A conductive elastic aerogel based on waterborne polyurethane / silsesquioxane / carbon nanotube ternary synergy, a preparation method and application thereof in piezoresistive sensors

Abstract

The application provides a kind of based on water-based polyurethane / silsesquioxane / carbon nanotube ternary synergistic conductive elastic aerogel, preparation method and its application in piezoresistive sensor, belongs to flexible electronic material and sensing technology field.The application is covalently bonded by hydroxylated silsesquioxane (HSQ) and water-based polyurethane (WPU), and combined with the physical compounding of multi-walled carbon nanotubes (MWCNTs), a "rigid island-flexible sea" hybrid three-dimensional network is constructed.The preparation method uses water as medium, and the process is green, simple and low in cost.The obtained aerogel has excellent mechanical properties and sensing characteristics;Meanwhile, the material has good thermal stability and biocompatibility.The application provides a kind of high-performance, high-reliability piezoresistive sensing material platform for wearable health monitoring, electronic skin and human-computer interaction fields.

Description

Technical Field

[0001] This invention relates to a conductive elastic aerogel based on a ternary synergy of waterborne polyurethane / silsesquioxane / carbon nanotubes, its preparation method, and its application in piezoresistive sensors, belonging to the field of flexible piezoresistive sensing technology. Background Technology

[0002] With the development of flexible electronics technology, conductive aerogel has become a key material in the field of piezoresistive sensing. Its unique tunable three-dimensional porous network structure endows the material with reversible deformation capability, which can efficiently control the internal conductive path. It has both high sensitivity and fast response characteristics. In addition, its advantages of simple structure and controllable cost have made it the core support for promoting the development of the next generation of high-performance wearable piezoresistive sensors, and it is widely applicable to diverse application scenarios such as health monitoring, human-computer interaction, and electronic skin.

[0003] However, traditional flexible piezoresistive sensor materials are prone to structural collapse and signal instability under high pressure, and they also have technical limitations in achieving both wide pressure range response and high durability. Summary of the Invention

[0004] To address the aforementioned problems, this invention provides a conductive elastic aerogel based on a ternary synergistic structure of waterborne polyurethane / silsesquioxane / carbon nanotubes, its preparation method, and its application in piezoresistive sensors. The preparation method uses water as a solvent, employs a green and environmentally friendly freeze-drying process, and can be molded in a single step via blending-freeze-drying, making it simple to operate, low in cost, and highly reproducible. The resulting conductive aerogel possesses comprehensive advantages such as high resilience, an ultra-wide pressure response range, high sensitivity, and excellent dynamic stability and durability. This material is particularly suitable for wide-range, high-reliability piezoresistive sensing scenarios requiring long-term stable operation in complex mechanical environments, such as health monitoring (e.g., body movement, pulse, foot pressure), human-computer interfaces, and electronic skin.

[0005] The technical solution of the present invention is as follows: On one hand, this invention provides a conductive elastic aerogel based on a ternary synergistic structure of waterborne polyurethane / silsesquioxane / carbon nanotubes. The conductive elastic aerogel is a composite material of hydroxylated silsesquioxane-modified waterborne polyurethane and multi-walled carbon nanotubes. The hydroxylated silsesquioxane-modified waterborne polyurethane is obtained by stepwise polymerization of a waterborne polyurethane prepolymer followed by chemical crosslinking with hydroxylated silsesquioxane. The waterborne polyurethane is a carboxylic acid-type waterborne polyurethane with the following structure: According to a preferred embodiment of the present invention, the hydroxylated silsesquioxane is obtained by ring-opening (nucleophilic addition reaction) of an epoxy silsesquioxane and diethanolamine, and has the following structure: Waterborne polyurethane (WPU) possesses excellent biocompatibility, flexible processability, and tunable mechanical properties. Its water solubility facilitates mixing with aqueous systems, and lightweight porous aerogels can be prepared through freeze-drying, making it an ideal flexible matrix. Silsesquioxane (SQ), with its rigid Si-O-Si cage-like structure, significantly enhances the strength and thermal stability of composite materials, and its surface functional groups can be chemically modified to optimize dispersibility and interfacial bonding. Multi-walled carbon nanotubes (MWCNTs), with their lightweight and high aspect ratio, combine excellent mechanical strength and electrical conductivity, effectively constructing three-dimensional conductive networks. When these three are combined synergistically, a "rigid island-flexible sea" hybrid framework is formed through covalent and hydrogen bonds. This achieves a perfect balance between mechanical properties and electrical conductivity, leveraging the macroscopic elasticity and deformation capabilities of the material with the help of waterborne polyurethane, the reinforcement of the framework structure with silsesquioxane, and the simultaneous mechanical reinforcement and conductive pathway construction with MWCNTs.

[0006] This composite system provides a high-performance material platform for conductive aerogels, contributing to the innovative development of next-generation flexible sensors. Simultaneously, it effectively solves the core challenges of single materials failing to balance mechanical and electrical properties, weak interfacial bonding between components, and uneven dispersion. It overcomes the limitations of traditional conductive aerogel sensors, which are only applicable to low-pressure, narrow-range applications, laying the foundation for the application of high-performance flexible sensing technology.

[0007] Secondly, the present invention provides a method for preparing the above-mentioned conductive elastic aerogel based on the ternary synergy of aqueous polyurethane / silsesquioxane / carbon nanotubes, comprising the following steps: Multi-walled carbon nanotubes (MWCNTs) were mixed with a waterborne polyurethane emulsion modified with hydroxylated silsesquioxane to obtain a uniform dispersion. The mixture was then freeze-dried to obtain a ternary conductive elastic aerogel of waterborne polyurethane / silsesquioxane / carbon nanotubes.

[0008] According to a preferred embodiment of the present invention, the mixing method of hydroxylated silsesquioxane-modified aqueous polyurethane emulsion and multi-walled carbon nanotubes can be achieved by ultrasonic dispersion or high-speed stirring dispersion.

[0009] According to the present invention, the mass ratio of hydroxylated silsesquioxane-modified waterborne polyurethane emulsion to multi-walled carbon nanotubes is preferably 1:0.15-0.35, and more preferably 1:0.15. The higher the proportion of multi-walled carbon nanotubes, the more difficult it is to disperse and the easier it is to agglomerate.

[0010] According to a preferred embodiment of the present invention, the multi-walled carbon nanotubes have an outer diameter of 20-50 nm and a length of ≤15 mm, and can be directly purchased commercially.

[0011] According to a preferred embodiment of the present invention, the conditions for freeze-drying the mixed dispersion are as follows: freezing at -60°C for 24-48 hours until the aqueous solution completely forms ice crystals to obtain the mixture; after the mixture is transferred to a freeze dryer, it needs to be vacuum dried, with the set temperature being -5°C, the vacuum pressure being 0-10 Pa, and the drying time being 24 hours, until the ice crystals completely sublimate.

[0012] Thirdly, the present invention provides a method for preparing the above-mentioned hydroxylated silsesquioxane-modified aqueous polyurethane emulsion, comprising the steps of: Oligomeric diols, hydrophilic chain extenders, and isocyanates were purified by dehydration and dissolved in solvent a. A prepolymerization reaction was carried out at 70°C to obtain an aqueous polyurethane prepolymer. Polymerization was continued stepwise until the -NCO content in the system reached the theoretical value. Triethylamine (TEA) was then added to the reaction system to neutralize the carboxyl groups in the chain segments. Next, hydroxylated silsesquioxane was added for chain extension and crosslinking. Finally, deionized water was slowly added dropwise to the resulting mixture under vigorous stirring to emulsify it. After solvent removal, a hydroxylated silsesquioxane-modified aqueous polyurethane emulsion was obtained.

[0013] More preferably, the oligomeric diol can be one or more of polycarbonate diol, polyether diol or polyester diol, and the molecular weight can be 1000, 1500 or 2000, preferably polycarbonate diol with a molecular weight of 2000 (PCDL2000).

[0014] More preferably, the hydrophilic chain extender can be one or more of 2,2-dihydroxymethylbutyric acid and 2,2-dihydroxymethylpropionic acid, preferably 2,2-dihydroxymethylbutyric acid (DMBA).

[0015] More preferably, the isocyanate can be one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, phenylmethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate, preferably dicyclohexylmethane-4,4'-diisocyanate (HMDI).

[0016] More preferably, solvent a can be one or more of acetone and tetrahydrofuran.

[0017] More preferably, the emulsification conditions are at room temperature and a stirring rate of 2000 r / min.

[0018] More preferably, the mass ratio of the waterborne polyurethane prepolymer to the hydroxylated silsesquioxane is 1:0.07-0.09. Increasing the content of the hydroxylated silsesquioxane increases the degree of crosslinking of the system.

[0019] More preferably, the molar ratio of triethylamine (TEA) to the hydrophilic chain extender is 1:1.

[0020] A further preferred method for preparing hydroxylated silsesquioxane is as follows: epoxy silsesquioxane and diethanolamine are dissolved in solvent b, and the mixture is heated and the solvent is removed to obtain hydroxylated silsesquioxane.

[0021] More preferably, the solvent b is one or more of tetrahydrofuran, acetone, and methanol.

[0022] More preferably, the molar ratio of epoxy silsesquioxane to diethanolamine is 1:1-10, preferably 1:5. Increasing the content of diethanolamine will increase the content of hydroxyl groups in the hydroxylated silsesquioxane, thereby increasing the degree of crosslinking of the system.

[0023] Fourthly, the present invention provides a method for preparing the above-mentioned epoxy silsesquioxane, comprising the steps of: A mixed solution of 3-glycidoxypropyltrimethoxysilane (GTMS) and tetraethylammonium hydroxide was stirred at room temperature for 10 h. The resulting mixture was then heated at 80 °C for 1 h. The mixture was subsequently washed with a saturated sodium chloride solution until neutral. Finally, the solvent was removed by vacuum distillation to obtain an epoxy silsesquioxane.

[0024] More preferably, the 3-glycidoxypropyltrimethoxysilane needs to be dissolved in xylene solution.

[0025] More preferably, the tetraethylamine hydroxide needs to be dissolved in isopropanol solution.

[0026] More preferably, the 3-glycidoxypropyltrimethoxysilane dissolved in xylene solution needs to be slowly added dropwise to the mixed solution of tetraethylammonium hydroxide and isopropanol.

[0027] Fifthly, the present invention provides the application of the above-mentioned conductive elastic aerogel based on the ternary synergy of aqueous polyurethane / silsesquioxane / carbon nanotube or the conductive elastic aerogel based on the ternary synergy of aqueous polyurethane / silsesquioxane / carbon nanotube obtained by the above preparation method, in the field of flexible piezoresistive sensing.

[0028] The technical features and beneficial effects of this invention are as follows: 1. This invention successfully prepared a WPU-HSQ / MWCNTs ternary composite conductive aerogel through the covalent bonding reaction between hydroxylated silsesquioxane (HSQ) and waterborne polyurethane (WPU) prepolymer, and the physical bonding and multi-level hydrogen bonding synergistic effect with multi-walled carbon nanotubes (MWCNTs). In this system, each component plays a key role: the rigid HSQ acts as a covalent cross-linking point, constructing "rigid islands" that support the overall structure; the flexible WPU segments form a "flexible sea" surrounding the islands, responsible for providing macroscopic elasticity and deformation capability; while MWCNTs are uniformly dispersed in the hybrid network, not only serving as a nano-reinforcing phase to improve mechanical properties, but also constructing a three-dimensional continuous conductive pathway throughout the aerogel.

[0029] 2. The preparation method adopted in this invention has the following significant characteristics and advantages: First, by establishing molecular-level covalent bonds between HSQ and WPU, the core problems of uneven filler dispersion and weak interfacial interactions in traditional physical blending are fundamentally solved, constructing a structure that combines rigidity and flexibility. Second, by cleverly utilizing the synergistic effect of covalent bonds and multiple hydrogen bonds, the emulsion template method facilitates the construction of a stable and elastic three-dimensional porous framework, ensuring structural integrity while endowing the material with excellent recoverability. Third, the freeze-drying process is green and efficient, resulting in a composite aerogel with uniform structure and controllable performance, providing a new strategy with strong universality and high reliability for the preparation of high-performance flexible sensing materials.

[0030] 3. The WPU-HSQ / MWCNTs composite aerogel prepared by this invention exhibits excellent comprehensive properties: in terms of mechanics, its compressive strength reaches 4.61 MPa, and its toughness reaches 0.73 MJ / m. 3 The material exhibits a robust yet flexible structure. In terms of sensing performance, it overcomes the limitations of traditional materials that are confined to low-pressure detection, demonstrating effective response across an ultra-wide pressure range of 0-5 MPa. This sensor also possesses excellent dynamic stability, with response / recovery times of approximately 0.60 s and 0.50 s, respectively, and can withstand over 600 compression cycles without signal attenuation. Furthermore, the material exhibits good thermal stability and has been successfully applied to human motion monitoring, demonstrating its immense potential as a core material for next-generation high-performance flexible sensors. Attached Figure Description

[0031] Figure 1 This is a particle size distribution curve of the emulsion nanoparticles obtained in Experiment 2-4; Figure 2 This is a particle size distribution curve of the composite dispersion nanoparticles obtained in Experiment 5-7; Figure 3 This is a pore size distribution curve of the composite aerogel prepared in Experiment Example 6; Figure 4This is a pore size distribution curve of the aerogel prepared in Comparative Example 2; Figure 5 This is a diagram showing the internal pore morphology of the aerogel prepared in Comparative Example 2; Figure 6 This is a diagram showing the internal pore morphology of the composite aerogel prepared in Example 6; Figure 7 These are stress-strain curves of the aerogels obtained in Examples 5-7 and Comparative Examples 1-3; Figure 8 This is the stress-strain curve of the composite aerogel prepared in Example 6 during 100 dynamic compression cycles. Figure 9 This is the stress-strain curve of the composite aerogel prepared in Comparative Example 2 during 100 dynamic compression cycles. Figure 10 These are the thermal degradation curves of the composite aerogels prepared in Examples 5-7; Figure 11 The thermal degradation curves of the aerogels prepared in Comparative Examples 1-3 are shown. Figure 12 This is a schematic diagram of the composite aerogel prepared in Example 6 illuminating an LED; Figure 13 This is a graph showing the relative resistance change of the composite aerogel prepared in Example 6 over a wide pressure range; Figure 14 This is a dynamic piezoresistive response curve of the composite aerogel prepared in Example 6 under different high compression rates; Figure 15 This is a graph showing the response and recovery time of the composite aerogel prepared in Example 6 under high compression rates; Figure 16 This is a graph showing the long-cycle pressure sensing stability test of the composite aerogel prepared in Example 6; Figure 17 This is a piezoresistive response curve for the encoded signal of the composite aerogel prepared in Example 6; Figure 18 This is a graph showing the human motion monitoring sensor signal of the composite aerogel prepared in Example 6. Detailed Implementation

[0032] The present invention will be further described below through specific embodiments, but is not limited thereto.

[0033] All raw materials used in the embodiments are conventional and commercially available; unless otherwise specified, the methods described are existing technologies. Example 1

[0034] Preparation of epoxy-based silsesquioxanes: (1) Dissolve 30g GTMS in 50mL xylene and slowly add it dropwise to a 250mL single-necked flask containing 7g 2wt% tetraethylammonium hydroxide aqueous solution and 100mL isopropanol, and then stir at room temperature for 10h. Then heat the resulting mixture at 80℃ for 1h.

[0035] (2) After the reaction was complete, the resulting mixture was washed with saturated sodium chloride solution until neutral and stirred at room temperature for 1 hour. Finally, the remaining solvent was removed by vacuum distillation to obtain epoxy silsesquioxane.

[0036] Preparation of hydroxylated silsesquioxanes: Preparation of hydroxylated silsesquioxanes with a molar ratio of epoxy-based silsesquioxanes and diethanolamine of 1:5 (diethanolamine and any five epoxy groups in the epoxy-based silsesquioxane react): (1) Add 30 mL of acetone, 3.34 g of epoxy sesquioxane and 1.05 g of diethanolamine to a 150 mL single-necked flask, stir well and heat at 70 °C for 2 h.

[0037] (2) After the reaction is complete, the solvent is removed by rotary evaporation and the solid is dried under vacuum for 24 hours to obtain a transparent solid. Example 2

[0038] The preparation steps for hydroxylated silsesquioxane-modified waterborne polyurethane emulsion are as follows: (1) The reaction was carried out in a 250ml four-necked flask under a nitrogen atmosphere. 6g PCDL2000, 0.3118g DMBA, 1.8846g HMDI and 0.1wt% (0.1wt% relative to the total amount of 6g PCDL2000, 0.3118g DMBA and 1.8846g HMDI) of dibutyltin dilaurate (DBTDL) were added to the flask. Solvent a was acetone. The mixture was 20ml and reacted at 70°C to obtain an aqueous polyurethane prepolymer. The prepolymer was gradually polymerized until the -NCO content reached the theoretical value. Subsequently, 0.2128g of TEA (the molar ratio of TEA to DMBA is 1:1) was added to neutralize the carboxyl groups in the chain segments, followed by the addition of 7% HSQ by mass for crosslinking (here, 7% refers to 7% of the total amount of waterborne polyurethane prepolymer (i.e., 6g PCDL2000, 0.3118g DMBA, 1.8846g HMDI, and 0.2128g TEA)).

[0039] (2) Then, under high-speed stirring, 25g of deionized water was slowly poured into the resulting mixture for emulsification (the emulsification conditions were room temperature and a stirring rate of 2000 r / min). Finally, the solvent was removed by rotary evaporation to obtain a hydroxylated silsesquioxane-modified waterborne polyurethane emulsion. Example 3

[0040] The preparation steps of the hydroxylated silsesquioxane modified waterborne polyurethane emulsion are as described in Example 2, except that the mass fraction of hydroxylated silsesquioxane is 8%. Example 4

[0041] The preparation steps of the hydroxylated silsesquioxane modified waterborne polyurethane emulsion are as described in Example 2, except that the mass fraction of hydroxylated silsesquioxane is 9%. Example 5

[0042] A conductive elastic aerogel based on a ternary synergistic structure of aqueous polyurethane / silsesquioxane / carbon nanotubes is prepared by the following steps: 15 wt% of MWCNTs (multi-walled carbon nanotubes with an outer diameter of 20-50 nm and a length of ≤15 mm) were added to the hydroxylated silsesquioxane-modified waterborne polyurethane emulsion in Example 2, and a uniformly dispersed composite dispersion was obtained by ultrasonic treatment. The dispersion was then frozen at -60°C for 24 h to allow complete crystallization. Finally, the frozen sample was transferred to a freeze dryer and dried at -5°C and 10 Pa for 24 h to allow complete sublimation of the ice crystals, ultimately yielding a conductive elastic aerogel (WPU-HSQ7 / CNT) based on a ternary synergy of waterborne polyurethane / silsesquioxane / carbon nanotubes. Example 6

[0043] A conductive elastic aerogel (WPU-HSQ8 / CNT) based on a ternary synergy of waterborne polyurethane / silsesquioxane / carbon nanotubes is prepared as described in Example 5, except that the mass fraction of hydroxylated silsesquioxane is 8%. Example 7

[0044] A conductive elastic aerogel (WPU-HSQ9 / CNT) based on a waterborne polyurethane / silsesquioxane / carbon nanotube ternary synergy is prepared as described in Example 5, except that the mass fraction of hydroxylated silsesquioxane is 9%.

[0045] Comparative Example 1 A hydroxylated silsesquioxane-modified aqueous polyurethane aerogel is prepared by the following steps: The hydroxylated silsesquioxane-modified waterborne polyurethane emulsion from Example 2 was frozen at -60°C for 24 hours to allow it to crystallize completely. Finally, the frozen sample was transferred to a freeze dryer and dried at -5°C and 10 Pa for 24 hours to allow the ice crystals to sublimate completely, thus obtaining a hydroxylated silsesquioxane-modified waterborne polyurethane aerogel (WPU-HSQ7).

[0046] Comparative Example 2 The hydroxylated silsesquioxane-modified waterborne polyurethane emulsion from Example 3 was frozen at -60°C for 24 hours to allow it to crystallize completely. Finally, the frozen sample was transferred to a freeze dryer and dried at -5°C and 10 Pa for 24 hours to allow the ice crystals to completely sublimate, ultimately yielding a hydroxylated silsesquioxane-modified waterborne polyurethane aerogel (WPU-HSQ8).

[0047] Comparative Example 3 The hydroxylated silsesquioxane-modified waterborne polyurethane emulsion from Example 4 was frozen at -60°C for 24 hours to allow it to crystallize completely. Finally, the frozen sample was transferred to a freeze dryer and dried at -5°C and 10 Pa for 24 hours to allow the ice crystals to sublimate completely, thus obtaining a hydroxylated silsesquioxane-modified waterborne polyurethane aerogel (WPU-HSQ9).

[0048] Experimental Example 1 The particle size distribution of the nanoparticles in the emulsions of Experiment 2-4 and the composite dispersions of Experiment 5-7 was measured using a Litesizer 500 nanoparticle size analyzer. The particle size distribution curves of the emulsion nanoparticles in Experiment 2-4 are shown below. Figure 1 As shown. The particle size distribution curves of the composite dispersion nanoparticles in Experimental Examples 5-7 are as follows. Figure 2 As shown.

[0049] Depend on Figure 1 As can be seen, the emulsions in Experiments 2-4 all exhibit a transparent light blue appearance, with an average particle size below 80 nm, and possess uniform distribution and excellent centrifugal stability. This indicates that the addition of HSQ did not disrupt the nanostructure of the emulsion. The silsesquioxane backbone and the hard and soft segments of WPU enhance the stability of the emulsion structure through hydrogen bonding and covalent bonding interactions.

[0050] Depend on Figure 2 As can be seen, after adding MWCNTs, the transparent emulsion transforms into a black nanoparticle dispersion. The average particle size of the composite dispersions in Experiments 5-7 exceeds 150 nm, and the particle size distribution widens. The system maintains excellent stability, demonstrating the WPU-HSQ system's ability to effectively disperse and stabilize carbon nanotubes.

[0051] Experimental Example 2 The pore size distribution of the aerogels in Experimental Example 6 and Comparative Example 2 was determined using mercury porosimetry with a Quantachrome Poremaster system. The pore size distribution curves of WPU-HSQ8 / CNT are shown below. Figure 3 As shown. The pore size distribution curve of WPU-HSQ8 is as follows. Figure 4 As shown.

[0052] like Figure 3 As shown, WPU-HSQ8 exhibits a uniform pore size distribution with an average pore size of 19.8 μm and a porosity as high as 87.51%. Its bulk density is 0.2498 g / cm³. 3 ) and apparent density (1.0132 g / cm³) 3 The lower temperature indicates that it is lightweight and can be easily placed on the flower's center.

[0053] like Figure 4 As shown, compared to WPU-HSQ8, WPU-HSQ8 / CNT exhibits a more concentrated pore size distribution, with an average pore size increased to 27 μm, while maintaining a high porosity of 77.83%. This is because, during the freezing process, the uniformly dispersed carbon nanotube network plays a crucial template role: its excellent thermal conductivity ensures more uniform heat transfer, promotes the uniform growth and nucleation of ice crystals, and allows the carbon nanotubes to be stabilized in the WPU-HSQ matrix through physical entanglement and interfacial interactions, ultimately forming a composite aerogel with a three-dimensional porous network structure.

[0054] Experimental Example 3 The internal pore morphology of WPU-HSQ8 / CNT and WPU-HSQ8 was analyzed using a Hitachi S-4800 field emission scanning electron microscope. The internal pore morphology of WPU-HSQ8 is shown below. Figure 5 As shown. The internal pore morphology of WPU-HSQ8 / CNT is as follows. Figure 6 As shown.

[0055] like Figure 5 As shown, the internal pores of WPU-HSQ8 exhibit a typical three-dimensional layered stacked porous structure, with relatively smooth skeleton surfaces and inner walls. This structure is formed due to the continuous growth of ice crystals during freezing, which compresses the polymer network to the grain boundaries. After the ice crystals sublimate, layered pores with relatively large interlayer spacing are formed.

[0056] like Figure 6 As shown, the internal pores of WPU-HSQ8 / CNT are more dense than those of WPU-HSQ8, exhibiting a three-dimensional porous network structure.

[0057] Test Example 4 Static compression test: Static compression tests were performed on the aerogels obtained in Examples 5-7 and Comparative Examples 1-3 using an Instron 3344 universal testing machine. The stress-strain curves of the aerogels obtained in Examples 5-7 and Comparative Examples 1-3 are shown below. Figure 7 As shown.

[0058] like Figure 7In the examples, WPU-HSQ represents the aerogels obtained in Comparative Examples 1-3, and WPU-HSQ / CNT represents the aerogels in Examples 5-7. In the aerogels obtained in Comparative Examples 1-3, it can be seen that when the HSQ content is increased from 7% to 8%, WPU-HSQ8 achieves higher compressive stress (3.43 MPa) and toughness (0.54 MJ / m). 3 This is because HSQ nanoparticles promote phase separation, resulting in a more ordered arrangement of WPU hard segments and the formation of a denser, more ordered multi-level hydrogen bond network. Simultaneously, this synergistic effect between covalent cross-linking and hydrogen bonding significantly improves the network's toughness and energy dissipation capacity. However, when the HSQ content further increases to 9%, the excessively high cross-linking density and the steric hindrance effect caused by the inorganic cage structure hinder the movement of polymer chain segments and the formation of an ordered hydrogen bond network. This weakens the network's toughness and energy dissipation capacity, causing the compressive stress of WPU-HSQ9 to drop to 2.98 MPa and the toughness to drop to 0.45 MJ / m. 3 Nevertheless, these values ​​still outperform the mechanical properties of WPU-HSQ7 (2.24 MPa, 0.29 MJ / m). 3 ).

[0059] Thanks to the physical entanglement and interfacial interactions of carbon nanotubes (CNTs) within the WPU-HSQ matrix, a coherent rigid reinforcing network is formed. This results in the aerogels prepared in Examples 5-7 exhibiting superior modulus and strength compared to the aerogels in Comparative Examples 1-3, thus demonstrating superior load-bearing and stress transfer capabilities. Consequently, WPU-HSQ8 / CNT exhibits the best compressive properties, with a compressive stress reaching 4.61 MPa and a strength of 0.73 MJ / m². 3 The high toughness indicates that the composite aerogel possesses both excellent compressive elasticity and strength, and has potential applications in pressure-sensitive sensor devices.

[0060] Experimental Example 5 Dynamic compression cycle test: WPU-HSQ8 / CNT and WPU-HSQ8 were subjected to 30% compressive deformation using an Instron 3344 universal testing machine, and 100 dynamic compression cycles were performed at a rate of 20 mm / min. The stress-strain curve of WPU-HSQ8 / CNT is shown below. Figure 8 As shown. The stress-strain curve of WPU-HSQ8 is as follows. Figure 9 As shown.

[0061] Figure 8 and Figure 9The results show that both materials exhibit nonlinear stress-strain curves with a significant hysteresis loop, reflecting the typical energy dissipation characteristics of viscoelastic materials under large deformations. After the first 10 cycles, the curves highly overlap, indicating that the materials stabilize rapidly and possess excellent fatigue resistance. After 100 cycles, the maximum compressive stress of WPU-HSQ8 slightly decreased from 0.20 MPa to 0.17 MPa, while the maximum compressive stress of WPU-HSQ8 / CNT decreased from 0.48 MPa to 0.39 MPa, indicating that both materials possess good structural robustness and elastic recovery capability.

[0062] As the number of cycles increases, the hysteresis loop area gradually decreases, reflecting reduced energy dissipation and a more stable internal structure. The energy dissipation of WPU-HSQ8 decreases from 30.46 kJ / m². 3 It dropped to 13.40 kJ / m 3 This is mainly attributed to the breaking of weak hydrogen bonds, plastic flow of polymer segments, and localized compaction of the pore walls. Meanwhile, the energy dissipation of WPU-HSQ8 / CNT decreases from 17.37 kJ / m³. 3 Significantly reduced to 6.41 kJ / m 3 In addition to the mechanisms mentioned above, the reduction in energy dissipation also benefits from interfacial slippage between carbon nanotubes (CNTs) and the matrix, as well as the synergistic reconstruction of the carbon nanotube network. This causes deformation to shift more towards an elastic response, significantly suppressing plastic energy dissipation. Extremely low steady-state energy dissipation (6.41 kJ / m³) 3 This indicates that the material exhibits structural stability and consistent responsiveness during long-term cycling, which provides a crucial guarantee for the long-term reliability and measurement accuracy of the sensor.

[0063] Experimental Example 6 Thermal stability testing: A TA SDT Q600 thermogravimetric analyzer was used to test the thermal stability of the samples under a nitrogen atmosphere, heating from ambient temperature to 700 °C at a rate of 20 °C / min. The thermal degradation curves of the aerogels corresponding to Example 57 and Comparative Example 13 are shown below. Figure 10 and Figure 11 As shown.

[0064] according to Figure 10 and Figure 11Thermogravimetric analysis (TGA) results show that the rigid backbone of HSQ provides structural support and constraint for the WPU segments, delaying the overall pyrolysis process and significantly increasing the initial decomposition temperature of the WPU-HSQ aerogel corresponding to Comparative Example 13 from 328.44℃ to 392.58℃. Above 500℃, the material enters the decomposition process of carbonized residues. At this stage, the inorganic Si-O-Si components in HSQ are retained, forming a stable framework. Together with the previously generated carbon-rich residues, they constitute a C / SiO2 composite ceramic phase, forming a dense protective layer on the material surface, thus effectively inhibiting thermo-oxidative diffusion. This significantly increases the carbon residue of the WPU-HSQ aerogel corresponding to Comparative Example 13 from 0.33% to 7.44%.

[0065] Compared with the WPU-HSQ aerogel corresponding to Comparative Example 13, the addition of CNTs further enhanced the continuity and stability of the carbon layer in the aerogel corresponding to Example 57, increasing the residual carbon content to 10.71%. This indicates that HSQ and CNTs synergistically construct an efficient thermal barrier system, significantly improving the overall thermal stability of the aerogel.

[0066] Experimental Example 7 Conductivity test: such as Figure 12 As shown, with increasing pressure, the material undergoes compressive deformation, its resistance decreases, and the brightness of the external LED increases accordingly, exhibiting a typical negative piezoresistive effect. This phenomenon stems from the high compressive elasticity and large deformation capacity endowed by its three-dimensional porous structure. During compression, the contact points and contact area between the pore walls continuously increase, forming more and shorter conductive paths, indicating that the WPUHSQ8 / CNT composite aerogel has significant pressure resistance response characteristics.

[0067] Experimental Example 8 High-sensitivity piezoresistive performance testing over a wide pressure range The piezoresistive response sensitivity of the WPU-HSQ8 / CNT composite aerogel is intuitively reflected by the relative resistance change (ΔR / R0). The formula for the relative resistance change is determined by the following equation: = Where R is the real-time resistance of the WPU-HSQ8 / CNT composite aerogel, and R0 is the initial resistance of the material.

[0068] like Figure 13As shown in the left figure, during the cyclic compression of the WPU-HSQ8 / CNT composite aerogel, when the pressure is in the low stress range (0.0268-0.0609 MPa), the corresponding ΔR / R0 value is between -7.38% and -20.98%. During this stage, the pore walls undergo reversible elastic bending, causing them to approach each other. The contact points and contact area increase with increasing pressure, shortening the conductive path and thus exhibiting sensitive piezoresistive characteristics. Figure 13 As shown in the right figure, upon entering the high-pressure region (1.1414-2.9994 MPa), the ΔR / R0 of the WPU-HSQ8 / CNT composite aerogel further changed from -1134.42% to -3762.22%. This corresponds to the plastic collapse and gradual densification of its pore walls, where previously isolated conductive pathways interconnect to form a dense network, leading to a sharp drop in resistance. These results demonstrate that this material exhibits high sensitivity, excellent reversibility, and stable cyclic piezoresistive sensing performance over a wide pressure range.

[0069] Experimental Example 9 Fast response and recovery performance test at high compression rates like Figure 14 As shown, under a constant pressure of 0.15 MPa, the WPUHSQ8 / CNT composite aerogel still exhibits a stable dynamic piezoresistive response within a high compression rate range of 150-300 mm / min. This is mainly due to the inherent viscoelastic properties of the material itself, which allow it to maintain a highly consistent piezoresistive response curve at different high compression rates, demonstrating excellent signal repeatability and response stability. Furthermore, from... Figure 15 As can be seen, this material responds rapidly during dynamic loading and unloading cycles; even under high-rate compression of 300 mm / min, its compression response time and resistance recovery time are only approximately 0.60 s and 0.50 s, respectively. These results further confirm its potential in high-rate dynamic sensing applications.

[0070] Experimental Example 10 Long-cycle pressure sensor stability and durability testing like Figure 16 The pressure sensing response curves of the WPUHSQ8 / CNT composite aerogel after more than 600 cycles at 0.15 MPa were recorded. The response signals of the initial and final 18 cycles during the long-term cycling process were compared, both exhibiting stable, continuous, and highly consistent electrical signal outputs. This indicates that the material possesses excellent cycling stability and structural integrity, showing no significant performance degradation or structural damage after long-term cyclic loading, and maintaining reliable and stable dynamic current response characteristics.

[0071] Experimental Example 11 Encoded signal recognition like Figure 17 As shown, when the WPU-HSQ8 / CNT composite aerogel material is pressed using Morse code to spell "SDU" and "SFM", the output electrical signal is stable and clearly distinguishable. This result fully demonstrates that the composite aerogel possesses sensitive, reversible, and stable resistance response characteristics to compressive stress.

[0072] Experimental Example 12 Human motion monitoring like Figure 18 As shown, when WPU-HSQ8 / CNT composite aerogel is attached to the surface of major human joints (such as the wrist, elbow, ankle, and knee), clear and repeatable piezoresistive signals can be monitored and recorded in real time under the subtle pressure generated by different bending movements. This result verifies the effectiveness and applicability of this material in physiological signal acquisition scenarios such as human motion monitoring.

[0073] In summary, the conductive elastic aerogel based on the ternary synergy of aqueous polyurethane / silsesquioxane / carbon nanotubes prepared in this invention exhibits excellent comprehensive properties. This material possesses a compressive strength as high as 4.61 MPa and a tensile strength of 0.73 MJ / m³. 3 The aerogel exhibits excellent toughness and outstanding mechanical properties; it possesses multi-level, highly sensitive piezoresistive response capabilities within an ultra-wide pressure range of 0-5 MPa. Dynamic testing shows that even after a high compression rate of 300 mm / min and more than 600 cyclic loading cycles, its signal remains highly consistent, demonstrating excellent dynamic stability and fatigue resistance. Furthermore, this aerogel can be successfully applied to real-time monitoring of joint movements in multiple parts of the human body, such as the elbow, wrist, knee, and ankle, and also exhibits good thermal stability. These characteristics collectively demonstrate that this material, as a high-performance piezoresistive sensing platform, has broad application potential in wearable health monitoring, electronic skin, and human-computer interaction.

Claims

1. A conductive elastic aerogel based on a ternary synergistic structure of waterborne polyurethane / silsesquioxane / carbon nanotubes, characterized in that: The conductive elastic aerogel is a composite material of hydroxylated silsesquioxane-modified waterborne polyurethane and multi-walled carbon nanotubes; the hydroxylated silsesquioxane-modified waterborne polyurethane is obtained by stepwise polymerization of waterborne polyurethane prepolymer followed by chemical crosslinking with hydroxylated silsesquioxane; the waterborne polyurethane is a carboxylic acid-type waterborne polyurethane with the following structure: 。 2. The conductive elastic aerogel based on the ternary synergistic structure of aqueous polyurethane / silsesquioxane / carbon nanotubes according to claim 1, characterized in that: Hydroxylated silsesquioxanes are obtained by a nucleophilic addition ring-opening reaction of epoxy silsesquioxanes and diethanolamine, and have the following structure: 。 3. A method for preparing a conductive elastic aerogel based on a ternary synergistic structure of aqueous polyurethane / silsesquioxane / carbon nanotubes as described in claim 1, characterized in that, Includes the following steps: Multi-walled carbon nanotubes were mixed with hydroxylated silsesquioxane-modified aqueous polyurethane emulsion to obtain a uniform mixed dispersion. The mixture was then freeze-dried to obtain a ternary conductive elastic aerogel of aqueous polyurethane / silsesquioxane / carbon nanotube.

4. The method for preparing the conductive elastic aerogel based on the ternary synergy of aqueous polyurethane / silsesquioxane / carbon nanotubes according to claim 3, characterized in that: The mass ratio of the hydroxylated silsesquioxane-modified waterborne polyurethane emulsion to the multi-walled carbon nanotubes is 1:0.15-0.

35. And / or, the multi-walled carbon nanotubes have an outer diameter of 20-50 nm and a length of ≤15 mm.

5. The method for preparing the conductive elastic aerogel based on the ternary synergy of aqueous polyurethane / silsesquioxane / carbon nanotubes according to claim 3, characterized in that: The conditions for freeze-drying the mixed dispersion are as follows: freeze at -60℃ for 24-48 h until the aqueous solution completely forms ice crystals to obtain the mixture; after the mixture is transferred to the freeze dryer, it needs to be vacuum dried at a set temperature of -5℃, a vacuum pressure of 0-10 Pa, and a drying time of 24 h until the ice crystals completely sublimate.

6. A method for preparing the hydroxylated silsesquioxane-modified waterborne polyurethane emulsion as described in claim 1, characterized in that, Includes the following steps: Oligomeric diol, hydrophilic chain extender, and isocyanate were dissolved in solvent a and prepolymerized at 70°C to obtain an aqueous polyurethane prepolymer. The prepolymer was gradually polymerized until the -NCO content in the system reached the theoretical value. Triethylamine was then added to the reaction system to neutralize the carboxyl groups in the chain segments. Next, hydroxylated silsesquioxane was added for chain extension and crosslinking. Finally, deionized water was slowly added dropwise to the resulting mixture for emulsification. After removing the solvent, an aqueous polyurethane emulsion modified with hydroxylated silsesquioxane was obtained.

7. The method for preparing the hydroxylated silsesquioxane-modified waterborne polyurethane emulsion according to claim 6, characterized in that: The oligomeric diol may be one or more of polycarbonate diol, polyether diol or polyester diol, and the molecular weight may be 1000, 1500 or 2000. And / or, the hydrophilic chain extender may be one or more of 2,2-dimethylolbutyric acid and 2,2-dimethylolpropionic acid; And / or, the isocyanate may be one or more of toluene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, phenylmethylene diisocyanate, and dicyclohexylmethane-4,4'-diisocyanate; And / or, the mass ratio of the aqueous polyurethane prepolymer to the hydroxylated silsesquioxane is 1:0.07-0.09; And / or, the molar ratio of triethylamine to the hydrophilic chain extender is 1:

1.

8. The method for preparing the hydroxylated silsesquioxane-modified waterborne polyurethane emulsion according to claim 6, characterized in that: The preparation method of the hydroxylated silsesquioxane is as follows: epoxy silsesquioxane and diethanolamine are dissolved in solvent b, and the hydroxylated silsesquioxane is obtained by heating and reacting and removing the solvent.

9. The method for preparing the hydroxylated silsesquioxane-modified waterborne polyurethane emulsion according to claim 8, characterized in that, The solvent b is one or more of tetrahydrofuran, acetone, and methanol; And / or, the molar ratio of the epoxy silsesquioxane to diethanolamine is 1:1-10.

10. The application of the conductive elastic aerogel based on the ternary synergy of waterborne polyurethane / silsesquioxane / carbon nanotube as described in any one of claims 1-2, or the conductive elastic aerogel based on the ternary synergy of waterborne polyurethane / silsesquioxane / carbon nanotube obtained by the preparation method described in any one of claims 3-9, in the field of flexible piezoresistive sensing.

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