Dual-mode visual humidity detection sensor based on structural color as well as preparation method and application of dual-mode visual humidity detection sensor

Abstract

The invention discloses a dual-mode visual humidity detection sensor based on structural color and a preparation method and application thereof, and belongs to the technical field of triboelectric materials.The dual-mode visual humidity detection sensor is characterized in that cellulose nanocrystals serve as a matrix, and a structural color cellulose liquid crystal film is prepared by introducing citric acid in a self-assembly mode; the obvious screw pitch change of the structural color cellulose liquid crystal film is observed under a scanning electron microscope by regulating the content of citric acid; the structural color cellulose liquid crystal film is used as a triboelectric positive electrode material, the sensor is prepared, the sensor has high electric output performance, and meanwhile electric output signals (voltage, current and charge quantity) and the film color have certain responsiveness to humidity; the electrical signals and the visual signals are learned and analyzed by utilizing a machine learning method, so that relatively high accuracy is obtained, and the structural color cellulose liquid crystal film has a potential application prospect in the field of sensors.

Description

Technical Field

[0001] This invention belongs to the field of triboelectric materials technology, and particularly relates to a dual-mode visual humidity detection sensor based on structural color, its preparation method and application. Background Technology

[0002] Structural color, also known as physical color, is a type of color produced by light wave reflection, diffraction, interference, and other processes, and can be observed in many natural organisms. Unlike pigment-derived colors, structural color originates from the interaction between light and the physical microstructure or nanostructure of materials. Its most important characteristic is its excellent chemical stability, making it ideal for various technological applications and preventing color fading over time. Inspired by nature, the properties of structural color are being developed for various industrial fields, including anti-counterfeiting labels, sensors, detectors, displays, and smart devices.

[0003] Triboelectric nanogenerator (TENG) sensors are energy devices based on contact electrification and electrostatic inductive coupling effects. TENG sensors require no external power source and can harvest energy from environmental mechanical motion (such as vibration, wind, water flow, and human activity), integrating energy harvesting and sensing. This makes them suitable for applications such as the Internet of Things (IoT) and wearable devices. Almost any material (polymers, metals, fabrics, paper, and even water) can be used to construct TENGs, making their manufacturing cost very low. Flexible, stretchable, transparent, and even biocompatible materials can be selected to meet the needs of different applications. However, most current sensors detect only a single signal, often resulting in limitations in reliability and accuracy.

[0004] Cellulose is an environmentally friendly natural polysaccharide organic compound, a linear polymer composed of β(1,4)-linked D-glucose units. Depending on the processing method, cellulose can be obtained in various sizes from micrometers to nanometers, mainly classified as: microcrystalline cellulose (MCC), nanocellulose (CNF), bacterial cellulose (BC), and cellulose nanocrystals (CNC). Among them, CNC, with its advantages of biocompatibility, renewability, and self-assembly, is used to manufacture various functional materials for various applications. It is prepared by hydrolyzing the amorphous regions of cellulose materials with acids, enzymes, or oxidants while preserving the crystalline regions. CNC suspensions can self-assemble to form thin films with cholesteric liquid crystal structures, exhibiting chiral optical properties and birefringence under a polarizing microscope. However, pure CNC films often exhibit high brittleness due to their inherent rigidity and lack of a flexible energy dissipation phase, making them difficult to apply in industrial production. To address this issue, polymer additives (such as polyvinyl alcohol, polyethylene glycol, waterborne polyurethane, citric acid, etc.) are used as plasticizers to improve the flexibility of CNC films. These composite films not only exhibit excellent flexibility but also demonstrate sensitive and effective color response.

[0005] The triboelectric signals acquired by flexible triboelectric sensors are complex, diverse, and noisy, causing varying degrees of interference to subsequent identification tasks. Traditional methods require defining and manually extracting feature values ​​from the raw data, which is time-consuming, labor-intensive, and inefficient. Furthermore, manual processing is difficult for complex problems and high-dimensional data, resulting in low reliability. Therefore, there is an urgent need for an application tool that automatically extracts features. Summary of the Invention

[0006] To address the aforementioned technical problems, this invention proposes a dual-mode visual humidity detection sensor based on structural color, its fabrication method, and its application. This invention prepares a highly flexible CNC thin film with structural color by introducing citric acid, using it as a friction material. This not only achieves excellent electrical output performance but also utilizes machine learning to construct a dual-mode humidity monitoring system that combines electrical and visual signals.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] This invention provides a method for fabricating a dual-mode visual humidity detection sensor based on structural color, comprising the following steps:

[0009] (1) Microcrystalline cellulose was mixed with sulfuric acid and reacted under water bath conditions. After the reaction was completed, a milky white liquid was obtained.

[0010] (2) Let the milky white liquid stand, discard the supernatant, centrifuge the resulting suspension, discard the supernatant, and repeat the centrifugation until the supernatant changes from colorless to light blue;

[0011] (3) Add the light blue supernatant obtained in step (2) to water and centrifuge again. Repeat the centrifugation until the supernatant becomes colorless.

[0012] (4) Transfer the colorless supernatant obtained in step (3) into a dialysis bag for dialysis until the dispersion in the dialysis bag is light blue and transparent, and the pH reaches a constant value, then end the dialysis.

[0013] (5) The dispersion obtained in step (4) is concentrated and ultrasonically treated to obtain a cellulose nanocrystal solution;

[0014] (6) Citric acid is mixed with the cellulose nanocrystal solution, and after sonication, the mixture is stirred evenly to obtain a mixed solution. The mixed solution is then used to prepare a structural color cellulose liquid crystal film.

[0015] (7) Apply double-sided tape to the support substrate and attach conductive material to the double-sided tape as an electrode layer; cut the structural color cellulose liquid crystal film to a suitable size and attach it to the electrode layer to obtain a positive electrode plate; prepare a negative electrode plate according to the above steps, assemble it and connect the wires to obtain the structural color-based dual-mode visual humidity detection sensor, which is a structural color-based dual-mode visual humidity detection TENG sensor.

[0016] The principle of this invention: The structural color cellulose liquid crystal film of this invention exhibits highly sensitive response to humidity. This film is formed by the self-assembly of cellulose nanocrystals (CNC) into a photonic crystal structure with a chiral nematic periodic arrangement. A 2 wt% CNC solution is prepared using sulfuric acid hydrolysis, and its helical structure is modulated using citric acid (CA), increasing the pitch from 310.2 nm (zero citric acid addition) to 491.4 nm (0.48 g citric acid addition), which also serves as the positive electrode triboelectric layer of the sensor. Changes in humidity synchronously alter the film's optical properties (structural color) and electrical properties (triboelectric output), thus achieving dual-mode detection. The pitch of the cellulose nanocrystal film changes with the relative humidity in the environment. The CA / CNC composite film formed after adding CA contains more -COOH and -OH groups. These hydrophilic groups absorb or release water molecules, causing a more significant increase or contraction in the pitch of the CA / CNC film, resulting in a more sensitive change in its color. Taking a structurally colored cellulose liquid crystal film with 0.36 g of citric acid as an example, the specific analysis is as follows: In an environment with a relative humidity of 43%-97%, the color of the structurally colored cellulose liquid crystal film with 0.36 g of citric acid changes sequentially from green to yellow, brown, and dark red, eventually becoming dark red, as the relative humidity increases. This change is reversible when the humidity decreases. Similarly, in an environment with a relative humidity of 43%-97%, the voltage value decreases sequentially with increasing relative humidity, specifically from 161.45 V to 132.67 V, 97.61 V, 43.15 V, and 9.48 V, also showing reversibility when the humidity decreases. Compared with the closest existing technology, CN102690358A utilizes a synergistic process of oxidant hydrolysis and mechanical defibrillation to prepare cellulose nanocrystals, obtaining nanocrystals with a length of 90±50 nm and a width of 10±4 nm, for use in pharmaceutical adhesives, food additives, and other fields; CN110194804A... Cellulose nanocrystals are prepared by hydrolyzing cellulose at relatively high temperatures (80-120℃) using a mixture of organic acids (such as maleic acid) and acid anhydrides (such as maleic anhydride) under the action of a catalyst (such as p-toluenesulfonic acid). This method is suitable for optical films and anti-counterfeiting materials. CN111355401A modifies cellulose nanofibers with polyethylene glycol methyl ether and improves their performance as a positive friction material by introducing methoxy and ether groups (weight ratio 1:1-5, reaction at 50-70℃ for 4-6 hours). This patent uses sulfuric acid to hydrolyze microcrystalline cellulose. The core innovation is to change the pitch of the cellulose nanocrystal film by adding citric acid, thereby improving its triboelectric properties and thus improving its sensitivity to electrical and visual signals. Specifically, it uses the hydrophilic groups of the CA / CNC composite film to achieve dual-mode detection of the electrical properties and color of the ambient humidity. At the same time, it uses machine learning to learn and analyze the electrical and visual signals to improve detection accuracy. Obviously, this invention differs significantly from the prior art in terms of preparation method and application field.

[0017] Further, in step (1), the mass ratio of microcrystalline cellulose to sulfuric acid is 1:(8-10); the concentration of sulfuric acid is 50-70 wt%.

[0018] Furthermore, in step (1), the temperature of the water bath is 40-50 ℃, and the time of the water bath is 1-1.5 h.

[0019] Furthermore, in step (2), the centrifugation speed is 8000-10000 rpm, the centrifugation time is 3-5 min each time, and the number of centrifugations is 2-4 times.

[0020] Furthermore, in step (3), the centrifugation speed is 10000-12000 rpm, the centrifugation time is 3-5 min each time, and the number of centrifugations is 2-4 times.

[0021] Furthermore, in step (4), the molecular weight cutoff of the dialysis bag is 3500 Da.

[0022] Furthermore, in step (6), the structural color cellulose liquid crystal film is prepared by self-assembly.

[0023] Further, in step (6), the mass ratio of the cellulose nanocrystals to the citric acid is 0.8: (0.12-0.48).

[0024] The present invention also provides a dual-mode visual humidity detection sensor based on structural color prepared according to the above preparation method.

[0025] This invention also provides the application of the above-mentioned structure color-based dual-mode visual humidity detection sensor in the fields of electronic detection devices and environmental monitoring.

[0026] Compared with the prior art, the present invention has the following advantages and technical effects:

[0027] This invention utilizes biomass raw materials, which are widely available and possess characteristics such as being green, environmentally friendly, biodegradable, and biocompatible, greatly promoting the application of the aforementioned sensors in electronic detection devices and environmental monitoring. This invention prepares a structurally colored cellulose liquid crystal film from biomass microcrystalline cellulose. The resulting structurally colored cellulose liquid crystal film exhibits stable shape, stable properties, and good flexibility. Transmission electron microscopy (TEM) observation of its surface morphology reveals that the aspect ratio of the obtained cellulose nanocrystal rods is 10⁻²³. Scanning electron microscopy (SEM) observation of its cross-section shows that the interlayer spacing gradually increases with the addition of citric acid (from 310.2 nm to 491.4 nm). Combining this with triboelectrone materials to fabricate a sensor, the resulting structurally colored dual-mode visual humidity detection sensor exhibits excellent performance. In closed environments with different saturated salt solutions, both the electrical and visual signals show a certain linear relationship. Using machine learning to analyze the electrical and visual signals, the average recognition accuracy is at a high level. Attached Figure Description

[0028] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0029] Figure 1 This is a transmission electron microscope image of the fiber nanocrystals in Example 1.

[0030] Figure 2 The images shown are digital photographs (a), polarized light micrographs (b), and scanning electron microscope cross-sectional images (c) of the structural color cellulose liquid crystal films prepared in Comparative Examples 1 and Examples 1-4 under visible light. (a) is a digital photograph (scale bar is 2 cm), (b) is a polarized light micrograph (scale bar is 10 μm), and (c) is a scanning electron microscope cross-sectional image (scale bar is 1 μm).

[0031] Figure 3 This is a graph showing the relationship between short-circuit current and time for the structural color cellulose liquid crystal thin film sensors prepared in Comparative Example 1 and Examples 1-4.

[0032] Figure 4 This is a graph showing the relationship between open-circuit voltage and time for the structural color cellulose liquid crystal thin film sensors prepared in Comparative Example 1 and Examples 1-4.

[0033] Figure 5 This is a graph showing the relationship between charge and time for the structural color cellulose liquid crystal thin film sensors prepared in Comparative Example 1 and Examples 1-4.

[0034] Figure 6 This is a graph showing the relationship between the open-circuit voltage and time of the dual-mode visual humidity detection sensor based on structural color in Example 1 under different humidity levels.

[0035] Figure 7 This is a linear fitting diagram of the open-circuit voltage of the dual-mode visual humidity detection sensor based on structural color in Example 1 under different humidity levels.

[0036] Figure 8 This is a graph showing the relationship between short-circuit current and time under different humidity levels for the dual-mode visual humidity detection sensor based on structural color in Example 1.

[0037] Figure 9 This is a graph showing the relationship between the charge amount and time of the dual-mode visual humidity detection sensor based on structural color in Example 1 under different humidity levels.

[0038] Figure 10 This is a graph showing the relationship between the film color and humidity of the dual-mode visual humidity detection sensor based on structural color in Example 1 under different humidity levels.

[0039] Figure 11 This is a linear fitting diagram of the RGB values ​​of the thin film color of the dual-mode visual humidity detection sensor based on structural color in Example 1 under different humidity conditions.

[0040] Figure 12 This is a deep learning recognition image of the open-circuit voltage of the dual-mode visual humidity detection sensor based on structural color under different humidity conditions in Example 1.

[0041] Figure 13 This is a deep learning recognition image of the RGB values ​​of the thin film color of the dual-mode visual humidity detection sensor based on structural color under different humidity conditions in Example 1. Detailed Implementation

[0042] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0043] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0044] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0045] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0046] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0047] Embodiments of the present invention provide a method for fabricating a dual-mode visual humidity detection sensor based on structural color, comprising the following steps:

[0048] (1) Microcrystalline cellulose was mixed with sulfuric acid and reacted under water bath conditions. After the reaction was completed, a milky white liquid was obtained.

[0049] (2) Let the milky white liquid stand, discard the supernatant to remove excess sulfuric acid and soluble microcrystalline cellulose, centrifuge the resulting suspension, discard the supernatant, and repeat the centrifugation until the supernatant changes from colorless to light blue.

[0050] (3) Add the light blue supernatant obtained in step (2) to water and centrifuge again. Repeat the centrifugation until the supernatant becomes colorless.

[0051] (4) Transfer the colorless supernatant obtained in step (3) into a dialysis bag for dialysis until the dispersion in the dialysis bag turns light blue and is transparent, and the pH reaches a constant value, then end the dialysis.

[0052] (5) The dispersion obtained in step (4) is concentrated and ultrasonically treated to obtain a cellulose nanocrystal solution;

[0053] (6) Mix citric acid with cellulose nanocrystal solution, sonicate and stir evenly to obtain a mixed solution, and use the mixed solution to prepare structural color cellulose liquid crystal film;

[0054] (7) Apply double-sided tape to the support substrate and attach conductive material to the double-sided tape as an electrode layer; cut the structural color cellulose liquid crystal film to a suitable size and attach it to the electrode layer to obtain a positive electrode plate; according to the above steps, prepare a negative electrode plate using triboelectric negative material, assemble it and connect the wire to obtain a dual-mode visual humidity detection sensor based on structural color.

[0055] In a preferred embodiment of the present invention, in step (1), the mass ratio of microcrystalline cellulose to sulfuric acid is 1:(8-10); the concentration of sulfuric acid is 50-70 wt%. The CNC-formed film obtained with the optimal mass ratio has better periodicity and fewer defects in its photonic crystal structure, resulting in more vibrant and uniform structural colors. When humidity changes, this regular layered structure expands / contracts more uniformly, leading to more acute and continuous color changes, thus improving the resolution and reliability of visual inspection. The purpose of sulfuric acid hydrolysis of microcrystalline cellulose is to selectively remove the amorphous regions of cellulose while retaining the crystalline regions, thereby facilitating the subsequent acquisition of rod-shaped cellulose nanocrystals with high aspect ratio and negatively charged (sulfonic acid groups) surfaces. When the acid dosage is low, the amorphous region cannot be effectively etched away, resulting in larger and less uniform particle sizes with lower aspect ratios. This leads to fewer sulfonic acid groups introduced and lower surface charge density of the CNC nanorods, resulting in poor dispersibility in water, easy aggregation, and difficulty in forming a uniform and stable liquid crystal phase. The structure-colored films obtained through self-assembly are dull and uneven in color, or even fail to produce structure color. When the acid dosage is high, the strong acid environment not only attacks the amorphous region but also further erodes the crystalline region, causing the CNC nanorods to become shorter. Short rod CNC nanorods are unable to form long-range ordered chiral nematic structures and cannot produce bright and stable structure color. This also leads to a deterioration in the mechanical properties of the film.

[0056] For example, in step (1), the sulfuric acid with a concentration of 50-70 wt% is obtained by diluting concentrated sulfuric acid with a concentration of 98 wt%.

[0057] In a preferred embodiment of the present invention, in step (1), the temperature of the water bath is 40-50 °C, and the water bath time is 1-1.5 h. Under the above-mentioned water bath reaction time and temperature, the well-organized CNC self-assembles into a long-range ordered photonic crystal, producing a bright and uniform structural color. This structure has well-organized nanopores and a hydrophilic surface, which can make a rapid and uniform expansion / contraction response to humidity changes, resulting in a sharp and reversible shift in color wavelength, providing a high-quality signal for machine learning visual recognition (97.91% accuracy).

[0058] In a preferred embodiment of the present invention, in step (1), after the water bath reaction for 1-1.5 h, ten times the volume of deionized water as sulfuric acid solution is quickly added to terminate the reaction.

[0059] In a preferred embodiment of the present invention, in step (2), the centrifugation speed is 8000-10000 rpm, the centrifugation time is 3-5 min each time, and the number of centrifugations is 2-4 times.

[0060] In a preferred embodiment of the present invention, in step (3), the centrifugation speed is 10000-12000 rpm, the centrifugation time is 3-5 min each time, and the number of centrifugations is 2-4 times.

[0061] In a preferred embodiment of the present invention, in step (4), the molecular weight cutoff of the dialysis bag is 3500 Da.

[0062] In a preferred embodiment of the present invention, in step (4), the dialysis time is 6-10 days.

[0063] In a preferred embodiment of the present invention, the concentration of the cellulose nanocrystal solution in step (5) is 2 wt%.

[0064] In a preferred embodiment of the present invention, the mass ratio of cellulose nanocrystals to citric acid in step (6) is 0.8:(0.12-0.48). The carboxyl groups of citric acid undergo a (partial) esterification reaction with the hydroxyl groups on the CNC surface, forming unreacted covalently bonded citric acid molecules or oligomers between adjacent CNCs, filling the spaces between the helical layers formed by the CNCs. These two effects jointly regulate the interlayer spacing and structural stiffness of the film. Excessive interlayer spacing can cause the reflection peak to shift out of the visible light range or the color to become cloudy. More importantly, the over-crosslinked structure is difficult to reversibly expand / contract with humidity, resulting in a significant decrease in the visual response sensitivity to humidity.

[0065] In a preferred embodiment of the present invention, in step (6), the ultrasonic time is 15 min and the stirring time is 3-6 h.

[0066] In a preferred embodiment of the present invention, in step (6), a structural color cellulose liquid crystal film is prepared by self-assembly, and its thickness is 60-110 μm. The cellulose nanocrystals in the structural color cellulose liquid crystal film of the present invention are rod-shaped nanoparticles with an aspect ratio of 10-23.

[0067] For example, the preparation method of the structural color cellulose liquid crystal film is as follows: the mixed solution is poured into a petri dish with a diameter of 10 cm, left to stand for 3-7 days, and after it is completely dry, the film is peeled off to obtain the structural color cellulose liquid crystal film. If the standing time is too short, film formation will not be possible; if the standing time is too long, over-drying will easily lead to cracking of the film.

[0068] For example, the supporting substrate in step (7) is an acrylic plate; the conductive material is copper foil; and the triboelectric material is polytetrafluoroethylene (PTFE).

[0069] Embodiments of the present invention also provide a dual-mode visual humidity detection sensor based on structural color prepared according to the above preparation method.

[0070] Embodiments of the present invention also provide the application of the above-described structure color-based dual-mode visual humidity detection sensor in the fields of electronic detection devices and environmental monitoring.

[0071] This invention uses cellulose nanocrystals as a matrix to prepare a structurally colored cellulose liquid crystal film through the self-assembly of citric acid. By controlling the citric acid content, a significant pitch change in the structurally colored cellulose liquid crystal film was observed under a scanning electron microscope. Furthermore, the structurally colored cellulose liquid crystal film was used as a triboelectric positive electrode material to prepare a sensor with high electrical output performance. Simultaneously, the electrical output signals (voltage, current, and charge) and the film color exhibit a certain degree of responsiveness to humidity. Using machine learning to learn and analyze both electrical and visual signals, high accuracy was achieved, demonstrating the potential application prospects of the structurally colored cellulose liquid crystal film in the sensor field.

[0072] The sensor of this invention is based on a contact-separation mode: during the periodic contact and separation of the structural cellulose liquid crystal film (positive electrode friction layer) and PTFE (negative electrode friction layer), electrons are transferred from the structural cellulose liquid crystal film to the PTFE due to differences in triboelectric sequences, generating triboelectric charges; electrostatic induction induces current in the external circuit. Under high humidity, water molecules adsorb on the film surface to form a water film, providing a leakage channel for the charge, accelerating the neutralization and dissipation of triboelectric charges, resulting in a decrease in sensor output (short-circuit current, open-circuit voltage, and amount of transferred charge). Water molecule adsorption changes the surface charge state and dielectric constant of the CNC, affecting the triboelectric charge density and charge retention capacity. The moisture absorption and expansion of the CNC may change the film thickness, surface morphology, and flexibility, thereby affecting the actual contact area, separation distance, and elastic energy conversion efficiency during the contact separation process. The sensor of this invention achieves the highest output (short-circuit current of 7.75 μA, open-circuit voltage of 187.17 V, and charge of 86.06 nC) under optimal conditions (citric acid addition of 0.36 g). These electrical signal parameters exhibit regular changes in different humidity environments (e.g., decreasing as humidity increases). By calibrating with a standard humidity environment, a quantitative relationship between electrical signals and humidity can be established. The sensor of this invention features high sensitivity, fast response, and ease of digital recording and remote transmission, making it suitable for real-time online monitoring. Simultaneously, visual signals can be quickly identified through visual inspection or image analysis, requiring no power supply and possessing anti-counterfeiting and aesthetic characteristics. The combination of these two methods allows for cross-verification, improving detection reliability and anti-interference capabilities (e.g., preventing misjudgments that may arise from single signals such as temperature fluctuations or mechanical vibrations).

[0073] The term "digital photograph" refers to a photograph of the actual object taken with a digital camera, used to show the macroscopic appearance characteristics of the thin film. The cellulose liquid crystal thin film prepared by this invention has structural color, and the digital photograph can intuitively show the color changes of the film under different ratios and conditions.

[0074] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0075] All raw materials and reagents used in the embodiments of this invention were purchased commercially. As an example, microcrystalline cellulose was purchased from Shanghai Maclean Biochemical Technology Co., Ltd., model number M909921.

[0076] It should be noted that all aspects not described in detail in this invention are conventional operating methods in the field and are not the focus of this invention. For example, specific methods such as the dilution method of concentrated sulfuric acid are all completed using conventional methods.

[0077] The technical solution of the present invention will be further illustrated by the following embodiments.

[0078] Comparative Example 1

[0079] A method for fabricating a sensor based on structural color, comprising the following steps:

[0080] (1) First, dilute the 98 wt% concentrated sulfuric acid to 64 wt% and set aside;

[0081] (2) Weigh 10 g of microcrystalline cellulose, and then add it to a beaker with a mechanical stirrer in a ratio of 1:8.75 between the mass of microcrystalline cellulose and sulfuric acid in step (1). Control the water bath temperature to 45 °C, stir at a constant speed for 1 h, and then quickly add deionized water (the volume of deionized water is ten times the volume of sulfuric acid solution) to terminate the reaction and obtain a milky white liquid.

[0082] (3) Let the milky white liquid obtained in step (2) stand overnight, pour off the supernatant to remove excess sulfuric acid and soluble microcrystalline cellulose, centrifuge the remaining suspension for 5 min at 8000 rpm, pour off the supernatant, repeat the centrifugation twice until the supernatant changes from colorless to light blue.

[0083] (4) Add the light blue supernatant obtained in step (3) to deionized water and centrifuge again for 5 min. Adjust the centrifuge speed to 10000 rpm. Collect the supernatant in the centrifuge tube each time and repeat the centrifugation 3 times until the supernatant becomes colorless.

[0084] (5) Transfer the colorless supernatant obtained in step (4) into a dialysis bag (molecular weight cutoff of 3500 D), place it in deionized water for dialysis, and dialyze for 8 days until the dispersion in the dialysis bag turns light blue and is transparent, and the pH reaches a constant value.

[0085] (6) The dispersion obtained in step (5) was then concentrated and ultrasonically treated to obtain a 2 wt% cellulose nanocrystal solution;

[0086] (7) Take 40 mL of the cellulose nanocrystal solution obtained in step (6) into a 50 mL beaker, sonicate for 15 min and stir at a constant speed for 3 h. Then pour the stirred solution into a 10 cm diameter petri dish and let it stand for 5 days. After it is completely dry, peel off the film to obtain a structural color cellulose liquid crystal film without citric acid, denoted as CNC, with a thickness of 60 μm.

[0087] (8) Cut the structured cellulose liquid crystal film prepared in step (7) into 3 cm × 3 cm to obtain the positive electrode material; use a 3 cm × 5 cm acrylic plate as a support, first stick 3 cm × 3 cm double-sided tape on the acrylic plate, then stick double-sided conductive copper foil and connect wires, and finally cover the positive electrode material on the copper foil to obtain the positive electrode plate; repeat the steps of sticking double-sided tape, copper foil and connecting wires on another acrylic plate, and finally stick polytetrafluoroethylene (PTFE) film on the copper foil to obtain the negative electrode plate; assemble the positive electrode plate and the negative electrode plate to obtain the structured cellulose liquid crystal film sensor without adding citric acid.

[0088] Example 1

[0089] A method for fabricating a dual-mode visual humidity detection sensor based on structural color, comprising the following steps:

[0090] (1) First, dilute the 98 wt% concentrated sulfuric acid to 64 wt% and set aside;

[0091] (2) Weigh 10 g of microcrystalline cellulose, and then add it to a beaker with a mechanical stirrer in a ratio of 1:8.75 of cellulose to sulfuric acid in step (1). Control the water bath temperature to 45 °C, stir at a constant speed for 1 h, and then quickly add deionized water (the volume of deionized water is ten times the volume of sulfuric acid solution) to terminate the reaction and obtain a milky white liquid.

[0092] (3) Let the milky white liquid obtained in step (2) stand overnight, pour off the supernatant to remove excess sulfuric acid and soluble microcrystalline cellulose, centrifuge the remaining suspension for 5 min at 8000 rpm, pour off the supernatant, repeat the centrifugation twice until the supernatant changes from colorless to light blue.

[0093] (4) Add the light blue supernatant obtained in step (3) to deionized water and centrifuge again for 5 min. Adjust the centrifuge speed to 10000 rpm. Collect the supernatant in the centrifuge tube each time and repeat the centrifugation 3 times until the supernatant becomes colorless.

[0094] (5) Transfer the colorless supernatant obtained in step (4) into a dialysis bag (with a molecular weight cutoff of 3500 Da), place it in deionized water for dialysis, and dialyze for 8 days until the dispersion in the dialysis bag turns light blue and is transparent, and the pH reaches a constant value.

[0095] (6) Subsequently, the dispersion obtained in step (5) was concentrated and sonicated to obtain a 2 wt% cellulose nanocrystal solution. The transmission electron microscopy image of the cellulose nanocrystals is shown below. Figure 1 As shown, the aspect ratio of cellulose nanocrystal rod-shaped particles is 10-23;

[0096] (7) Take 40 mL of the cellulose nanocrystal solution obtained in step (6) into a 50 mL beaker, then add 0.36 g of citric acid to prepare a mixed solution. Sonicate for 15 min and stir at a constant speed for 3 h. Then pour the resulting solution into a 10 cm diameter petri dish and let it stand for 5 days. After it is completely dry, peel off the film to obtain the structural color cellulose liquid crystal film with added citric acid, denoted as CA. 0.36 / CNC, with a thickness of 100 μm;

[0097] (8) Cut the citric acid-added cellulose liquid crystal film prepared in step (7) into 3 cm × 3 cm pieces to obtain the positive electrode material. Use a 3 cm × 5 cm acrylic plate as a support. First, stick 3 cm × 3 cm double-sided tape on the acrylic plate, then attach double-sided conductive copper foil and connect wires. Finally, cover the positive electrode material on the copper foil to obtain the positive electrode plate. Repeat the steps of attaching double-sided tape, copper foil and connecting wires on another acrylic plate. Finally, attach the tetrafluoroethylene film (PTFE) on the copper foil to obtain the negative electrode plate. After assembling the positive electrode plate and the negative electrode plate, the citric acid-added cellulose liquid crystal film sensor is obtained, which is a dual-mode visual humidity detection sensor based on structural color.

[0098] Example 2

[0099] A method for preparing a dual-mode visual humidity detection sensor based on structural color is described. The specific steps are the same as in Example 1, except that the amount of citric acid added in step (7) is 0.12 g. The resulting citric acid-added structural color cellulose liquid crystal film is denoted as CA. 0.12 / CNC, with a thickness of 80 μm.

[0100] Example 3

[0101] A method for preparing a dual-mode visual humidity detection sensor based on structural color is described. The specific steps are the same as in Example 1, except that the amount of citric acid added in step (7) is 0.24 g, and the resulting structural color cellulose liquid crystal film with added citric acid is denoted as CA. 0.24 / CNC, with a thickness of 90 μm.

[0102] Example 4

[0103] A method for preparing a dual-mode visual humidity detection sensor based on structural color is described. The specific steps are the same as in Example 1, except that the amount of citric acid added in step (7) is 0.48 g, and the resulting structural color cellulose liquid crystal film with added citric acid is denoted as CA. 0.48 / CNC, with a thickness of 110 μm.

[0104] As can be seen from Comparative Example 1 and Examples 1-4, the amount of citric acid added affects the thickness of the structural color cellulose liquid crystal film.

[0105] Figure 1 The image shown is a transmission electron microscope image of the cellulose nanocrystals in Example 1, which shows that the aspect ratio of the rod-shaped cellulose nanocrystal particles is 10-23.

[0106] Figure 2 The images shown are digital photographs (a), polarized light micrographs (b), and scanning electron microscope cross-sectional images (c) of the structural color cellulose liquid crystal films prepared in Comparative Examples 1 and Examples 1-4. In (a), the digital photographs are shown (scale bar is 2 cm), (b), the polarized light micrographs are shown (scale bar is 10 μm), and (c), the scanning electron microscope cross-sectional images are shown (scale bar is 1 μm). It can be seen that with the addition of citric acid, the interlayer spacing of cellulose nanocrystals gradually increases (from 310.2 nm to 491.4 nm).

[0107] Figure 3 The graph shows the relationship between short-circuit current and time for the structural color cellulose liquid crystal film sensors prepared in Comparative Example 1 and Examples 1-4. It can be seen that the maximum short-circuit current of the structural color cellulose liquid crystal film sensor prepared in Comparative Example 1 is 2.66 μA; the dual-mode visual humidity detection sensor based on structural color prepared in Example 1 has the best performance, with a maximum short-circuit current of 7.75 μA; the maximum short-circuit current of the dual-mode visual humidity detection sensor based on structural color prepared in Example 2 is 4.40 μA; the maximum short-circuit current of the dual-mode visual humidity detection sensor based on structural color prepared in Example 3 is 5.78 μA; and the maximum short-circuit current of the dual-mode visual humidity detection sensor based on structural color prepared in Example 4 is 6.28 μA.

[0108] Figure 4The graph shows the relationship between open-circuit voltage and time for the structural color cellulose liquid crystal film sensors prepared in Comparative Example 1 and Examples 1-4. It can be seen that the maximum open-circuit voltage of the structural color cellulose liquid crystal film sensor prepared in Comparative Example 1 is 80.94 V; the dual-mode visual humidity detection sensor based on structural color prepared in Example 1 has the best performance, with a maximum open-circuit voltage of 187.17 V; the maximum open-circuit voltage of the dual-mode visual humidity detection sensor based on structural color prepared in Example 2 is 109.03 V; the maximum open-circuit voltage of the dual-mode visual humidity detection sensor based on structural color prepared in Example 3 is 132.60 V; and the maximum open-circuit voltage of the dual-mode visual humidity detection sensor based on structural color prepared in Example 4 is 145.07 V.

[0109] Figure 5 The graph shows the relationship between charge and time for the structural color cellulose liquid crystal film sensors prepared in Comparative Example 1 and Examples 1-4. It can be seen that the maximum charge of the structural color cellulose liquid crystal film sensor prepared in Comparative Example 1 is 45.91 nC; the dual-mode visual humidity detection sensor based on structural color prepared in Example 1 has the best performance, with a maximum charge of 86.06 nC; the maximum charge of the dual-mode visual humidity detection sensor based on structural color prepared in Example 2 is 59.84 nC; the maximum charge of the dual-mode visual humidity detection sensor based on structural color prepared in Example 3 is 70.40 nC; and the maximum charge of the dual-mode visual humidity detection sensor based on structural color prepared in Example 4 is 76.16 nC.

[0110] Taking the dual-mode visual humidity detection sensor based on structural color prepared in Example 1 as an example, its triboelectric properties under different humidity levels were tested, and the color change of the thin film structural color was observed. The specific process is as follows: Saturated salt solutions of K2CO3, NaBr, NaCl, KCl, and K2SO4 were prepared respectively, placed in sealed bottles, and then placed in a constant temperature and humidity environment at 20 ℃. The dual-mode visual humidity detection sensor based on structural color in Example 1 was placed in the sealed bottles containing the above-mentioned saturated salt solutions with different humidity levels (Table 1), and the triboelectric properties under different humidity levels were tested, while the color change of the thin film structural color was observed.

[0111] Table 1. Relative humidity values ​​of saturated solutions of different salts at 20 °C

[0112]

[0113] In Example 1, the maximum open-circuit voltage of the dual-mode visual humidity detection sensor based on structural color under different humidity conditions is as follows: Figure 6As shown, the voltage is 161.74 V at 43% RH, 132.67 V at 58% RH, 97.61 V at 75% RH, 43.15 V at 85% RH, and 9.48 V at 97% RH, exhibiting a linear relationship (e.g., ...). Figure 7 (As shown); the maximum short-circuit current under different humidity levels is as follows: Figure 8 As shown, the current is 6.60 μA at 43% RH, 5.48 μA at 58% RH, 4.02 μA at 75% RH, 1.76 μA at 85% RH, and 0.39 μA at 97% RH; the maximum charge at different humidity levels is as follows. Figure 9 As shown, the charge is 78.18 nC at 43% RH, 63.65 nC at 58% RH, 46.18 nC at 75% RH, 18.95 nC at 85% RH, and 4.73 nC at 97% RH; the structural color under different humidity conditions is as follows... Figure 10 As shown, the film color changes sequentially from green to yellow, brown, dark red, and finally to dark red as humidity increases. This change is reversible as humidity decreases, and the RGB values ​​of the film exhibit a linear relationship (e.g., ...). Figure 11 As shown); by using machine learning to learn and analyze electrical and visual signals, the average recognition accuracy reached 95.90% (e.g. Figure 12 (as shown) and 97.91% (as shown) Figure 13 (As shown).

[0114] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for fabricating a dual-mode visual humidity detection sensor based on structural color, characterized in that, Includes the following steps: (1) Microcrystalline cellulose was mixed with sulfuric acid and reacted under water bath conditions. After the reaction was completed, a milky white liquid was obtained. (2) Let the milky white liquid stand, discard the supernatant, centrifuge the resulting suspension, discard the supernatant, and repeat the centrifugation until the supernatant changes from colorless to light blue; (3) Add the light blue supernatant obtained in step (2) to water and centrifuge again. Repeat the centrifugation until the supernatant becomes colorless. (4) Transfer the colorless supernatant obtained in step (3) into a dialysis bag for dialysis until the dispersion in the dialysis bag is light blue and transparent, and the pH reaches a constant value, then end the dialysis. (5) The dispersion obtained in step (4) is concentrated and ultrasonically treated to obtain a cellulose nanocrystal solution; (6) Citric acid is mixed with the cellulose nanocrystal solution, and after sonication, the mixture is stirred evenly to obtain a mixed solution. The mixed solution is then used to prepare a structural color cellulose liquid crystal film. (7) Apply double-sided tape to the support substrate and attach conductive material to the double-sided tape as an electrode layer; The structural color cellulose liquid crystal film is cut to a suitable size and attached to the electrode layer to obtain the positive electrode plate; Following the steps described above, a negative electrode plate is prepared using a triboelectric negative material, assembled, and connected with wires to obtain the dual-mode visual humidity detection sensor based on structural color.

2. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, In step (1), the mass ratio of microcrystalline cellulose to sulfuric acid is 1:(8-10); the concentration of sulfuric acid is 50-70 wt%.

3. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, In step (1), the temperature of the water bath is 40-50 ℃, and the time of the water bath is 1-1.5 h.

4. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, In step (2), the centrifugation speed is 8000-10000 rpm, the centrifugation time is 3-5 min each time, and the number of centrifugations is 2-4 times.

5. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, In step (3), the centrifugation speed is 10000-12000 rpm, the centrifugation time is 3-5 min each time, and the number of centrifugations is 2-4 times.

6. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, In step (4), the molecular weight cutoff of the dialysis bag is 3500 Da.

7. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, The mass ratio of cellulose nanocrystals to citric acid in step (6) is 0.8: (0.12-0.48).

8. The method for fabricating a dual-mode visual humidity detection sensor based on structural color according to claim 1, characterized in that, In step (6), the structural color cellulose liquid crystal film is prepared by self-assembly.

9. A dual-mode visual humidity detection sensor based on structural color, characterized in that, It is prepared according to any one of claims 1-8.

10. An application of the structured color-based dual-mode visual humidity detection sensor as described in claim 9 in the fields of electronic detection devices and environmental monitoring.

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