A single-sided adherable biomass thermochromic porous membrane and a preparation method thereof

Abstract

The application discloses a single-surface-adhesive biomass thermochromic porous membrane and a preparation method thereof, and belongs to the field of intelligent stimulus-responsive materials. The method uses weakly acidic polyhydroxy biomass or biomass derivatives to replace the toxic bisphenol A color developing agent for preparing biomass thermochromic dyes; a polydimethylsiloxane gel membrane with a large number of pore structures is prepared through a salt template method, and a gradient cross-linking strategy is introduced to give the gel membrane single-surface adhesion; the biomass thermochromic dye is filled into the pore structure of the porous gel membrane through a vacuum pressure impregnation process, and a single-surface-adhesive biomass thermochromic porous membrane with shape stability is obtained. The biomass thermochromic porous membrane prepared by the application shows good temperature response color change performance and cycle reversibility, has single-surface adhesion, shape stability, excellent self-supporting flexibility and solid-solid phase change characteristics.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of intelligent stimuli-responsive materials, in particular to a single-sided adhesive biomass thermochromic porous film and a preparation method thereof. BACKGROUND

[0002] The thermochromic dye composed of leuco dye, color developer and phase change solvent has excellent temperature response color change and phase change performance, and can provide real-time and intuitive response to temperature through color. It has attracted the attention of many researchers due to its high color saturation, suitable color change temperature and easy availability. However, it also has the problems of single color and safety of color developer. As a key component in three-component thermochromic dye, color developer is usually a weakly acidic compound with electron-withdrawing ability. Among them, bisphenol A (BPA) is used as the main source of color developer for thermochromic dye due to its high color forming efficiency and low cost, such as bank printing paper strips, supermarket shopping receipts and other thermal sensitive papers. Although bisphenol A is the most widely used high-efficiency color developer in current research and application, it is an organic compound with 96 toxicities, endocrine disruptors and potential carcinogens. Long-term exposure to bisphenol A can cause various problems that harm human health, including breast cancer, heart disease, infertility and neurodevelopmental disorders, and widespread exposure to bisphenol A has become an important public health problem. For this reason, safer analogues such as bisphenol S (BPS), bisphenol F (BPF) and bisphenol AF (BPAF) have been introduced into the market to replace them. Studies have found that, compared with bisphenol A, bisphenol S and bisphenol F and other similar substitutes are less destructive to cardiac electrophysiological balance and endocrine system, but they are not completely safe. In view of the harm of bisphenol color developer to human body, the development of green and healthy bisphenol A substitute color developer is still a challenge.

[0003] In addition, thermochromic dyes with phase change characteristics can exhibit corresponding color changes while absorbing or releasing a large amount of latent heat, and are considered as ideal carriers for temperature visualization and heat storage composite materials, and have wide application prospects in functional textiles, intelligent temperature regulating clothing, wearable temperature control, building energy saving, flexible electronic devices and other aspects. However, due to its solid-liquid phase change characteristics, thermochromic dye mainly exists in the form of low-temperature solid state or high-temperature molten state, which has the problems of solid state rigidity and molten state leakage, which greatly limits its application.

[0004] The thermochromic materials with temperature indicating function studied more widely are mostly materials responding to temperature with solid-liquid phase transition, which change in transparency at the same time of phase transition, and utilize the change in transparency to indicate temperature. In patent EP1281946, paraffin is prepared into regular composite material as temperature indicating phase change material, which changes from white opaque state to transparent state due to crystal state change of paraffin when temperature rises above the melting point of paraffin, thereby playing the role of indicating temperature. Since paraffin changes from white to colorless due to temperature, the composite material with paraffin as temperature indicating phase change material also only changes from white to colorless, and the color of discoloration is relatively single. Patent US4428321 designs a three-layer structure of temperature indicating label. The uppermost layer is a transparent blended coating layer containing rubber and crystallizable material. The coating layer has fluidity at a certain temperature. The middle layer is a porous film layer shielding layer, which is used to shield the color of the bottom layer. The bottom layer is a color layer. When reaching a certain temperature, the uppermost layer material begins to have fluidity and penetrates into the porous shielding layer, making the shielding layer transparent, thereby revealing the color of the bottom layer, playing the role of indication. Since the physical behavior of the uppermost layer material penetrating into the porous shielding layer is not only related to temperature, but also related to time. Therefore, even if the coloration is observed, the temperature indicated by the label cannot be estimated. SUMMARY

[0005] In order to solve the above problems, the present application provides a preparation method of a single-side adherable biomass thermochromic porous film, and the prepared biomass thermochromic porous film has good temperature response discoloration performance and cycle reversibility, can effectively prevent solvent leakage and is environmentally friendly.

[0006] The present application provides a preparation method of a single-side adherable biomass thermochromic porous film, which specifically comprises the following steps:

[0007] (1) heating a solid-liquid phase change solvent to a molten state, adding a weakly acidic polyhydroxy biomass or biomass derivative, boron nitride nanosheet, and leuco dye, and preparing a biomass thermochromic dye by heating reaction in a vacuum environment;

[0008] (2) modifying the surface of a cleaned glass sheet with 3-(2-aminoethyl)-aminopropyl trimethoxysilane (AEAPS) to obtain an AEAPS modified glass; uniformly mixing vinyl dimethylsilane, a salt template agent, silicone oil and a platinum catalyst, and removing bubbles under vacuum to obtain a film forming liquid; pouring the film forming liquid on the surface of the AEAPS modified glass using a gradient crosslinking strategy, and diffusing the platinum catalyst towards the modified glass to form a gradient crosslinking structure, and then removing salt by ultrasonic treatment to obtain a porous structure, and drying to obtain a polydimethylsiloxane porous gel film;

[0009] (3) heating and melting the biomass thermochromic dye prepared in step (1), filling into the pore structure of the polydimethylsiloxane porous gel film in step (2) by vacuum pressure impregnation process, obtaining a single-sided adhesive biomass thermochromic porous film, which can undergo color transition from colored to colorless with the increase of temperature.

[0010] In an embodiment of the present application, in step (1), the weakly acidic polyhydroxyl biomass or biomass derivative is an organic weakly acidic biomass or biomass derivative compound with electron accepting property, which is one of L-ascorbic acid, L-ascorbyl palmitate, tea polyphenol, lauryl gallate, tannic acid.

[0011] In an embodiment of the present application, in step (1), the leuco dye is an electron-donating organic compound, which is one of crystal violet lactone, methyl red, bromocresol green, bromocresol purple, phenol red, 1',3'-dimethyl-6'-diethylamino fluoroflavan, 3',6'-dimethoxy fluoroflavan, 3,3-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide, 7,7-bis(4-(diethylamino)-2-ethoxyphenyl)furo[3,4-b]pyridine-5(7H)-one.

[0012] In an embodiment of the present application, in step (1), the solid-liquid phase change solvent refers to a solid-liquid phase change solvent that can be converted from a solid state to a molten state when heated above the phase transition temperature of the phase change solvent, and the solid-liquid phase change solvent is one or more of lauryl alcohol, myristyl alcohol, cetyl alcohol, stearyl alcohol, tetradecanol, hexadecanol, octadecanol, docosanol, oleyl alcohol.

[0013] In an embodiment of the present application, in step (1), the amount of boron nitride nanosheet added is 0.1% to 15% of the total mass of the solid-liquid phase change solvent, the weakly acidic polyhydroxyl biomass or biomass derivative, the boron nitride nanosheet, and the leuco dye.

[0014] In an embodiment of the present application, in step (1), the biomass thermochromic dye is prepared by heating reaction in a vacuum environment, wherein the vacuum degree is -0.1 MPa to -0.06 MPa, and the heating temperature is 40-120℃.

[0015] In an embodiment of the present application, in step (1), the mass ratio of the leuco dye to the weakly acidic polyhydroxyl biomass or biomass derivative is 1:0.2-15, and the mass ratio of the leuco dye to the solid-liquid phase change solvent is 1:50-1:300.

[0016] In an embodiment of the present application, in step (2), the salt template agent is one or more of sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, sodium sulfate; and the ultrasonic desalting time is 6h-72h.

[0017] In an embodiment of the present application, in step (2), the total mass ratio of vinyl dimethyl silane, silicon oil and platinum catalyst is 5-30:1; the total mass ratio of salt template agent, vinyl dimethyl silane, silicon oil and platinum catalyst is 0.1-1.2:1.

[0018] In an embodiment of the present application, in step (2), the curing temperature is 70-150℃.

[0019] The present application provides a single-sided adherable biomass thermochromic porous film prepared by the above-mentioned method.

[0020] The single-sided adherable biomass thermochromic porous film of the present application has applications in the fields of wearable sensors, surface temperature indication of instruments and equipment, and flexible electronic devices.

[0021] [Advantages]

[0022] (1) The present application introduces a safe and renewable weakly acidic polyhydroxy biomass or biomass derivative as a color developer of thermochromic dyes, replacing the commonly used bisphenol A color developer in the current market, for the preparation of biomass thermochromic dyes, which can effectively avoid the harm of bisphenol A and improve the safety of thermochromic dyes;

[0023] (2) The present application introduces boron nitride nanosheets in the preparation of thermochromic dyes, which can improve the thermal conductivity of thermochromic dyes and thus improve the color change sensitivity of thermochromic porous films; at the same time, the two-dimensional structure of boron nitride nanosheets is beneficial to preventing the leakage of thermochromic dyes at high temperatures in the thermochromic porous film, thereby improving the stability of the biomass thermochromic porous film;

[0024] (3) The present application uses 3-(2-aminoethyl)-aminopropyltrimethoxysilane (AEAPS) to modify the surface of the cleaned glass sheet, which can capture platinum catalysts near the modified glass, thereby forming a gradient concentration of platinum catalysts and constructing a film with a gradient cross-linked structure. The two amine groups in the molecular structure of AEAPS can coordinate with platinum atoms to form a stable five-membered ring, so the platinum catalysts near the surface of the AEAPS modified glass are captured and lose their catalytic ability. Then, the platinum catalysts in the uniform film-forming solution diffuse to the modified glass due to the concentration difference, forming a gradient of platinum concentration; the film-forming solution begins to gel in a high-temperature environment, which can prevent the diffusion of platinum catalysts and produce a gradient cross-linked polysiloxane film.

[0025] (4) The present application uses vinyl dimethyl silane and silicon oil to prepare a polydimethylsiloxane gel film with a large number of pore structures by a salt template method, and introduces a gradient cross-linking strategy to give the gel film single-sided adhesion.

[0026] (5) The single-side adherable biomass thermochromic porous film prepared by the application can indicate temperature changes through color, and as the temperature rises, the shape-stable biomass thermochromic porous film changes from a colored solid state (any one of blue, red, green, purple, yellow) to a white solid state, widening the color change spectrum and exhibiting good temperature-responsive color-changing performance, without solvent leakage problems; and has reversible cycling properties and can be reused;

[0027] (6) The application encapsulates biomass thermochromic dyes with solid-liquid phase change characteristics by using the space threshold effect of the pore structure in the porous gel film, wherein the smaller pores in the porous gel film can provide sufficient capillary force for the liquid state thermochromic dye, and have strong adsorption effect on the phase change solvent, effectively solving the problem of easy leakage of liquid state dyes; and the large number of interconnected larger pores in the porous gel film can fill more biomass thermochromic dyes, greatly increasing the amount of dyes and improving the thermal energy storage performance, which is conducive to fully exerting the dual performance of temperature-responsive color change and thermal energy storage of biomass thermochromic dyes, and through establishing the relationship between color and stored heat, the state of thermal energy storage can be intuitively reflected in real time, realizing the visualization of thermal energy storage;

[0028] (7) The preparation method is simple and easy to operate, greatly saving the preparation cost compared with the traditional microcapsule encapsulation method, and the single-side adherable biomass thermochromic porous film prepared by the application can indicate the environmental temperature through color change, overcoming the defect of complicated steps in the traditional encapsulation process, and having good application prospect;

[0029] (8) The biomass thermochromic porous film prepared by the application has excellent self-supporting flexibility. BRIEF DESCRIPTION OF DRAWINGS

[0030] Figure 1 is a preparation method flowchart of the single-side adherable biomass thermochromic porous film of the application;

[0031] Figure 2 is a temperature-responsive color change diagram of the biomass thermochromic dye in Example 1 of the application;

[0032] Figure 3 is a temperature-responsive color change diagram of the biomass thermochromic porous film in Example 1 of the application;

[0033] Figure 4 is the color difference value change of the biomass thermochromic porous film in Example 1 of the application at different temperatures;

[0034] Figure 5 is the differential scanning calorimetry (DSC) curve of the biomass thermochromic porous film in Example 1;

[0035] Figure 6 This is the color difference value change (ΔE) curve of the biomass thermochromic porous membrane in Example 1 of the present invention under 25 alternating cycles of heating and cooling;

[0036] Figure 7 Optical images of the biomass thermochromic porous membrane in Example 1 in its initial, folded, and rolled-up states;

[0037] Figure 8 This is the temperature response color change diagram of the biomass thermochromic dye in Example 2 of the present invention;

[0038] Figure 9 This is a cross-sectional SEM image of the porous gel membrane in Embodiment 2 of the present invention;

[0039] Figure 10 This is a cross-sectional SEM image of the biomass thermochromic porous membrane in Embodiment 2 of the present invention;

[0040] Figure 11 The temperature-responsive color change of the four colors of biomass thermochromic porous membranes—blue, red, yellow, and green—is described in Embodiment 3 of this invention.

[0041] Figure 12 This is a temperature-response color change diagram of the biomass thermochromic dye in Comparative Example 2 of the present invention. Detailed Implementation

[0042] Example 1

[0043] A method for preparing a single-sided adhesive biomass thermochromic porous membrane is as follows: Figure 1 As shown, the specific steps include:

[0044] (1) The solid-liquid phase change solvent tetradecyl alcohol is heated to a molten state, and weakly acidic polyhydroxy biomass or biomass derivative tea polyphenols, leuco dye crystal violet lactone, and boron nitride nanosheets are added. The mass ratio of crystal violet lactone, tea polyphenols, and tetradecyl alcohol is 1:0.3:100, and the amount of boron nitride nanosheets is 3% of the total mass (3% of the total mass of solid-liquid phase change solvent, weakly acidic polyhydroxy biomass or biomass derivatives, boron nitride nanosheets, and leuco dye). The mixture is heated to 120°C and stirred for 3 hours. Then it is placed in an 80°C vacuum chamber with a vacuum degree of -0.1 MPa for 3 hours to obtain a biomass thermochromic dye.

[0045] Figure 2 The temperature response color change diagram of the biomass thermochromic dye in Example 1 shows that when the ambient temperature is lower than the melting point of the phase change solvent, the biomass thermochromic dye is in a blue solid state. As the temperature increases, when the ambient temperature is higher than the melting point of the phase change solvent, the biomass thermochromic dye is in a colorless liquid state, exhibiting significant temperature response color change performance.

[0046] (2) The surface of the cleaned glass sheet is modified by AEAPS to obtain an AEAPS-modified glass sheet. 3.0 g of vinyl dimethyl silane and 2.64 g of a salt template agent, sodium chloride, are mixed and uniformly dispersed, and then 0.3 g of a mixture of a platinum catalyst and a silicone oil is added. The mixture is stirred rapidly until it is uniformly dispersed, and then bubbles in the solution are removed under vacuum for 10 min to obtain a film-forming solution. The film-forming solution is cast on the surface of the AEAPS-modified glass sheet using a gradient crosslinking strategy. The platinum catalyst diffuses toward the modified glass for 30 min, and then the gel film containing the template agent is obtained by curing at 80℃ for 3 h. The gel film is immersed in deionized water, and ultrasonic treatment is performed at 25℃ for 24 h, with the water being replaced every 2 h to remove the template agent in the gel film. Subsequently, the gel film is taken out and placed in a 65℃ air-drying oven for 2 h to remove the water in the gel film, and a monovinyl dimethyl siloxane porous gel film is obtained.

[0047] (3) The biomass thermochromic dye prepared in step (1) is heated and melted to form an impregnation phase solution. The porous gel film prepared in step (2) is immersed in the molten thermochromic dye, and the dye is allowed to fully fill the pore structure of the porous gel film by impregnating at 80℃ under vacuum for 5 h. Subsequently, the gel film is taken out and placed in a 60℃ oven, and the thermochromic dye on the surface of the gel film is repeatedly absorbed with oil-absorbing paper until no dye leaks upon repeated heating. A shape-stable biomass thermochromic porous film is obtained, which has a thermal conductivity of 0.36 W / (m·K) and exhibits a color change from blue to white as the temperature increases.

[0048] Figure 3 The temperature-responsive color change diagram of the biomass thermochromic porous film in Example 1 is shown in FIG. 1. As the temperature increases, the shape-stable biomass thermochromic porous film changes from a blue solid state to a white solid state, exhibiting good temperature-responsive color change performance and no solvent leakage problem.

[0049] Figure 4 The color difference value change of the biomass thermochromic porous film at different temperatures in Example 1 is shown in FIG. 2. The color difference value of the thermochromic porous film increases as the temperature increases. When the temperature increases from 41℃ to 43℃, the color difference value increases from 2.7 to 16.7, and the color of the film changes from blue to white.

[0050] Figure 5For the differential scanning calorimetry curve (DSC) of the biomass thermochromic porous film in Example 1, it can be obtained from the DSC curve that the phase transition temperature of the thermochromic porous film in Example 1 is 40℃, the temperature at the end of heat absorption is 43℃, and the heat storage density is 48 J / g. The color performance test of the biomass thermochromic porous film shows that the thermochromic porous film absorbs heat and changes from blue to white as the temperature rises, the color change temperature range is 41-43℃, the temperature at the end of heat absorption is 43℃, and the heat storage density is 48 J / g when the temperature is higher than 43℃.

[0051] Figure 6 For the color difference value change (ΔE) curve of the biomass thermochromic film in Example 1 under 25 times of alternating cycles of heating and cooling, it can be obtained from the DSC curve that the color difference value change (ΔE) of the biomass thermochromic film in Example 1 is 0.1 under 25 times of alternating cycles of heating and cooling. Figure 6 It can be seen that the biomass thermochromic film prepared has good temperature response color change performance and cycle reversibility.

[0052] Figure 7 For the optical images of the biomass thermochromic porous film in Example 1 in the initial state, the folded state and the curled state, the thermochromic porous film shows good flexibility and mechanical toughness when it is in the original, folded and curled state in the heating / cooling cycle, indicating that it has good self-supporting flexibility. At the same time, the good self-supporting performance of the thermochromic porous film does not affect its temperature response color change performance.

[0053] Example 2

[0054] (1) The solid-liquid phase change solvent octadecanol was heated to a molten state, and the weakly acidic polyhydroxyl biomass or biomass derivative L-ascorbic acid and the leuco dye 1',3'-dimethyl-6'-diethylaminofluorane, boron nitride nanosheet were added to the molten phase change solvent octadecanol, wherein the mass ratio of 1',3'-dimethyl-6'-diethylaminofluorane, L-ascorbic acid, octadecanol was 1:12:80, and the amount of boron nitride nanosheet was 10% (10% of the total mass of the solid-liquid phase change solvent, the weakly acidic polyhydroxyl biomass or biomass derivative, boron nitride nanosheet, and the leuco dye). It was heated to 120℃ and stirred for 3h, and then placed in a vacuum box with a vacuum degree of -0.1 MPa at 80℃ for 3h to obtain a biomass thermochromic dye;

[0055] Figure 8 For the temperature response color change diagram of the biomass thermochromic dye in Example 2, when the environmental temperature is lower than the melting point of the dye, the biomass thermochromic dye is in a red solid state, and as the temperature rises, when the environmental temperature is higher than the melting point of the dye, the thermochromic dye is in a colorless liquid state, showing significant temperature response color change performance.

[0056] (2) The AEAPS was used to modify the surface of the cleaned glass sheet to obtain the AEAPS modified glass sheet. The vinyl dimethyl silane 2.0 g was mixed with 2.0 g of the salt template agent potassium chloride, and then the mixture was uniformly dispersed. Then, 0.1 g of the mixture of platinum catalyst and silicone oil was added, and the mixture was uniformly dispersed by rapid stirring. Then, the bubbles in the solution were removed under the condition of 25 °C and vacuum for 30 min to obtain a film forming solution. The film forming solution was cast on the surface of the AEAPS modified glass sheet by using the gradient crosslinking strategy. After the platinum catalyst diffused to the modified glass for 30 min, the gel film containing the template agent was obtained by curing at 70 °C for 6 h. Then, the gel film was immersed in deionized water, and ultrasonic treatment was performed at 40 °C for 10 h, wherein the water was replaced every 2 h to remove the template agent sodium chloride in the gel film. Subsequently, the gel film was taken out and placed in a blast drying oven at 65 °C for 2 h to remove the water in the gel film, thereby obtaining a polydimethylsiloxane porous gel film.

[0057] Figure 9 For the cross-sectional SEM image of the porous gel film in Example 2, after the salt template agent was removed, the single-sided adhesive porous gel film had a large number of micrometer-sized pore structures, which provided space for the filling of the biomass thermochromic dye and the volume expansion after melting.

[0058] (3) The biomass thermochromic dye prepared in step (1) was heated and melted to obtain an impregnation phase solution. The porous gel film prepared in step (2) was immersed in the molten thermochromic dye, and the dye was allowed to fill into the pore structure of the porous gel film under the condition of 120 °C and vacuum for 5 h. Subsequently, the gel film was taken out and placed in an oven at 80 °C, and the thermochromic dye on the surface of the gel film was repeatedly absorbed by an oil absorption paper until no dye leaked after repeated heating. Thus, a biomass thermochromic flexible film was obtained, which could change color from red to white as the temperature increased.

[0059] Figure 10 For the cross-sectional SEM image of the shape-stable biomass thermochromic porous film in Example 2, the Figure 10 It can be seen that the thermochromic dye has been filled into the pore structure of the porous gel film, and the crystalline thermochromic dye is tightly wrapped by the support material of the porous gel film. This is mainly due to the strong capillary force and surface tension of the micrometer-sized pore structure on the molten dye, which is beneficial to the stability of the molten thermochromic dye and prevents leakage.

[0060] Example 3

[0061] (1) The solid-liquid phase change solvent octadecanol is heated to a molten state, and the weakly acidic polyhydroxyl biomass or biomass derivative tannic acid and leuco dye crystal violet lactone, boron nitride nanosheet are added to the molten phase change solvent octadecanol, wherein the mass ratio of crystal violet lactone, tannic acid, octadecanol is 1:12:80, and the amount of boron nitride nanosheet is 1% (1% of the total mass of solid-liquid phase change solvent, weakly acidic polyhydroxyl biomass or biomass derivative, boron nitride nanosheet, leuco dye), heated to 120℃ and stirred for 3h, then placed in a vacuum box with a vacuum degree of-0.1MPa at 80℃ for 3h, to obtain a biomass thermochromic dye;

[0062] (2) The surface of the cleaned glass sheet is modified by AEAPS to obtain an AEAPS modified glass sheet; by salt template method, 3.0g of vinyl dimethyl silane is mixed with 1.32g of salt template agent sodium chloride, and after uniform dispersion, 0.3g of a mixture of platinum catalyst and silicone oil is added, and stirred quickly to disperse uniformly, and then the gas bubbles in the solution are removed under vacuum conditions at 25℃ for 30min to obtain a film forming solution; by using a gradient crosslinking strategy, the film forming solution is cast on the surface of the AEAPS modified glass sheet, the platinum catalyst diffuses to the modified glass direction for 30min, and then the template agent containing polysiloxane gel film is obtained by curing at 100℃ for 2h, the gel film is immersed in deionized water, and ultrasonic treatment is carried out at 40℃ for 12h, wherein the water is changed every 2h, to remove the template agent sodium chloride in the gel film, and then it is taken out and placed in a 65℃ air drying oven for 2h to remove the water in the gel film, to obtain a polydimethylsiloxane porous gel film;

[0063] (3) The biomass thermochromic dye prepared in step (1) is heated to melt, which is used as an impregnation phase solution, and the porous gel film prepared in step (2) is immersed in the molten state thermochromic dye, and the dye is fully filled into the pore structure of the porous gel film under vacuum conditions at 80℃ for 5h, and then the gel film is taken out and placed in a 60℃ oven, and the thermochromic dye on the surface of the gel film is repeatedly absorbed by oil absorption paper until no dye leaks after repeated heating, to obtain a yellow biomass thermochromic porous film with a color change temperature of 60℃.

[0064] Example 4

[0065] The preparation method is consistent with that of Example 1, and the only difference is that the leuco dye is 3',6'-dimethoxyfluorane, and a yellow biomass thermochromic porous film is obtained.

[0066] Example 5

[0067] The preparation method is consistent with that of Example 1, and the only difference is that the leuco dye is 7,7-bis(4-(diethylamino)-2-ethoxyphenyl)furo[3,4-b]pyridine-5(7H)-one, and a green biomass thermochromic porous film is obtained.

[0068] Figure 11 The temperature response color change diagram of the biomass thermochromic porous film of blue, red, yellow, and green in Examples 1, 2, 4, and 5 shows that the biomass thermochromic porous film changes from color to white as the temperature rises, showing good temperature response color change performance, and there is no solvent leakage problem.

[0069] Comparative Example 1

[0070] (1) The solid-liquid phase change solvent octadecanol was heated to a molten state, and the weakly acidic polyhydroxyl biomass or biomass derivative L-ascorbic acid and the leuco dye 1',3'-dimethyl-6'-diethylaminofluorane, boron nitride nanosheet were added to the molten fatty alcohol phase change solvent octadecanol, wherein the mass ratio of 1',3'-dimethyl-6'-diethylaminofluorane, L-ascorbic acid, octadecanol was 1:12:80, and the amount of boron nitride nanosheet was 10% (10% of the total mass of solid-liquid phase change solvent, weakly acidic polyhydroxyl biomass or biomass derivative, boron nitride nanosheet, and leuco dye), heated to 120°C and stirred for 3h, and then placed in a vacuum box at 80°C with a vacuum degree of -0.1 MPa for 3h to obtain a biomass thermochromic dye;

[0071] (2) The surface of the cleaned glass sheet was modified using AEAPS to obtain an AEAPS-modified glass sheet. Vinyl dimethyl silane 2.0 g was added to a mixture of platinum catalyst and silicone oil 0.1 g, and rapidly stirred until uniformly dispersed. Then, the solution was degassed under vacuum at 25°C for 30 min to obtain a film-forming solution. The film-forming solution was cast on the surface of the AEAPS-modified glass sheet, and the platinum catalyst diffused towards the modified glass for 30 min. Then, the polydimethylsiloxane gel film was obtained by curing at 70°C for 6h;

[0072] (3) The biomass thermochromic dye prepared in step (1) was heated to a molten state, which was used as an impregnation phase solution. The polydimethylsiloxane gel film prepared in step (2) was immersed in the molten thermochromic dye, and the dye was allowed to fully fill the pore structure of the porous gel film under vacuum at 120°C for 5h. Then, the gel film was taken out and placed in an 80°C oven, and the thermochromic dye on the surface of the gel film was repeatedly absorbed with oil-absorbing paper until no dye leaked upon repeated heating. A stable-shaped biomass thermochromic film was obtained.

[0073] The biomass thermochromic dye prepared in step (1) can change from red to colorless state with the increase of temperature. The thermochromic film changes from white to colorless state with the increase of temperature, and the color change temperature is 60℃. The film shows temperature response color change performance, but only the change of transparency, which is white when the temperature is lower than 60℃, and cannot show color, which is mainly due to the fact that the amount of salt template added in the preparation process of polysiloxane gel film in step (2) is 0, and there is no pore structure in the film. The polysiloxane gel film without pore structure is not conducive to the filling of biomass thermochromic dye in the film according to the original proportion, so it cannot show colored state.

[0074] Comparative example 2

[0075] (1) The solid-liquid phase change solvent tetradecanol was heated to a molten state, and the weakly acidic polyhydroxyl biomass or biomass derivative tannic acid and leuco dye crystal violet lactone, boron nitride nanosheet were added into the molten phase change solvent tetradecanol, wherein the mass ratio of crystal violet lactone, tannic acid and octadecanol was 1:30:100, and the amount of boron nitride nanosheet was 10% (10% of the total mass of solid-liquid phase change solvent, weakly acidic polyhydroxyl biomass or biomass derivative, boron nitride nanosheet and leuco dye), heated to 120℃ and stirred for 3h, then placed in a vacuum box with a vacuum degree of-0.1MPa at 80℃ for 3h, to obtain a biomass thermochromic dye;

[0076] (2) The AEAPS was used to modify the surface of the cleaned glass sheet to obtain an AEAPS modified glass sheet. The salt template method was used to mix 3.0g of vinyl dimethyl silane with 1.32g of salt template potassium chloride, and then 0.3g of a mixture of platinum catalyst and silicone oil was added after uniform dispersion, and then the mixture was quickly stirred to uniformly disperse, and then the gas bubbles in the solution were removed under the condition of vacuum at 25℃ for 30min to obtain a film forming liquid. The film forming liquid was cast on the surface of the AEAPS modified glass sheet by using the gradient crosslinking strategy, and the platinum catalyst diffused to the modified glass for 30min, and then the gel film was obtained by curing at 100℃ for 2h. The gel film was immersed in deionized water at a temperature of 40℃ for 12h, and the water was changed every 2h to remove the template salt sodium chloride in the gel film, and then it was taken out and placed in a blowing drying oven at 65℃ for 2h to remove the water in the gel film, to obtain a porous gel film.

[0077] (3) The biomass thermochromic dye prepared in step (1) is heated and melted to form an impregnation solution, and the porous gel film prepared in step (2) is immersed in the molten thermochromic dye. The dye is allowed to fully fill the porous structure of the porous gel film by impregnating for 5 h under vacuum at 80°C. Then the gel film is taken out and placed in an oven at 60°C. The thermochromic dye on the surface of the gel film is repeatedly absorbed with oil-absorbing paper until no dye is leaked after repeated heating. A shape-stable biomass thermochromic porous film is obtained. The gel film is blue at both high and low temperatures and does not have temperature-responsive color-changing performance.

[0078] Figure 12 For the temperature-responsive color-changing diagram of the biomass thermochromic dye in Comparative Example 2, the biomass thermochromic dye is in a blue solid state when the environmental temperature is lower than the melting point of the dye. As the temperature rises, the biomass thermochromic dye is in a blue liquid state when the environmental temperature is higher than the melting point of the dye. Only a solid-liquid phase transition occurs, but no color change occurs. Therefore, the biomass thermochromic dye does not have temperature-responsive color-changing performance. In the process of preparing the single-sided adhesive biomass thermochromic porous film in the present application, the thermochromic dye based on a three-component color-changing system is used as the filling material of the porous gel film. The mass ratio of the three components, i.e., the leuco dye, the weakly acidic polyhydroxyl biomass or biomass derivative, and the phase change solvent, is crucial to the performance of the thermochromic dye. A suitable ratio needs to be controlled to prepare a thermochromic dye with good temperature-responsive color-changing performance. In Comparative Example 2, the weakly acidic polyhydroxyl biomass or biomass derivative in the three-component ratio accounts for too high a proportion in the system, which causes the leuco dye / developer complex to be unable to separate after formation, the leuco dye / developer complex to continuously exist, and the crystal violet lactone to always exist in an open ring conjugated form. Therefore, the biomass thermochromic porous film fails to be prepared, and the color does not change with temperature.

[0079] Comparative Example 3

[0080] The preparation method and Example 1 are consistent, except that no boron nitride nanosheet is added in step (1). A shape-stable biomass thermochromic porous film is prepared, and the thermal conductivity is 0.23 W / (m·K). As the temperature rises, the color can change from blue to white. Compared with the thermochromic porous film in Example 1 in which 3% of boron nitride is introduced as a thermal conductive material, the thermal conductivity decreases from 0.36 W / (m·K) to 0.23 W / (m·K), indicating that the introduction of boron nitride can improve the thermal conductivity of the thermochromic porous film.

[0081] The examples provided above are not intended to limit the scope covered by the present application, and the described steps are not intended to limit the execution order. Those skilled in the art can make obvious improvements to the present application in combination with existing common knowledge, which also falls within the protection scope defined by the claims of the present application.

Claims

1. A method for preparing a thermochromic porous membrane, characterized in that, Includes the following steps: (1) The solid-liquid phase change solvent is heated to a molten state, and weakly acidic polyhydroxy biomass or biomass derivatives, boron nitride nanosheets, and leuco dyes are added. The reaction is carried out in a vacuum environment to prepare a biomass thermochromic dye. The mass ratio of leuco dye to weakly acidic polyhydroxy biomass or biomass derivatives is 1:0.2~15; the mass ratio of leuco dye to solid-liquid phase change solvent is 1:50~300. (2) The surface of the glass slide was modified with 3-(2-aminoethyl)-aminopropyltrimethoxysilane to obtain modified glass; vinyl dimethylsilane, salt template agent, hydrogenated silicone oil and platinum catalyst were uniformly mixed by salt template method, and the film-forming liquid was obtained by vacuum degassing; the film-forming liquid was cast onto the modified glass using a gradient crosslinking strategy, and then cured, ultrasonically desalted and dried to obtain polydimethylsiloxane porous gel membrane; (3) The biomass thermochromic dye prepared in step (1) is heated and melted, and then filled into the pores of the polydimethylsiloxane porous gel membrane in step (2) by vacuum pressure impregnation process to obtain a single-sided adhesive biomass thermochromic porous membrane with a porous structure.

2. The method for preparing the thermochromic porous membrane according to claim 1, characterized in that, In step (1), the weakly acidic polyhydroxy biomass or biomass derivative is an organic weakly acidic biomass or biomass-derived compound that has electron-accepting properties, and is one of L-ascorbic acid, L-ascorbyl palmitate, tea polyphenols, gallic acid lauryl ester, and tannic acid.

3. The method for preparing the thermochromic porous membrane according to claim 1, characterized in that, In step (1), the leuco dye is an electron-donating organic compound, and is one of crystal violet lactone, methyl red, bromocresol green, bromocresol purple, phenol red, 1′,3′-dimethyl-6′-diethylaminofluorane, 3′,6′-dimethoxyfluorane, 3,3-bis(4-diethylamino-2-ethoxyphenyl)-4-azaphthalide, and 7,7-bis(4-(diethylamino)-2-ethoxyphenyl)furano[3,4-b]pyridine-5(7H)-one.

4. The method for preparing a thermochromic porous membrane according to claim 1, characterized in that, In step (1), the solid-liquid phase change solvent refers to the solid-liquid phase change solvent that can change from solid to molten state when heated to above the phase change temperature of the phase change solvent. The solid-liquid phase change solvent is one or more of lauryl alcohol, myristol, cetyl alcohol, stearyl alcohol, and oleyl alcohol.

5. The method for preparing a thermochromic porous membrane according to claim 1, characterized in that, In step (1), the solid-liquid phase change solvent is one or more of tetradecyl alcohol, hexadecyl alcohol, octadecyl alcohol, and docosyl alcohol.

6. The method for preparing a thermochromic porous membrane according to claim 1, characterized in that, In step (1), the amount of boron nitride nanosheets added is 0.1% to 15% of the total mass of the solid-liquid phase change solvent, weakly acidic polyhydroxy biomass or biomass derivatives, boron nitride nanosheets, and leuco dye.

7. The method for preparing the thermochromic porous membrane according to claim 1, characterized in that, In step (2), the salt template agent is one or more of sodium nitrate, potassium nitrate, sodium chloride, potassium chloride, and sodium sulfate; the ultrasonic desalination time is 6 h to 72 h.

8. The method for preparing a thermochromic porous membrane according to claim 1, characterized in that, In step (2), the mass ratio of vinyl dimethylsilane to the total mass of hydrogenated silicone oil and platinum catalyst is 5~30:1; the mass ratio of salt template agent to the total mass of vinyl dimethylsilane, hydrogenated silicone oil and platinum catalyst is 0.1~1.2:

1.

9. A single-sided adhesive biomass thermochromic porous membrane prepared by any one of claims 1 to 8.

10. The application of the single-sided adhesive biomass thermochromic porous membrane of claim 9 in the fields of wearable sensors, surface temperature indication of instruments and equipment, and flexible electronic devices.

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