.1 mL / min respectively; b, after spinning is completed, it is immersed in the coagulation bath liquid (deionized water) for solidification for 12 h to complete solidification, and then heated at 60℃ for 1 h with ultrasonic, so that the pore-forming agent (sodium chloride particles) is completely dissolved to obtain a hollow fiber, which obtains a small pore elastomer layer (pore size is 20 μm, thickness is 200 μm), a large pore elastomer layer (pore size is 100 μm, thickness is 200 μm) and an internal hollow part (diameter is 500 μm) from outside to inside; c, the both ends of the hollow fiber are cut open with scissors and air dried for 12 h.

[0039] 2, Preparation of mixed liquid metal: 24.5 g of metal indium is added to 75.5 g of metal gallium, and heated and stirred at 60℃ until completely mixed to obtain a mixed liquid metal.

[0040] 3, Preparation of liquid metal pressure sensing fiber: 5 mL of the above prepared mixed liquid metal is taken with a 10 mL syringe and directly injected into the above cut hollow fiber layer, and after injection is completed, both ends are packaged (the packaging method is: packaged with conductive copper foil glue) to obtain a liquid metal conductive core layer pressure sensing fiber, thereby forming a liquid metal pressure sensing fiber (diameter is 1300 μm).

[0041] Example 2

[0042] A liquid metal pressure sensing fiber, the specific preparation method comprising the following steps:

[0043] 1, Preparation of hollow fiber with small pore elastomer layer, large pore elastomer layer, internal hollow part from outside to inside:

[0044] (1) Preparation of polyurethane spinning solution: 30 g of polyurethane particles is dissolved in 70 g of dimethylformamide, stirred for 3 h and heated at 60℃ for 2 h to obtain a 30 wt.% polyurethane spinning solution.

[0045] (2) The above polyurethane solution is mixed with sodium chloride particles according to a mass ratio of 1:1 to obtain a mixed spinning solution.

[0046] (3) Preparation of hollow fiber: a, the coagulation bath liquid (deionized water), 30wt.% polyurethane spinning solution prepared in step (1) and mixed spinning solution prepared in step (2) are coaxially wet spun as inner layer spinning solution, middle layer spinning solution and outer layer spinning solution respectively, with a rate of 0.03mL / min, 0.15mL / min, 0.15mL / min respectively; b, after spinning, immerse it in the coagulation bath liquid (deionized water) for 12h to complete solidification, then heat at 60℃ for 1h with ultrasonic, so that the pore-forming agent (sodium chloride particles) is completely dissolved to obtain a hollow fiber, which obtains a small pore elastomer layer (pore size is 20μm, thickness is 200μm), a large pore elastomer layer (pore size is 100μm, thickness is 200μm) and an internal hollow part (diameter is 500μm) from outside to inside; c, cut the both ends of the hollow fiber with scissors and air dry for 12h.

[0047] 2, Preparation of mixed liquid metal: add 25g of metal indium into 75g of metal gallium, heat and stir at 60℃ until completely mixed to obtain a mixed liquid metal.

[0048] 3, Preparation of liquid metal pressure sensing fiber: use a 10mL syringe to suck 5mL of the above prepared mixed liquid metal, directly inject into the above cut hollow fiber layer, after injection, seal both ends (sealing method: use conductive copper foil adhesive to seal) to obtain a liquid metal conductive core layer pressure sensing fiber, thereby forming a liquid metal pressure sensing fiber (diameter is 1300μm).

[0049] Comparative example 1

[0050] A liquid metal pressure sensing fiber, the specific preparation method comprising the following steps:

[0051] 1, Preparation of hollow fiber with small pore elastomer layer, large pore elastomer layer, internal hollow part from outside to inside:

[0052] (1) Preparation of polyurethane spinning solution: weigh 30g of polyurethane particles and dissolve in 70g of dimethylformamide, stir for 3h and then heat at 60℃ for 2h to obtain a 30wt.% polyurethane spinning solution.

[0053] (2) Preparation of hollow fiber: a, the coagulation bath liquid (deionized water), the 30wt.% polyurethane spinning solution prepared in step (1) and the 30wt.% polyurethane spinning solution prepared in step (1) are respectively coaxial wet spinning inner layer spinning solution, middle layer spinning solution and outer layer spinning solution, coaxial wet spinning is carried out at a rate of 0.03mL / min, 0.15mL / min, 0.15mL / min respectively; b, after spinning, immerse it in the coagulation bath liquid (deionized water) for 12h to complete solidification, then heat at 60℃ for 1h under ultrasonic to obtain a hollow fiber, which obtains a macroporous elastomer layer (pore size is 100μm, thickness is 400μm) and an internal hollow part (diameter is 500μm) from outside to inside; c, cut the both ends of the hollow fiber with scissors and air dry for 12h.

[0054] 2, Preparation of mixed liquid metal: add 25g of metal indium into 75g of metal gallium, heat and stir at 60℃ until completely mixed to obtain a mixed liquid metal.

[0055] 3, Preparation of liquid metal pressure sensing fiber: use a 10mL syringe to suck 5mL of the above prepared mixed liquid metal, directly inject into the above cut hollow fiber layer, after injection, seal both ends (sealing method: use conductive copper foil adhesive to seal) to obtain a liquid metal conductive core layer pressure sensing fiber, thereby forming a liquid metal pressure sensing fiber (diameter is 1300μm).

[0056] Performance test

[0057] The preparation process of the liquid metal pressure sensing fiber of the present application is shown in Figure 1 , wherein 1 is deionized water, 2 is polyurethane solution, 3 is a mixture of polyurethane and sodium chloride particles, 4 is a three-layer coaxial spinning needle, 5 is a hollow hollow fiber layer, 6 is a mixed liquid metal, 7 is a liquid metal pressure sensing fiber (from outside to inside, small pore elastomer layer 8, macroporous elastomer layer 9, liquid metal conductive core layer 10).

[0058] Use a scanning electron microscope to observe the fiber prepared in example 2 above, which is from outside to inside a small pore polyurethane layer, a macroporous polyurethane layer and a hollow layer, and the obtained SEM diagram is shown in Figure 2 . From Figure 2 , it can be seen that the liquid metal pressure sensing fiber prepared in example 2 is from outside to inside a small pore elastomer layer, a macroporous elastomer layer and a hollow hollow fiber layer, which has clear structure levels.

[0059] The stress-strain curves of the products obtained by adding sodium chloride porogen and not adding porogen in the preparation of the above example 2 and comparative example 1 are compared as shown in Figure 3 . FromFigure 3 As can be seen, whether or not a pore-forming agent is added during the preparation of liquid metal pressure sensing fibers has little effect on the mechanical tensile properties of the prepared liquid metal pressure sensing fibers.

[0060] Two 10cm lengths were cut from the fibers prepared in Example 2 and Comparative Example 1, respectively. A 2cm conductive copper wire was inserted into each end of these two fiber segments, and they were then sealed with conductive copper foil tape. The two ends of the fibers from Example 2 and Comparative Example 1 were then stacked together in a cross shape to form a capacitor. The response to pressure was as follows: Figure 4 As shown. From Figure 4 It can be seen that the response curves of capacitors composed of porous fibers, regardless of whether they have a porous structure or not, are divided into two segments within the applicable pressure range. For capacitors composed of porous fibers, the slope of the fitted line reaches 109.73 in the small pressure range and 13.18 in the larger pressure range. For capacitors composed of non-porous fibers, the slope of the fitted line reaches 59.35 in the small pressure range and 2.56 in the large pressure range. The slope of the fitted line indicates the sensitivity; therefore, this porous structure can significantly improve the sensitivity of fiber pressure sensing, regardless of whether the pressure range is large or small.

[0061] Similarly, the stress-strain curve and pressure response tests were performed on the liquid metal pressure sensing fiber prepared in Example 1. The results were similar to those in Example 2, indicating that the liquid metal pressure sensing fiber prepared by the present invention has good tensile and pressure sensing properties and has good application prospects in the preparation of flexible wearable electronic products.

[0062] In addition, the liquid metal pressure sensing fiber of different specifications (such as the diameter of the liquid metal pressure sensing fiber is 100-2000 μm; the thickness of the small-pore elastomer layer is 10-1500 μm; the thickness of the large-pore elastomer layer is 101-1500 μm; the diameter of the liquid metal wire core is 10-1500 μm) can be obtained by adjusting the conditions in the preparation process in Embodiment 1 and Embodiment 2 (such as the liquid metal is selected from any one or several of pure gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, bismuth-indium-tin alloy; the spinning rate of the outer spinning solution, the middle spinning solution and the inner spinning solution is respectively changed in the range of 0.01-0.5 mL / min, 0.01-0.5 mL / min, 0.01-0.5 mL / min; the mass ratio of sodium chloride particles to the elastic polymer capable of wet spinning (including but not limited to polyester resin, polyamide resin or cellulose and its derivatives) is selected in the range of 99:1-1:1). After relevant performance test, the test results are similar to those in Embodiment 1 and Embodiment 2, and the liquid metal pressure sensing fiber has good tensile property and pressure sensing property, and has good application prospect in the preparation of flexible wearable electronic products.

[0063] In summary, the liquid metal pressure sensing fiber disclosed in the present application is a pressure sensing fiber from outside to inside in turn comprising a small-pore elastomer layer, a large-pore elastomer layer and a liquid metal conductive core layer. The liquid metal pressure sensing fiber disclosed in the present application has the following advantages: on the one hand, due to the multi-layer structure, when two fibers are used to form a capacitive pressure sensor, the segmented sensing effect is exhibited when the pressure is sensed; on the other hand, due to the multi-layer structure containing a porous structure, under the same pressure, the distance between the liquid metal cores of the two fibers without the porous structure is reduced more, so that the capacitance change is larger, that is, the porous structure improves the sensitivity of the pressure sensing fiber, and therefore the liquid metal pressure sensing fiber has good application prospect in the preparation of flexible wearable electronic products. In addition, the present application also discloses a preparation method of the liquid metal pressure sensing fiber, which mainly comprises mixing a porogen in a spinning solution to prepare a hollow fiber from outside to inside in turn comprising a small-pore elastomer layer, a large-pore elastomer layer and an internal hollow part, and then filling the liquid metal in the internal hollow part to obtain the liquid metal pressure sensing fiber, which has the advantages of simple preparation method and easy operation, and is suitable for mass production.

[0064] Finally, it should be pointed out that the above embodiments are only used to illustrate the technical solutions of the present application but not limit the present application. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the present application, and all of them should be covered in the scope of the claims of the present application.

Claims

1. A liquid metal pressure sensing fiber, characterized in that, The liquid metal pressure sensing fiber consists of a small-pore elastomer layer, a large-pore elastomer layer, and a liquid metal conductive core layer, arranged from the outside to the inside. The pore size of the pores in the microporous elastomer layer is 1~99 μm, and the thickness of the microporous elastomer layer is 10~1500 μm; The pore size of the macroporous elastomer layer is 100~200 μm, and the thickness of the macroporous elastomer layer is 101~1500 μm; The diameter of the liquid metal pressure sensing fiber is 232~2000 μm, and the diameter of the liquid metal wire core is 10~1500 μm; The elastomer is an elastic polymer capable of wet spinning, and the liquid metal is any one or more of gallium, gallium alloy, bismuth, or bismuth alloy.

2. The liquid metal pressure sensing fiber according to claim 1, characterized in that, The elastomer is any one of polyester resin, polyamide resin, or cellulose and its derivatives.

3. The liquid metal pressure sensing fiber according to claim 1, characterized in that, The liquid metal includes any one or more of pure gallium, gallium-indium alloy, gallium-indium-tin alloy, gallium-indium-tin-zinc alloy, pure bismuth, and bismuth-indium-tin alloy.

4. The method for preparing the liquid metal pressure sensing fiber according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: (1) Preparation of hollow fibers: A mixture of a pore-forming agent and an elastic polymer solution capable of wet spinning, a separate wet spinning elastic polymer solution, and a coagulation bath liquid are used as the outer layer spinning solution, the middle layer spinning solution, and the inner layer spinning solution, respectively. Coaxial wet spinning is carried out at spinning rates of 0.01~0.5 mL / min, 0.01~0.5 mL / min, and 0.01~0.5 mL / min, respectively. After spinning, the fibers are soaked in a coagulation bath for 1~24 h until they are completely solidified. The pore-forming agent is then completely dissolved by heating and sonication to obtain hollow fibers. From the outside to the inside, a small-pore elastomer layer, a large-pore elastomer layer, and an inner hollow part are obtained in sequence. (2) Preparation of pressure sensing fiber: Liquid metal is injected into the hollow part inside the hollow fiber prepared in step (1), and after encapsulation, pressure sensing fiber with liquid metal conductive core layer is obtained.

5. The preparation method according to claim 4, characterized in that, The mass ratio of the pore-forming agent to the elastic polymer capable of wet spinning is 99:1 to 1:

1.

6. The preparation method according to claim 4, characterized in that, The pore-forming agent is sodium chloride particles that are insoluble in organic solvents.

7. The preparation method according to claim 4, characterized in that, The encapsulation method is as follows: encapsulation with conductive copper foil adhesive.

8. The preparation method according to claim 4, characterized in that, The coagulation bath liquid is deionized water.

9. The application of the liquid metal pressure sensing fiber according to any one of claims 1 to 3 in the preparation of flexible wearable electronic products.

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