Wood sponge-based underwater micro-force sensor and its preparation method and application

Abstract

The present invention discloses a wood sponge-based underwater micro-force sensor, comprising a wood sponge and conductive sheets arranged on the upper and lower surfaces of the wood sponge, wherein the wood sponge is a micro-nano porous network structure obtained by processing wood, and the surface and pores of the micro-nano porous network structure are loaded with a super-hydrophobic coating. The present invention also provides a preparation method and application of the above-mentioned wood sponge-based underwater micro-force sensor. The preparation method of the wood sponge-based underwater micro-force sensor provided by the present invention is simple to operate, has low material cost, does not require packaging, utilizes the underwater liquid-gas interface for electrical signal response, does not require the wood sponge to be loaded with a conductive coating, and has low preparation cost. The anisotropic structure of the wood sponge can give the material higher sensitivity and a wider range of water depth application, providing ideas for the high-value utilization of wood in the field of underwater sensing.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular relates to a wood-based sensor and a preparation method and application thereof. Background Art

[0002] As land resources become increasingly scarce, people have gradually turned their attention to the development and utilization of marine resources. However, due to the complex and changeable underwater environment and inconvenient communication conditions, traditional monitoring methods are no longer applicable to the field of marine exploration. Therefore, the underwater monitoring system based on flexible stress sensors has played a great role, effectively expanding the monitoring range and improving the real-time nature of data. It is of great significance in the development and utilization of water resources, prevention and control of water pollution, and marine scientific research.

[0003] Flexible stress sensors typically require encapsulation for underwater use, but this inevitably reduces their sensitivity. For example, while they can detect pressure changes as low as 0.005 Pa in air, the most advanced underwater piezoelectric sensors can only detect pressure changes as small as 10 Pa. Existing flexible stress sensors also suffer from high prices. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies and defects mentioned in the above background technology and provide a low-cost wood sponge-based underwater micro-force sensor that does not require packaging, as well as a preparation method and application thereof.

[0005] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0006] A wood sponge-based underwater micro-force sensor comprises a wood sponge and conductive sheets arranged on the upper and lower surfaces of the wood sponge. The wood sponge is a micro-nano porous network structure obtained by processing wood, and the surface and pores of the micro-nano porous network structure are loaded with a super-hydrophobic coating.

[0007] The wood sponge-based underwater micro-force sensor of the present invention does not require packaging or loading of conductive agents. It uses the conductivity of water to establish a current path and the movement of the underwater liquid-gas interface to transmit electrical signals (air stored in the micro-nano porous network structure), which is completely different from existing conventional stress sensors.

[0008] As a general technical concept, the present invention also provides a method for preparing the above-mentioned wood sponge-based underwater micro-force sensor, comprising the following steps:

[0009] (1) delignifying and delignifying wood to obtain delignified wood;

[0010] (2) converting the delignified wood obtained in step (1) into a wood sponge by TEMPO oxidation treatment;

[0011] (3) subjecting the wood sponge obtained in step (2) to a superhydrophobic modification treatment to obtain a superhydrophobic modified wood sponge;

[0012] (4) Using silver glue, one end of the two copper foils is respectively pasted on the upper and lower surfaces of the super-hydrophobic wood sponge obtained in step (3), thereby obtaining a wood sponge-based underwater micro-force sensor.

[0013] In the above-mentioned preparation method, preferably, the wood sponge obtained in step (2) is again subjected to TEMPO oxidation treatment, grinding and shearing dispersion to obtain a cellulose nanofiber dispersion liquid; the wood sponge obtained in step (2) is then impregnated into the above-mentioned cellulose nanofiber dispersion liquid, and after vacuum impregnation, freeze-dried, and then steps (3) and (4) are performed. The above-mentioned steps can be used to modify the pore structure inside the wood sponge, extend the underwater triple-phase line length for the subsequent super-hydrophobic wood sponge, improve anti-infiltration properties, and act together with the subsequent super-hydrophobic coating, so that the super-hydrophobic effect is better. In addition, the cellulose nanofiber dispersion liquid of the present invention is derived from the wood sponge and is again subjected to TEMPO oxidation treatment, grinding and shearing dispersion, and the cellulose nanofiber dispersion liquid and the wood sponge to be loaded have homology, and the modification effect is better.

[0014] In above-mentioned preparation method, preferably, nano silicon is added in described cellulose nanofiber dispersion liquid, and through ultrasonic dispersion treatment, described nano silicon is 0.1-0.3wt% in mass concentration in cellulose nanofiber dispersion liquid.After nano silicon is dispersed in cellulose nanofiber dispersion liquid, it is conducive to the uniform load of nano silicon. Add nano silicon, on the one hand can improve hydrophobicity, on the other hand provide in situ growth site when being conducive to subsequent super-hydrophobic coating load, improve coating load effect. Meanwhile, in order to ensure that each material is evenly dispersed in cellulose nanofiber dispersion liquid, dispersant can also be added, and specific dispersant kind can be unlimited. Nano silicon addition is too much, can cause dispersibility to be bad, and addition is too little, and its effect is limited.

[0015] In the above preparation method, preferably, when the wood sponge obtained in step (2) is impregnated into the cellulose nanofiber dispersion for vacuum impregnation, the impregnation time is 5-15 minutes, and the concentration of the cellulose nanofiber dispersion is 0.3-0.7 mg / mL. Continuous stirring can be performed during vacuum impregnation. The concentration of the above cellulose nanofiber dispersion needs to be reasonably controlled. If the amount used is too small, the modification effect on the interior of the wood sponge will be poor, and the hydrophobicity of the wood sponge will be affected. If the amount used is too large, the pore structure inside the wood sponge will be too few or too small, which will affect the use of the sensor.

[0016] In the above preparation method, preferably, when the wood sponge is subjected to TEMPO oxidation treatment again, the oxidation treatment conditions in step (2) are repeated until the delignified wood tends to be dispersed; the grinding and shearing dispersion is performed by using a disc grinder to shear it so that it is dispersed into a cellulose nanofiber dispersion liquid, and the rotation speed of the disc grinder is 1500-2000 rpm, and it is repeated multiple times, such as 3 times.

[0017] In the above preparation method, preferably, step (1) includes the following steps: immersing the wood in a mixed aqueous solution of sodium hydroxide and sodium sulfite and boiling it, then immersing it in a hydrogen peroxide solution, heating it in a water bath, taking it out and washing it, and freeze-drying it to obtain delignified wood; controlling the concentration of sodium hydroxide to 2-3 mol / L, the concentration of sodium sulfite to 0.2-0.5 mol / L, the boiling time to 1-3 hours, the concentration of the hydrogen peroxide solution to 2-3 mol / L, the heating temperature of the water bath to 70-80°C, and the freeze-drying conditions to freeze it at -50 to -40°C for 10-14 hours, and then vacuum drying it for 45-50 hours.

[0018] In the above preparation method, preferably, the oxidizing solution during TEMPO oxidation treatment is a sodium phosphate aqueous solution, and the pH value of the sodium phosphate aqueous solution is adjusted to 6.5-7.0 using acetic acid. TEMPO and sodium chlorite are added to the sodium phosphate aqueous solution, and the concentration of TEMPO is controlled to be 0.1-0.3 mol / L, and the concentration of sodium chlorite is 0.1-0.2 mol / L. At the same time, a mixed aqueous solution of sodium hypochlorite and sodium acetate is added to the sodium phosphate aqueous solution, and the volume ratio of the mixed aqueous solution of sodium hypochlorite and sodium acetate to the sodium phosphate aqueous solution is 1:8-12. In the mixed aqueous solution of sodium hypochlorite and sodium acetate, the concentration of sodium hypochlorite is 0.1-0.2 mol / L, and the concentration of sodium acetate is 0.1-0.3 mol / L. After the mixed aqueous solution of sodium hypochlorite and sodium acetate and the sodium phosphate aqueous solution are mixed, they are placed at room temperature in the dark for 10-14 hours.

[0019] In the above preparation method, preferably, during the TEMPO oxidation treatment, the reaction temperature is controlled to be 60° C., the reaction time is 48 h, and after the reaction is completed, freeze drying and then vacuum drying are performed. The freeze drying is performed by freezing at -50° C. for 12 h and then vacuum drying for 48 h.

[0020] In the above preparation method, preferably, when the wood sponge is subjected to super-hydrophobic modification treatment in step (3), the wood sponge is immersed in a n-hexane solution of silica and PDMS, vacuum impregnated, and taken out and dried to obtain a super-hydrophobic modified wood sponge; the mass concentration of PDMS in the n-hexane solution is 1.2-1.8wt%, the mass concentration of silica in the n-hexane solution is 0.4-0.6wt%, the immersion time during vacuum impregnation is 5-15min, and the drying temperature during drying is 70-90°C.

[0021] In the above preparation method, preferably, the copper foil is adhered to the upper and lower radial sections of the superhydrophobic wood sponge using silver glue.

[0022] In the above preparation method, preferably, the width of the copper foil can be 1 cm, the length is not less than the water depth where the sensor is located, and the wood is balsa wood (light wood).

[0023] As a general technical concept, the present invention also provides an application of a wood-sponge-based underwater micro-force sensor for real-time underwater monitoring. This wood-sponge-based underwater micro-force sensor is applicable to ocean exploration, effectively expanding the monitoring range and improving the real-time nature of data. It holds significant significance in water resource development and utilization, water pollution prevention and control, and marine science research.

[0024] More specifically, the method for preparing the wood sponge-based underwater micro-force sensor of the present invention may include the following steps:

[0025] (1) The wood is immersed in a mixed aqueous solution of sodium hydroxide and sodium sulfite and boiled. After sufficient reaction, the wood is washed in water until neutral;

[0026] (2) immersing the wood treated in step (1) in a hydrogen peroxide solution, heating it in a water bath, taking it out, washing it, and freeze-drying it to obtain delignified wood;

[0027] (3) preparing a sodium phosphate aqueous solution with a pH value of 6.5-7.0, adding a mixed aqueous solution of TEMPO, sodium sulfite, sodium hypochlorite and sodium acetate to the solution, mixing and then allowing to stand;

[0028] (4) placing the delignified wood prepared in step (2) into the mixed solution prepared in step (3) to undergo a full oxidation reaction;

[0029] (5) taking out the delignified wood after the reaction in step (4) and immersing it in ethanol, then washing it until it is neutral, taking it out and freeze-drying it to obtain a wood cellulose matrix;

[0030] (6) placing the delignified wood after the oxidation reaction in step (4) into the mixed solution prepared in step (3) again for further reaction until the wood cellulose tends to decompose, taking it out and washing it to neutrality to obtain a fiber aggregate;

[0031] (7) immersing the fiber aggregate prepared in step (6) in deionized water and shearing it using a disc grinder to disperse it into a cellulose nanofiber dispersion (nanosilica may be optionally added thereto);

[0032] (8) impregnating the wood cellulose matrix obtained in step (5) in the cellulose nanofiber dispersion prepared in step (7), vacuum impregnating, and then taking out and freeze-drying to obtain a wood sponge;

[0033] (9) immersing the wood sponge obtained in step (8) in a n-hexane solution of silica and PDMS, vacuum impregnating, taking out and drying to obtain a superhydrophobic modified wood sponge;

[0034] (10) Using silver glue, one end of the two copper foils is respectively pasted on the upper and lower surfaces of the superhydrophobic modified wood sponge obtained in step (9) to obtain a wood sponge-based underwater micro-force sensor.

[0035] Wood, a natural, renewable resource, has become a popular biomass material due to its excellent strength-to-weight ratio, favorable environmental profile, and processability. Using wood as a substrate for flexible stress sensors offers promising application prospects due to its low cost. However, wood's insulating properties mean its use in sensors typically requires impregnation with conductive nanomaterials such as graphene, MXene, and carbon nanotubes to create a conductive network. The preparation of these conductive nanomaterials is complex and costly. Furthermore, the liquid-air interface of the wood-based superhydrophobic structure is susceptible to failure under high hydrostatic pressure, limiting the depth range of underwater applications for wood-based flexible stress sensors.

[0036] Based on this, the present invention uses low-cost wood as the substrate for the flexible stress sensor. The elastic wood sponge obtained through structural and component manipulation has anisotropic mechanical properties. After superhydrophobic treatment, it can withstand high hydrostatic pressure. The large number of micro- and nano-scale pores inside provide space for air capture and storage, providing a structural foundation to prevent air escape under high hydrostatic pressure. The nanocellulose loaded on the cell wall surface can further improve the material's resistance to infiltration by increasing the length of the three-phase line. Therefore, the improved wood of the present invention has unique structural and mechanical characteristics for underwater micro-force sensing.

[0037] Specifically, in the present invention, sodium hydroxide, sodium sulfite and hydrogen peroxide can remove lignin and hemicellulose in wood, and make the wood into delignified wood; during TEMPO oxidation treatment, a mixed aqueous solution of sodium phosphate to which a mixed aqueous solution of TEMPO, sodium sulfite, sodium hypochlorite and sodium acetate is added can separate the cell wall into a microfibril nanonetwork structure through the electrostatic repulsion between carboxyl groups, and make the delignified wood into a highly elastic wood cellulose matrix with good support; the highly elastic wood cellulose matrix can be prepared into a cellulose nanofiber dispersion by further TEMPO oxidation, grinding and shear dispersion; when the wood cellulose matrix and the cellulose nanofiber dispersion are mixed and impregnated, the cellulose nanofibers can construct a wood cellulose network in the wood cellulose matrix, modify the interior of the wood cellulose matrix, extend the underwater triple-phase line length for the subsequent super-hydrophobic wood sponge, and improve the anti-infiltration property; in the preferred embodiment, nano-silica is also added to the cellulose nanofiber dispersion, which can improve the hydrophobic effect on the one hand, and is beneficial to the loading of the subsequent hydrophobic coating on the other hand, serving as a precursor substance of the hydrophobic coating to improve the hydrophobic effect. Finally, through a superhydrophobic modification process, PDMS and silica, acting as surface modifiers for the wood sponge sensor material, are evenly dispersed on the surface of the sensor material, thereby reducing the surface energy and creating a superhydrophobic surface. This superhydrophobic strategy eliminates the need for encapsulation of the sensor material and allows it to retain air underwater. After this treatment, the wood sponge has a large internal micron- and nanometer-scale pore structure, providing space for capturing and storing air. Furthermore, the wood sponge's superhydrophobic structure is highly resistant to infiltration. When placed underwater, the air within it cannot escape. The underwater air layer acts as a pneumatic spring, ultrasensitively capturing micro-force changes such as micro-vibrations, giving the sensor material ultrahigh spatial resolution.

[0038] Compared with the prior art, the advantages of the present invention are:

[0039] 1. The wood sponge-based sensing material of the present invention is different from conventional stress sensors. It does not require conductive nanomaterial loading or packaging. It changes the underwater current propagation path, uses the conductivity of water to establish a current path, and uses the movement of the underwater liquid-gas interface to transmit electrical signals. The air layer stored in the wood sponge acts as a pneumatic spring to ultra-sensitively capture micro-force changes, giving the sensing material ultra-high spatial resolution. The overall advantages are simple preparation process, low cost, and high sensitivity.

[0040] 2. The present invention utilizes the anisotropic structure and micrometer- and nanometer-scale pore structure of wood sponge to improve the stability of the liquid-gas interface of the sensing material, enabling its underwater air layer to exist stably and not easily fail under high hydrostatic pressure. This creates conditions for achieving high-sensitivity and stable underwater sensing, and increases the application depth range of underwater superhydrophobic mechanical sensing materials from 1.8m to 8m.

[0041] 3. The present invention transforms wood into an underwater micro-force sensor that does not require conductive treatment through modification, which greatly improves the use value of wood, broadens the application range of wood, and provides support for the monitoring and exploration of marine resources.

[0042] Overall, the method for preparing a wood sponge-based underwater micro-force sensor provided by this invention is simple to operate, has low material costs, and requires no packaging. It utilizes the underwater liquid-air interface for electrical signal response, eliminating the need for a conductive coating on the wood sponge and resulting in low production costs. The anisotropic structure of the wood sponge imparts high sensitivity and a wide range of water depth applicability, providing insights into the high-value utilization of wood in underwater sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0044] Figure 1 This is a comparison chart of the Fourier infrared transmittance of balsa wood, wood sponge and superhydrophobic wood sponge in Example 2.

[0045] Figure 2 This is a graph of 100 repeated compression stresses of the superhydrophobic wood sponge prepared in Example 2.

[0046] Figure 3 Compression-release photos of the superhydrophobic wood sponge prepared in Example 2 (from left to right: before compression, during compression, and after compression).

[0047] Figure 4 This is a comparison diagram of the contact angles of the superhydrophobic wood sponges prepared in Example 1, Example 2, and Example 3.

[0048] Figure 5 This is a photo of the underwater sensing application of the wood sponge-based underwater micro-force sensor prepared in Example 1.

[0049] Figure 6 This is a diagram showing the change in water level sensing resistance of the wood sponge-based underwater micro-force sensor prepared in Example 1.

[0050] Figure 7 This is a graph showing the underwater micro-vibration induced resistance change of the wood sponge-based underwater micro-force sensor prepared in Example 1.

[0051] Figure 8 This is a resistance response signal diagram of the wood sponge-based underwater micro-force sensor prepared in Example 1 for different underwater micro-vibrations. DETAILED DESCRIPTION

[0052] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0053] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0054] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0055] Example 1:

[0056] A method for preparing a wood sponge-based underwater micro-force sensor comprises the following steps:

[0057] (1) Preparation of delignified wood:

[0058] Use a bandsaw to slice balsa wood into 12 mm slices, and remove any surface saw marks with a blade. Cut balsa wood into 10 × 10 × 10 mm cubes along the cross-section parallel to the wood rays. Rinse the balsa wood blocks with deionized water and allow them to air dry in a well-ventilated environment. Use an alkaline solution delignification method with a 2.5 mol / L sodium hydroxide and 0.4 mol / L sodium sulfite aqueous solution. Immerse the balsa wood blocks in this solution and boil for 48 hours to remove lignin and hemicellulose. After partially removing the lignin and hemicellulose, rinse the blocks several times in deionized water to remove any internal chemicals. Then, immerse them in a 2.5 mol / L hydrogen peroxide solution and boil at 75°C for 2 hours to further remove the lignin and hemicellulose. Repeatedly rinse to remove any residual chemicals and reagents. After removing the lignin and hemicellulose, place the blocks in a freeze dryer's cold trap at -50°C for 12 hours. After taking it out, it is quickly placed in the upper layer of the freeze dryer and vacuum dried for 48 hours to obtain delignified wood.

[0059] (2) Preparation of highly elastic wood cellulose matrix and wood sponge:

[0060] Prepare 2 L of a 0.1 mol / L sodium phosphate aqueous solution and add acetic acid dropwise to adjust the pH of the sodium phosphate aqueous solution to 6.8. Add 0.2 mol / L TEMPO and 0.125 mol / L sodium chlorite to the sodium phosphate aqueous solution. Prepare 200 mL of a mixed aqueous solution of sodium hypochlorite and sodium acetate (0.1 mol / L sodium hypochlorite and 0.2 mol / L sodium acetate). Add this 200 mL of the mixed aqueous solution of sodium hypochlorite and sodium acetate to the sodium phosphate aqueous solution containing TEMPO and sodium chlorite. The mixed solution is allowed to stand at room temperature, protected from light, for 12 hours. Delignified wood is immersed in the mixed solution at 60°C for 48 hours. The wood is then removed and immersed in ethanol, washed until neutral, and placed in a freeze dryer cold trap at -50°C for 12 hours. After removal, the wood is quickly placed in the upper layer of the freeze dryer and vacuum dried for 48 hours to obtain a wood fiber cellulose matrix.

[0061] The wood cellulose matrix was further TEMPO-oxidized and then ground and sheared to obtain a cellulose nanofiber dispersion with a concentration of 0.4 mg / mL. The wood cellulose matrix was then immersed in the cellulose nanofiber dispersion and vacuum-impregnated for 10 minutes. The matrix was then removed and placed in a freeze dryer cold trap at -50°C for 12 hours. The wood sponge was then quickly placed in the upper layer of the freeze dryer and vacuum-dried for 48 hours.

[0062] (3) Construction of super-hydrophobic surface of wood sponge:

[0063] Weigh 1.5g of PDMS and 0.5g of silica, dissolve them in 100g of n-hexane, and stir thoroughly. Immerse a wood sponge sample in the prepared silica / PDMS n-hexane solution and place it in a vacuum apparatus for vacuum impregnation to ensure that the wood sponge is fully loaded with silica and PDMS. After soaking in the mixed solution for 10 minutes, remove the sample, gently squeeze to remove excess solution, and then dry it in a forced air drying oven at 80°C to obtain a superhydrophobic wood sponge.

[0064] (4) Assembly of underwater micro-force sensor:

[0065] Conductive silver paint was evenly applied to both radially cut surfaces of the conductive wood sponge. 1cm-wide strips of high-purity copper foil were attached to each end to reduce the effects of resistance. The ends of the copper foil were connected to the source-meter probes. For securement, the device connecting to the sample was affixed to a glass slide to minimize data fluctuations caused by sample movement during testing.

[0066] Example 2:

[0067] A method for preparing a wood sponge-based underwater micro-force sensor comprises the following steps:

[0068] (1) Preparation of delignified wood:

[0069] Use a bandsaw to slice balsa wood into 12 mm slices, and remove any surface saw marks with a blade. Cut balsa wood into 10 × 10 × 10 mm cubes along the cross-section parallel to the wood rays. Rinse the balsa wood blocks with deionized water and allow them to air dry in a well-ventilated environment. Use an alkaline solution delignification method with a 2.5 mol / L sodium hydroxide and 0.4 mol / L sodium sulfite aqueous solution. Immerse the balsa wood blocks in this solution and boil for 48 hours to remove lignin and hemicellulose. After partially removing the lignin and hemicellulose, rinse the blocks several times in deionized water to remove any internal chemicals. Then, immerse them in a 2.5 mol / L hydrogen peroxide solution and boil at 75°C for 2 hours to further remove the lignin and hemicellulose. Repeatedly rinse to remove any residual chemicals and reagents. After delignification and hemicellulose removal, place the blocks in a freeze dryer's cold trap at -50°C for 12 hours. After taking it out, it is quickly placed in the upper layer of the freeze dryer and vacuum dried for 48 hours to obtain delignified wood.

[0070] (2) Preparation of highly elastic wood cellulose matrix and wood sponge:

[0071] Prepare 2 L of a 0.1 mol / L sodium phosphate aqueous solution and add acetic acid dropwise to adjust the pH of the sodium phosphate aqueous solution to 6.8. Add 0.2 mol / L TEMPO and 0.125 mol / L sodium chlorite to the sodium phosphate aqueous solution. Prepare 200 mL of a mixed aqueous solution of sodium hypochlorite and sodium acetate (0.1 mol / L sodium hypochlorite and 0.2 mol / L sodium acetate). Add this 200 mL of the mixed aqueous solution of sodium hypochlorite and sodium acetate to the sodium phosphate aqueous solution containing TEMPO and sodium chlorite. The mixed solution is allowed to stand at room temperature, protected from light, for 12 hours. Delignified wood is immersed in the mixed solution at 60°C for 48 hours. The wood is then removed and immersed in ethanol, washed until neutral, and placed in a freeze dryer cold trap at -50°C for 12 hours. After removal, the wood is quickly placed in the upper layer of the freeze dryer and vacuum dried for 48 hours to obtain a wood fiber cellulose matrix.

[0072] The wood cellulose matrix was subjected to TEMPO oxidation treatment, followed by grinding and shear dispersion to obtain a cellulose nanofiber dispersion with a concentration of 0.4 mg / mL. Nanosilica was then added to the cellulose nanofiber dispersion and ultrasonically dispersed to a nanosilica concentration of 0.2 wt%. The wood cellulose matrix was then immersed in the cellulose nanofiber dispersion and vacuum-impregnated for 10 minutes. The matrix was then removed and placed in a freeze dryer cold trap at -50°C for 12 hours. The wood sponge was then quickly placed on the upper layer of the freeze dryer and vacuum-dried for 48 hours to obtain the wood sponge.

[0073] (3) Construction of super-hydrophobic surface of wood sponge:

[0074] Weigh 1.5g of PDMS and 0.5g of silica, dissolve them in 100g of n-hexane, and stir thoroughly. Immerse a wood sponge sample in the prepared silica / PDMS n-hexane solution and place it in a vacuum apparatus for vacuum impregnation to ensure that the wood sponge is fully loaded with silica and PDMS. After soaking in the mixed solution for 10 minutes, remove the sample, gently squeeze to remove excess solution, and then dry it in a forced air drying oven at 80°C to obtain a superhydrophobic wood sponge.

[0075] (4) Assembly of underwater micro-force sensor:

[0076] Conductive silver paint was evenly applied to both radially cut surfaces of the conductive wood sponge. 1cm-wide strips of high-purity copper foil were attached to each end to reduce the effects of resistance. The ends of the copper foil were connected to the source-meter probes. For securement, the device connecting to the sample was affixed to a glass slide to minimize data fluctuations caused by sample movement during testing.

[0077] The Fourier infrared transmittance comparison of balsa wood, wood sponge and super hydrophobic wood sponge in this embodiment is shown in the figure below. Figure 1 As shown in the figure, it can be seen that wood and hemicellulose are successfully removed, and silica and PDMS are successfully loaded.

[0078] The 100-times repeated compression stress diagram of the super-hydrophobic wood sponge prepared in this embodiment is shown in FIG. Figure 2 The results show that the wood sponge can still show good high recovery ability after repeated compression, and has excellent fatigue resistance when used for sensing. The compression-release photos of the super hydrophobic wood sponge prepared in this example are shown in FIG. Figure 3 As shown in the figure, it can be seen that the wood sponge can recover to its pre-compression shape after compression.

[0079] Example 3:

[0080] A method for preparing a wood sponge-based underwater micro-force sensor comprises the following steps:

[0081] (1) Preparation of delignified wood:

[0082] Use a bandsaw to slice balsa wood into 12 mm slices, and remove any surface saw marks with a blade. Cut balsa wood into 10 × 10 × 10 mm cubes along the cross-section parallel to the wood rays. Rinse the balsa wood blocks with deionized water and allow them to air dry in a well-ventilated environment. Use an alkaline solution delignification method with a 2.5 mol / L sodium hydroxide and 0.4 mol / L sodium sulfite aqueous solution. Immerse the balsa wood blocks in this solution and boil for 48 hours to remove lignin and hemicellulose. After partially removing the lignin and hemicellulose, rinse the blocks several times in deionized water to remove any internal chemicals. Then, immerse them in a 2.5 mol / L hydrogen peroxide solution and boil at 75°C for 2 hours to further remove the lignin and hemicellulose. Repeatedly rinse to remove any residual chemicals and reagents. After delignification and hemicellulose removal, place the blocks in a freeze dryer's cold trap at -50°C for 12 hours. After taking it out, it is quickly placed in the upper layer of the freeze dryer and vacuum dried for 48 hours to obtain delignified wood.

[0083] (2) Preparation of wood sponge:

[0084] Prepare 2 L of a 0.1 mol / L sodium phosphate aqueous solution and add acetic acid dropwise to adjust the pH to 6.8. Add 0.2 mol / L TEMPO and 0.125 mol / L sodium chlorite to the sodium phosphate aqueous solution. Prepare 200 mL of a mixed aqueous solution of sodium hypochlorite and sodium acetate (0.1 mol / L sodium hypochlorite and 0.2 mol / L sodium acetate). Add this 200 mL of the mixed aqueous solution of sodium hypochlorite and sodium acetate to the sodium phosphate aqueous solution containing TEMPO and sodium chlorite. Incubate the mixture at room temperature in the dark for 12 hours. Immerse delignified wood in the mixed solution at 60°C for 48 hours, remove it, immerse it in ethanol, wash it until neutral, remove it, and freeze it in a freeze dryer at -50°C for 12 hours. Remove it and quickly place it in the upper layer of the freeze dryer. Vacuum dry it for 48 hours to obtain a wood sponge.

[0085] (3) Construction of super-hydrophobic surface of wood sponge:

[0086] Weigh 1.5g of PDMS and 0.5g of silica, dissolve them in 100g of n-hexane, and stir thoroughly. Immerse a wood sponge sample in the prepared silica / PDMS n-hexane solution and place it in a vacuum apparatus for vacuum impregnation to ensure that the wood sponge is fully loaded with silica and PDMS. After soaking in the mixed solution for 10 minutes, remove the sample, gently squeeze to remove excess solution, and then dry it in a forced air drying oven at 80°C to obtain a superhydrophobic wood sponge.

[0087] (4) Assembly of underwater micro-force sensor:

[0088] Conductive silver paint was evenly applied to both radially cut surfaces of the conductive wood sponge. 1cm-wide strips of high-purity copper foil were attached to each end to reduce the effects of resistance. The ends of the copper foil were connected to the source-meter probes. For securement, the device connecting to the sample was affixed to a glass slide to minimize data fluctuations caused by sample movement during testing.

[0089] The contact angle test was performed on the super-hydrophobic wood sponges prepared in Example 1, Example 2, and Example 3. The results are as follows: Figure 4 As shown in the figure, it can be seen that the contact angles of Example 1 and Example 2 are significantly larger. In Example 2, the cellulose nanofiber dispersion containing nano-silica is used for impregnation, and the contact angle is larger and the hydrophobicity is better.

[0090] The underwater sensing application photo of the wood sponge-based underwater micro-force sensor prepared in Example 1 is as follows: Figure 5 As shown, the application status of the wood sponge-based underwater micro-force sensor is demonstrated. The hydrophobicity of the wood sponge makes it have an obvious silver mirror phenomenon underwater, indicating that the air layer around the wood sponge exists stably underwater.

[0091] Using silver glue, attach one end of two 1-cm-wide copper foil strips to the top and bottom surfaces of the superhydrophobic wood sponge sensor material. Connect the device to a digital source meter. The digital source meter outputs a constant voltage of 2V and records the resistance curve of the sensor device.

[0092] The water level sensing resistance change diagram of the wood sponge-based underwater micro-force sensor prepared in Example 1 is as follows: Figure 6 As shown in the figure, the wood sponge-based underwater micro-force sensor is placed in a sealed water container, and then pressurized by a pressurizing device to simulate a water depth of 0 to 8 meters by adding hydraulic pressure. As can be seen from the figure, the wood sponge-based underwater micro-force sensor can accurately monitor the water level within a wide water pressure range of 0-8m.

[0093] The underwater micro-vibration induced resistance change diagram of the wood sponge-based underwater micro-force sensor prepared in Example 1 is as follows: Figure 7 As shown in the figure, the wood sponge-based underwater micro-force sensor is placed in a sealed water container, which is then placed on a table. A heavy object is used to hit the table, and the table transmits the vibration to the container, simulating underwater micro-vibration. As can be seen from the figure, the wood sponge-based underwater micro-force sensor is repeatable and stable for monitoring underwater micro-vibration.

[0094] The resistance response signal diagram of the wood sponge-based underwater micro-force sensor prepared in Example 1 for different underwater micro-vibrations. Figure 8 (b)), knocking on the container wall ( Figure 8 (c)), ultrasonic vibration ( Figure 8 (d) in the middle), blowing ( Figure 8 (e)), stirring ( Figure 8 The wood sponge-based underwater micro-force sensor shows different resistance response signals, indicating that it has the accuracy to sense underwater micro-vibration.

Claims

1. A method for preparing a wood sponge-based underwater micro-force sensor, characterized in that: The wood sponge-based underwater micro-force sensor includes a wood sponge and conductive sheets arranged on the upper and lower surfaces of the wood sponge. The wood sponge is a micro-nano porous network structure obtained by processing wood, and the surface and pores of the micro-nano porous network structure are loaded with a superhydrophobic coating; The preparation method comprises the following steps: (1) delignifying and delignifying the wood to obtain delignified wood; (2) converting the delignified wood obtained in step (1) into a wood sponge through TEMPO oxidation treatment; (3) subjecting the wood sponge obtained in step (2) to superhydrophobic modification to obtain a superhydrophobic modified wood sponge; (4) Using silver glue, one end of the two copper foils is respectively pasted on the upper and lower surfaces of the super-hydrophobic wood sponge obtained in step (3), thereby obtaining a wood sponge-based underwater micro-force sensor; The oxidizing solution during TEMPO oxidation treatment is a sodium phosphate aqueous solution, and acetic acid is used to adjust the pH value of the sodium phosphate aqueous solution to 6.5-7.

0. TEMPO and sodium chlorite are added to the sodium phosphate aqueous solution, and the concentration of TEMPO is controlled to be 0.1-0.3 mol / L, and the concentration of sodium chlorite is controlled to be 0.1-0.2 mol / L. At the same time, a mixed aqueous solution of sodium hypochlorite and sodium acetate is added to the sodium phosphate aqueous solution, and the volume ratio of the mixed aqueous solution of sodium hypochlorite and sodium acetate to the sodium phosphate aqueous solution is 1:8-12. In the mixed aqueous solution of sodium hypochlorite and sodium acetate, the concentration of sodium hypochlorite is 0.1-0.2 mol / L, and the concentration of sodium acetate is 0.1-0.3 mol / L. After the mixed aqueous solution of sodium hypochlorite and sodium acetate and the sodium phosphate aqueous solution are mixed, they are placed at room temperature in the dark for 10-14 hours.

2. The preparation method according to claim 1, characterized in that The wood sponge obtained in step (2) is subjected to TEMPO oxidation treatment again, and then ground and sheared to disperse to obtain a cellulose nanofiber dispersion; The wood sponge obtained in step (2) is then impregnated into the above-mentioned cellulose nanofiber dispersion, vacuum impregnated, freeze-dried, and then steps (3) and (4) are carried out.

3. The preparation method according to claim 2, characterized in that Nano-silicon dioxide is added to the cellulose nanofiber dispersion and is subjected to ultrasonic dispersion treatment. The mass concentration of the nano-silicon dioxide in the cellulose nanofiber dispersion is 0.1-0.3 wt %.

4. The preparation method according to claim 2, characterized in that When the wood sponge obtained in step (2) is impregnated into the cellulose nanofiber dispersion by vacuum impregnation, the impregnation time is 5-15 minutes, and the concentration of the cellulose nanofiber dispersion is 0.3-0.7 mg / mL.

5. The preparation method according to claim 1, characterized in that When the wood sponge is subjected to TEMPO oxidation treatment again, the oxidation treatment conditions in step (2) are repeated until the delignified wood tends to be dispersed; the grinding and shearing dispersion is performed by using a disc grinder to shear it so that it is dispersed into a cellulose nanofiber dispersion liquid, and the rotation speed of the disc grinder is 1500-2000 rpm, which is repeated multiple times.

6. The preparation method according to claim 1, characterized in that Step (1) comprises the following steps: immersing the wood in a mixed aqueous solution of sodium hydroxide and sodium sulfite and boiling it, then immersing it in a hydrogen peroxide solution, heating it in a water bath, taking it out and washing it, and freeze-drying it to obtain delignified wood; controlling the concentration of sodium hydroxide to be 2-3 mol / L, the concentration of sodium sulfite to be 0.2-0.5 mol / L, the boiling time to be 1-3 hours, the concentration of the hydrogen peroxide solution to be 2-3 mol / L, the heating temperature of the water bath to be 70-80°C, and the freeze-drying conditions to be freezing at -50~-40°C for 10-14 hours, and then vacuum drying for 45-50 hours.

7. The preparation method according to claim 1, characterized in that In step (3), when the wood sponge is subjected to super-hydrophobic modification, the wood sponge is immersed in a n-hexane solution of silica and PDMS, vacuum impregnated, and then taken out and dried to obtain a super-hydrophobic modified wood sponge; The mass concentration of PDMS in the n-hexane solution is 1.2-1.8 wt %, the mass concentration of silicon dioxide in the n-hexane solution is 0.4-0.6 wt %, the immersion time during vacuum impregnation is 5-15 min, and the drying temperature during drying is 70-90° C.

8. Use of a wood sponge-based underwater micro-force sensor prepared by the preparation method according to any one of claims 1 to 7 in underwater real-time monitoring.

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