Directional gradient pore aerogel, preparation method thereof and application of directional gradient pore aerogel in flexible sensor

Abstract

The invention belongs to the technical field of 3D printing aerogel, and particularly relates to oriented gradient hole aerogel, a preparation method thereof and application of the oriented gradient hole aerogel in a flexible sensor. A low-temperature 3D printing method is adopted, composite material ink is printed on a low-temperature freezing platform, a preformed body is obtained, the composite material ink comprises a cellulose material, a carbon nanomaterial and water, the cellulose material comprises cellulose and / or cellulose derivatives, and the temperature of the low-temperature freezing platform is 1t; 0 DEG C; and carrying out freeze drying on the preformed body to obtain the oriented gradient pore aerogel. According to the invention, the oriented gradient hole aerogel material is subjected to magnetron sputtering and packaging to obtain the wearable flexible sensor. The wearable flexible sensor provided by the invention has the advantages of high sensitivity, wide detection range and quick response capability; and meanwhile, the fiber has excellent mechanical performance and good flexibility, and is suitable for application of real-time monitoring and rapid feedback, including scenes of health monitoring, motion tracking and the like.

Description

Technical Field

[0001] The present invention belongs to the technical field of 3D printing aerogels, and in particular relates to an oriented gradient pore aerogel and a preparation method thereof, and an application thereof in a flexible sensor. Background Art

[0002] The rapid development of modern science and technology and electronic information technology has ushered human society into a new era of intelligent manufacturing. Flexible sensors are a type of sensor that has good flexibility and stretchability and can convert external mechanical stimulation signals (such as pressure, deformation, vibration, etc.) into electrical signals (resistance, capacitance, etc.) output to achieve real-time sensing and monitoring functions. They are an important foundation for intelligent manufacturing.

[0003] Aerogel is a new type of material known for its extremely low density, high porosity, high specific surface area, low thermal conductivity, low dielectric constant and low sound velocity, and has extremely broad application prospects. Aerogel is prepared by mixing carbon nanotubes, graphene oxide, silver nanowires and other nanomaterials to form composite aerogels, which can be used in the field of flexible sensing.

[0004] However, the pore structure of the current composite aerogel cannot be effectively regulated, or the porous structure is too fragile and prone to shrinkage and collapse during the preparation process, resulting in the flexible sensor being unable to adapt well to different deformations and pressure changes, having low sensitivity, and being unable to respond and recover quickly, making it unsuitable for application scenarios such as real-time monitoring and rapid feedback. Summary of the invention

[0005] The purpose of the present invention is to provide a directional gradient pore aerogel, a preparation method thereof and an application in a flexible sensor. The wearable flexible sensor obtained by the directional gradient pore aerogel material prepared by the present invention has high sensitivity, wide detection range and rapid response capability; at the same time, it has excellent mechanical properties and good flexibility, and is suitable for applications of real-time monitoring and rapid feedback, including health monitoring, sports tracking and other scenarios.

[0006] In order to achieve the above object, the present invention provides the following technical solutions: The present invention provides a method for preparing a directional gradient pore aerogel material, comprising the following steps: A low-temperature 3D printing method is used to print composite material ink on a low-temperature freezing platform to obtain a preform, wherein the composite material ink includes a cellulose material, a carbon nanomaterial and water, and the cellulose material includes cellulose and / or a cellulose derivative, and the temperature of the low-temperature freezing platform is <0°C; The preform is freeze-dried to obtain the oriented gradient pore aerogel material.

[0007] Preferably, the cellulose comprises cellulose nanofibers and / or cellulose nanocrystals; the cellulose derivative comprises one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose and cellulose acetate; The mass percentage of the cellulose material in the composite material ink is 1-20%.

[0008] Preferably, the carbon nanomaterial includes one or more of carbon nanotubes, carbon nanofibers, carbon nanospheres, carbon nanorods, graphene and graphene oxide; The mass percentage of the carbon nanomaterial in the composite material ink is 0.1-5%.

[0009] Preferably, the temperature of the low-temperature freezing platform is -10~-90°C; The conditions of the low-temperature 3D printing method include: a printing speed of 1-50 mm / s, a nozzle diameter of 0.2-2 mm, the composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.01-0.2 MPa.

[0010] Preferably, the temperature of the freeze-drying equipment cavity is -50~-90°C, and the time is >12 h.

[0011] The present invention provides an oriented gradient pore aerogel material prepared by the preparation method described in the above technical solution.

[0012] The present invention provides an application of the directional gradient pore aerogel material described in the above technical solution in a wearable flexible sensor.

[0013] The present invention provides a wearable flexible sensor, comprising the directional gradient pore aerogel material described in the above technical solution.

[0014] The present invention provides a method for preparing the wearable flexible sensor described in the above technical solution, comprising the following steps: Depositing a conductive metal coating on the pore wall surface of the oriented gradient pore aerogel material described in the above technical solution to obtain an aerogel with a conductive metal coating; Wires are arranged at both ends of the aerogel with a conductive metal coating, and then the aerogel is coated and packaged with a polymer to obtain the wearable flexible sensor.

[0015] Preferably, the conductive metal coating is deposited by magnetron sputtering; the conditions of the magnetron sputtering include: deposition time of 1 to 20 min, power of 50 to 200 W, and vacuum degree ≤ 1 Pa; The conductive metal coating comprises a gold coating and / or a silver coating; The polymer includes polydimethylsiloxane (PDMS), Ecoflex, thermoplastic polyurethane elastomer (TPU) or polyethylene terephthalate (PET).

[0016] The present invention provides a method for preparing a directional gradient pore aerogel material, comprising the following steps: using a low-temperature 3D printing method to print a composite material ink on a low-temperature freezing platform to obtain a preform, wherein the composite material ink includes a cellulose material, a carbon nanomaterial and water, wherein the cellulose material includes cellulose and / or a cellulose derivative, and the temperature of the low-temperature freezing platform is <0°C; freeze-drying the preform to obtain the directional gradient pore aerogel material. On the one hand, the present invention adopts a low-temperature 3D printing method, and by controlling the temperature of the low-temperature freezing platform to be <0°C, in the vertical direction, the upper surface of the composite material ink is in contact with the air and has a high temperature, and the lower surface of the composite material ink is in contact with the low-temperature freezing platform and has a low temperature, thereby forming a temperature gradient in the vertical direction; in the horizontal direction, the temperature of the composite material ink at the end of the 3D printing nozzle is high, and the temperature of the composite material ink far away from the nozzle section (distal end) is low, thereby forming a horizontal temperature gradient with the 3D printing nozzle as the center; mutually perpendicular dual temperature gradient fields (such as Fig. 9 and Fig.10 The water in the composite ink is guided to freeze, and the ice crystals grow in a directional manner, with the volume increasing from the low temperature area to the high temperature area in the dual temperature gradient field (as shown in Fig. Fig.11 and Fig.12 As shown), a one-dimensional, two-dimensional or three-dimensional preform is formed, and finally the oriented gradient pore aerogel material with a precisely controlled pore structure is obtained by freeze-drying. On the other hand, the composite material ink used in the present invention includes a compound of cellulose materials and carbon nanomaterials. The cellulose materials can assist the carbon nanomaterials in forming a stable conductive network in the aerogel material, thereby giving the oriented gradient pore aerogel material better conductivity and stronger structural stability. In summary, the oriented gradient pore aerogel material prepared by the present invention is customizable due to the non-uniformity of the pore structure in the product, and the performance of different regions can be designed according to needs; it also has high sensitivity, a wide detection range and rapid response capabilities; at the same time, it has excellent mechanical properties and good flexibility, and the resulting wearable flexible sensor is suitable for health monitoring, sports tracking and other scenarios.

[0017] At the same time, the preparation method provided by the present invention overcomes the disadvantage that the directional freezing method must use a mold, and adopts low-temperature 3D printing combined with freeze-drying, which has the characteristics of rapid and large-scale preparation.

[0018] The present invention provides a wearable flexible sensor, comprising the oriented gradient pore aerogel material described in the above technical solution. Compared with the prior art, the wearable flexible sensor provided by the present invention has the following advantages: (1) Customizability. The pore size and porosity of the pore structure of the oriented gradient pore aerogel material provided by the present invention change gradually along a specific direction (the direction of the dual temperature gradient). This structure makes the mechanical properties of the aerogel material (such as stiffness, toughness, strength, etc.) also change with the change of the gradient structure, so that sensors with different performances in different regions can be designed according to needs to meet complex application requirements.

[0019] (2) High sensitivity, wide detection range and fast response capability. Wearable flexible sensors made of oriented gradient pore aerogel materials have high sensitivity, wide detection range and fast response capability. They can detect both extremely small and large external stimuli at the same time, respond to the stimuli in a short time, and quickly return to their original state after the stimulus disappears. This feature is very beneficial for application scenarios with real-time monitoring and fast feedback, such as health monitoring, sports tracking, etc.

[0020] (3) Excellent mechanical properties and good flexibility. Due to the porous structure and gradient change characteristics of the oriented gradient pore material, the specific strength and flexibility of the wearable flexible sensor provided by the present invention are greatly improved, and it can withstand large bending and torsional deformations. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a schematic diagram of the pore structure of a single fiber of the oriented gradient pore aerogel material prepared in Example 1 of the present invention; Figure 2 This is an enlarged schematic diagram of the pore and pore wall structure network of the oriented gradient pore aerogel material prepared in Example 1 of the present invention; Figure 3 This is a schematic diagram of a sample of an oriented gradient pore aerogel material prepared by cryo3D printing in Example 1 of the present invention; Figure 4 This is a schematic diagram of the oriented gradient pore aerogel material prepared in Example 1 of the present invention being placed on the surface of a petal and bearing three weights; Figure 5 A physical picture of the wearable flexible sensor prepared in Example 1 of the present invention; Figure 6 Dynamic current changes of the wearable flexible sensor prepared in Example 1 of the present invention when touched by a 0.02 g feather and a 200 g weight; Figure 7 This is a recognition diagram of different mechanical changes of the back of the hand by the wearable flexible sensor prepared in Example 1 of the present invention; Figure 8 This is a diagram showing the recognition result of the pulse signal by the wearable flexible sensor prepared in Example 1 of the present invention; Fig. 9This is a curve showing the temperature variation over time at different positions of a single fiber in a frozen 3D printed embodiment of the present invention; Fig.10 This is a schematic diagram of the simulation of the gradient temperature field of a single fiber in the frozen 3D printing according to an embodiment of the present invention; Fig.11 This is a SEM image of the oriented gradient holes in the contact area of ​​two fibers in parallel and crossed states printed by cryo-3D printing according to an embodiment of the present invention; Fig.12 This is a schematic diagram of the simulation of the gradient temperature field in the contact area of ​​two fibers in parallel and crossed states when cryo-3D printing is performed according to an embodiment of the present invention; Fig.13 This is the relationship between the tensile strength of a single fiber frozen in 3D printing and the freezing platform temperature in an embodiment of the present invention. DETAILED DESCRIPTION

[0022] The present invention provides a method for preparing a directional gradient pore aerogel material, comprising the following steps: A low-temperature 3D printing method is used to print composite material ink on a low-temperature freezing platform to obtain a preform, wherein the composite material ink includes a cellulose material, a carbon nanomaterial and water, and the cellulose material includes cellulose and / or a cellulose derivative, and the temperature of the low-temperature freezing platform is <0°C; The preform is freeze-dried to obtain the oriented gradient pore aerogel material.

[0023] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well known to those skilled in the art.

[0024] The present invention adopts a low-temperature 3D printing method to print a composite material ink on a low-temperature freezing platform to obtain a preform, wherein the composite material ink includes a cellulose material, a carbon nanomaterial and water, wherein the cellulose material includes cellulose and / or a cellulose derivative, and the temperature of the low-temperature freezing platform is <0°C. In the present invention, the water is preferably deionized water. The cellulose preferably includes cellulose nanofibers and / or cellulose nanocrystals. The cellulose derivative preferably includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose and cellulose acetate. In an embodiment of the present invention, the cellulose material may be sodium carboxymethyl cellulose. The mass percentage of the cellulose material in the composite material ink is preferably 1-20%, preferably 2-15%, more preferably 3-10%, and in an embodiment, it may be 4%, 4.5%, and 5%. In the present invention, the carbon nanomaterial preferably includes one or more of carbon nanotubes, carbon nanofibers, carbon nanospheres, carbon nanorods, graphene and graphene oxide, and in an embodiment, it may be carbon nanotubes. The mass percentage of the carbon nanomaterial in the composite material ink is preferably 0.1-5%, more preferably 0.5-4%, more preferably 1-3%, and further preferably 1.5-2.5%, and in embodiments it may be 2%, 1.51% or 2.49%. In the present invention, the mass ratio of the cellulose material to the carbon nanomaterial is preferably 4:1.5-2.5, and in embodiments it may be 4:2.5, 4:2 or 4:1.5.

[0025] In the present invention, the preparation method of the composite material ink preferably comprises: dispersing the carbon nanomaterial in water to obtain a carbon nanomaterial dispersion; mixing the carbon nanomaterial dispersion and the cellulose material and then allowing to stand to obtain the composite material ink. The dispersion is preferably ultrasonic dispersion, and the ultrasonic dispersion is preferably performed using an ultrasonic cell disruptor, and the dispersion time is preferably ≥1 h. The mixing is preferably performed at room temperature, and the mixing is preferably performed under stirring, and the mixing time is preferably ≥1 h. The standing temperature is preferably room temperature, and the standing time is preferably ≥24 h.

[0026] In the present invention, the low-temperature 3D printing is preferably carried out using a 3D printing molding device. The low-temperature 3D printing preferably uses software to design a 3D printing pattern, and the 3D printing pattern is preferably a one-dimensional silk thread, a two-dimensional grid, and preferably a three-dimensional structure, corresponding to a one-dimensional, two-dimensional or three-dimensional preform. In the present invention, the cold source of the low-temperature freezing platform is preferably liquid nitrogen. The temperature of the low-temperature freezing platform is preferably -10~-90 ℃, more preferably -30~-90 ℃, and in the embodiment it can be -30 ℃, -40 ℃, -50 ℃, -60 ℃, -70 ℃, -80 ℃ or -90 ℃. In the present invention, the conditions of the low-temperature 3D printing method preferably include: the printing speed is preferably 1~50 mm / s, preferably 10~40 mm / s, more preferably 20~30 mm / s, and in the embodiment it can be 25 mm / s; the nozzle diameter is preferably 0.2~2 mm, more preferably 0.3~1.5 mm, further preferably 0.5~1 mm, and in the embodiment it can be 0.6 mm. The composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is preferably 0.01-0.2 MPa, preferably 0.02-0.15 MPa, further preferably 0.05-0.1 MPa, and can be 0.07 MPa in an embodiment.

[0027] After obtaining the preform, the present invention freeze-dries the preform to obtain the oriented gradient pore aerogel material. In the present invention, the freeze drying is preferably performed in a freeze dryer. The temperature of the freeze drying equipment cavity is preferably -50~-90 °C, more preferably -60 °C, the time is preferably >12 h, and in the embodiment it can be 48 h; the freeze drying pressure is preferably ≤10 Pa.

[0028] The present invention provides an oriented gradient pore aerogel material prepared by the preparation method described in the above technical solution. In the present invention, the oriented gradient pore aerogel material has oriented and arranged elongated pores (that is, the pore structure of the oriented gradient pore aerogel material provided by the present invention is an elongated pore structure, and the elongated pore structure is arranged in layers), and the elongated pores are distributed in a gradient along the temperature field direction.

[0029] The present invention provides an application of the directional gradient pore aerogel material described in the above technical solution in a wearable flexible sensor.

[0030] The present invention provides a wearable flexible sensor, comprising the oriented gradient pore aerogel material described in the above technical solution. The wearable flexible sensor provided by the present invention is customizable and can design the performance of different regions according to needs; it also has high sensitivity, wide detection range and fast response capability; it also has excellent mechanical properties and good flexibility, and is suitable for health monitoring, sports tracking and other scenarios.

[0031] The present invention provides a method for preparing the wearable flexible sensor described in the above technical solution, comprising the following steps: Depositing a conductive metal coating on the pore wall surface of the oriented gradient pore aerogel material described in the above technical solution to obtain an aerogel with a conductive metal coating; Wires are arranged at both ends of the aerogel with a conductive metal coating, and then the aerogel is coated and packaged with a polymer to obtain the wearable flexible sensor.

[0032] The present invention deposits a conductive metal coating on the pore wall surface of the oriented gradient pore aerogel material described in the above technical solution to obtain an aerogel with a conductive metal coating. In the present invention, the deposition method of the conductive metal coating is preferably magnetron sputtering. The magnetron sputtering is preferably performed using a multi-target magnetron sputtering apparatus. The conditions of the magnetron sputtering preferably include: the deposition time is preferably 1 to 20 min, more preferably 10 min; the power is preferably 50 to 200 W, which can be 200 W in the embodiment, and the vacuum degree is preferably ≤1 Pa. The present invention preferably sputters conductive metal nanoparticles on the pore wall surface of the oriented gradient pore aerogel material by a magnetron sputtering method, and the conductive metal nanoparticles form a conductive metal coating on the pore wall surface of the oriented gradient pore aerogel material. The conductive metal coating preferably includes a gold coating and / or a silver coating.

[0033] After obtaining the aerogel with a conductive metal coating, the present invention sets wires at both ends of the aerogel with a conductive metal coating, and then uses a polymer to encapsulate and package it to obtain the wearable flexible sensor. In the present invention, the wire can be copper conductive. The method for setting the wire preferably includes: wrapping the two ends of the aerogel with a conductive metal coating with a conductive copper foil tape, and then leading the copper wires from both ends. In the present invention, the polymer preferably includes polydimethylsiloxane (PDMS), Ecoflex, thermoplastic polyurethane elastomer (TPU) or polyethylene terephthalate (PET). In a specific embodiment of the present invention, the polymer can be PDMS. The specific method for encapsulating the PDMS preferably includes: immersing the aerogel product with wires at both ends into a polydimethylsiloxane (PDMS) prepolymer for encapsulation, taking it out and heating and polymerizing it to obtain the wearable flexible sensor. In the present invention, the PDMS prepolymer preferably includes a dimethylsiloxane monomer and a cross-linking agent. The mass ratio of the dimethylsiloxane monomer to the cross-linking agent is preferably 5~15:1, and more preferably 10:1. The preparation method of the PDMS prepolymer preferably comprises: mechanically mixing the dimethylsiloxane monomer and the crosslinking agent and then removing bubbles to obtain the PDMS prepolymer. The degassing is preferably carried out in a vacuum environment, and the degassing time is preferably 2 to 3 minutes. The heating polymerization is preferably carried out in a vacuum box, and the temperature of the heating polymerization is preferably 80 to 90 ° C, and the time is preferably 1 to 2 hours.

[0034] In the present invention, the polymer encapsulation is to use the polymer to embed and encapsulate the outer surface of the aerogel product with wires at both ends, and will not enter the pores of the aerogel product. The wearable flexible sensor obtained by the present invention has a core-shell combination, the shell layer is a polymer encapsulation layer, and the core is an aerogel product with wires at both ends.

[0035] In order to further illustrate the present invention, the technical solutions provided by the present invention are described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0036] Example 1 This embodiment provides a method for preparing a directional gradient pore aerogel material, which specifically includes the following steps: Step 1: Weigh 2g of carbon nanotubes, 4g of sodium carboxymethyl cellulose, and 94g of deionized water using an electronic scale, and pour the deionized water into a beaker for later use. First, mix the carbon nanotubes into the deionized water and use an ultrasonic cell disruptor to ultrasonically disperse for 1 hour. Then, add sodium carboxymethyl cellulose, stir with a stirrer at room temperature for 1 hour, and let it stand for 24 hours to obtain a composite material ink.

[0037] Step 2: Use software to design the 3D printing pattern.

[0038] Step 3: Use low-temperature 3D printing to print the composite ink prepared in the first step on a low-temperature freezing platform according to the 3D printing pattern designed in the second step. Obtain a preform. The low-temperature freezing platform uses liquid nitrogen as a cold source at a temperature of -30 °C. Low-temperature 3D printing is performed using low-temperature 3D printing equipment. The printing speed of the low-temperature 3D printing molding setting is 25 mm / s, the nozzle diameter is 0.6 mm, and the composite ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.07 MPa.

[0039] Step 4: The preform obtained in the third step is placed in a freeze dryer (-60 °C, 10Pa) for freeze drying for 48 h to obtain a directional gradient pore aerogel material.

[0040] Microstructure characterization diagram of the oriented gradient pore aerogel material prepared in this example Figure 1 and Figure 2 As stated, Figure 1 It can be observed that the surface of the aerogel product prepared in this embodiment presents a gradient pore distribution; Figure 2 It can be observed that in the layered pore structure of the aerogel product prepared in this embodiment, the carbon nanotubes are entangled with each other to form a conductive network. This entanglement of the carbon nanotubes gives the aerogel better conductivity and stronger structural stability.

[0041] Figure 3 This is a schematic diagram of a sample of oriented gradient pore aerogel material prepared by 3D printing in this embodiment.

[0042] Figure 4 The oriented gradient pore aerogel material prepared in this embodiment is placed on the petal surface and subjected to three weights. Figure 4 The left picture in the figure shows the ultra-light quality characteristics of the oriented gradient pore aerogel material prepared in this example on the flower. Figure 4 The right figure in the figure shows that the oriented gradient pore aerogel material prepared in this example can withstand a load that is 1000 times greater than its own weight, showing the characteristic of super strong bearing capacity.

[0043] This embodiment provides a method for preparing a wearable flexible sensor, which specifically includes the following steps: Step 5: Use a multi-target magnetron sputtering apparatus to perform magnetron sputtering on the oriented gradient pore aerogel material obtained in step 4, and deposit a silver coating on the pore wall surface of the oriented gradient pore aerogel material. The magnetron sputtering treatment time is 10 min, the power is 200 W, and the vacuum degree is ≤1 Pa.

[0044] Step 6: Wrap the two ends of the aerogel with silver coating deposited on the pore wall obtained in the fifth step with conductive copper foil tape, and lead copper wires at both ends, then immerse it in polydimethylsiloxane (PDMS) prepolymer for coating and packaging, and then put it into a vacuum drying oven for heating and curing, the heating temperature is 90 ° C, and the heating time is 1h, to obtain a wearable flexible sensor with a core-shell structure. The preparation method of polydimethylsiloxane (PDMS) prepolymer includes: putting 10g of dimethylsiloxane monomer and 1g of silane crosslinker into a clean container, mixing them evenly with a centrifuge, and then placing it under vacuum for 30 minutes to remove bubbles therein to obtain polydimethylsiloxane (PDMS) prepolymer.

[0045] The actual picture of the wearable flexible sensor prepared in this embodiment is as follows Figure 5 shown.

[0046] The wearable flexible sensor prepared in this embodiment was subjected to performance testing.

[0047] Figure 6 The dynamic current change of the wearable flexible sensor prepared in this embodiment when touched by a 0.02g feather and a 200g weight. Figure 6 The results show that the wearable flexible sensor prepared in this example exhibits high sensitivity and a wide detection range.

[0048] Figure 7 Recognition diagram of different mechanical changes of the back of the hand by the wearable flexible sensor prepared in this embodiment; Figure 8 This is a diagram showing the recognition result of the pulse signal by the wearable flexible sensor prepared in this embodiment. Figure 7 and Figure 8 The results show that the wearable flexible sensor prepared in this embodiment exhibits high stability, high sensitivity and fast response capability.

[0049] Example 2 This embodiment provides a method for preparing a directional gradient pore aerogel material, which specifically includes the following steps: Step 1: Weigh 1.5g of carbon nanotubes, 4g of sodium carboxymethyl cellulose, and 94g of deionized water using an electronic scale, and pour the deionized water into a beaker for later use. First, mix the carbon nanotubes into the deionized water and use an ultrasonic cell disruptor to ultrasonically disperse for 1 hour. Then, add sodium carboxymethyl cellulose, stir with a stirrer at room temperature for 1 hour, and let it stand for 24 hours to obtain a composite material ink.

[0050] Step 2: Use software to design the 3D printing pattern.

[0051] Step 3: Use low-temperature 3D printing to print the composite ink prepared in the first step on a low-temperature freezing platform according to the 3D printing pattern designed in the second step. Obtain a preform. The low-temperature freezing platform uses liquid nitrogen as a cold source at a temperature of -30 °C. Low-temperature 3D printing is performed using low-temperature 3D printing equipment. The printing speed of the low-temperature 3D printing molding setting is 25 mm / s, the nozzle diameter is 0.6 mm, and the composite ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.07 MPa.

[0052] Step 4: The preform obtained in the third step is placed in a freeze dryer (-60 °C, 10Pa) for freeze drying for 48 h to obtain a directional gradient pore aerogel material.

[0053] This embodiment provides a method for preparing a wearable flexible sensor, which specifically includes the following steps: Step 5: Use a multi-target magnetron sputtering apparatus to perform magnetron sputtering on the oriented gradient pore aerogel material obtained in step 4, and deposit a silver coating on the pore wall surface of the oriented gradient pore aerogel material. The magnetron sputtering treatment time is 10 min, the power is 200 W, and the vacuum degree is ≤1 Pa.

[0054] Step 6: Wrap the two ends of the aerogel with silver coating deposited on the pore wall obtained in the fifth step with conductive copper foil tape, and lead copper wires at both ends, then immerse it in polydimethylsiloxane (PDMS) prepolymer for coating and packaging, and then put it into a vacuum drying oven for vacuuming and heating curing, the heating temperature is 90 ° C, and the heating time is 1 hour, to obtain a wearable flexible sensor with a core-shell structure. Among them, the preparation method of polydimethylsiloxane (PDMS) prepolymer includes: putting 10g of dimethylsiloxane monomer and 1g of silane cross-linking agent into a clean container, mixing them evenly with a centrifuge, and then placing it under vacuum for 30 minutes to remove bubbles therein to obtain polydimethylsiloxane (PDMS) prepolymer.

[0055] Example 3 This embodiment provides a method for preparing a directional gradient pore aerogel material, which specifically includes the following steps: Step 1: Weigh 2.5g of carbon nanotubes, 4g of sodium carboxymethyl cellulose, and 94g of deionized water using an electronic scale, and pour the deionized water into a beaker for later use. First, mix the carbon nanotubes into the deionized water and use an ultrasonic cell disruptor to ultrasonically disperse for 1 hour. Then, add sodium carboxymethyl cellulose, stir with a stirrer at room temperature for 1 hour, and let it stand for 24 hours to obtain a composite material ink.

[0056] Step 2: Use software to design the 3D printing pattern.

[0057] Step 3: Use low-temperature 3D printing to print the composite ink prepared in the first step on a low-temperature freezing platform according to the 3D printing pattern designed in the second step. Obtain a preform. The low-temperature freezing platform uses liquid nitrogen as a cold source at a temperature of -30 °C. Low-temperature 3D printing is performed using low-temperature 3D printing equipment. The printing speed of the low-temperature 3D printing molding setting is 25 mm / s, the nozzle diameter is 0.6 mm, and the composite ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.07 MPa.

[0058] Step 4: The preform obtained in the third step is placed in a freeze dryer (-60 °C, 10Pa) for freeze drying for 48 h to obtain a directional gradient pore aerogel material.

[0059] This embodiment provides a method for preparing a wearable flexible sensor, which specifically includes the following steps: Step 5: Use a multi-target magnetron sputtering apparatus to perform magnetron sputtering on the oriented gradient pore aerogel material obtained in step 4, and deposit a silver coating on the pore wall surface of the oriented gradient pore aerogel material. The magnetron sputtering treatment time is 10 min, the power is 200 W, and the vacuum degree is ≤1 Pa.

[0060] Step 6: Wrap the two ends of the aerogel with silver coating deposited on the pore wall obtained in the fifth step with conductive copper foil tape, and lead copper wires at both ends, then immerse it in polydimethylsiloxane (PDMS) prepolymer for coating and packaging, and then put it into a vacuum drying oven for vacuuming and heating curing, the heating temperature is 90 ° C, and the heating time is 1 hour, to obtain a wearable flexible sensor with a core-shell structure. Among them, the preparation method of polydimethylsiloxane (PDMS) prepolymer includes: putting 10g of dimethylsiloxane monomer and 1g of silane cross-linking agent into a clean container, mixing them evenly with a centrifuge, and then placing it under vacuum for 30 minutes to remove bubbles therein to obtain polydimethylsiloxane (PDMS) prepolymer.

[0061] After testing, the performance of the wearable flexible sensors prepared in Examples 2 and 3 is similar to that of the wearable flexible sensor prepared in Example 1.

[0062] Example 4 The preparation method of the oriented gradient pore aerogel material is basically the same as that described in Example 1, except that the temperature of the low-temperature freezing platform is -50°C, -70°C or -90°C.

[0063] The mechanical properties (stress) of the oriented gradient pore aerogels prepared in Example 1 and Example 4 are as follows: Fig.13 As shown. Fig.13It can be seen that the aerogel materials printed at different cold stage temperatures will have different mechanical strengths in terms of mechanical properties, which increases as the cold stage temperature decreases.

[0064] It can be seen from the above embodiments that, on the one hand, the present invention adopts a low-temperature 3D printing method, and controls the temperature of the low-temperature freezing platform to form a mutually perpendicular dual temperature gradient field to guide the water in the composite ink to freeze, thereby obtaining the oriented gradient pore aerogel material whose pore structure can be precisely controlled. On the other hand, the composite ink used in the present invention includes a compound of cellulose materials and carbon nanomaterials. The cellulose material can assist the carbon nanomaterial in forming a stable conductive network in the aerogel material, thereby giving the oriented gradient pore aerogel material better conductivity and stronger structural stability. In summary, the oriented gradient pore aerogel material prepared by the present invention is customizable due to the non-uniform characteristics of the pore structure in the product, and the performance of different regions can be designed according to needs; it also has high sensitivity, wide detection range and rapid response capability; at the same time, it has excellent mechanical properties and good flexibility, and the resulting wearable flexible sensor is suitable for health monitoring, sports tracking and other scenarios.

[0065] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a directional gradient pore aerogel material, characterized in that: The following steps are involved: A low-temperature 3D printing method is used to print composite material ink on a low-temperature freezing platform to obtain a preform, wherein the composite material ink includes a cellulose material, a carbon nanomaterial and water, and the cellulose material includes cellulose and / or a cellulose derivative, and the temperature of the low-temperature freezing platform is <0°C; The preform is freeze-dried to obtain the oriented gradient pore aerogel material.

2. The preparation method according to claim 1, wherein the cellulose comprises cellulose nanofibers and / or cellulose nanocrystals; and the cellulose derivative comprises one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose and cellulose acetate; The mass percentage of the cellulose material in the composite material ink is 1-20%.

3. The preparation method according to claim 1, characterized in that: The carbon nanomaterial includes one or more of carbon nanotubes, carbon nanofibers, carbon nanospheres, carbon nanorods, graphene and graphene oxide; The mass percentage of the carbon nanomaterial in the composite material ink is 0.1-5%.

4. The preparation method according to any one of claims 1 to 3, characterized in that The temperature of the low-temperature freezing platform is -10~-90°C; The conditions of the low-temperature 3D printing method include: a printing speed of 1-50 mm / s, a nozzle diameter of 0.2-2 mm, the composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.01-0.2 MPa.

5. The preparation method according to claim 1, characterized in that: The temperature of the freeze-drying equipment cavity is -50~-90°C, and the time is >12 h.

6. The oriented gradient pore aerogel material prepared by the preparation method according to any one of claims 1 to 5.

7. Application of the oriented gradient pore aerogel material according to claim 6 in wearable flexible sensors.

8. A wearable flexible sensor, characterized in that: The invention comprises the oriented gradient pore aerogel material as described in claim 6.

9. The method for preparing the wearable flexible sensor according to claim 8, characterized in that: The following steps are involved: Depositing a conductive metal coating on the pore wall surface of the oriented gradient pore aerogel material according to claim 6 to obtain an aerogel having a conductive metal coating; Wires are arranged at both ends of the aerogel with a conductive metal coating, and then the aerogel is coated and packaged with a polymer to obtain the wearable flexible sensor.

10. The preparation method according to claim 9, characterized in that: The conductive metal coating is deposited by magnetron sputtering; the conditions of the magnetron sputtering include: deposition time of 1 to 20 min, power of 50 to 200 W, and vacuum degree ≤ 1 Pa; The conductive metal coating comprises a gold coating and / or a silver coating; The polymer includes polydimethylsiloxane, Ecoflex, thermoplastic polyurethane elastomer or polyethylene terephthalate.

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