An Oriented Gradient Pore Aerogel and Its Preparation Method and Application in Flexible Sensors

Abstract

The present invention belongs to the technical field of 3D printing aerogel, and specifically relates to an oriented gradient pore aerogel, a preparation method thereof, and an application thereof in a flexible sensor. 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. The composite material ink includes a cellulose-based material, a carbon nanomaterial, and water. The cellulose-based material includes cellulose and / or a cellulose derivative. The temperature of the low-temperature freezing platform is <0 °C; the preform is freeze-dried to obtain the oriented gradient pore aerogel. The present invention subjects the oriented gradient pore aerogel material to magnetron sputtering and encapsulation to obtain a wearable flexible sensor. The wearable flexible sensor provided by the present invention has high sensitivity, a wide detection range, and a fast response ability; at the same time, it has excellent mechanical properties and good flexibility, and is suitable for applications requiring real-time monitoring and rapid feedback, including scenarios such as health monitoring and motion tracking.

Description

Technical Field

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

[0002] With the rapid development of modern science and technology and electronic information technology, human society has entered a new era of intelligent manufacturing. A flexible sensor is a sensor with good flexibility and stretchability, which can convert external mechanical stimulus signals (such as pressure, deformation, vibration, etc.) into electrical signals (such as resistance, capacitance, etc.) for output, realizing real-time sensing and monitoring functions, and is an important basis for intelligent manufacturing.

[0003] An 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. Mixing aerogels with nanomaterials such as carbon nanotubes, graphene oxide, and silver nanowires to prepare composite aerogels can be applied to the field of flexible sensing.

[0004] However, at present, the pore structure of composite aerogels cannot be effectively regulated, or the porous structure is too fragile and prone to shrinkage and collapse during the preparation process, resulting in that the flexible sensor cannot well adapt to different deformations and pressure changes, with low sensitivity, unable to respond and recover quickly, and thus cannot be applied to application scenarios of real-time monitoring and rapid feedback. Summary of the Invention

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

[0006] In order to achieve the above purpose, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of an oriented gradient pore aerogel material, comprising the following steps:

[0008] Adopting a low-temperature 3D printing method, printing a composite material ink on a low-temperature freezing platform to obtain a preform, wherein the composite material ink comprises a cellulose-based material, a carbon nanomaterial, and water, the cellulose-based material comprises cellulose and / or a cellulose derivative, and the temperature of the low-temperature freezing platform is <0 °C;

[0009] Performing freeze-drying on the preform to obtain the oriented gradient pore aerogel material.

[0010] Preferably, the cellulose includes cellulose nanofibers and / or cellulose nanocrystals; the cellulose derivative includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, and cellulose acetate;

[0011] The mass percentage content of the cellulose-based material in the composite ink is 1-20%.

[0012] Preferably, the carbon nanomaterial includes one or more of carbon nanotubes, carbon nanofibers, carbon nanospheres, carbon nanorods, graphene, and graphene oxide;

[0013] The mass percentage content of the carbon nanomaterial in the composite ink is 0.1-5%.

[0014] Preferably, the temperature of the low-temperature freezing platform is -10~-90 °C;

[0015] The conditions of the low-temperature 3D printing method include: the printing speed is 1-50 mm / s, the nozzle diameter is 0.2-2 mm, the composite ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.01-0.2 MPa.

[0016] Preferably, the temperature of the equipment cavity for freeze-drying is -50~-90 °C, and the time > 12 h.

[0017] The present invention provides an oriented gradient pore aerogel material prepared by the preparation method described in the above technical solution.

[0018] The present invention provides the application of the oriented gradient pore aerogel material described in the above technical solution in a wearable flexible sensor.

[0019] The present invention provides a wearable flexible sensor, including the oriented gradient pore aerogel material described in the above technical solution.

[0020] The present invention provides a preparation method of the wearable flexible sensor described in the above technical solution, including the following steps:

[0021] Deposit 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;

[0022] Set wires at both ends of the aerogel with the conductive metal coating, and then coat and encapsulate with a polymer to obtain the wearable flexible sensor.

[0023] Preferably, the deposition method of the conductive metal coating is magnetron sputtering; the conditions of the magnetron sputtering include: the deposition time is 1-20 min, the power is 50-200 W, and the vacuum degree ≤ 1 Pa;

[0024] The conductive metal coating includes a gold coating and / or a silver coating;

[0025] The polymer includes polydimethylsiloxane (PDMS), Ecoflex, thermoplastic polyurethane elastomer (TPU), or polyethylene terephthalate (PET).

[0026] 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, printing a composite material ink on a low-temperature freezing platform to obtain a preform, the composite material ink including a cellulose-based material, a carbon nanomaterial, and water, the cellulose-based material including cellulose and / or a cellulose derivative, the temperature of the low-temperature freezing platform being < 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. 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 contacts the air and has a high temperature, while the lower surface of the composite material ink contacts the low-temperature freezing platform and has a low temperature, forming a temperature gradient in the vertical direction; in the horizontal direction, the temperature of the composite material ink at the nozzle end of the 3D printing is high, and the temperature of the composite material ink far from the nozzle section (the distal end) is low, forming a temperature gradient in the horizontal direction centered on the 3D printing nozzle; the mutually perpendicular dual temperature gradient fields (as Figure 9 and Figure 10 shown) guide the water in the composite material ink to freeze, and the ice crystals grow directionally, with the volume increasing from small to large from the low-temperature region to the high-temperature region of the dual temperature gradient field (as Figure 11 and Figure 12 shown), forming a one-dimensional, two-dimensional, or three-dimensional preform, and finally obtaining the directional gradient pore aerogel material with precisely controllable pore structure through freeze-drying. On the other hand, the composite material ink used in the present invention includes a cellulose-based material and a carbon nanomaterial in a compound form. The cellulose-based material can assist the carbon nanomaterial in forming a stable conductive network in the aerogel material, thereby endowing the directional gradient pore aerogel material with better electrical conductivity and stronger structural stability. In summary, due to the non-uniformity of the pore structure in the product, the directional gradient pore aerogel material prepared by the present invention has customizability and can be designed with different regional properties according to needs; it also has high sensitivity, a wide detection range, and a fast response ability; at the same time, it has excellent mechanical properties and good flexibility, and the obtained wearable flexible sensor is suitable for scenarios such as health monitoring and sports tracking.

[0027] Meanwhile, the preparation method provided by the present invention overcomes the drawback that the directional freezing method must use a mold, and adopts low-temperature 3D printing combined with freeze-drying, featuring rapid and large-scale preparation.

[0028] The present invention provides a wearable flexible sensor, which includes the directional 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:

[0029] (1) Customizability. The pore size and porosity of the pore structure of the directional gradient pore aerogel material provided by the present invention change in a gradient along a specific direction (the dual temperature gradient direction). This structure enables the mechanical properties (such as stiffness, toughness, strength, etc.) of the aerogel material to also change with the change of the gradient structure, so that sensors with different properties in different regions can be designed according to needs to meet complex application requirements.

[0030] (2) High sensitivity, wide detection range and fast response ability. The wearable flexible sensor prepared from the directional gradient pore aerogel material has high sensitivity, wide detection range and fast response ability. It can simultaneously detect extremely small and large external stimuli, respond to the stimuli within a short time, and quickly return to the original state after the stimuli disappear. This feature is very beneficial for application scenarios such as real-time monitoring and rapid feedback, such as health monitoring, sports tracking, etc.

[0031] (3) Excellent mechanical properties and good flexibility. Due to the porous structure and gradient change characteristics of the directional 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 amounts of bending and torsional deformation. Description of the Drawings

[0032] Figure 1 Schematic diagram of the pore structure of a single fiber of the directional gradient pore aerogel material prepared in Example 1 of the present invention;

[0033] Figure 2 Magnified schematic diagram of the pore and pore wall structure network of the directional gradient pore aerogel material prepared in Example 1 of the present invention;

[0034] Figure 3 Schematic diagram of the sample of the directional gradient pore aerogel material prepared by freeze 3D printing in Example 1 of the present invention;

[0035] Figure 4 Schematic diagram of the directional gradient pore aerogel material prepared in Example 1 of the present invention placed statically on the petal surface and bearing 3 weights;

[0036] Figure 5 Physical diagram of the wearable flexible sensor prepared in Example 1 of the present invention;

[0037] Figure 6 Dynamic current change of the wearable flexible sensor prepared in Example 1 of the present invention under the touch of a 0.02 g feather and a 200 g weight;

[0038] Figure 7 Recognition diagram of the wearable flexible sensor prepared in Example 1 of the present invention for different mechanical changes on the back of the hand;

[0039] Figure 8 Recognition result diagram of the wearable flexible sensor prepared in Example 1 of the present invention for pulse signals;

[0040] Figure 9 Variation curve of the temperature at different positions of a single fiber in cryogenic 3D printing in Example 1 of the present invention with time;

[0041] Figure 10 Schematic diagram of the simulated gradient temperature field of a single fiber in cryogenic 3D printing in Example 1 of the present invention;

[0042] Figure 11 SEM diagram of the directional gradient holes in the contact area of two fibers in cryogenic 3D printing in Example 1 of the present invention in parallel and cross states;

[0043] Figure 12 Schematic diagram of the simulated gradient temperature field in the contact area of two fibers in cryogenic 3D printing in Example 1 of the present invention in parallel and cross states;

[0044] Figure 13 Relationship between the tensile strength of a single fiber in cryogenic 3D printing and the cryogenic platform temperature in Example 1 of the present invention. Detailed implementation manners

[0045] The present invention provides a preparation method of a directional gradient pore aerogel material, comprising the following steps:

[0046] Adopt a low-temperature 3D printing method to print a composite material ink on a low-temperature freezing platform to obtain a preform. The composite material ink includes a cellulose-based material, a carbon nanomaterial, and water. The cellulose-based material includes cellulose and / or cellulose derivatives. The temperature of the low-temperature freezing platform < 0 °C;

[0047] Freeze-dry the preform to obtain the directional gradient pore aerogel material.

[0048] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0049] 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. The composite material ink includes a cellulose-based material, a carbon nanomaterial, and water. The cellulose-based material includes cellulose and / or cellulose derivatives. 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 the embodiments of the present invention, the cellulose-based material can be sodium carboxymethyl cellulose. The mass percentage content of the cellulose-based material in the composite material ink is preferably 1-20%, more preferably 2-15%, and even more preferably 3-10%. In the embodiments, it can be 4%, 4.5%, or 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, etc. In the embodiments, it can be carbon nanotubes. The mass percentage content of the carbon nanomaterial in the composite material ink is preferably 0.1-5%, more preferably 0.5-4%, even more preferably 1-3%, and further preferably 1.5-2.5%. In the embodiments, it can be 2%, 1.51%, or 2.49%. In the present invention, the mass ratio of the cellulose-based material to the carbon nanomaterial is preferably 4:1.5-2.5. In the embodiments, it can be 4:2.5, 4:2, or 4:1.5.

[0050] In the present invention, the preparation method of the composite material ink preferably includes: dispersing the carbon nanomaterial in water to obtain a carbon nanomaterial dispersion; mixing the carbon nanomaterial dispersion and the cellulose-based material and then standing to obtain the composite material ink. The dispersion is preferably ultrasonic dispersion, and the ultrasonic dispersion is preferably carried out using an ultrasonic cell disruptor. The dispersion time is preferably ≥1 h. The mixing is preferably carried out at room temperature and preferably under stirring conditions. The mixing time is preferably ≥1 h. The standing temperature is preferably room temperature, and the standing time is preferably ≥24 h.

[0051] In the present invention, the low-temperature 3D printing is preferably carried out using a 3D printing forming device. The low-temperature 3D printing preferably uses software to design the 3D printing pattern, and the 3D printing pattern is preferably a one-dimensional wire, a two-dimensional grid, and preferably a three-dimensional structure body, corresponding to obtain 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 °C, more preferably -30~-90 °C, and can be -30 °C, -40 °C, -50 °C, -60 °C, -70 °C, -80 °C or -90 °C in the examples. 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 can be 25 mm / s in the examples; the nozzle diameter is preferably 0.2~2 mm, more preferably 0.3~1.5 mm, further preferably 0.5~1 mm, and can be 0.6 mm in the examples. 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 the examples.

[0052] 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 carried out in a freeze-dryer. The temperature of the equipment cavity for the freeze-drying is preferably -50~-90 °C, more preferably -60 °C, the time is preferably >12 h, and can be 48 h in the examples; the pressure for the freeze-drying is preferably ≤10 Pa.

[0053] 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 slender pores arranged in an oriented manner (that is, the pore structure of the oriented gradient pore aerogel material provided by the present invention is a slender pore structure, and the slender pore structures are arranged in layers), and the slender pores are distributed in a gradient along the temperature field direction.

[0054] The present invention provides an application of the oriented gradient pore aerogel material described in the above technical solution in a wearable flexible sensor.

[0055] The present invention provides a wearable flexible sensor, including the oriented gradient pore aerogel material described in the above technical solution. The wearable flexible sensor provided by the present invention has customizability and can design the performance of different regions according to needs; it also has high sensitivity, a wide detection range and a fast response ability; at the same time, it has excellent mechanical properties and good flexibility, and is suitable for scenarios such as health monitoring and sports tracking.

[0056] The present invention provides a method for preparing the wearable flexible sensor described in the above technical solution, comprising the following steps:

[0057] Deposit a conductive metal coating on the pore wall surface of the directional gradient pore aerogel material described in the above technical solution to obtain an aerogel with a conductive metal coating;

[0058] Set wires at both ends of the aerogel with the conductive metal coating, and then use a polymer for coating and encapsulation to obtain the wearable flexible sensor.

[0059] In the present invention, a conductive metal coating is deposited on the pore wall surface of the directional 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 carried out by using a multi-target magnetron sputtering instrument. The conditions of the magnetron sputtering preferably include: the deposition time is preferably 1 to 20 minutes, more preferably 10 minutes; the power is preferably 50 to 200 W, and can be 200 W in the examples, and the vacuum degree is preferably ≤1 Pa. The present invention preferably sputters conductive metal nanoparticles on the pore wall surface of the directional gradient pore aerogel material by magnetron sputtering, and the conductive metal coating is formed on the pore wall surface of the directional gradient pore aerogel material by the conductive metal nanoparticles. The conductive metal coating preferably includes a gold coating and / or a silver coating.

[0060] After obtaining the aerogel with a conductive metal coating, the present invention sets wires at both ends of the aerogel with the conductive metal coating, and then uses a polymer for coating and encapsulation to obtain the wearable flexible sensor. In the present invention, the wire can be copper-conductive. The method for setting the wire preferably includes: winding conductive copper foil tape around both ends of the aerogel with the conductive metal coating, and then leading out copper wires at 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 coating and encapsulating with PDMS preferably includes: immersing the aerogel product with wires set at both ends into the polydimethylsiloxane (PDMS) prepolymer for coating and encapsulation, and after taking it out, heating and polymerizing to obtain the wearable flexible sensor. In the present invention, the PDMS prepolymer preferably includes dimethylsiloxane monomer and a crosslinking agent. The mass ratio of the dimethylsiloxane monomer to the crosslinking agent is preferably 5-15:1, more preferably 10:1. The preparation method of the PDMS prepolymer preferably includes: mechanically mixing the dimethylsiloxane monomer and the crosslinking agent and then removing air bubbles to obtain the PDMS prepolymer. The air bubble removal is preferably carried out in a vacuum environment, and the time for air bubble removal is preferably 2-3 min. The heating and polymerization is preferably carried out in a vacuum box, the temperature for heating and polymerization is preferably 80-90 °C, and the time is preferably 1-2 h.

[0061] In the present invention, the polymer coating and encapsulation is to embed and encapsulate on the outer surface of the aerogel product with wires set at both ends by using the polymer, and will not enter the pores inside the aerogel product. The wearable flexible sensor obtained in 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 set at both ends.

[0062] In order to further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they cannot be understood as limiting the protection scope of the present invention.

[0063] Example 1

[0064] This embodiment provides a preparation method of a directional gradient pore aerogel material, which specifically includes the following steps:

[0065] The first step: Weigh 2 g of carbon nanotubes, 4 g of sodium carboxymethyl cellulose, and 94 g of deionized water with an electronic balance, and pour the deionized water into a beaker for standby. First, mix the carbon nanotubes into the deionized water and disperse them by ultrasonic treatment with an ultrasonic cell disruptor for 1 h. Subsequently, add sodium carboxymethyl cellulose and stir with a stirrer at room temperature for 1 h, and then let it stand for 24 h to obtain a composite material ink.

[0066] Step 2: Design the 3D printing pattern using software.

[0067] Step 3: Using the method of low-temperature 3D printing, print the composite material ink prepared in the first step on a low-temperature freezing platform according to the 3D printing pattern designed in the second step to obtain a preform. Among them, the low-temperature freezing platform uses liquid nitrogen as a cold source, and the temperature is -30 °C. The low-temperature 3D printing is carried out using a low-temperature 3D printing forming device. The printing speed set for the low-temperature 3D printing forming is 25 mm / s, the nozzle diameter is 0.6 mm, and the composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.07 MPa.

[0068] Step 4: Place the preform obtained in the third step in a freeze dryer (-60 °C, 10 Pa) for freeze drying for 48 h to obtain a directional gradient pore aerogel material.

[0069] Microstructure characterization diagram of the directional gradient pore aerogel material prepared in this example Figure 1 and Figure 2 as described Figure 1 It can be observed that the surface of the aerogel product prepared in this example presents a gradient pore distribution; Figure 2 It can be observed that in the layered pore structure of the aerogel product prepared in this example, the carbon nanotubes are intertwined with each other to form a conductive network. This intertwining effect of the carbon nanotubes endows the aerogel with better conductivity and stronger structural stability.

[0070] Figure 3 Schematic diagram of the sample of the directional gradient pore aerogel material prepared by 3D printing in this example.

[0071] Figure 4 Schematic diagram of the directional gradient pore aerogel material prepared in this example placed on the surface of a petal and bearing 3 weights. Place the directional gradient pore aerogel material prepared in this example on the petal, as shown in Figure 4 the left figure in, indicating the ultra-light mass characteristic of the directional gradient pore aerogel material prepared in this example on the flower. Figure 4 The right figure in shows that the directional gradient pore aerogel material prepared in this example can withstand a load of more than 1000 times its own weight, showing the characteristic of super strong bearing capacity.

[0072] This example provides a preparation method for a wearable flexible sensor, which specifically includes the following steps:

[0073] Step 5: Use a multi-target magnetron sputtering instrument to perform magnetron sputtering treatment on the directional gradient pore aerogel material obtained in the fourth step, and deposit a silver coating on the pore wall surface of the directional gradient pore aerogel material. The time for the magnetron sputtering treatment is 10 min, the power is 200 W, and the vacuum degree ≤ 1 Pa.

[0074] Step 6: Wrap both ends of the aerogel with a silver-coated pore wall obtained in the fifth step with conductive copper foil tape, lead out copper wires at both ends, then immerse them in a polydimethylsiloxane (PDMS) prepolymer for encapsulation, and then place them in a vacuum drying oven for heating and curing. The heating temperature is 90 °C and the heating time is 1 h to obtain a core-shell structured wearable flexible sensor. Among them, the preparation method of the polydimethylsiloxane (PDMS) prepolymer includes: putting 10 g of dimethylsiloxane monomer and 1 g of silane crosslinking agent into a clean container, mixing them evenly with a centrifuge, and then placing them under vacuum for 30 min to remove the bubbles therein to obtain the polydimethylsiloxane (PDMS) prepolymer.

[0075] The physical picture of the wearable flexible sensor prepared in this embodiment is as Figure 5 shown.

[0076] Perform performance tests on the wearable flexible sensor prepared in this embodiment.

[0077] Figure 6 This is the dynamic current change of the wearable flexible sensor under the touch of 0.02 g of feathers and 200 g of weights. From Figure 6 the results show that the wearable flexible sensor prepared in this embodiment exhibits high sensitivity and a wide detection range.

[0078] Figure 7 This is the recognition map of different mechanical changes on the back of the hand by the wearable flexible sensor prepared in this embodiment; Figure 8 This is the recognition result map of the pulse signal by the wearable flexible sensor prepared in this embodiment. From 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 ability.

[0079] Example 2

[0080] This embodiment provides a preparation method of a directional gradient pore aerogel material, which specifically includes the following steps:

[0081] Step 1: Weigh 1.5 g of carbon nanotubes, 4 g of sodium carboxymethyl cellulose, and 94 g of deionized water with an electronic balance, and pour the deionized water into a beaker for standby. First, mix the carbon nanotubes into the deionized water and ultrasonically disperse them for 1 h using an ultrasonic cell disrupter. Subsequently, add sodium carboxymethyl cellulose and stir with a stirrer at room temperature for 1 h, and then let it stand for 24 h to obtain a composite material ink.

[0082] Step 2: Design the pattern of 3D printing using software.

[0083] Step 3: Using the method of low-temperature 3D printing, print the composite material ink prepared in the first step on the low-temperature freezing platform according to the 3D printing pattern designed in the second step to obtain a preform. Among them, the low-temperature freezing platform uses liquid nitrogen as a cold source and has a temperature of -30 °C. The low-temperature 3D printing is carried out using a low-temperature 3D printing and forming device. The printing speed set for the low-temperature 3D printing and forming is 25 mm / s, the nozzle diameter is 0.6 mm, and the composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.07 MPa.

[0084] Step 4: Place the preform obtained in the third step in a freeze dryer (-60 °C, 10 Pa) for freeze drying for 48 h to obtain a directional gradient pore aerogel material.

[0085] This embodiment provides a preparation method for a wearable flexible sensor, which specifically includes the following steps:

[0086] Step 5: Use a multi-target magnetron sputtering instrument to perform magnetron sputtering treatment on the directional gradient pore aerogel material obtained in the fourth step to deposit a silver coating on the pore wall surface of the directional gradient pore aerogel material. The time for the magnetron sputtering treatment is 10 min, the power is 200 W, and the vacuum degree is ≤1 Pa.

[0087] Step 6: Wrap conductive copper foil tape around both ends of the aerogel with a silver coating deposited on the pore wall obtained in the fifth step, lead out copper wires at both ends, then immerse them in a polydimethylsiloxane (PDMS) prepolymer for coating and encapsulation, and then place them in a vacuum drying oven for vacuum pumping and heating curing. The heating temperature is 90 °C and the heating time is 1 h to obtain a core-shell structured wearable flexible sensor. Among them, the preparation method of the polydimethylsiloxane (PDMS) prepolymer includes: putting 10 g of dimethylsiloxane monomer and 1 g of silane cross-linking agent into a clean container, mixing them evenly with a centrifuge, and then placing them under vacuum for 30 min to remove the bubbles therein to obtain the polydimethylsiloxane (PDMS) prepolymer.

[0088] Example 3

[0089] This embodiment provides a preparation method for a directional gradient pore aerogel material, which specifically includes the following steps:

[0090] Step 1: Weigh 2.5 g of carbon nanotubes, 4 g of sodium carboxymethyl cellulose, and 94 g of deionized water with an electronic scale, and pour the deionized water into a beaker for standby. First, mix the carbon nanotubes into the deionized water and disperse them by ultrasonic treatment with an ultrasonic cell disrupter for 1 h. Subsequently, add sodium carboxymethyl cellulose and stir with a stirrer at room temperature for 1 h, and then let it stand for 24 h to obtain a composite material ink.

[0091] Step 2: Design the 3D printing pattern using software.

[0092] Step 3: Using the method of low-temperature 3D printing, print the composite material ink prepared in the first step on a low-temperature freezing platform according to the 3D printing pattern designed in the second step to obtain a preform. Among them, the low-temperature freezing platform uses liquid nitrogen as a cold source, and the temperature is -30 °C. The low-temperature 3D printing is carried out by using a low-temperature 3D printing forming device. The printing speed set for the low-temperature 3D printing forming is 25 mm / s, the nozzle diameter is 0.6 mm, and the composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.07 MPa.

[0093] Step 4: Place the preform obtained in the third step in a freeze dryer (-60 °C, 10 Pa) for freeze drying for 48 h to obtain a directional gradient pore aerogel material.

[0094] This embodiment provides a preparation method for a wearable flexible sensor, specifically including the following steps:

[0095] Step 5: Use a multi-target magnetron sputtering instrument to perform magnetron sputtering treatment on the directional gradient pore aerogel material obtained in the fourth step, and deposit a silver coating on the pore wall surface of the directional gradient pore aerogel material. The time for the magnetron sputtering treatment is 10 min, the power is 200 W, and the vacuum degree is ≤1 Pa.

[0096] Step 6: Wrap conductive copper foil tapes around both ends of the aerogel with a silver coating deposited on the pore walls obtained in the fifth step, and lead out copper wires at both ends. Then immerse them in a polydimethylsiloxane (PDMS) prepolymer for coating and encapsulation, and then place them in a vacuum drying oven for vacuum pumping and heat curing. The heating temperature is 90 °C, and the heating time is 1 h to obtain a core-shell structured wearable flexible sensor. Among them, the preparation method of the polydimethylsiloxane (PDMS) prepolymer includes: putting 10 g of dimethylsiloxane monomer and 1 g of silane crosslinking agent into a clean container, uniformly mixing them with a centrifuge, and then placing them under vacuum for 30 min to remove the bubbles therein to obtain the polydimethylsiloxane (PDMS) prepolymer.

[0097] After testing, the performance of the wearable flexible sensors prepared in Example 2 and Example 3 is similar to that of the wearable flexible sensor prepared in Example 1.

[0098] Example 4

[0099] It is basically the same as the preparation method of the directional gradient pore aerogel material described in Example 1, except that: the temperatures of the low-temperature freezing platform are -50 °C, -70 °C or -90 °C respectively.

[0100] The mechanical properties (stress) of the directional gradient pore aerogels prepared in Example 1 and Example 4 are as Figure 13 shown. From Figure 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 increase as the cold stage temperature decreases.

[0101] As can be seen from the above embodiments, on the one hand, the present invention adopts a low-temperature 3D printing method to form a mutually perpendicular double temperature gradient field by controlling the temperature of a low-temperature freezing platform to guide the freezing of water in a composite material ink, thereby obtaining the oriented gradient pore aerogel material with accurately controllable pore structure. On the other hand, the composite material ink adopted in the present invention comprises a compound of a cellulose-based material and a carbon nanomaterial. The cellulose-based material can assist the carbon nanomaterial to form a stable conductive network in the aerogel material, thereby endowing the oriented gradient pore aerogel material with better electrical conductivity and stronger structural stability. In summary, due to the non-uniformity characteristics of the pore structure in the product, the oriented gradient pore aerogel material prepared by the present invention has customizability and can be designed with different regional properties according to needs; it also has high sensitivity, a wide detection range and fast response ability; at the same time, it has excellent mechanical properties and good flexibility, and the obtained wearable flexible sensor is applicable to scenarios such as health monitoring and sports tracking.

[0102] Although the above embodiments have made a detailed description of the present invention, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained based on these embodiments without creative efforts, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A preparation method of a directional gradient pore aerogel material, characterized in that, It includes the following steps: Adopt a low-temperature 3D printing method to print a composite material ink on a low-temperature freezing platform to obtain a preform. The composite material ink includes a cellulose-based material, a carbon nanomaterial, and water. The cellulose-based material includes cellulose and / or a cellulose derivative. The cellulose derivative includes one or more of sodium carboxymethyl cellulose, hydroxyethyl cellulose, and cellulose acetate. The mass percentage content of the cellulose-based material in the composite material ink is 4-5%. The carbon nanomaterial is a carbon nanotube. The mass percentage content of the carbon nanomaterial in the composite material ink is 1.5-2.5%. The temperature of the low-temperature freezing platform is -30~-90 °C. The conditions of the low-temperature 3D printing method include: the printing speed is 20~30 mm / s, the nozzle diameter is 0.5~1 mm, the composite material ink is extruded by an air pump through a pressure regulating valve, and the extrusion pressure is 0.05~0.1 MPa; Freeze-dry the preform. The temperature of the equipment cavity for freeze-drying is -50~-90 °C to obtain the oriented gradient pore aerogel material.

2. According to the preparation method described in claim 1, the cellulose includes cellulose nanofibers and / or cellulose nanocrystals.

3. The preparation method according to claim 1, characterized in that, The freeze-drying time > 12 h.

4. The oriented gradient pore aerogel material prepared by the preparation method described in any one of claims 1 to 3.

5. Application of the oriented gradient pore aerogel material described in claim 4 in a wearable flexible sensor.

6. A wearable flexible sensor, characterized in that, It includes the oriented gradient pore aerogel material described in claim 4.

7. The preparation method of the wearable flexible sensor according to claim 6, characterized in that, It includes the following steps: Deposit a conductive metal coating on the pore wall surface of the oriented gradient pore aerogel material described in claim 4 to obtain an aerogel with a conductive metal coating; Set wires at both ends of the aerogel with the conductive metal coating, and then coat and encapsulate it with a polymer to obtain the wearable flexible sensor.

8. The preparation method according to claim 7, wherein The deposition method of the conductive metal coating is magnetron sputtering. The conditions of the magnetron sputtering include: the deposition time is 1~20 min, the power is 50~200 W, and the vacuum degree ≤ 1 Pa; The conductive metal coating includes a gold coating and / or a silver coating; The polymer includes polydimethylsiloxane, Ecoflex, thermoplastic polyurethane elastomer, or polyethylene terephthalate.

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