Piezoelectric composite hydrogel material and preparation method thereof

Abstract

The invention discloses a piezoelectric composite hydrogel material and a preparation method thereof, and belongs to the technical field of high polymer materials, the piezoelectric composite hydrogel material provided by the invention is prepared by the following steps: immersing polyvinyl alcohol in deionized water, adding guar gum hydroxypropyl trimethyl ammonium chloride, modified MXene nanosheets and BaTiO3 (at) PDA core-shell particles into the deionized water while stirring, and stirring to obtain a mixture; the preparation method comprises the following steps: mixing the raw materials, stirring at room temperature to obtain hydrogel, performing freezing-thawing circulation on the hydrogel for three times, fully swelling, applying a 3kV / mm direct-current electric field to the swelled product for polarization treatment for 4-5 minutes, and standing for 12 hours to obtain the piezoelectric composite hydrogel material. According to the invention, self-made filler modified MXene nanosheets and BaTiO3 coated PDA core-shell particles are added into the piezoelectric composite hydrogel material, so that coexistence of high piezoelectricity (greater than or equal to 2.5 V) and high elongation (greater than or equal to 400%) is finally realized on the basis of reducing the total use amount of the filler.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer materials, and in particular relates to a piezoelectric composite hydrogel material and a preparation method thereof. Background Art

[0002] With the rapid development of flexible electronic devices, piezoelectric hydrogels have shown great potential in wearable health monitoring (such as heart rate sensing), soft robotics, and self-powered systems because they can convert mechanical energy into electrical energy. Traditional hydrogels have good biocompatibility and flexibility, but lack piezoelectric properties. Existing technologies impart piezoelectricity to hydrogels by adding piezoelectric ceramic particles (such as barium titanate), but this method has significant drawbacks.

[0003] The weak interfacial bonding between piezoelectric ceramic particles (such as BaTiO3) and the hydrogel matrix results in low stress transfer efficiency and insufficient piezoelectric output performance (open-circuit voltage is typically less than 1.0 V). Furthermore, high filler content (>15wt%) can degrade the stretchability (elongation at break <200%) and self-healing properties of the hydrogel.

[0004] Flexible electronic devices urgently require materials that combine high piezoelectricity (output voltage ≥ 2.5V), high ductility (elongation ≥ 400%), and rapid self-healing capabilities. Existing technologies are unable to balance these three characteristics, severely restricting their application in dynamic environments (such as human joint monitoring). The development of new piezoelectric hydrogels has industrial value. Summary of the Invention

[0005] The purpose of the present invention is to provide a piezoelectric composite hydrogel material with high piezoelectricity (output voltage ≥ 2.5V), high ductility (elongation ≥ 400%) and rapid self-healing ability.

[0006] The purpose of the present invention can be achieved through the following technical solutions: A method for preparing a piezoelectric composite hydrogel material comprises the following steps: Polyvinyl alcohol was immersed in deionized water, and guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles were added thereto with stirring, and stirred at room temperature for 1 to 2 hours to obtain a hydrogel. The hydrogel was then frozen at -20°C for 10 to 12 hours and thawed at room temperature for 2 hours. After three freeze-thaw cycles, a composite hydrogel was obtained. The composite hydrogel was then immersed in a NaCl solution with a concentration of 0.1 mol / L. After it was fully swollen, a 3 kV / mm DC electric field polarization treatment was applied to the swollen product for 4 to 5 minutes. After completion, it was allowed to stand for 12 hours to obtain a piezoelectric composite hydrogel material.

[0007] Furthermore, the number average molecular weight Mn of the polyvinyl alcohol is 89,000 to 98,000; the alcoholysis degree of the polyvinyl alcohol is 99%; and the viscosity of the guar gum hydroxypropyltrimethylammonium chloride is ≥2,000 mPa·s.

[0008] Furthermore, the usage ratio of the polyvinyl alcohol, deionized water, guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles is 1.5 g:50 mL:1 g:0.25 g:0.2-0.25 g.

[0009] Furthermore, the modified MXene nanosheets are prepared by the following steps: A1. Lithium fluoride, hydrochloric acid, and deionized water were mixed and stirred for 10 to 30 minutes, and titanium aluminum carbide was added thereto. The mixture was stirred at room temperature for 5 to 10 minutes, and then centrifuged at 3500 rpm for 50 to 60 minutes. After completion, the solid component was collected by filtration and ultrasonically washed with deionized water, and then dried at room temperature for 12 hours to obtain MXene nanosheets. A2. The MXene nanosheets are then dispersed in a 50% by volume ethanol solution, KH-550 is added thereto with stirring, and the mixture is stirred at 60-80°C for 5-6 hours. After completion, the solid component is collected by centrifugation and vacuum dried to obtain modified MXene nanosheets.

[0010] Furthermore, the usage ratio of lithium fluoride, hydrochloric acid, deionized water, and titanium aluminum carbide in A1 is 1 g:15-20 mL:1 mL:1.0-1.2 g.

[0011] Furthermore, the usage ratio of the MXene nanosheets, the 50% by volume ethanol solution, and KH-550 described in A2 is 1 g:50 mL:0.2-0.3 g.

[0012] Furthermore, the BaTiO3@PDA core-shell particles are prepared by the following steps: Barium titanate was dispersed in Tris-HCl buffer, and dopamine hydrochloride was added thereto with stirring three times: the first time, 20 wt% to 30 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 6 to 8 hours. The second time, 20 wt% to 30 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 6 to 8 hours. Finally, 40 wt% to 50 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 6 to 8 hours. After completion, the solid component was collected by centrifugation, washed three times with pure water, and then freeze-dried to obtain BaTiO3@PDA core-shell particles.

[0013] Furthermore, the particle size of the barium titanate is 100±10 nm.

[0014] Furthermore, the usage ratio of the barium titanate, Tris-HCl buffer and dopamine hydrochloride is 1 g:200 mL:0.5-1.0 g.

[0015] Furthermore, the piezoelectric composite hydrogel material is prepared by the above preparation steps.

[0016] Beneficial effects of the present invention: The present invention provides a piezoelectric composite hydrogel material and a preparation method thereof. By adding self-made filler-modified MXene nanosheets and BaTiO3@PDA core-shell particles to the piezoelectric composite hydrogel material, the present invention ultimately achieves the coexistence of high piezoelectricity (≥2.5V) and high elongation (≥400%) while reducing the total amount of filler. The specific analysis is as follows: (1) Interface synergistic strengthening: The present invention introduces -NH2 groups by modifying MXene with KH-550, forming a dynamic hydrogen bond network with the phenolic hydroxyl groups of BaTiO3@PDA, and at the same time, significantly improving the stress transfer efficiency and self-healing properties (compared with traditional physical mixing).

[0017] (2) Gradient conductive layer design: When preparing the BaTiO3@PDA core-shell structure, the present invention forms a gradient conductive layer by coating PDA three times to enhance the interfacial charge transfer with MXene. At the same time, the piezoelectric effect and the conductive path are coupled to improve the charge collection efficiency.

[0018] (3) Low filler and high output: The total amount of filler in the piezoelectric composite hydrogel material provided by the present invention only accounts for 8.3wt% to 9.7wt% of the matrix, breaking through the limitation that traditional piezoelectric hydrogels require >15wt% filler, and achieving the coexistence of high piezoelectricity (≥2.5V) and high elongation (≥400%). DETAILED DESCRIPTION

[0019] Below in conjunction with the embodiment of the present invention, the technical scheme in the embodiment of the present invention is clearly and completely described, it is obvious that described embodiment is only a part of embodiment of the present invention, rather than whole embodiment. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Meanwhile, raw materials, reagents or devices used in the following examples, unless otherwise specified, can be obtained from conventional commercial channels, or can be obtained by existing known methods.

[0020] Example 1

[0021] Preparation of modified MXene nanosheets: A1. Lithium fluoride (LiF, ≥99.0%, Sinopharm Group), hydrochloric acid (HCl, 36.0%-38.0%, Sinopharm Group) and deionized water were mixed and stirred for 10 minutes, and then MAX precursor material titanium aluminum carbide (Ti3AlC2, Sigma-Aldrich) was added thereto. The mixture was stirred at room temperature for 5 minutes, and then centrifuged at 3500 rpm for 50 minutes. After completion, the solid component was collected by filtration and ultrasonically washed with deionized water, and then dried at room temperature for 12 hours to obtain MXene nanosheets. The amount ratio of lithium fluoride, hydrochloric acid, deionized water and MAX precursor material titanium aluminum carbide was 1g:15mL:1mL:1.0g; A2. The MXene nanosheets were dispersed in a 50% by volume ethanol solution, and KH-550 (pure ≥98%, Aladdin) was added thereto with stirring. The mixture was stirred at 60°C for 5 h. After completion, the solid component was collected by centrifugation and vacuum dried to obtain modified MXene nanosheets. The ratio of MXene nanosheets, 50% by volume ethanol solution, and KH-550 was 1 g:50 mL:0.2 g.

[0022] Example 2

[0023] Preparation of modified MXene nanosheets: A1. Lithium fluoride (LiF, ≥99.0%, Sinopharm Group), hydrochloric acid (HCl, 36.0%-38.0%, Sinopharm Group) and deionized water were mixed and stirred for 30 minutes, and then MAX precursor material titanium aluminum carbide (Ti3AlC2, Sigma-Aldrich) was added thereto. The mixture was stirred at room temperature for 10 minutes, and then centrifuged at 3500 rpm for 60 minutes. After completion, the solid component was collected by filtration and ultrasonically washed with deionized water, and then dried at room temperature for 12 hours to obtain MXene nanosheets. The amount ratio of lithium fluoride, hydrochloric acid, deionized water and MAX precursor material titanium aluminum carbide was 1g:20mL:1mL:1.1g; A2. The MXene nanosheets were dispersed in a 50% by volume ethanol solution, and KH-550 (pure ≥98%, Aladdin) was added thereto with stirring. The mixture was stirred at 80°C for 6 h. After completion, the solid component was collected by centrifugation and vacuum dried to obtain modified MXene nanosheets. The amount ratio of MXene nanosheets, 50% by volume ethanol solution, and KH-550 was 1 g:50 mL:0.25 g.

[0024] Example 3

[0025] Preparation of modified MXene nanosheets: A1. Lithium fluoride (LiF, ≥99.0%, Sinopharm Group), hydrochloric acid (HCl, 36.0%-38.0%, Sinopharm Group) and deionized water were mixed and stirred for 30 minutes, and then MAX precursor material titanium aluminum carbide (Ti3AlC2, Sigma-Aldrich) was added thereto. The mixture was stirred at room temperature for 10 minutes, and then centrifuged at 3500 rpm for 60 minutes. After completion, the solid component was collected by filtration and ultrasonically washed with deionized water, and then dried at room temperature for 12 hours to obtain MXene nanosheets. The amount ratio of lithium fluoride, hydrochloric acid, deionized water and MAX precursor material titanium aluminum carbide was 1g:20mL:1mL:1.2g; A2. The MXene nanosheets were dispersed in a 50% by volume ethanol solution, and KH-550 (pure ≥98%, Aladdin) was added thereto with stirring. The mixture was stirred at 80°C for 6 h. After completion, the solid component was collected by centrifugation and vacuum dried to obtain modified MXene nanosheets. The ratio of MXene nanosheets, 50% by volume ethanol solution, and KH-550 was 1 g:50 mL:0.3 g.

[0026] Example 4

[0027] Preparation of BaTiO3@PDA core-shell particles: Barium titanate (BaTiO3, particle size 100±10 nm, Sinopharm Group) was dispersed in Tris-HCl buffer (pH=8.5), and dopamine hydrochloride (purity 98%, Aladdin) was added thereto three times with stirring. Specifically, 30 wt% of dopamine hydrochloride was added thereto for the first time, and after the addition was completed, it was stirred at room temperature for 6 hours. 30 wt% of dopamine hydrochloride was added thereto again, and after the addition was completed, it was stirred at room temperature for 6 hours. Finally, 40 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, it was stirred at room temperature for 6 hours. After completion, the solid component was collected by centrifugation, washed three times with pure water, and then freeze-dried to obtain BaTiO3@PDA core-shell particles, wherein the amount ratio of barium titanate, Tris-HCl buffer and dopamine hydrochloride was 1 g:200 mL:1 g.

[0028] Example 5

[0029] Preparation of BaTiO3@PDA core-shell particles: Barium titanate (BaTiO3, particle size 100±10 nm, Sinopharm Group) was dispersed in Tris-HCl buffer (pH=8.5), and dopamine hydrochloride (purity 98%, Aladdin) was added thereto three times with stirring. Specifically, 30 wt% of dopamine hydrochloride was added thereto for the first time, and after the addition was completed, it was stirred at room temperature for 8 hours. 20 wt% of dopamine hydrochloride was added thereto again, and after the addition was completed, it was stirred at room temperature for 8 hours. Finally, 50 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, it was stirred at room temperature for 8 hours. After completion, the solid component was collected by centrifugation, washed three times with pure water, and then freeze-dried to obtain BaTiO3@PDA core-shell particles, wherein the amount ratio of barium titanate, Tris-HCl buffer and dopamine hydrochloride was 1 g:200 mL:1 g.

[0030] Example 6

[0031] Preparation of BaTiO3@PDA core-shell particles: Barium titanate (BaTiO3, particle size 100±10 nm, Sinopharm Group) was dispersed in Tris-HCl buffer (pH=8.5), and dopamine hydrochloride (purity 98%, Aladdin) was added thereto three times with stirring. Specifically, a total amount of 20 wt% of dopamine hydrochloride was added thereto for the first time, and after the addition was completed, the mixture was stirred at room temperature for 8 hours. A total amount of 30 wt% of dopamine hydrochloride was added thereto again, and after the addition was completed, the mixture was stirred at room temperature for 8 hours. Finally, a total amount of 50 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 8 hours. After completion, the solid component was collected by centrifugation, washed three times with pure water, and then freeze-dried to obtain BaTiO3@PDA core-shell particles, wherein the amount ratio of barium titanate, Tris-HCl buffer and dopamine hydrochloride was 1 g:200 mL:1 g.

[0032] Comparative Example 1 Comparative Example 1 is the control group of Example 6, except that the step of adding dopamine hydrochloride in stages in Example 6 is cancelled and all dopamine hydrochloride is added at one time. Specifically, the scheme of Comparative Example 1 is as follows: barium titanate (BaTiO3, particle size 100±10 nm, Sinopharm Group) is dispersed in Tris-HCl buffer (pH=8.5), and then dopamine hydrochloride (purity 98%, Aladdin) is added thereto with stirring, and stirred at room temperature for 24 hours. After completion, the solid component is collected by centrifugation, washed three times with pure water, and then freeze-dried to obtain BaTiO3@PDA core-shell particles, wherein the amount ratio of barium titanate, Tris-HCl buffer and dopamine hydrochloride is 1g:200mL:1g.

[0033] Example 7

[0034] Preparation of piezoelectric composite hydrogel materials: Polyvinyl alcohol (PVA, Aladdin, Mn = 89000-98000, alcoholysis degree 99%, Maclean Biochemical) was immersed in deionized water, and guar gum hydroxypropyltrimonium chloride (CGG, viscosity ≥ 2000 mPa·s; N: 1.3%-1.7%, Maclean Biochemical), the modified MXene nanosheets prepared in Example 1, and the BaTiO3@PDA core-shell particles prepared in Example 4 were added thereto with stirring, and stirred at room temperature for 1 hour to obtain a hydrogel. The hydrogel was then frozen at -20°C for 10 hours and then thawed at room temperature for 2 hours. After three freeze-thaw cycles, a composite hydrogel was obtained. The composite hydrogel was then immersed in a 0.1 mol / L NaCl solution. After it was fully swollen, the swollen product was subjected to a 3 kV / mm DC electric field polarization treatment for 4 minutes. After completion, it was allowed to stand for 12 hours to obtain a piezoelectric composite hydrogel material, wherein the amount ratio of polyvinyl alcohol, deionized water, guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles was 1.5 g:50 mL:1 g:0.25 g:0.2 g.

[0035] Example 8

[0036] Preparation of piezoelectric composite hydrogel materials: Polyvinyl alcohol (PVA, Aladdin, Mn = 89000-98000, alcoholysis degree 99%, McLean Biochemical) was immersed in deionized water, and guar gum hydroxypropyltrimethylammonium chloride (CGG, viscosity ≥ 2000 mPa·s; N: 1.3%-1.7%, McLean Biochemical), the modified MXene nanosheets prepared in Example 2, and the BaTiO3@PDA core-shell particles prepared in Example 5 were added thereto with stirring, and stirred at room temperature for 2 h to obtain a hydrogel. The hydrogel was then frozen at -20°C for 12 h and then thawed at room temperature for 2 h. After three freeze-thaw cycles, a composite hydrogel was obtained. The composite hydrogel was then immersed in a 0.1 mol / L NaCl solution. After it was fully swollen, the swollen product was subjected to a 3 kV / mm DC electric field polarization treatment for 5 minutes. After completion, it was allowed to stand for 12 hours to obtain a piezoelectric composite hydrogel material, wherein the amount ratio of polyvinyl alcohol, deionized water, guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles was 1.5 g:50 mL:1 g:0.25 g:0.25 g.

[0037] Example 9

[0038] Preparation of piezoelectric composite hydrogel materials: Polyvinyl alcohol (PVA, Aladdin, Mn = 89000-98000, alcoholysis degree 99%, Maclean Biochemical) was immersed in deionized water, and guar gum hydroxypropyltrimethylammonium chloride (CGG, viscosity ≥ 2000 mPa·s; N: 1.3%-1.7%, Maclean Biochemical), the modified MXene nanosheets prepared in Example 3, and the BaTiO3@PDA core-shell particles prepared in Example 6 were added thereto with stirring, and stirred at room temperature for 2 h to obtain a hydrogel. The hydrogel was then frozen at -20°C for 12 h and then thawed at room temperature for 2 h. After three freeze-thaw cycles, a composite hydrogel was obtained. The composite hydrogel was then immersed in a 0.1 mol / L NaCl solution. After it was fully swollen, the swollen product was subjected to a 3 kV / mm DC electric field polarization treatment for 5 minutes. After completion, it was allowed to stand for 12 hours to obtain a piezoelectric composite hydrogel material, wherein the amount ratio of polyvinyl alcohol, deionized water, guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles was 1.5 g:50 mL:1 g:0.25 g:0.25 g.

[0039] Comparative Example 2 Comparative Example 2 is the control group of Example 9. The modified MXene nanosheets prepared in Example 3 of the raw materials in Example 9 are replaced by the MXene nanosheets prepared in step A1 of Example 3, that is, the modification process of the MXene nanosheets is cancelled. The remaining raw materials, raw material amounts, and preparation steps are consistent with those in Example 9, and finally a piezoelectric composite hydrogel material is obtained.

[0040] Comparative Example 3 Comparative Example 3 is the control group of Example 9. The BaTiO3@PDA core-shell particles prepared in Example 6 using the raw materials in Example 9 are replaced with the raw material barium titanate (BaTiO3, particle size 100±10 nm, Sinopharm Group) in Example 6, that is, the coating modification process is cancelled. The remaining raw materials, raw material amounts, and preparation steps are kept consistent with those in Example 9, and finally a piezoelectric composite hydrogel material is obtained.

[0041] Comparative Example 4 Comparative Example 4 is the control group of Example 9. The BaTiO3@PDA core-shell particles prepared in Example 6 of Example 9 are replaced by the BaTiO3@PDA core-shell particles prepared in Comparative Example 1. The remaining raw materials, raw material amounts, and preparation steps are consistent with those in Example 9, and a piezoelectric composite hydrogel material is finally obtained.

[0042] Comparative Example 5 Comparative Example 5 is the control group of Example 9. The polarization treatment step of Example 9 "further applying a 3 kV / mm DC electric field polarization treatment to the swollen product for 5 minutes" is removed. The remaining raw materials, raw material amounts, and preparation steps are consistent with those in Example 9, and finally a piezoelectric composite hydrogel material is obtained.

[0043] Test Example 1 The piezoelectric composite hydrogel materials prepared in Examples 7 to 9 and Comparative Examples 2 to 5 were subjected to performance tests. The performance test process is as follows, and the test results are shown in Table 1: (1) Piezoelectric output performance test: Methods: The piezoelectric composite hydrogel material was cut into samples (20×20×2mm 3 ), connected to a digital oscilloscope (Tektronix TBS1102B). Apply periodic pressure (10N, frequency 2Hz, contact area 1cm 2 ), record the open circuit voltage (V) and short circuit current (μA), and take the average value of 10 peak values.

[0044] (2) Mechanical properties test: Methods: The piezoelectric composite hydrogel material was cut into dumbbell-shaped specimens according to ASTM D638 and tested using a universal material testing machine (Instron 5967) at a tensile rate of 100 mm / min. The elongation at break (%) and tensile strength (σ, MPa) were recorded.

[0045] (3) Self-healing test: Methods: The piezoelectric composite hydrogel material was cut into samples (20×20×2mm 3 ) and cut the specimen with a blade (1 mm in depth) and allowed to heal at room temperature for 10 min. The healing efficiency (η%) was determined using the mechanical properties test results and procedure described above. Healing efficiency (η%) = (healed tensile strength / original tensile strength) × 100%.

[0046] (4) Swelling stability test: Methods: The piezoelectric composite hydrogel material was placed at 80℃ constant temperature for 24h and then cooled to room temperature. The dry weight (W0) was measured and the surface moisture was wiped off after immersing in physiological saline (0.9wt% NaCl) for 24h. The wet weight (W0) was measured. s ), calculate the swelling ratio (SR), swelling ratio (SR) = [(W s -W0) / W0]×100%.

[0047] Table 1 Test results project Example 7 Example 8 Example 9 Comparative Example 2 Comparative Example 3 Comparative Example 4 Comparative Example 5 Open circuit voltage (V) 2.65 2.78 2.82 1.20 0.85 1.80 0.35 Short-circuit current (μA) 13.5 14.2 14.8 5.8 4.5 9.0 1.5 Elongation at break (%) 420 435 440 380 320 395 430 Tensile strength (σ, MPa) 0.87 0.91 0.94 0.75 0.60 0.82 0.87 Healing efficiency (η%) 88 90 92 65 50 83 91 Swelling ratio (SR) 320 315 310 290 325 305 312 According to the data analysis in Table 1: 1. Piezoelectric output performance (open circuit voltage and short circuit current): (1) Examples 7 to 9: The open circuit voltage (2.65 to 2.82 V) and short circuit current (13.5 to 14.8 μA) were significantly higher than those of the other groups.

[0048] Speculated reasons: a. The -NH2 of the modified MXene forms a hydrogen bond network with the phenolic hydroxyl groups of BaTiO3@PDA, efficiently transferring stress to the piezoelectric particles (BaTiO3).

[0049] b. Gradient coating of BaTiO3@PDA (Examples 4 to 6) enhances charge collection efficiency (the gradient conductive layer promotes interfacial charge transfer).

[0050] c. Polarization treatment (3 kV / mm) aligns the dipoles and activates piezoelectricity.

[0051] Trend: Example 9 > Example 8 > Example 7, which is due to the increase in the amount of BaTiO3@PDA (0.20g→0.25g) and optimized coating (the gradient of Example 6 is better).

[0052] (2) Comparative Example 2 (no MXene modification): open circuit voltage 1.20 V, short circuit current 5.8 μA, significantly lower than Example 9 (-57% / -61%).

[0053] Speculated reasons: Unmodified MXene has no -NH2 groups and cannot form a hydrogen bond network, resulting in low stress transfer efficiency and weakened piezoelectric output.

[0054] (3) Comparative Example 3 (without BaTiO3 coating): open circuit voltage 0.85 V, short circuit current 4.5 μA, which are the lowest values ​​(-70% / -70% respectively compared with Example 9).

[0055] Speculated reasons: The original BaTiO3 particles have weak interface bonding with the hydrogel matrix (no PDA layer), charge transfer is hindered; particle agglomeration exacerbates stress concentration.

[0056] (4) Comparative Example 4 (one-time coating of BaTiO3@PDA): open circuit voltage 1.80 V, short circuit current 9.0 μA, better than Comparative Example 3 but lower than Example 9 (-36% / -39%).

[0057] Speculated reasons: One-time coating (Comparative Example 1) leads to uneven PDA layer, lack of gradient conductive structure, and lower charge collection efficiency than gradient coating (Example 6).

[0058] (5) Comparative Example 5 (no polarization treatment): open circuit voltage 0.35 V, short circuit current 1.5 μA, extremely low (-88% / -90% compared with Example 9, respectively).

[0059] Speculated reason: Polarization treatment is a key step in activating the piezoelectricity of BaTiO3; after its cancellation, the dipoles are misaligned and the piezoelectric effect is almost lost.

[0060] Conclusion: Modified MXene and gradient BaTiO3@PDA are the core of high-voltage power output, and polarization treatment is indispensable. Gradient coating (Example 6) significantly improves performance compared to single-use coating (Comparative Example 1).

[0061] 2. Mechanical properties (elongation at break and tensile strength): (1) Examples 7 to 9: Elongation at break 420% to 440% (≥400%), tensile strength 0.87 to 0.94 MPa, meeting the goals of high strength and high ductility.

[0062] Speculated reasons: a. Low total filler content (<20wt%) to avoid rigidity degradation.

[0063] b. Hydrogen bond network (MXene-NH2 / BaTiO3@PDA-OH) disperses stress and improves toughness.

[0064] Trend: Example 9 > Example 8 > Example 7, which is related to the increase in the amount of BaTiO3@PDA (enhanced interfacial cross-linking).

[0065] (2) Comparative Example 2 (no MXene modification): elongation at break 380%, tensile strength 0.75 MPa, lower than Example 9 (-14% / -20%).

[0066] Speculated reasons: Unmodified MXene has poor dispersion, weak interface bonding, and stress concentration leading to decreased ductility.

[0067] (3) Comparative Example 3 (without BaTiO3 coating): elongation at break 320%, tensile strength 0.60 MPa, the worst (9% to 27% / -36% compared with the example).

[0068] Speculated reason: Uncoated BaTiO3 particles agglomerate, destroying the hydrogel network and significantly reducing strength and ductility.

[0069] (4) Comparative Example 4 (one-time coating of BaTiO3@PDA): elongation at break 395%, tensile strength 0.82 MPa, close to but lower than Example 9 (-10% / -13%).

[0070] Speculated reasons: The PDA layer exists but has poor uniformity (one-time coating) and the hydrogen bond network efficiency is slightly low.

[0071] (5) Comparative Example 5 (non-polarized): elongation at break 430%, tensile strength 0.87 MPa, equivalent to Example 9.

[0072] Speculated reasons: Polarization treatment only affects piezoelectricity and does not affect the mechanical network; the integrity of hydrogen bonds is preserved.

[0073] Conclusion: The modified fillers enhance the mechanical properties through hydrogen bonding networks; unmodified or uncoated fillers lead to significant deterioration.

[0074] 3. Self-healing (healing efficiency): (1) Examples 7 to 9: Healing efficiency of 88% to 92%, indicating rapid self-healing ability (healing within 10 minutes).

[0075] Speculated reason: The dynamic hydrogen bond network (MXene-NH2 / BaTiO3@PDA-OH) quickly reorganizes after breaking.

[0076] (2) Comparative Example 2 (no MXene modification): Healing efficiency 65%, 9% to 29% higher than that of the embodiment.

[0077] Speculated reason: Unmodified MXene lacks -NH2 groups, the number of hydrogen bonds is reduced, and the self-healing ability is reduced.

[0078] (3) Comparative Example 3 (without BaTiO3 coating): Healing efficiency is 50%, the worst (9% to 46% compared with the examples).

[0079] Speculated reason: There is no PDA layer, no hydrogen bonding sites, and the self-healing property is almost lost.

[0080] (4) Comparative Example 4 (one-time coating of BaTiO3@PDA): The healing efficiency is 83%, which is lower than that of Example 9 (-10%).

[0081] Speculated reason: One-time coating leads to uneven distribution of PDA and slightly low hydrogen bond network efficiency.

[0082] (5) Comparative Example 5 (no polarization): The healing efficiency is 91%, which is equivalent to that of Example 9.

[0083] Speculated reason: Polarization does not affect the hydrogen bond recombination mechanism.

[0084] Conclusion: The self-healing property directly depends on the interfacial hydrogen bond network, and both modified MXene and BaTiO3@PDA are indispensable.

[0085] 4. Swelling stability (swelling rate): All groups: The swelling ratio was 290% to 325%, with small differences (<12%), indicating good hydrogel network stability.

[0086] Examples 7-9 (310%-320%): The slightly higher swelling may be due to the enhanced network hydrophilicity of the filler.

[0087] Comparative Example 3 (325%): The agglomeration of uncoated BaTiO3 may increase porosity and enhance swelling.

[0088] Comparative Example 2 (290%): The unmodified MXene has poor dispersion, dense network, and slightly low swelling.

[0089] Conclusion: The swelling rate is affected by the dispersion of the filler, but it is not a core indicator; all groups showed acceptable stability.

[0090] V. Comprehensive analysis results: (1) Coexistence of high piezoelectricity and high ductility: Examples 7 to 9 simultaneously achieve an open circuit voltage ≥ 2.65 V (piezoelectricity) and an elongation at break ≥ 420% (flexibility), overcoming the limitation of traditional piezoelectric hydrogels requiring high filler (> 15 wt%).

[0091] (2) Interface synergistic strengthening mechanism: Comparative Examples 2 to 3 demonstrate that the hydrogen bond network of modified MXene (-NH2) and BaTiO3@PDA (-OH) is the key to improving stress transfer, self-healing, and mechanical properties (e.g., the healing efficiency of Comparative Example 3 is only 50% vs. 92% of Example 9).

[0092] (3) Gradient coating design value: The piezoelectric and mechanical properties of comparative example 4 (one-time coating) are lower than those of example 9, which confirms that gradient coating (three steps) optimizes charge transfer and interface bonding.

[0093] (4) Necessity of polarization treatment: The piezoelectric performance of Example 5 collapsed (voltage 0.35 V), highlighting the decisive role of polarization in activating piezoelectricity.

[0094] (5) Control of total filler content: Examples 7 to 9 achieved the goal with low filler content, which is in line with the "low filler, high output" principle of the invention.

[0095] It should be noted that, in this document, terms such as "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements that are inherent to such process, method, article or apparatus.

[0096] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a piezoelectric composite hydrogel material, characterized in that: The following steps are involved: Polyvinyl alcohol was immersed in deionized water, and guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles were added thereto with stirring, and stirred at room temperature for 1 to 2 hours to obtain a hydrogel. The hydrogel was then frozen at -20°C for 10 to 12 hours and thawed at room temperature for 2 hours. After three freeze-thaw cycles, a composite hydrogel was obtained. The composite hydrogel was then immersed in a NaCl solution with a concentration of 0.1 mol / L. After it was fully swollen, a 3 kV / mm DC electric field polarization treatment was applied to the swollen product for 4 to 5 minutes. After completion, it was allowed to stand for 12 hours to obtain a piezoelectric composite hydrogel material.

2. The method for preparing a piezoelectric composite hydrogel material according to claim 1, wherein: The number average molecular weight Mn of the polyvinyl alcohol is 89,000 to 98,000; the alcoholysis degree of the polyvinyl alcohol is 99%; and the viscosity of the guar gum hydroxypropyltrimethylammonium chloride is ≥2,000 mPa·s.

3. The method for preparing a piezoelectric composite hydrogel material according to claim 1, wherein: The usage ratio of the polyvinyl alcohol, deionized water, guar gum hydroxypropyltrimethylammonium chloride, modified MXene nanosheets and BaTiO3@PDA core-shell particles is 1.5g:50mL:1g:0.25g:0.2-0.25g.

4. The method for preparing a piezoelectric composite hydrogel material according to claim 1, wherein: The modified MXene nanosheets are prepared by the following steps: A1. Lithium fluoride, hydrochloric acid, and deionized water were mixed and stirred for 10 to 30 minutes, and titanium aluminum carbide was added thereto. The mixture was stirred at room temperature for 5 to 10 minutes, and then centrifuged at 3500 rpm for 50 to 60 minutes. After completion, the solid component was collected by filtration and ultrasonically washed with deionized water, and then dried at room temperature for 12 hours to obtain MXene nanosheets. A2. The MXene nanosheets are then dispersed in a 50% by volume ethanol solution, KH-550 is added thereto with stirring, and the mixture is stirred at 60-80°C for 5-6 hours. After completion, the solid component is collected by centrifugation and vacuum dried to obtain modified MXene nanosheets.

5. The method for preparing a piezoelectric composite hydrogel material according to claim 4, characterized in that: The usage ratio of lithium fluoride, hydrochloric acid, deionized water, and titanium aluminum carbide in A1 is 1 g:15-20 mL:1 mL:1.0-1.2 g.

6. The method for preparing a piezoelectric composite hydrogel material according to claim 4, wherein: The usage ratio of the MXene nanosheets, 50% ethanol solution and KH-550 described in A2 is 1 g:50 mL:0.2-0.3 g.

7. The method for preparing a piezoelectric composite hydrogel material according to claim 1, characterized in that: The BaTiO3@PDA core-shell particles are prepared by the following steps: Barium titanate was dispersed in Tris-HCl buffer, and dopamine hydrochloride was added thereto with stirring three times: the first time, 20 wt% to 30 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 6 to 8 hours. The second time, 20 wt% to 30 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 6 to 8 hours. Finally, 40 wt% to 50 wt% of dopamine hydrochloride was added thereto, and after the addition was completed, the mixture was stirred at room temperature for 6 to 8 hours. After completion, the solid component was collected by centrifugation, washed three times with pure water, and then freeze-dried to obtain BaTiO3@PDA core-shell particles.

8. The method for preparing a piezoelectric composite hydrogel material according to claim 7, characterized in that: The particle size of the barium titanate is 100±10 nm.

9. The method for preparing a piezoelectric composite hydrogel material according to claim 7, characterized in that: The usage ratio of the barium titanate, Tris-HCl buffer and dopamine hydrochloride is 1g:200mL:0.5-1.0g.

10. A piezoelectric composite hydrogel material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 9.