A double-network composite aerogel and its preparation method and application

Abstract

The present invention discloses a double-network composite aerogel and its preparation method and application. The preparation method comprises: mixing waterborne polyurethane, graphene nanoribbons and water, ultrasonically dispersing to obtain a dispersion, placing the dispersion in a carbon nanotube dispersion after ice-template treatment and directional freeze-drying, and then ice-template treatment and directional freeze-drying again to obtain a double-network composite aerogel. The graphene nanoribbons are obtained by electrochemical depolymerization and have strong mechanical properties and electrical conductivity. A double-network composite aerogel with a muscle-like structure is prepared, which also has strong mechanical properties and high sensitivity, as well as waterproofness and thermal insulation properties. It can be used as a flexible pressure sensing material to monitor different degrees of movement of different parts of the human body in the air and underwater. The preparation method provided by the present invention is green and simple, and is of great significance to the application of aerogel in pressure sensing materials.

Description

Technical Field

[0001] The invention belongs to the technical field of pressure sensing materials and relates to a double-network composite aerogel and a preparation method and application thereof. Background Art

[0002] Flexible pressure sensing materials, with their excellent flexibility and ability to conform to any curved surface, have been widely used in fields such as human-computer interaction, healthcare, and robotic touch. To meet the need for conformability to human skin, paper, fiber membranes, and elastic polymer materials have been used in the construction of flexible pressure sensors due to their relatively soft and resilient properties. Aerogel is a nanoscale porous solid material formed by the sol-gel method, where gas replaces the liquid phase in the gel under dry conditions. Its three-dimensional network structure, low density, and excellent flexibility offer unique structural advantages for the construction of flexible pressure sensors.

[0003] However, existing aerogel pressure sensors struggle to achieve both high mechanical properties and high sensitivity. Their preparation processes are complex, often involving hydrothermal reactions or the addition of organic solvents, and their application scenarios are limited. Patent CN112194180A discloses a modification method for enhancing the mechanical properties of aerogels. Lead acetate trihydrate, tetrabutyl titanate, zirconium n-propoxide, and ethylene glycol methyl ether are heated in a water bath to form a lead zirconate titanate precursor. Deionized water is then added and allowed to hydrolyze. Deionized water, propylene oxide, and carbon nanotubes are then added to produce a carbon nanotube-doped lead zirconate titanate sol. The surface is then coated with an organic solvent, aged, and allowed to stand to form a wet gel with a stable network structure. This gel is then replaced with an ethanol solvent and supercritically dried to produce a composite aerogel. The resulting composite aerogel exhibits excellent thermal insulation, mechanical, and piezoelectric properties. However, the preparation process is complex and time-consuming. Therefore, it is of great significance to propose a method for preparing aerogels that combines high mechanical properties with high sensitivity, while also being environmentally friendly and simple to manufacture. Summary of the Invention

[0004] To address the existing challenges of achieving both high mechanical properties and high sensitivity, complex preparation processes, and limited applicability, the present invention provides a dual-network composite aerogel, its preparation method, and its application. Graphene nanoribbons are prepared via an electrochemical depolymerization method, exhibiting strong mechanical properties and electrical conductivity. Using graphene nanoribbons, water-based polyurethane, and water as raw materials, the dual-network composite aerogel exhibits high mechanical properties and sensitivity. The preparation method is environmentally friendly and simple, with strong water resistance and adaptability to diverse environments.

[0005] To achieve the technical objectives of the present invention, on the one hand, the present invention provides a method for preparing a double-network composite aerogel, comprising: mixing waterborne polyurethane, graphene nanoribbons and water, ultrasonically dispersing to obtain a dispersion, treating the dispersion by an ice template method and performing a first directional freeze-drying to obtain a composite aerogel, placing the composite aerogel in a carbon nanotube dispersion, performing an ice template method and performing a second directional freeze-drying to obtain a double-network composite aerogel.

[0006] Furthermore, in the preparation method of the present invention, the graphene nanoribbons are obtained by electrochemical depolymerization, which is achieved by an electrochemical reaction device; the graphene nanoribbons are prepared using carbon nanotubes as raw materials, and the carbon nanotubes are at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes. The current density during the electrochemical depolymerization is 0.3 to 0.7 mA / cm 2 The reaction time is 3 to 11 hours. The raw materials for preparing the double-network composite aerogel include 5 to 21 wt% of water as the effective content of the waterborne polyurethane, 43 wt% of the effective content of the waterborne polyurethane, and 1 to 5 wt% of the graphene nanoribbons as the effective content of the waterborne polyurethane.

[0007] Furthermore, in the preparation method of the present invention, the conditions for the first directional freeze-drying are: vacuum ≤ 30 Pa, temperature ≤ -56°C, and drying time of 72 to 140 hours. The concentration of the carbon nanotube dispersion is 2 wt%, and the carbon nanotube dispersion accounts for 0.5 to 2.5 wt% of the composite aerogel. The conditions for the second directional freeze-drying are: vacuum ≤ 30 Pa, temperature ≤ -56°C, and drying time of 8 to 72 hours.

[0008] In another aspect, the present invention provides a dual-network composite aerogel prepared using the method described herein, wherein the first network layer is composed of graphene nanoribbons and waterborne polyurethane, and the second network layer is composed of carbon nanotubes. Specifically, the aerogel comprises the following steps:

[0009] 1) Preparation of graphene nanoribbons: Weigh carbon nanotubes and ultrasonically disperse them uniformly with anhydrous ethanol. Vacuum filter the electrochemical reaction raw materials onto a glass fiber filter to obtain a multi-walled carbon nanotube filter membrane. Assemble the carbon nanotube filter membrane, platinum sheet, and platinum wire ring current collector to form a working electrode, place it in a polytetrafluoroethylene fixture and secure it with hexagonal screws. Use another platinum wire ring as the counter electrode. Place the two electrodes in sulfuric acid electrolyte and connect them to the positive and negative electrodes of a DC power supply, respectively. At 0.3-0.7 mA / cm 2 After the reaction, the working electrode assembly was removed and the reaction was quenched with deionized water. The product on the filter membrane was collected by ultrasonic wave, filtered through a polytetrafluoroethylene filter, washed, and collected, and then dispersed in anhydrous ethanol. The product was centrifuged at 8000 rpm for 10 minutes, and the supernatant was collected and freeze-dried to obtain graphene nanoribbons.

[0010] 2) Preparing a dispersion: Deionized water and graphene nanoribbons accounting for 1 to 5 wt% of the effective content of aqueous polyurethane were added to a test tube, and after ultrasonic mixing for 1 hour, aqueous polyurethane accounting for 5 to 21 wt% of the effective content of water was added, and stirred in a magnetic stirrer at room temperature for 30 minutes to uniformly disperse the dispersion.

[0011] 3) Preparation of composite aerogel: Precool a copper table with liquid nitrogen, pour the dispersion into a sealed plastic mold box, place the mold box on the precooled copper table, and perform directional freeze-drying. After obtaining solid ice cubes, transfer them to a freeze dryer and freeze-dry them at a pressure below 30 Pa and a temperature below -56°C for 72 to 140 hours to obtain a composite aerogel.

[0012] 4) Preparation of a double-network composite aerogel: 0.5-2.5 wt% (based on the mass of the composite aerogel) of a carbon nanotube dispersion was weighed and sonicated for 30 minutes to ensure uniform dispersion. The composite aerogel was then immersed in the carbon nanotube dispersion. The immersed composite aerogel was placed on a copper table pre-cooled with liquid nitrogen for directionally frozen and then freeze-dried in a freeze dryer. The freeze-drying process was performed at a pressure below 30 Pa and a temperature below -56°C for 8-72 hours to obtain a double-network composite aerogel.

[0013] In addition, the present invention provides the application of double-network composite aerogel in wearable pressure sensors. The present invention prepares a double-network composite aerogel with a muscle-like structure through the "physical blending-directional freeze-drying-impregnation-directional freeze-drying" method. It has high mechanical strength and sensing sensitivity, with a sensitivity coefficient (GF) of 29.64 to 62.42, and has thermal insulation and water resistance. It can accurately monitor the movement of different joints of the human body above and below water, and can be used as a multi-functional, multi-scenario flexible wearable material.

[0014] Compared with the prior art, the technical solution provided by the present invention has at least the following beneficial effects or advantages:

[0015] The composite aerogel prepared by the present invention has a muscle-like dual-network structure, achieving high mechanical strength and sensor sensitivity, and can be used as a flexible wearable material for multifunctional applications. The first network layer is composed of waterborne polyurethane and graphene nanoribbons, which have excellent water resistance and mechanical strength. The graphene nanoribbons are obtained by electrochemical depolymerization. As a nanoreinforcement material, they have a larger aspect ratio and flatter microstructure than graphene. They also contain a small amount of oxygen-containing functional groups, which can increase contact sites with the waterborne polyurethane and form hydrogen bonds with polar groups on it, thereby enhancing the mechanical properties of the composite aerogel and imparting electrical conductivity. The second network layer is composed of carbon nanotubes, which can intertwine with the inner network and form hydrogen bonds. This not only further enhances the mechanical properties of the dual-network composite aerogel, but also significantly improves its electrical conductivity. When subjected to external forces, they can form "multi-level contact sites," amplifying the piezoresistive effect and thus increasing the aerogel's sensor sensitivity. The preparation method is simple, low-cost, and environmentally friendly, without the need for high-energy, high-temperature hydrothermal reactions or the addition of organic solvents. Due to the swelling effect of water-based polyurethane, the prepared double-network composite aerogel has excellent water resistance and can accurately monitor the movement of different joints of the human body above and below water.

[0016] The double-network composite aerogel provided by the present invention has a porous structure and a layered structure in cross section, and has good sensitivity, fatigue resistance and compression resilience; it has excellent mechanical properties, with an axial compressive strength of 91.38 kPa and a radial compressive strength of 60.82 kPa; it has an anisotropic structure and thermal insulation performance similar to that of muscle, and exhibits axial heat conduction and radial heat insulation; it has good sensitivity, with a sensitivity coefficient of 29.64 to 62.42; it can identify human activities with different strains, such as knee activities and finger activities; it can be used as a pressure sensing material to monitor different degrees of human activities in different environments. Without the use of graphene nanoribbons, the prepared double-network composite aerogel has large fluctuations in sensing signals, and even cannot monitor changes in resistance when subjected to pressure, and the sensing sensitivity is greatly reduced. Without impregnation with a carbon nanotube dispersion, the prepared composite aerogel cannot form a double-network structure, the compressive strength is greatly reduced, the conductivity is poor, and pressure sensing is impossible. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention.

[0018] Figure 1This diagram shows the assembly of the electrodes and components of the electrochemical reaction device. A is the carbon nanotube filter membrane working electrode; B is the platinum wire ring counter electrode; C is the polytetrafluoroethylene clamp used to secure the working electrode, consisting of upper and lower clips and four hexagonal screws; D is a photo of the assembled working electrode and clamp C.

[0019] Figure 2 These are surface SEM images and cross-sectional SEM images of the double-network composite aerogel prepared in Example 1. A is a surface SEM image; B is a cross-sectional SEM image.

[0020] Figure 3 1 is a graph showing axial and radial cyclic compressive stress-strain curves of the double-network composite aerogel prepared in Example 1. A is a graph showing axial cyclic compressive stress-strain curves; B is a graph showing radial cyclic compressive stress-strain curves.

[0021] Figure 4 3 is a graph of thermal conductivity of the double-network composite aerogel prepared in Example 1.

[0022] Figure 5 This is a sensitivity diagram of the double-network composite aerogel prepared in Example 1.

[0023] Figure 6 This is a resistance change diagram of the double-network composite aerogel prepared in Example 1 when monitoring human knee activity.

[0024] Figure 7 This is a resistance change diagram of the double-network composite aerogel prepared in Example 1 monitoring human finger activities.

[0025] Figure 8 This is the "SOS" Morse code diagram caused by the resistance change of the double-network composite aerogel prepared in Example 1 monitoring underwater pressure.

[0026] Figure 9 This is a sensitivity diagram of the double-network composite aerogel prepared in Example 2.

[0027] Figure 10 This is a sensitivity diagram of the double-network composite aerogel prepared in Example 3.

[0028] Figure 11 This is a sensitivity diagram of the double-network composite aerogel prepared in Comparative Example 1.

[0029] Figure 12 This is a graph showing the pressure-resistance variation of the double-network composite aerogel prepared in Comparative Example 1.

[0030] Figure 13 This is a diagram of the axial and radial compressive strength of the composite aerogel prepared in Comparative Example 2.

[0031] Figure 14This is a graph showing the pressure resistance change of the composite aerogel prepared in Comparative Example 2. DETAILED DESCRIPTION

[0032] The technical solutions of the present invention are now described with reference to the following examples. However, the present invention is not limited to the following examples. The experimental methods and detection methods described in the following examples are conventional methods unless otherwise specified; the reagents and materials described are commercially available unless otherwise specified.

[0033] The electrochemical unzipping method of the present invention comprises an electrochemical reaction device ( Figure 1 D) completed; the electrochemical reaction device includes: a carbon nanotube filter membrane working electrode ( Figure 1 A) Fixture for fixing the working electrode ( Figure 1 C) and platinum wire ring counter electrode (( Figure 1 B) The working electrode includes a carbon nanotube filter membrane, a platinum sheet electrode, and a platinum wire ring current collector.

[0034] The carbon nanotube filter membrane is the basic part of the working electrode. The electrochemically depolymerized raw materials are evenly dispersed by ultrasonication using anhydrous ethanol and then fixed on the glass fiber filter membrane by vacuum filtration to load the raw materials for the electrochemical reaction; the platinum sheet electrode can form good electrical contact with the carbon nanotube filter membrane, generate a conductive path and promote the smooth progress of the reaction; the platinum wire ring current collector can form good electrical contact with the platinum sheet electrode and is used to connect to the positive electrode wire of the power supply.

[0035] The fixture used to secure the working electrode consists of two PTFE sheets and four hexagonal screws. The PTFE sheet is designed in a circular ring shape to ensure the penetration of the electrolyte and the smooth progress of the oxidation process. The counter electrode is composed of a platinum wire loop with a diameter 10mm larger than the filter membrane. It can be connected to the negative terminal of the power supply to form a conductive circuit.

[0036] Example 1

[0037] This embodiment provides a preparation method and application of a double-network composite aerogel, which specifically includes the following steps:

[0038] Step 1: Weigh 0.3g of multi-walled carbon nanotube powder (purchased from Shanghai MacLean Biochemical Technology Co., Ltd., purity ≥95%), use anhydrous ethanol to ultrasonically disperse it evenly, and fix the multi-walled carbon nanotube dispersion on the glass fiber filter membrane by vacuum filtration. Assemble the carbon nanotube filter membrane, platinum sheet electrode and platinum wire ring current collector into the carbon nanotube filter membrane working electrode, place it in a polytetrafluoroethylene fixture and fix it with hexagonal screws, and use another platinum wire ring as the counter electrode ( Figure 1 B) Place the two electrodes in sulfuric acid electrolyte and connect them to the positive and negative electrodes of a DC power supply respectively. 2After the reaction, the carbon nanotube filter membrane working electrode was removed and the reaction was quenched with deionized water. The product on the filter membrane was collected by ultrasonic wave, filtered through a polytetrafluoroethylene filter membrane, cleaned, and collected. The product was then dispersed in anhydrous ethanol and centrifuged at 8000 rpm for 10 minutes. The supernatant was collected and freeze-dried to produce graphene nanoribbons.

[0039] Step 2: Add 20 g of deionized water and 0.13 g of graphene nanoribbons to a test tube, mix ultrasonically for 1 h, then add 6.05 g of aqueous polyurethane emulsion (No. DG-6156, purchased from Yantai Daocheng Chemical Co., Ltd., with a solid content of 42±1%), and place in a magnetic stirrer at room temperature for 30 min to evenly disperse the mixture.

[0040] Step 3: Precool the copper table with liquid nitrogen, pour the dispersion into a sealed plastic mold box, place the mold box on the precooled copper table, and perform directional freeze-drying. After obtaining solid ice cubes, transfer them to a freeze dryer and freeze-dry them at a pressure of 20 Pa and a temperature of -40°C for 120 hours to obtain a composite aerogel.

[0041] Step 4: Weigh 1.5 wt% (based on the mass of the composite aerogel) of a carbon nanotube dispersion (purchased from Chengdu Organic Chemistry Co., Ltd., Chinese Academy of Sciences) and sonicate for 30 minutes to ensure uniform dispersion. The composite aerogel is then immersed in the carbon nanotube dispersion. The immersed composite aerogel is then placed on a copper table pre-cooled with liquid nitrogen for directional freezing and freeze-dried in a freeze dryer at a pressure of 20 Pa and a temperature of -40°C for 24 hours to obtain a double-network composite aerogel.

[0042] The scanning electron microscope images of the surface and cross section of the double network composite aerogel prepared in Example 1 are as follows: Figure 2 As shown, the axial and radial cyclic compression stress-strain curves of the double-network composite aerogel prepared in Example 1 are as follows: Figure 3 As shown in the figure, the thermal conductivity of the double network composite aerogel prepared in Example 1 is as follows Figure 4 As shown, the sensitivity diagram of the double network composite aerogel prepared in Example 1 is as follows Figure 5 As shown in the figure, the pressure sensing performance verification of the double network composite aerogel prepared in Example 1 in air and water is shown in Figure 6 、 Figure 7 、 Figure 8 shown.

[0043] Depend on Figure 2It can be seen that the double-network composite aerogel has a porous structure and a layered structure in cross section, indicating that the double-network composite aerogel prepared by the present invention has high sensing sensitivity, good compressive resistance, fatigue resistance and high resilience. The porous structure of the double-network composite aerogel can provide a basis and support for the load of carbon nanotubes, promote the formation of the double-network aerogel and improve the sensing sensitivity. The layered structure of the double-network composite aerogel radially presents a "spring-like" lamellar structure. When subjected to stress, the layers squeeze each other, and the layered "sheets" evenly share the stress, having good compressive resistance; after the stress is removed, due to the discontinuous growth and loose arrangement of the layers, the material will rebound quickly, thereby giving the material good fatigue resistance and compression resilience.

[0044] Depend on Figure 3 It can be seen that the axial and radial compressive strengths of the double-network composite aerogel are both high, with the axial compressive strength being 91.38 kPa (corresponding to the vertex) and the radial compressive strength being 60.82 kPa (corresponding to the vertex). The curve after 20 compression cycles coincides with the curve of the first compression rebound, and there is no obvious decrease in the axial and radial compressive strengths, indicating that the double-network composite aerogel prepared by the present invention has excellent compressive strength and compression rebound performance, and excellent mechanical properties.

[0045] Depend on Figure 4 It can be seen that the double network composite aerogel shows thermal anisotropy, with an axial thermal conductivity of 0.227W / (m·k) and a radial thermal conductivity of 0.074W / (m·k), showing axial thermal conduction and radial thermal insulation, and has thermal insulation properties. Figure 5 It can be seen that the double-network composite aerogel has a sensitivity coefficient (GF) of 62.18 in the pressure range of 0.6-1.1 kPa and a sensitivity coefficient of 21.55 in the pressure range of 1.1-1.9 kPa, which shows good sensitivity.

[0046] Depend on Figure 6 、 Figure 7 It can be seen that the dual-network composite aerogel can recognize human activities with different strains, such as knee movements and finger movements. Figure 8 It can be seen that the dual-network composite aerogel can detect the "SOS" Morse code caused by pressure underwater. It can be seen that the dual-network composite aerogel provided by the present invention can be used as a pressure sensing material to monitor different levels of human activity in different environments.

[0047] Example 2

[0048] This embodiment provides a preparation method and application of a double-network composite aerogel, which specifically includes the following steps:

[0049] Step 1: Weigh 0.3g of single-walled carbon nanotube powder (purchased from Suzhou Carbon Graphene Technology Co., Ltd., product number HQNANO-CNTs-00, purity>90wt%), use anhydrous ethanol to ultrasonically disperse it evenly, and fix the single-walled carbon nanotube dispersion on a glass fiber filter membrane by vacuum filtration. Assemble the carbon nanotube filter membrane, platinum sheet electrode and platinum wire ring current collector into a carbon nanotube filter membrane working electrode, place it in a polytetrafluoroethylene fixture and fix it with a hexagonal screw. Use another platinum wire ring as the counter electrode, place the two electrodes in sulfuric acid electrolyte, connect them to the positive and negative poles of a DC power supply respectively, and charge and discharge at 0.7mA / cm 2 After the reaction, the working electrode assembly was removed and the reaction was quenched with deionized water. The product on the filter membrane was collected by ultrasonic wave, filtered through a polytetrafluoroethylene filter, cleaned, and collected. The product was then dispersed in anhydrous ethanol and centrifuged at 8000 rpm for 10 minutes. The supernatant was collected and freeze-dried to obtain graphene nanoribbons.

[0050] Step 2: Add 20 g of deionized water and 0.03 g of graphene nanoribbons into a test tube, mix them ultrasonically for 1 h, then add 2.33 g of aqueous polyurethane emulsion, and stir in a magnetic stirrer at room temperature for 30 min to evenly disperse the mixture.

[0051] Step 3: Precool the copper table with liquid nitrogen, pour the dispersion into a sealed plastic mold box, place the mold box on the precooled copper table, and perform directional freeze-drying. After obtaining solid ice cubes, transfer them to a freeze dryer and freeze-dry them at a pressure of 15 Pa and a temperature of -56°C for 72 hours to obtain a composite aerogel.

[0052] Step 4: Weigh 2.5 wt% (based on the mass of the composite aerogel) of a carbon nanotube dispersion and sonicate for 30 minutes to ensure uniform dispersion. The composite aerogel is then immersed in the carbon nanotube dispersion. The immersed composite aerogel is then placed on a copper table pre-cooled with liquid nitrogen for directional freezing and freeze-dried in a freeze dryer at a pressure of 30 Pa and a temperature of -56°C for 8 hours to obtain a double-network composite aerogel.

[0053] The double network composite aerogel prepared in Example 2 has an axial compressive strength of 80.11 kPa and a radial compressive strength of 52.25 kPa, and has high mechanical strength; the axial thermal conductivity is 0.196 W / (m·k), and the radial thermal conductivity is 0.086 W / (m·k), showing axial heat conduction and radial heat insulation, and has thermal insulation properties. The sensitivity diagram of the double network composite aerogel prepared in Example 2 is shown in FIG. Figure 9 As shown by Figure 9 It can be seen that in the pressure range of 0.6~1.1kPa, the sensitivity coefficient is 62.18, and in the pressure range of 1.1~1.9kPa, the sensitivity coefficient is 21.55, which is relatively high.

[0054] Example 3

[0055] This embodiment provides a preparation method and application of a double-network composite aerogel, which specifically includes the following steps:

[0056] Step 1: Mix single-walled carbon nanotubes and multi-walled carbon nanotubes in a mass ratio of 1:1, weigh 0.3g of the mixed carbon nanotube powder, and use anhydrous ethanol to ultrasonically disperse it evenly. Fix the carbon nanotube dispersion on the glass fiber filter membrane by vacuum filtration. Assemble the carbon nanotube filter membrane, platinum sheet and platinum wire ring current collector into the carbon nanotube filter membrane working electrode, place it in a polytetrafluoroethylene fixture and fix it with hexagonal screws. Use another platinum wire ring as the counter electrode, place the two electrodes in sulfuric acid electrolyte, connect them to the positive and negative poles of the DC power supply respectively, and charge at 0.3mA / cm 2 After the reaction, the working electrode assembly was removed and the reaction was quenched with deionized water. The product on the filter membrane was collected by ultrasonic wave, filtered through a polytetrafluoroethylene filter, cleaned, and collected. The product was then dispersed in anhydrous ethanol and centrifuged at 8000 rpm for 10 minutes. The supernatant was collected and freeze-dried to produce graphene nanoribbons.

[0057] Step 2: Add 20 g of deionized water and 0.042 g of graphene nanoribbons into a test tube, mix them ultrasonically for 1 h, then add 9.77 g of aqueous polyurethane emulsion, and stir in a magnetic stirrer at room temperature for 30 min to evenly disperse the mixture.

[0058] Step 3: Precool the copper table with liquid nitrogen, pour the dispersion into a sealed plastic mold box, place the mold box on the precooled copper table, and perform directional freeze-drying. After obtaining solid ice cubes, transfer them to a freeze dryer and freeze-dry them at a pressure of 30 Pa and a temperature of -50°C for 140 hours to obtain a composite aerogel.

[0059] Step 4: Weigh 0.5 wt% (based on the mass of the composite aerogel) of a carbon nanotube dispersion and sonicate for 30 minutes to ensure uniform dispersion. The composite aerogel is then immersed in the carbon nanotube dispersion. The immersed composite aerogel is then placed on a copper table pre-cooled with liquid nitrogen for directionally frozen and then freeze-dried in a freeze dryer at a pressure of 20 Pa and a temperature of -25°C for 72 hours to obtain a double-network composite aerogel.

[0060] The double network composite aerogel prepared in Example 3 has an axial compressive strength of 101.25 kPa and a radial compressive strength of 74.13 kPa, and has high mechanical strength; the axial thermal conductivity is 0.241 W / (m·k), and the radial thermal conductivity is 0.091 W / (m·k), showing axial heat conduction and radial heat insulation, and has thermal insulation properties. The sensitivity diagram of the double network composite aerogel prepared in Example 3 is shown in FIG. Figure 10 As shown by Figure 10 It can be seen that in the pressure range of 0.6~1.1kPa, the sensitivity coefficient is 60.22, and in the pressure range of 1.1~1.9kPa, the sensitivity coefficient is 20.74, which is relatively high.

[0061] Comparative Example 1

[0062] The difference between the preparation method of the composite aerogel in this comparative example and that in Example 1 is that no graphene nanoribbons are used.

[0063] Figure 11 This is the sensitivity diagram of the double-network composite aerogel prepared in Comparative Example 1. Figure 12 This is a verification diagram of the sensing performance of the double-network composite aerogel prepared in Comparative Example 1 under a pressure of 1.9 kPa.

[0064] Depend on Figure 11 and Figure 12 The sensitivity is 19.72 within the pressure range of 0.6 to 1.1 kPa, and 7.58 within the pressure range of 1.1 to 1.9 kPa. When a constant pressure of 1.9 kPa is applied, the signal response is small, with the relative resistance change fluctuating around 20%, indicating instability. This indicates that omitting the addition of graphene nanoribbons during the preparation of the dual-network composite aerogel significantly reduces the sensing sensitivity and produces significant fluctuations in the sensing signal, making it impossible to detect resistance changes when subjected to pressure.

[0065] Comparative Example 2

[0066] The difference between the preparation method of the composite aerogel in this comparative example and that in Example 1 is that step 4 is omitted.

[0067] Figure 13 The axial and radial compressive strength diagrams of the composite aerogel prepared in Comparative Example 2 are shown in FIG. Figure 14 This is a graph showing the relative resistance change of the composite aerogel prepared in Comparative Example 2 when pressed.

[0068] Depend on Figure 13 and Figure 14 It can be seen that the axial compressive strength of the composite aerogel prepared in Comparative Example 2 is 59.37 kPa, and the radial compressive strength is 40.28 kPa, which is significantly lower than the compressive strength of the double-network composite aerogel prepared in Example 1. No regular piezoresistive sensing signal is generated when pressed, and pressure sensing is not possible.

[0069] The composite aerogel prepared in Comparative Example 2 could not form a double network structure, and had a resistance of 1732 kΩ, indicating poor conductivity.

[0070] It can be seen from the above embodiments and comparative examples that the double-network composite aerogel provided by the present invention has a porous structure and a layered structure in cross section, and has good sensitivity, fatigue resistance and compression resilience; it has excellent mechanical properties, with an axial compressive strength of 91.38 kPa and a radial compressive strength of 60.82 kPa; it has thermal insulation properties, which are manifested as axial heat conduction and radial heat insulation; it has good sensitivity, with a sensitivity coefficient of 29.64 to 62.42; it can identify human activities with different strains, such as knee activities and finger activities; it can be used as a pressure sensing material to monitor different degrees of human activities in different environments. Without the use of graphene nanoribbons, the prepared double-network composite aerogel has large fluctuations in sensing signals, and even cannot monitor changes in resistance when subjected to pressure, and the sensing sensitivity is greatly reduced. Without impregnation with carbon nanotube dispersion, the prepared composite aerogel cannot form a double-network structure, the compressive strength is greatly reduced, the conductivity is poor, and pressure sensing is impossible.

[0071] As described above, the basic principles, main features and advantages of the present invention are well described. The above embodiments and descriptions are merely descriptions of preferred embodiments of the present invention, and the present invention is not limited to the above embodiments. Various changes and improvements made to the technical solutions of the present invention by those skilled in the art without departing from the spirit and scope of the present invention should fall within the scope of protection determined by the present invention.

Claims

1. A method for preparing a double-network composite aerogel, characterized in that: include: Aqueous polyurethane, graphene nanoribbons and water are mixed and ultrasonically dispersed to obtain a dispersion. The dispersion is treated by an ice template method and subjected to a first directional freeze-drying to obtain a composite aerogel. The composite aerogel is placed in a carbon nanotube dispersion, treated by an ice template method and subjected to a second directional freeze-drying to obtain a double-network composite aerogel.

2. The method for preparing the double-network composite aerogel according to claim 1, characterized in that: The graphene nanoribbons are obtained by electrochemical depolymerization; The current density of the electrochemical unzipping of the graphene nanoribbon is 0.3-0.7 mA / cm 2 , the reaction time is 3 to 11 hours.

3. The method for preparing the double-network composite aerogel according to claim 2, characterized in that: The graphene nanoribbons are prepared using carbon nanotubes as raw materials, and the carbon nanotubes are at least one of single-walled carbon nanotubes and multi-walled carbon nanotubes.

4. The method for preparing the double-network composite aerogel according to claim 1, wherein: The effective content of the waterborne polyurethane is 5 to 21 wt% of water; The graphene nanoribbons account for 1 to 5 wt % of the effective content of the waterborne polyurethane.

5. The method for preparing the double-network composite aerogel according to claim 1, wherein: The conditions for the first directional freeze-drying are: vacuum degree ≤ 30 Pa, temperature ≤ -56°C, and drying time 72 to 140 hours.

6. The method for preparing the double-network composite aerogel according to claim 1, characterized in that: The concentration of the carbon nanotube dispersion is 2 wt %; The carbon nanotube dispersion accounts for 0.5 to 2.5 wt% of the composite aerogel.

7. The method for preparing the double-network composite aerogel according to claim 1, characterized in that: The conditions for the second directional freeze-drying are: vacuum degree ≤ 30 Pa, temperature ≤ -56°C, and drying time of 8 to 72 hours.

8. An aerogel, characterized in that Prepared by the method according to any one of claims 1 to 7.

9. A pressure sensing material, characterized in that: Comprising the aerogel according to claim 8.

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