CN110746640B - Capacitive sensor material and preparation method and application thereof - Google Patents

Abstract

The invention provides a preparation method of a capacitive sensor material, which comprises the following steps: treating wood with an acid-base solution, fully washing the wood with water, immersing the washed wood in tert-butyl alcohol to replace deionized water in the wood, freeze-drying the wood immersed in tert-butyl alcohol to obtain wood aerogel, and polymerizing the wood aerogel with an aqueous solution containing a polyelectrolyte monomer, a cross-linking agent, an initiator and a catalyst to prepare the wood aerogel; and further discloses a capacitive sensor containing the sensor material and a preparation method thereof. The sensor material prepared by the method has excellent mechanical property and ionic conductivity, and the flexible capacitive mechanical sensor further prepared has very high sensitivity and very wide sensing range.

Description

Capacitive sensor material and preparation method and application thereof

Technical Field

The invention belongs to the technical field of composite materials, and particularly relates to a capacitive sensor material as well as a preparation method and application thereof.

Background

The hydrogel, as a soft substance, is formed by an ordered three-dimensional structure, has good hydrophilicity and biocompatibility, and can effectively reduce rejection when used as a bioimplant. In addition, the hydrogel is a flexible material, has very similar properties with many active tissues of organisms such as articular cartilage, muscle tissue and the like, namely has good mechanical strength and compression resilience, and has high sensitivity and monitoring function on external stress. Therefore, the hydrogel is an ideal substitute material for soft tissues such as artificial muscles, artificial joints, artificial skin and the like, and in recent years, development of materials such as flexible skin, wearable equipment, photoelectric sensing and the like by using the hydrogel has become a research hotspot, and the hydrogel has attracted wide attention and applications in the field of biomedical materials.

Hydrogels are mainly divided into two main categories, depending on the source of the material: one is synthetic hydrogel based on petroleum source, such as polyacrylic acid and its ester hydrogel, polyvinyl alcohol hydrogel, etc. the material has high energy consumption and no environmental requirement; the second is a non-synthetic hydrogel using natural polymer as main body or starting material, such as starch-based hydrogel belonging to polysaccharide, cellulose-based hydrogel, etc., and the preparation of such hydrogel is basically environmentally friendly and degradable in starting preparation material, and has wide raw material sources, but the hydrogel is usually not high in mechanical strength and narrow in sensing stress range.

The wood is a natural renewable polymer organism, has rich hydroxyl and porous structures, unique texture structures or fiber anisotropism, high down-the-fiber tensile strength and certain chordwise and radial compression properties. Therefore, the construction of a wood-based polyelectrolyte composite force-sensitive sensing device with wide stress range and high sensitivity by utilizing the special pore structure and the fiber mechanical property of the wood fiber material and matching with the ion migration capability of the polyelectrolyte material is a huge challenge and key technology.

Disclosure of Invention

The invention aims to provide wood-based polyelectrolyte composite hydrogel with good grain tensile strength and chord-wise or radial compression resilience, a capacitive pressure sensor manufactured by using the hydrogel and a preparation method of the product.

In order to solve the above technical problem, an aspect of the present invention provides a method for preparing a capacitive sensor material, including the following steps:

s1: treating the wood with an acidic solution to obtain acid-treated wood;

s2: treating the acid-treated wood obtained in the step S1 with an alkaline solution to obtain alkali-treated wood;

s3: soaking the alkali-treated wood obtained in the step S2 in deionized water, fully washing the alkali-treated wood with the deionized water, soaking the alkali-treated wood in tert-butyl alcohol to replace the deionized water in the wood, and freeze-drying the wood soaked with the tert-butyl alcohol to obtain wood aerogel;

s4: reacting the wood aerogel obtained in the step S3 with an aqueous solution containing a polyelectrolyte monomer, a cross-linking agent, an initiator and a catalyst to prepare the wood aerogel;

further optionally, the wood is poplar or balsa wood;

more preferably, the size of the wood is (10-25 mm) × (10-25 mm) × (10-25 mm);

further, the step of S1 includes: adding wood into deionized water containing 0.005-0.01 ml glacial acetic acid and 0.005-0.01 g NaClO₂Heating the solution for 0.5-2 hours at 70-90 ℃, repeating the operation for 5-8 times, and washing with water to obtain acid-treated wood;

further, the step of S2 includes: immersing the acid-treated wood obtained in S1 in a solution containing 2 to 3 mol.L^-1NaOH and 0.2 to 0.5 mol/L^-1Na₂SO₃In the solution (A) is heated at 100 ℃ for 5-8 h, and then 2-3 mol.L at 100 DEG^{- 1}H₂O₂Heating the wood in the aqueous solution for 6-12 hours to obtain alkali-treated wood;

further, the step of S3 includes: soaking the alkali-treated wood obtained in the step S2 in deionized water, fully washing the alkali-treated wood until the pH value of the surface of the wood is neutral, then soaking the alkali-treated wood in tert-butyl alcohol to replace the deionized water in the wood, replacing the tert-butyl alcohol for 2-4 times during the soaking for 3-6 hours each time, and then freeze-drying the tert-butyl alcohol-soaked wood to obtain wood aerogel, wherein the density of the wood aerogel is 0.1-0.2 g-cm^-3；

Preferably, the density of the wood aerogel is 0.1-0.2 g-cm^-3(ii) a Preferably, the temperature of the freeze-drying is: the temperature is between 60 ℃ below zero and 40 ℃ below zero, and the vacuum degree is less than or equal to 20 Pa);

further, the polyelectrolyte monomer described in S4 is acrylic acid, 3- (1-vinyl-3-propanesulfonate imidazole) (abbreviated as VImPS) and/or 2-acrylamido-2-methyl-1-propanesulfonic acid (abbreviated as AMPS);

further optionally, when the polyelectrolyte monomer is acrylic acid, the concentration of the acrylic acid in the aqueous solution is 2.5-4 mol/L;

preferably, the aqueous solution further contains a metal ion compound;

preferably, the cross-linking agent is N, N' -methylene bisacrylamide, and the addition amount of the cross-linking agent is 0.2-0.5% of the mass fraction of the polyelectrolyte monomer; the catalyst is tetramethylethylenediamine, and the addition amount of the catalyst is 0.06-0.1% of the volume fraction of the aqueous solution; the initiator is ammonium persulfate, and the addition amount of the initiator is 0.5-1.0% of the mass fraction of the polyelectrolyte monomer; the metal ion compound is AlCl₃Or FeCl₃The addition amount of the polyelectrolyte monomer is 0.2-1.0% of the mole fraction of the polyelectrolyte monomer;

further optionally, when the polyelectrolyte monomer is 3- (1-vinyl-3-propane sulfonate imidazole) and 2-acrylamido-2-methyl-1-propane sulfonic acid, the concentration of the polyelectrolyte monomer in the aqueous solution is 1.5-3 mol/L;

preferably, the crosslinking agent is N, N' -methylene bisacrylamide, and the addition amount of the crosslinking agent is 0.2-1.0 mol% of the mole fraction of the 3- (1-vinyl-3-propane sulfonate imidazole); the catalyst is tetramethylethylenediamine, and the addition amount of the catalyst is 0.06-0.1% of the volume fraction of the aqueous solution; the initiator is ammonium persulfate, and the addition amount of the initiator is 0.15-0.5% of the mole fraction of 3- (1-vinyl-3-propane sulfonate imidazole);

in a second aspect, the invention provides a capacitive sensor material prepared by any one of the above methods.

A third aspect of the invention provides the use of any one of the capacitive sensor materials described above in the manufacture of a flexible capacitive stress sensor.

The fourth aspect of the present invention further provides a flexible capacitive stress sensor, and the preparation method of the sensor comprises the following steps:

s1: cutting any one of the capacitive sensor materials into sheets with the thickness of 1-3 mm, wherein the preferred grain direction is chord direction or radial direction, and obtaining a hydrogel dielectric layer;

s2: preparing an electrode-hydrogel dielectric layer-electrode sandwich-like structure by using the hydrogel dielectric layer obtained in the step S1 and an electrode material;

s3: and packaging the sandwich-like structure obtained in the step S2 by using polyimide film insulating gummed paper to obtain the capacitive sensor.

Further optionally, the electrode of S2 is a graphene film electrode or a foamed nickel electrode;

preferably, the preparation method of the graphene film electrode comprises the following steps: preparing 4-8 mg/mL graphene oxide suspension by using a Hummer's method, spreading the graphene oxide suspension, reducing the spread graphene oxide suspension by using 55% hydriodic acid (HI) to obtain a graphene film, then pulling an acrylic acid elastic adhesive tape (VHB 4905, 3M) to 200% of the original length of the graphene film, then adhering the graphene film to the graphene film, and loosening the adhesive tape to recover the original length to obtain a folded graphene film electrode;

preferably, the thickness of the foamed nickel electrode is 100-150 μm.

Advantageous effects

The invention has the following beneficial effects:

1. after the acid method and the alkaline method are adopted to remove the lignin and the hemicellulose in the wood, a large amount of pore structures are exposed in the obtained wood aerogel, the arrangement form of the fibers is maintained, and the obtained wood aerogel still has anisotropic and unique microscopic pore structures (as shown in figure 1).

2. The wood-based polyelectrolyte composite hydrogel (wood-based polyacrylic acid and wood-based polyamphiphatic ionic liquid composite hydrogel) prepared by the method has the advantages of tensile strength along grains and elastic resilience in chordwise or radial compression; the wood-based polyacrylic acid hydrogel prepared in example 5 and the wood-based polyamphiphonic liquid hydrogel prepared in example 8 were used as examples: the longitudinal tensile strength of the former can reach 2.30MPa, the chord-direction compressive strength and the maximum compression deformation are respectively 1.73MPa and 69.4 percent, and the radial compressive strength and the maximum compression deformation are respectively 0.60MPa and 47.0 percent; the tensile strength of the latter grain can reach 1.40MPa, the compressive strength and the maximum compression deformation in the chord direction are respectively 1.29MPa and 74.7 percent, and the compressive strength and the maximum compression deformation in the radial direction are respectively 0.39MPa and 48.8 percent.

3. The capacitive sensor material (namely the wood-based polyelectrolyte composite hydrogel) prepared by the method has excellent mechanical property and ionic conductivity, the wood-based polyacrylic acid and the wood-based polyampholyte ionic liquid composite hydrogel both have ionic conductivity, and the wood-based polyacrylic acid hydrogel prepared in example 5 and the wood-based polyampholyte ionic liquid hydrogel prepared in example 8 are taken as examples: the conductivity of the former can reach 0.016 S.m^-1The conductivity of the latter can reach 6.25 S.m^-1。

4. The flexible capacitive mechanical sensor prepared by the method has very high sensitivity and very wide sensing range. The embodiment 6-11 can reflect that the prepared capacitor has good sensitivity and good sensing effect.

Drawings

FIG. 1: scanning electron micrographs of the wood aerogel prepared in example 1: a represents a cross section; b denotes a radial section.

FIG. 2: a represents a scanning electron micrograph of the wood-based polyacrylic acid hydrogel prepared in example 5; b represents a graph of the compression properties of the wood-based polyacrylic acid hydrogel prepared in example 5; c represents the sensitivity of the wood-based polyacrylic acid hydrogel capacitive sensor prepared in example 5 (the electrode is a graphene corrugated electrode).

FIG. 3: a represents a scanning electron micrograph of the wood-based polyamphiphatic liquid hydrogel prepared in example 8; b represents a graph of the compression properties of the wood-based polyamphiphatic liquid hydrogel prepared in example 8; and c represents the sensitivity of the wood-based poly zwitterionic liquid hydrogel capacitive sensor prepared in example 8 and example 9 (the electrode is a graphene corrugated electrode).

FIG. 4: signal diagram of wood-based polyelectrolyte composite hydrogel (string slice) capacitive sensor in detecting boxing effect: a represents a signal of the wood-based polyacrylic acid hydrogel sensor during boxing; b represents the signal of wood-based poly-zwitterionic hydrogel sensor during boxing

Detailed Description

Hereinafter, embodiments of the present invention will be described in detail. The following examples are only for illustrating the technical solutions of the present invention more clearly, and therefore are only examples, and the protection scope of the present invention is not limited thereby. It is to be noted that, unless otherwise specified, technical or scientific terms used herein shall have the ordinary meaning as understood by those skilled in the art to which the invention pertains.

Example 1: preparation of wood aerogels

S1, sawing the poplar wood into 10mm × 10mm × 10mm wood blocks by a circular saw, adding the wood blocks into 325mL deionized water containing 2.5mL glacial acetic acid and 3g NaClO₂Heating at 75 deg.C for 1h, repeating the above operation for 5 times, and washing with water to obtain acid-treated wood; s2: immersing the acid-treated wood obtained in S1 in a solution containing 2.5 mol. L^-1NaOH and 0.4 mol. L^-1Na₂SO₃In the solution (2) at 100 ℃ for 5 hours, and then at 100 ℃ for 2.5 mol.L^-1H₂O₂Heating the wood in the aqueous solution for 8 hours to obtain alkali-treated wood; s3: soaking the alkali-treated wood obtained in S2 in deionized water for full water washing, then soaking in tert-butyl alcohol for full replacement of deionized water in wood blocks, and freeze-drying (temperature is-50 ℃, vacuum degree is less than or equal to 20Pa) to obtain wood aerogel, wherein the density of the wood aerogel is 0.11 g-cm^-3See figure 1.

Example 2: preparation of wood aerogels

The wood aerogel obtained in example 1 under the same preparation conditions as in example 1 except that "poplar raw wood" was replaced with "balsa raw wood", was 0.05g cm in density^-3。

Example 3: preparation of wood aerogels

The "sawing of the sapwood into 10mm × 10mm × 10mm wood blocks with a circular saw" in example 1 was changed to "sawing of the sapwood into 20mm × 20mm × 10mm wood blocks with a circular saw" in example 1". Other preparation conditions were the same as in example 1, and the obtained wood aerogel had a density of 0.21g cm^-3。

Example 4: preparation of wood aerogels

S1, sawing the poplar wood into wood blocks of 20mm × 20mm × 10mm by a circular saw machine, adding the wood blocks into 325mL deionized water containing 2.5mL glacial acetic acid and 3g NaClO₂Heating the wood to 75 ℃ for 1h, repeating the operation for 8 times, and washing the wood with water to obtain acid-treated wood; s2: immersing the acid-treated wood obtained in S1 in a solution containing 2.5 mol. L^-1NaOH and 0.4 mol. L^-1Na₂SO₃In the solution (2) at 100 ℃ for 6 hours, and then at 100 ℃ for 2.5 mol. L^-1H₂O₂Heating in water solution for 12h to obtain alkali treated wood; s3: soaking the alkali-treated wood obtained in S2 in deionized water for full water washing, then soaking in tert-butyl alcohol for full replacement of deionized water in wood blocks, and freeze-drying (temperature is minus 50 ℃, vacuum degree is less than or equal to 20Pa) to obtain wood aerogel, wherein the density of the wood aerogel is 0.12g cm^-3。

Example 5: preparation of capacitance type sensor material-wood based polyacrylic acid composite hydrogel

Preparation of a gel precursor aqueous solution: dissolving polyelectrolyte monomer, cross-linking agent, initiator, catalyst and metal ion oxide in water according to a certain proportion to obtain the product; in the gel precursor aqueous solution, the concentration of an acrylic acid monomer was 3.5mol/L, the crosslinking agent was N, N' -methylenebisacrylamide, the addition amount was 0.3 wt% (relative to acrylic acid), the catalyst was tetramethylethylenediamine, the addition amount was 0.8. mu.L/mL of the aqueous solution, the initiator was ammonium persulfate, the addition amount was 0.8 wt% (relative to acrylic acid), the metal ion was aluminum chloride, and the addition amount was 1.0 mol% (relative to acrylic acid). The density is less than or equal to 0.12g cm^-3The wood aerogel is immersed in the monomer precursor water solution, stands for 30min in vacuum, and is polymerized for 12h at 50 ℃ to obtain the wood-based polyacrylic acid composite hydrogel. The density and water content of the product were 1.1 g/cm^-3And 76%. In addition, fig. 2a is a scanning electron micrograph of the hydrogel showing its topographical features; FIG. 2b reflects the compressive properties of the hydrogel, "cross "represents a cross section; "tan" means a tangent plane; "rad" refers to a diametral section, and as summarized above, this figure illustrates that wood-based polyacrylic acid composite hydrogels have a significant layered structure with polyacrylic acid uniformly distributed in the pore structure of the wood and causing some swelling. The compressive strength and the maximum compression deformation of the cross section, the radial chord direction slice and the chord direction slice of the composite hydrogel are respectively as follows: 1.3MPa and 4.9%, 0.6MPa and 47.0% and 1.73MPa and 69.4%.

Example 6: preparation of wood-based polyacrylic acid composite hydrogel capacitive sensor

Firstly, the specific manufacturing method of the folded reduced graphene oxide film electrode comprises the following steps: the reduced graphene oxide suspension is prepared by a Hummer's method, the concentration of the suspension is adjusted to 5mg/mL, the suspension is ultrasonically crushed for 15min, the suspension is spread on a watch glass, the surface glass is dried at 50 ℃, the HI solution with the same volume of 55% is added, and the reduced graphene oxide film is obtained after reduction for 6h at room temperature. And stretching the VHB (3M 4905) to 200%, adhering the graphene film to the VHB, and loosening the VHB to recover the original length of the VHB so as to obtain the folded reduced graphene oxide film. The wood-based hydrogel of example 5 was cut into 1.5mm thick slices (chordwise and radially) as an intermediate dielectric layer, which functioned both as a separator and an electrolyte. Assembling a sensing device: and (3) forming a corrugated reduced graphene oxide film electrode on one side of the wood-based hydrogel dielectric layer, forming a non-corrugated reduced graphene oxide film electrode on the other side of the wood-based hydrogel dielectric layer, respectively leading out a copper wire from each electrode, tightly attaching the copper wires, and sealing the electrodes by using polyimide film insulating gummed paper to obtain the capacitive stress sensor with the reduced graphene electrodes at two ends and the wood-based hydrogel in the middle. Fig. 2c reflects the sensitivity of a folded graphene electrode wood-based polyacrylic acid hydrogel sensor, where "tan" represents a chord section; "rad" denotes radial section. The graph shows that the chord sensitivity is 61.5MPa^-1(in the range of 0.4 MPa), the chord sensitivity of the strain gauge is gradually reduced to 27.0MPa as the stress is increased to 1.6MPa^-1(ii) a Radial sensitivity of 58.4MPa^-1(in the range of 0.1 MPa), the radial sensitivity gradually decreases to 8.9MPa as the stress increases to 0.5MPa^-1. The tangential plane is far superior to the radial plane in both stress test range and sensitivity.

Example 7: preparation of wood-based polyacrylic acid composite hydrogel capacitive sensor

The conditions for preparing the gel and the sensor were the same as those of examples 5 and 6 except that "the acrylic acid monomer concentration was 3.5 mol/L" in example 5 was changed to "the acrylic acid monomer concentration was 3.0 mol/L", and the density and the water content of the obtained wood/polyacrylic acid gel were 1.0g cm^-378%, three-directional strength of 1.1MPa (vertical fiber direction), 0.4MPa (radial direction) and 1.3MPa (chord direction), and the chord direction sensitivity of the prepared sensor is 97MPa^-1(in the range of 0.3 MPa), gradually decreases to 26MPa with the increase of the stress^-1. It was demonstrated that the decrease in the polyacrylic acid content is advantageous for the improvement of the sensitivity. However, when the content of polyacrylic acid is increased to a certain amount, the sensitivity is not increased any more, so that the concentration of polyacrylic acid is determined to be 2.5-4 mol/L.

Example 8: preparation of wood-based poly-zwitterionic liquid composite hydrogel capacitive sensor

Preparing a polyelectrolyte monomer solution: the concentrations of VImPS and AMPS are both 2mol/L, the cross-linking agent is N, N' -methylene bisacrylamide, the addition amount is 1.0 mol% (relative to VImPS), the catalyst is tetramethylethylenediamine, the addition amount is 0.8 muL/mL monomer solution, the initiator is ammonium persulfate, and the addition amount is 0.3 mol% (relative to VImPS). The density is less than or equal to 0.12g cm^-3The wood aerogel is soaked in the monomer precursor solution, stands for 15min in vacuum, and is polymerized for 6h at 50 ℃ to obtain the wood/poly-zwitterionic liquid composite hydrogel. The sensor assembly was the same as in example 6. The density and water content of the product were 1.3g cm^-3And 42%. FIG. 3a reflects the microscopic morphology of wood-based polyamphiphatic liquid hydrogels; FIG. 3b wood-based polyamphiphatic liquid hydrogel compressibility; figure 3c wood-based polyamphiphatic liquid hydrogel sensor sensitivity (folded graphene electrode). Wherein, cross: a cross-section; tan: cutting into a string; rad: and (5) cutting the surface into a radial section. In summary, the figure illustrates that the polyampholyte does not disrupt the fibrous structure of the wood aerogel, but is uniformly distributed and encapsulated within the pore structure and on the surface of the fibers. The three-dimensional compressive strength of the composite gel is respectively as follows: 1.2MPa (perpendicular to the fibre direction), 0.4MPa (radial) and 1.3MPa (chord direction); the chord sensitivity of the sensor prepared when the cross-linking agent is 1.0 mol% is 1972MPa^-1(in the range of 0.1 MPa), gradually decreases to 132MPa as the stress increases to 1.2MPa^-1。

Example 9:

the conditions for preparing the other gels and sensors were the same as in example 8 except that "the crosslinking agent was N, N '-methylenebisacrylamide" and the amount of addition was 1.0 mol% (relative to VImPS) "in example 8 was changed to" the crosslinking agent was N, N' -methylenebisacrylamide and the amount of addition was 0.6 mol% (relative to VImPS) ", and the density and the water content of the obtained wood/polyampholyte composite hydrogel were 1.4g cm^-3And 40%, the three-dimensional strength is 0.9MPa (vertical fiber direction), 0.3MPa (radial direction) and 0.9MPa (chord direction) respectively. The chord sensitivity of the prepared sensor is 1515MPa^-1(in the range of 0.1 MPa), gradually decreases to 110MPa along with the increase of the stress^-1。

Example 10:

the wrinkled and non-wrinkled reduced graphene oxide film electrodes in the example 8 are replaced by foamed nickel electrodes (thickness 100 mu m), other gel and sensor preparation conditions are the same as those in the example 8, and the chord sensitivity of the obtained wood/poly-zwitterionic liquid composite hydrogel sensor is 902MPa^-1(in the range of 0.1 MPa), gradually decreases to 38MPa along with the increase of the stress^-1Although the sensitivity value is reduced compared with that of the graphene electrode, the sensing stability is better.

Example 11:

the corrugated and non-corrugated reduced graphene oxide thin film electrodes in the example 9 are replaced by foamed nickel electrodes (thickness 100 micrometers), other gel and sensor preparation conditions are the same as those of the example 9, and the chord-direction sensitivity of the obtained wood/poly-zwitterionic liquid composite hydrogel sensor is 446MPa^-1(in the range of 0.1 MPa), gradually decreases to 35MPa along with the increase of the stress^-1Although the sensitivity value is reduced compared with that of the graphene electrode, the sensing stability is better.

Example 12

When a boxing match is carried out, a sensor is manufactured by using the hydrogel chordwise slice of the embodiment 6 or 8 of the invention to sense the boxing intensity, and the experimental result is reflected in fig. 4, wherein fig. 4a is a signal of a wood-based polyacrylic acid hydrogel sensor during boxing action; FIG. 4b shows signals of wood-based poly (zwitterionic hydrogel) sensor in boxing. The results show that both materials can monitor the boxing action progress and the acting force magnitude in real time, but obviously, the wood-based poly-zwitterionic liquid hydrogel has higher sensitivity and better stability.

Finally, it should be noted that: the above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same; while the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some or all of the technical features may be equivalently replaced; such modifications and substitutions do not depart from the spirit and scope of the present invention, and they should be construed as being included in the following claims and description.

Claims (18)

1. A preparation method of a capacitive sensor material is characterized by comprising the following steps:

s1: treating the wood with an acidic solution to obtain acid-treated wood;

s2: treating the acid-treated wood obtained in the step S1 with an alkaline solution to obtain alkali-treated wood;

s3: soaking the alkali-treated wood obtained in the step S2 in deionized water, fully washing the alkali-treated wood with the deionized water, soaking the alkali-treated wood in tert-butyl alcohol to replace the deionized water in the wood, and freeze-drying the wood soaked with the tert-butyl alcohol to obtain wood aerogel;

s4: and (3) reacting the wood aerogel obtained in the step (S3) with an aqueous solution containing a polyelectrolyte monomer, a cross-linking agent, an initiator and a catalyst to obtain the wood aerogel.

2. The method of claim 1, wherein the step of S1 includes: adding wood into deionized water containing 0.005-0.01 ml glacial acetic acid and 0.005-0.01 g NaClO₂In the solution of (1), then in the range of 70-9Heating for 0.5-2 h at 0 ℃, then repeating the operation for 5-8 times, and washing with water to obtain the acid-treated wood.

3. The method of claim 1, wherein the step of S2 includes: immersing the acid-treated wood obtained in S1 in a solution containing 2 to 3 mol.L^-1NaOH and 0.2 to 0.5 mol/L^-1Na₂SO₃In the solution (A) is heated at 100 ℃ for 5-8H, and then 2-3 mol.L-1H is added at 100 DEG₂O₂And heating the wood in the aqueous solution for 6-12 hours to obtain the alkali-treated wood.

4. The method of claim 1, wherein the step of S3 includes: and (3) soaking the alkali-treated wood obtained in the step (S2) in deionized water, fully washing until the pH value of the surface of the wood is neutral, then soaking the wood in tert-butyl alcohol to replace the deionized water in the wood, replacing the tert-butyl alcohol for 2-4 times during the period, soaking for 3-6 hours each time, and then freeze-drying the wood soaked in the tert-butyl alcohol to obtain wood aerogel, wherein the density of the wood aerogel is 0.1-0.2 g-cm & lt-3 & gt.

5. The method according to claim 1, wherein the polyelectrolyte monomer in S4 is acrylic acid, 3- (1-vinyl-3-propanesulfonate imidazole) and/or 2-acrylamido-2-methyl-1-propanesulfonic acid.

6. The method according to claim 5, wherein in S4, when the polyelectrolyte monomer is acrylic acid, the concentration of acrylic acid in the aqueous solution is 2.5 to 4mol/L.

7. The method according to claim 6, wherein S4 further contains a metal ion compound in the aqueous solution.

8. The method according to claim 6, wherein in S4, the cross-linking agent is N, N' -methylenebisacrylamide, and the amount of the cross-linking agent added is 0.2 to 0.5% by mass of the polyelectrolyte monomer.

9. The method according to claim 6, wherein the catalyst in S4 is tetramethylethylenediamine, and the amount of the tetramethylethylenediamine added is 0.06-0.1% by volume of the aqueous solution.

10. The preparation method according to claim 6, wherein in S4, the initiator is ammonium persulfate, and the addition amount of the initiator is 0.5-1.0% of the mass fraction of the polyelectrolyte monomer.

11. The method according to claim 7, wherein in S4, the metal ion compound is AlCl₃Or FeCl₃The addition amount of the polyelectrolyte is 0.2-1.0% of the mole fraction of the polyelectrolyte monomer.

12. The method according to claim 5, wherein in S4, when the polyelectrolyte monomer is 3- (1-vinyl-3-propanesulfonate imidazole) or 2-acrylamido-2-methyl-1-propanesulfonic acid, the concentration of the polyelectrolyte monomer in the aqueous solution is 1.5 to 3 mol/L.

13. The method according to claim 12, wherein the crosslinking agent is N, N' -methylenebisacrylamide in S4 in an amount of 0.2 to 1.0 mol% based on the mole fraction of 3- (1-vinyl-3-propanesulfonate imidazole).

14. The method according to claim 12, wherein the catalyst in S4 is tetramethylethylenediamine, and the amount of the tetramethylethylenediamine added is 0.06 to 0.1% by volume based on the volume fraction of the aqueous solution.

15. The method according to claim 12, wherein in S4, the initiator is ammonium persulfate, and the addition amount thereof is 0.15-0.5% of the mole fraction of 3- (1-vinyl-3-propanesulfonate imidazole).

16. A capacitive sensor material prepared by the method of any one of claims 1 to 15.

17. Use of the capacitive sensor material of claim 16 in the manufacture of a flexible capacitive stress sensor.

18. A flexible capacitive stress sensor is characterized in that the preparation method of the sensor comprises the following steps:

s1: cutting the capacitive sensor material of claim 16 into slices with the thickness of 1-3 mm, wherein the grain direction is the chord direction or the radial direction, so as to obtain a hydrogel dielectric layer;

s2: preparing an electrode-hydrogel dielectric layer-electrode sandwich-like structure by using the hydrogel dielectric layer obtained in the step S1 and an electrode material;

s3: and packaging the sandwich-like structure obtained in the step S2 by using polyimide film insulating gummed paper to obtain the flexible capacitive stress sensor.

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