Preparation method and application of stretchable temperature-sensitive color-changing film device based on liquid crystal microcapsules

Abstract

The invention discloses a preparation method and application of a stretchable temperature-sensitive color-changing film device based on liquid crystal microcapsules. The cholesteric liquid crystal is packaged through a microencapsulation technology, so that stable protection of liquid crystal molecules is realized, the stability of the material under a mechanical deformation condition is remarkably improved, and flowing and performance degradation of the liquid crystal in a device bending process are effectively prevented. The liquid crystal microcapsule can be processed in an organic solvent system through the solvent-resistant shell layer, a stretchable color-changing film device with excellent mechanical properties and temperature response characteristics is successfully developed by compounding the microencapsulated liquid crystal and a thermoplastic elastomer, and the stretchable color-changing film device can be stably applied to complex curved surfaces and dynamic wrinkle scenes and has wide application prospects. And three-dimensional surface temperature field visualization is realized.

Description

Technical Field

[0001] The present invention belongs to the technical field of liquid crystal materials, and particularly relates to a preparation method and application of a stretchable temperature-sensitive color-changing film device based on liquid crystal microcapsules. Background Art

[0002] As a key physical quantity, the accurate characterization and real-time monitoring of temperature are of great significance to production and life. The visual mapping of the temperature field on the surface of an object can convert complex temperature distribution data into intuitive spatial images, providing an effective means for the analysis and understanding of the temperature field, and having wide application value in the fields of medical diagnosis, industrial detection, scientific research, etc.

[0003] As a core physical quantity characterizing the thermodynamic state of an object, the accurate measurement and dynamic monitoring of temperature are crucial in the fields of industrial production, medical health, and scientific research, etc. The visual mapping technology of the temperature field on the surface of an object provides key support for heat conduction analysis, abnormal hot spot location, etc. by converting the abstract temperature distribution into an intuitive spatial image. However, there are still significant bottlenecks in the prior art in terms of accuracy, cost, and surface adaptability.

[0004] Infrared thermal imaging technology is widely used in the mapping of the temperature field of objects. Although it can achieve non-contact high-precision temperature measurement, it relies on expensive infrared detectors, and the equipment cost is relatively high, which greatly limits its popularization in clinical or daily scenarios. At the same time, this technology is easily affected by uneven surface emissivity and environmental reflection interference, and is prone to temperature measurement deviation on complex curved surfaces (such as human joints or mechanical gears), and complex algorithms are required for compensation.

[0005] The resistive temperature sensor proposed in Patent CN119354355A realizes surface fitting through the serpentine layout of wires and is used for the analysis of the temperature field on three-dimensional surfaces. These sensors rely on external processing circuits for signal analysis, resulting in a large hardware system. In addition, the size and array integration of resistive sensors also limit their spatial resolution ability for measuring temperature field distribution.

[0006] Due to its helical molecular structure, cholesteric liquid crystal materials can dynamically respond to external temperature changes and exhibit selective reflection, making them ideal materials for preparing flexible temperature-sensitive devices.

[0007] The thermochromic liquid crystal film provides a temperature field measurement technology with low cost and no external power supply. For example, Patent CN119329160A obtains a thermochromic liquid crystal film by coating a thermochromic liquid crystal mixture on a polyester flexible substrate and encapsulating it, which can be used for temperature control monitoring. However, existing thermochromic liquid crystal film products usually use polyester as the substrate, lack ductility, and can only be used under flat or simply bent conditions, and cannot conform to three-dimensional curved surfaces for temperature measurement. In addition, the temperature-sensitive devices directly prepared from liquid crystal liquids are prone to uneven thickness of the functional layer during the flexure process, resulting in performance degradation.

[0008] Microcapsule technology can achieve the stabilization of liquid crystal materials. In the application of liquid crystal microcapsules, traditional processes mostly use water-based polymers as matrix materials for coating or film formation. For example, Patent CN112898992A proposes a liquid crystal microcapsule coated with acrylic resin, which is mixed with an aqueous solution of a polymer resin and dried to form a film, having a temperature-sensitive color display function; Patents CN209087263U and CN116376416A mix liquid crystal microcapsules with water-based resins and cure them to form a film to achieve the temperature-sensitive color display function. The water-based resins mentioned include polymers of polyvinyl alcohol, polyacrylate, and polyurethane. Such polymers have limitations of insufficient ductility and low mechanical strength, and it is difficult to meet the mechanical property requirements of flexible devices.

[0009] High-performance elastomeric materials, such as styrene thermoplastic elastomers and polydimethylsiloxane, have excellent stretchability, but their forming process involves an organic solvent system, which conflicts with the aqueous dispersion system commonly used for microcapsules. Summary of the Invention

[0010] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the specification of this application, to avoid obscuring the purpose of this part, the abstract, and the title, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0011] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0012] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for preparing liquid crystal microcapsules.

[0013] To solve the above technical problems, the present invention provides the following technical solutions:

[0014] Mix nematic liquid crystal and a temperature-sensitive chiral dopant evenly according to a mass ratio of 2.1 - 2.8:1, heat and melt, and then cool to obtain cholesteric liquid crystal;

[0015] The suspension obtained by dispersing cholesteric liquid crystal and cellulose nanocrystals is emulsified at a mass ratio of 1:3 to 10 to obtain an oil-in-water type liquid crystal emulsion;

[0016] Formaldehyde and melamine are mixed at a molar ratio of 2 - 3:1, deionized water is added to obtain Solution I, and it is heated and stirred to obtain a melamine-formaldehyde resin prepolymer solution;

[0017] The melamine-formaldehyde resin prepolymer solution is dropped into the liquid crystal emulsion to obtain Solution II. After stirring and reacting Solution II, it is cooled, filtered, washed, and dried to obtain liquid crystal microcapsules;

[0018] Among them, the mass ratio of the melamine-formaldehyde resin prepolymer to the liquid crystal is 1:6.5 to 7.5.

[0019] As a preferred embodiment of the preparation method of the liquid crystal microcapsules of the present invention, wherein: the cholesteric liquid crystal is obtained by heating and melting and then cooling, and the temperature of heating and melting is 60 - 90 °C.

[0020] As a preferred embodiment of the preparation method of the liquid crystal microcapsules of the present invention, wherein: the concentration of cellulose nanocrystals in the suspension is 0.02 - 0.1 wt%.

[0021] As a preferred embodiment of the preparation method of the liquid crystal microcapsules of the present invention, wherein: the pH of Solution I is adjusted to 8 - 10 by a sodium hydroxide solution; the melamine-formaldehyde resin prepolymer solution is obtained by heating and stirring, wherein the temperature of heating and stirring is 70 - 85 °C, and the time of heating and stirring is 20 - 40 min.

[0022] As a preferred embodiment of the preparation method of the liquid crystal microcapsules of the present invention, wherein: the pH of Solution II is adjusted to 4 - 5 by a hydrochloric acid solution; Solution II is stirred and reacted, wherein the stirring speed is 600 - 1000 rpm / min, the reaction temperature is 70 - 85 °C, and the reaction time is 1 - 3 h.

[0023] Another object of the present invention is to overcome the deficiencies in the prior art and provide a liquid crystal microcapsule prepared by the preparation method of the liquid crystal microcapsule.

[0024] Another object of the present invention is to overcome the deficiencies in the prior art and provide a preparation method of a stretchable temperature-sensitive color-changing film device.

[0025] To solve the above technical problems, the present invention provides the following technical solutions:

[0026] An elastomer solution obtained by dissolving a thermoplastic elastomer in toluene is mixed with plant carbon black powder and spin-coated on a silane-modified glass, and the solvent volatilizes to form a flexible black light-absorbing substrate;

[0027] Disperse the liquid crystal microcapsules described in claim 6 and the elastomer solution evenly at a mass ratio of 1:1 to 3, print them on a flexible black light-absorbing substrate using a hollow mold, and dry to obtain a temperature-sensitive color-changing film.

[0028] Mix 6 kinds of oil-based pigments with the elastomer solution respectively, print them around the temperature-sensitive color-changing film on a flexible black light-absorbing substrate using a hollow mold, and dry to obtain 6 color temperature calibration color films.

[0029] Spin-coat a layer of elastomer solution on the whole of the black light-absorbing substrate, the temperature-sensitive color-changing film and the color temperature calibration color films, and dry to obtain a stretchable temperature-sensitive color-changing film device.

[0030] Wherein, the thermoplastic elastomer includes one of styrene thermoplastic elastomer and styrene-ethylene / butene-styrene thermoplastic elastomer, and the concentration of the thermoplastic elastomer in the elastomer solution is 10-30 wt%.

[0031] Another object of the present invention is to overcome the deficiencies in the prior art and provide a stretchable temperature-sensitive color-changing film device prepared by a preparation method of a stretchable temperature-sensitive color-changing film device.

[0032] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of a stretchable temperature-sensitive color-changing film device in the visualization of a three-dimensional surface temperature field.

[0033] Another object of the present invention is to overcome the deficiencies in the prior art and provide a method for visualizing a three-dimensional surface temperature field.

[0034] To solve the above technical problems, the present invention provides the following technical solutions:

[0035] Under a standard light source with a known color temperature, place the stretchable temperature-sensitive color-changing film device described in claim 8 on a standard heating table, change the temperature of the standard heating table, and photograph the color-changing film device at different temperatures with a camera to obtain photos of the color-changing film device at different temperatures.

[0036] Extract the color information of 6 calibration colors and the color-changing film device in the photo, and convert the RGB value into the CIE1931 chromaticity coordinate value (x, y) through formula (A) and formula (B);

[0037] x = (0.4124R + 0.3576G + 0.1805B) / (0.6443R + 1.192G + 1.2032B) formula (A);

[0038] y = (0.2126R + 0.7152G + 0.0722B) / (0.6443R + 1.192G + 1.2032B) formula (B);

[0039] Among them, the color information is the average intensity of each of the R, G, and B channels;

[0040] The relationship between color and temperature is established by three-dimensional curve fitting using the CIE1931 chromaticity coordinate values (x, y) of the color-changing film device and the corresponding temperature, so that any (x, y) coordinate value corresponds to a temperature value;

[0041] The intensity values of the RGB channels in the photos of 6 color temperature calibration colors in two color temperature environments are used to establish the linear calibration curves of the corresponding R, G, and B color channels;

[0042] Under an unknown color temperature, the stretchable temperature-sensitive color-changing film device described in claim 8 is placed on the three-dimensional surface to be measured, a photo is taken with a camera, the picture of the color-changing film area is imported into the MATLAB program for image processing, each pixel of the picture is traversed, and the intensity values of the R, G, and B channels of each pixel are substituted into the linear calibration curves of the R, G, and B color channels to obtain the corresponding intensity values of the R, G, and B channels under the known color temperature, and the picture after color temperature calibration is output;

[0043] The picture after color temperature calibration is processed with the MATLAB program, each pixel of the picture is traversed, the intensity values of the R, G, and B channels of each pixel are converted into CIE1931 chromaticity coordinate values (x, y) according to formulas (A) and (B), the chromaticity coordinate values (x, y) of each pixel are calculated and compared with the three-dimensional fitting curve to obtain the closest distance point, and the temperature value corresponding to the closest distance point is the temperature of this area, and finally a visual three-dimensional surface temperature field image is output.

[0044] Advantages of the present invention:

[0045] (1) The present invention utilizes the orthogonal solvent theory, coats the liquid crystal with a shell material resistant to organic solvents and optimizes the corresponding process parameters. The prepared microcapsules are not prone to swelling and dissolution during the compounding process with the elastomer, maintaining their temperature-responsive function and realizing the stabilization protection of liquid crystal molecules;

[0046] (2) The stretchable temperature-sensitive color-changing film prepared based on the liquid crystal microcapsules of the present invention significantly improves the stability of the material under mechanical deformation conditions, effectively preventing the flow and performance attenuation of the liquid crystal during the deformation of the device; the solvent-resistant shell enables the liquid crystal microcapsules to be processed in an organic solvent system. By compounding the microencapsulated liquid crystal with a thermoplastic elastomer, a stretchable color-changing film device with excellent mechanical properties and temperature-responsive characteristics is successfully developed, which can be stably applied to complex curved surfaces and dynamic folding scenarios;

[0047] (3) The three-dimensional surface temperature field visualization method of the present invention has the following remarkable advantages: First, by adopting a simplified data acquisition method, rapid mapping and analysis of the three-dimensional surface temperature field can be achieved; second, it has excellent environmental light adaptability and can work stably under different lighting conditions; third, through a low-cost preparation process, a high-performance three-dimensional surface temperature field analysis function is realized, and it has broad application prospects in the fields of industrial detection, biomedicine, etc. Description of the Drawings

[0048] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Among them:

[0049] Figure 1 It is the reflection spectrum diagram of the cholesteric liquid crystal prepared in Example 1 of the present invention at different temperatures.

[0050] Figure 2 It is the reflection spectrum diagram of the liquid crystal microcapsules prepared in Example 1 of the present invention at different temperatures.

[0051] Figure 3 It is the schematic structural diagram of the thermochromic film and 6 color temperature calibration color films on the flexible black light-absorbing substrate in Example 2 of the present invention.

[0052] Figure 4 It is the micrograph of the stretchable thermochromic film prepared in Example 2 of the present invention.

[0053] Figure 5 It is the uniaxial tensile property diagram of the stretchable thermochromic film prepared in Example 2 of the present invention.

[0054] Figure 6 It is the reflection spectrum diagram of the stretchable thermochromic film device prepared in Example 2 of the present invention at different temperatures.

[0055] Figure 7 It is the photo of the stretchable thermochromic film device at different temperatures under the standard light source with a color temperature of 6500K in Example 3 of the present invention.

[0056] Figure 8 It is the three-dimensional curve graph of the fitted color and temperature in Example 3 of the present invention.

[0057] Figure 9 It is the linear calibration curve of the R, G, and B color channels in Example 3 of the present invention.

[0058] Figure 10Schematic diagram of the three-dimensional surface of the back of the hand to be measured with the thermochromic film device in Embodiment 3 of the present invention.

[0059] Figure 11 Visualized three-dimensional temperature field image output in Embodiment 3 of the present invention.

[0060] Figure 12 Reflection spectra of the liquid crystal microcapsules prepared in Embodiment 4 of the present invention at different temperatures.

[0061] Figure 13 Morphology image of the liquid crystal microcapsules prepared in Comparative Example 1 of the present invention under a microscope.

[0062] Figure 14 Morphology image of the liquid crystal microcapsules prepared in Comparative Example 2 of the present invention under a microscope.

[0063] Figure 15 Morphology image of the liquid crystal microcapsules prepared in Comparative Example 3 of the present invention under a microscope.

[0064] Figure 16 Morphology image of the color-changing film prepared in Comparative Example 4 of the present invention under a microscope at 10% tensile deformation. Detailed implementation manners

[0065] To make the above objects, features and advantages of the present invention more obvious and understandable, the following detailed description of the specific implementation manners of the present invention is made in conjunction with the embodiments of the specification.

[0066] Many specific details are set forth in the following description in order to fully understand the present invention, but the present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0067] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure or characteristic that can be included in at least one implementation manner of the present invention. The "in one embodiment" that appears in different places in this specification does not all refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0068] The raw materials used in the present invention are commercially available without special instructions.

[0069] Embodiment 1

[0070] This embodiment provides a method for preparing liquid crystal microcapsules, specifically as follows:

[0071] (1) The nematic liquid crystal GXV-7822-075 and the temperature-sensitive chiral dopant TP811 were mixed evenly according to a mass ratio of 2.4:1, heated and melted at 80 °C, and slowly cooled to room temperature to obtain a cholesteric liquid crystal.

[0072] (2) The cellulose nanocrystals were ultrasonically dispersed with an ultrasonic cell disruptor to obtain a suspension. Among them, the concentration of cellulose nanocrystals in the suspension was 0.05 wt%. The cholesteric liquid crystal obtained in step (1) and the suspension obtained by dispersing cellulose nanocrystals were ultrasonically emulsified for 20 min according to a mass ratio of 1:5 with an ultrasonic cell disruptor to obtain an oil-in-water type liquid crystal emulsion;

[0073] (3) Formaldehyde and melamine were mixed according to a molar ratio of 3:1, deionized water was added to obtain solution I, and the pH was adjusted to 8-10 with a sodium hydroxide solution, and stirred at 70 °C for 20 min until the solution became clear to obtain a melamine-formaldehyde resin prepolymer solution;

[0074] (4) Under the condition of 70 °C, the melamine-formaldehyde resin prepolymer solution prepared in step (3) was slowly added dropwise to the liquid crystal emulsion prepared in step (2) to obtain solution II, and the pH was adjusted to 4-5 with a hydrochloric acid solution, and stirred at a speed of 800 rpm for in-situ polymerization reaction for 2 h. After the reaction, it was slowly cooled to room temperature, and the precipitate obtained from the reaction was filtered, washed, and dried to obtain the liquid crystal microcapsules of this example. Among them, the mass ratio of the melamine-formaldehyde resin prepolymer to the liquid crystal was 1:7.

[0075] The reflection spectra of the cholesteric liquid crystal and the liquid crystal microcapsules prepared in Test Example 1 at different temperatures were tested, and the results are as Figures 1 - 2 shown.

[0076] Figure 1 is the reflection spectrum of the cholesteric liquid crystal at different temperatures. It can be seen from this figure that the reflection band of the cholesteric liquid crystal changes with temperature and has temperature-variable properties.

[0077] Figure 2 is the reflection spectrum of the liquid crystal microcapsules at different temperatures. It can be seen that the reflection band of this microcapsule also changes with temperature and has temperature-variable properties.

[0078] Example 2

[0079] This example provides a preparation method of a stretchable temperature-sensitive color-changing film device doped with the liquid crystal microcapsules of Example 1, specifically as follows:

[0080] (1) The styrene thermoplastic elastomer (SIS) is dissolved in toluene to obtain an elastomer solution, wherein the concentration of SIS in the elastomer solution is 20 wt%; the elastomer solution is mixed with plant carbon black powder and spin-coated on glass modified with octadecyltrichlorosilane (OTS). After the solvent naturally evaporates, a uniform flexible black light-absorbing substrate is formed;

[0081] (2) The liquid crystal microcapsules prepared in Example 1 are dispersed evenly with the elastomer solution in step (1) according to a mass ratio of 1:1, and printed on the flexible black light-absorbing substrate in step (1) with a 50-μm-thick hollow mold. After drying the solvent at 40 °C, a thermosensitive color-changing film is formed;

[0082] (3) Six oily pigments are respectively mixed evenly with the elastomer solution in step (1) according to a mass ratio of 3:2. Referring to Figure 3 , they are printed around the thermosensitive color-changing film on the flexible black light-absorbing substrate in step (2) with a 200-μm-thick hollow mold, and dried to obtain six color temperature calibration color films, which are white (R255, G255, B255), gray (R210, G230, B230), black (R30, G30, B50), red (R210, G40, B20), green (R0, G200, B65), and blue (R0, G160, B255);

[0083] (4) On the whole of the black light-absorbing substrate, the thermosensitive color-changing film and the color temperature calibration color film, a layer of the elastomer solution in step (1) is spin-coated and dried to encapsulate the entire device, and the stretchable thermosensitive color-changing film device of this example is obtained.

[0084] Observe the morphology of the stretchable thermosensitive color-changing film prepared in step (2) of Example 2 under a microscope, and the results are as Figure 4 shown.

[0085] Conduct a uniaxial tensile property test on the stretchable thermosensitive color-changing film prepared in step (2) of Example 2, and the results are as Figure 5 shown. It can be seen from Figure 5 that the thermosensitive color-changing film still has the temperature-responsive color-changing function under a 150% tensile deformation.

[0086] Test the reflection spectrum of the stretchable thermosensitive color-changing film device prepared in Example 2 at different temperatures, and the results are as Figure 6 shown. It can be seen that in the temperature range of 30-40 °C, the reflection band of the stretchable thermosensitive color-changing film device changes with the temperature.

[0087] Example 3

[0088] This example provides a three-dimensional surface temperature field visualization method using the stretchable thermosensitive color-changing film device of Example 2, specifically as follows:

[0089] (1) Calibrating the device under a fixed color temperature environment: Under a standard light source with a known color temperature of 6500K, place the stretchable temperature-sensitive color-changing film device prepared in Example 2 on a standard heating table, change the temperature of the standard heating table, and use a camera to photograph the color-changing film device at different temperatures respectively to obtain photos of the color-changing film in the color-changing film device at different temperatures, as Figure 7 shown;

[0090] Extract the color information of the color-changing film in the photo, that is, the average intensity value of each channel of RGB. Convert the obtained RGB values into CIE1931 chromaticity coordinate values (x, y) through Equation (A) and Equation (B), where Equation (A) and Equation (B) are as follows:

[0091] x = (0.4124R + 0.3576G + 0.1805B) / (0.6443R + 1.192G + 1.2032B) Equation (A);

[0092] y = (0.2126R + 0.7152G + 0.0722B) / (0.6443R + 1.192G + 1.2032B) Equation (B);

[0093] Establish the relationship between color and temperature by three-dimensional curve fitting using the CIE1931 chromaticity coordinate values (x, y) of the color-changing film and the corresponding temperature, so that any (x, y) coordinate value corresponds to the temperature value, as Figure 8 shown.

[0094] (2) Photo information processing: Use the RGB channel intensity values in the photos of 6 color temperature calibration colors under two color temperature environments to establish linear calibration curves for the corresponding R, G, and B color channels, as Figure 9 shown, where the two color temperature environments are 6500K color temperature and 3000K color temperature during image acquisition.

[0095] (3) Three-dimensional surface temperature image acquisition: Under an unknown color temperature, place the stretchable temperature-sensitive color-changing film device prepared in Example 2 at the three-dimensional surface position to be measured, and use a camera to take a photo, where the three-dimensional surface to be measured is the back of the hand skin, as Figure 10 ;

[0096] Import the picture of the color-changing film area into the MATLAB program for image processing, traverse each pixel of the picture, substitute the RGB channel intensity values of each pixel into the linear calibration curves of the R, G, and B color channels obtained in step (2) to obtain the corresponding RGB channel intensity values under the known color temperature of 6500K, and output the picture after color temperature calibration;

[0097] Use the MATLAB program to process the pictures after color temperature calibration. Traverse each pixel of the picture, convert the R, G, and B channel intensity values of each pixel into CIE1931 chromaticity coordinate values (x, y) according to the formula in step (1), calculate the comparison between the chromaticity coordinate values (x, y) of each pixel and the three-dimensional fitting curve obtained in step (1), obtain the nearest distance point, and the temperature value corresponding to the nearest distance point is the temperature of this area. Finally, output a visual three-dimensional temperature field image, such as Figure 11 shown.

[0098] From Figure 11 it can visually display the temperature information of the three-dimensional surface of the dorsal hand skin.

[0099] Example 4

[0100] This example provides a method for preparing liquid crystal microcapsules. The difference from Example 1 is that the nematic liquid crystal GXV-7822-075 is adjusted to the nematic liquid crystal E7, the thermosensitive chiral dopant TP811 is adjusted to the thermosensitive chiral dopant R811, and the mass ratio of the nematic liquid crystal to the thermosensitive chiral dopant is adjusted to 2.8:1. The rest of the preparation process is the same as that of Example 1, and the liquid crystal microcapsules of this example are prepared.

[0101] Test the reflection spectra of the liquid crystal microcapsules prepared in Example 4 at different temperatures. The results are as Figure 12 shown. It can be seen from this figure that the reflection band of this microcapsule still changes with temperature, and only the temperature response interval and the reflection peak width are slightly different from those of the microcapsules prepared in Example 1.

[0102] Example 5

[0103] This example provides a method for preparing a stretchable thermosensitive color-changing film device. The difference from Example 2 is that the type of elastomer is adjusted to styrene-ethylene / butene-styrene thermoplastic elastomer (SEBS), and the rest of the preparation process is the same as that of Example 2, and the stretchable thermosensitive color-changing film device of this example is prepared.

[0104] Comparative Example 1

[0105] This comparative example provides a method for preparing liquid crystal microcapsules. The difference from Example 1 is that the melamine-formaldehyde resin wall material is adjusted to urea-formaldehyde resin, and the rest of the preparation process is the same as that of Example 1, and the liquid crystal microcapsules of this comparative example are prepared.

[0106] When the microcapsules prepared in Comparative Example 1 are mixed with an elastomer solution using toluene as a solvent to prepare a color-changing film device, the liquid crystal microcapsules prepared using urea-formaldehyde resin as the wall material swell under the action of toluene, and the microcapsule structure is damaged, resulting in the loss of the thermosensitive color-changing function of the liquid crystal microcapsules, as Figure 13 shown.

[0107] Comparative Example 2

[0108] This comparative example provides a method for preparing liquid crystal microcapsules. The difference from Example 1 is that the mass ratio of melamine-formaldehyde resin prepolymer to liquid crystal in step (4) is adjusted to 1:6, and the rest of the preparation process is the same as that of Example 1, and the liquid crystal microcapsules of this comparative example are prepared.

[0109] The morphology of the liquid crystal microcapsules prepared in Comparative Example 2 was tested, and the results are as Figure 14 shown.

[0110] From Figure 14 it can be seen that the excessive concentration of melamine-formaldehyde resin prepolymer leads to an unsatisfactory microcapsule morphology, resulting in massive adhesion, and the rough capsule wall causes severe diffuse reflection, masking part of the structural color of the cholesteric liquid crystal.

[0111] Comparative Example 3

[0112] This comparative example provides a method for preparing liquid crystal microcapsules. The difference from Example 1 is that the mass ratio of melamine-formaldehyde resin prepolymer to liquid crystal in step (4) is adjusted to 1:8, and the rest of the preparation process is the same as that of Example 1, and the liquid crystal microcapsules of this comparative example are prepared.

[0113] The morphology of the liquid crystal microcapsules prepared in Comparative Example 3 was tested, and the results are as Figure 15 shown.

[0114] From Figure 15 it can be seen that the too low concentration of the prepolymer fails to effectively coat the liquid crystal to form microcapsules, which easily leads to the rupture of the microcapsules during subsequent processing in an organic solution and the leakage of the liquid crystal.

[0115] Comparative Example 4

[0116] This example provides a method for preparing a thermochromic film device. The difference from Example 2 is that the styrene thermoplastic elastomer (SIS) in step (1) dissolved in toluene to obtain an elastomer solution is adjusted to polyvinyl alcohol dissolved in water to obtain a polyvinyl alcohol solution, and the rest of the preparation process is the same as that of Example 2, and the color-changing film device of this example is prepared.

[0117] The tensile properties of the color-changing film device prepared in Comparative Example 4 were tested, and it was found that the ductility of the color-changing film was less than 10%, and it could only be simply bent, unable to fit complex curved surfaces, and could not meet the requirements of flexible temperature measurement.

[0118] When the tensile deformation was 10%, the morphology of the color-changing film was tested, as Figure 16As shown, it can be seen that in the color-changing film prepared with an aqueous solution of polyvinyl alcohol, the microcapsules embedded in the matrix are structurally damaged under stress, thereby affecting the thermochromic function.

[0119] In summary, the present invention provides a method for preparing a stretchable thermochromic film device based on liquid crystal microcapsules and its application. The stretchable thermochromic film device has obvious stretching and deformation capabilities, can conform to complex three-dimensional curved surfaces to display their surface temperatures, and can extract temperature field information through the processing of photos.

[0120] Compared with the prior art, this solution effectively solves the bottleneck problem of temperature-responsive color-changing materials in temperature field measurement applications, that is, although traditional cholesteric liquid crystals have thermochromic properties, they are easily interfered by external mechanical stress during actual use, resulting in performance degradation. The present invention encapsulates cholesteric liquid crystals through microencapsulation technology, which not only realizes the stable protection of liquid crystal molecules but also significantly improves the stability of the material under mechanical deformation conditions, effectively preventing the flow and performance attenuation of liquid crystals during the flexure of the device.

[0121] Furthermore, by compounding microencapsulated liquid crystals with thermoplastic elastomers, a stretchable color-changing film device with excellent mechanical properties and temperature-responsive characteristics has been successfully developed, which can be stably applied to complex curved surfaces and dynamic wrinkling scenarios.

[0122] The three-dimensional surface temperature field visualization method of the present invention has the following remarkable advantages: First, a simplified data acquisition method is adopted, which can realize the rapid mapping and analysis of the three-dimensional surface temperature field; second, it has excellent environmental light adaptability and can work stably under different lighting conditions; third, a high-performance three-dimensional surface temperature field analysis function is realized through a low-cost preparation process, and it has broad application prospects in industrial inspection, biomedicine and other fields.

[0123] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing liquid crystal microcapsules, characterized in that: Comprising, Mixing a nematic liquid crystal and a temperature-sensitive chiral dopant uniformly in a mass ratio of 2.1 - 2.8:1, heating and melting, and cooling to obtain a cholesteric liquid crystal; Emulsifying the suspension obtained by dispersing the cholesteric liquid crystal and cellulose nanocrystals in a mass ratio of 1:3 - 10 to obtain an oil-in-water type liquid crystal emulsion; Mixing formaldehyde and melamine in a molar ratio of 2 - 3:1, adding deionized water to obtain Solution I, and heating and stirring to obtain a melamine-formaldehyde resin prepolymer solution; Dropping the melamine-formaldehyde resin prepolymer solution into the liquid crystal emulsion to obtain Solution II, stirring and reacting Solution II, then cooling, filtering, washing, and drying to obtain liquid crystal microcapsules; Wherein, the mass ratio of the melamine-formaldehyde resin prepolymer to the liquid crystal is 1:6.5 - 7.

5.

2. The preparation method of the liquid crystal microcapsule according to claim 1, wherein: For the heating, melting, and cooling to obtain the cholesteric liquid crystal, the heating and melting temperature is 60 - 90 °C.

3. The preparation method of the liquid crystal microcapsules according to claim 1, wherein: The concentration of cellulose nanocrystals in the suspension is 0.02 - 0.1 wt%.

4. The preparation method of the liquid crystal microcapsule according to claim 1, characterized in that: Adjusting the pH of Solution I to 8 - 10 with a sodium hydroxide solution; for the heating and stirring to obtain the melamine-formaldehyde resin prepolymer solution, the heating and stirring temperature is 70 - 85 °C, and the heating and stirring time is 20 - 40 min.

5. The preparation method of the liquid crystal microcapsules according to claim 1, characterized in that: Adjusting the pH of Solution II to 4 - 5 with a hydrochloric acid solution; for the stirring and reacting of Solution II, the stirring speed is 600 - 1000 rpm / min, the reaction temperature is 70 - 85 °C, and the reaction time is 1 - 3 h.

6. The liquid crystal microcapsules prepared by the preparation method according to any one of claims 1 - 5.

7. A preparation method of a stretchable temperature-sensitive color-changing film device, characterized in that: Comprising, Dissolving a thermoplastic elastomer in toluene to obtain an elastomer solution, mixing it evenly with plant carbon black powder, spin-coating on a silane-modified glass, and volatilizing the solvent to form a flexible black light-absorbing substrate; Dispersing the liquid crystal microcapsules according to claim 6 and the elastomer solution evenly in a mass ratio of 1:1 - 3, printing with a hollow mold on the flexible black light-absorbing substrate, and drying to obtain a temperature-sensitive color-changing film; Mixing 6 kinds of oil-based pigments with the elastomer solution respectively, printing with a hollow mold around the temperature-sensitive color-changing film on the flexible black light-absorbing substrate, and drying to obtain 6 color temperature calibration color films; Spin-coating a layer of elastomer solution on the whole of the black light-absorbing substrate, the temperature-sensitive color-changing film, and the color temperature calibration color films, and drying to obtain a stretchable temperature-sensitive color-changing film device; Wherein, the thermoplastic elastomer includes one of a styrene thermoplastic elastomer and a styrene-ethylene / butylene-styrene thermoplastic elastomer, and the concentration of the thermoplastic elastomer in the elastomer solution is 10 - 30 wt%.

8. The stretchable temperature-sensitive color-changing film device prepared by the preparation method according to claim 7.

9. Application of the stretchable temperature-sensitive color-changing film device according to claim 8 in three-dimensional surface temperature field visualization.

10. A method for visualizing a three-dimensional surface temperature field, characterized in that: Comprising, Under a standard light source with a known color temperature, placing the stretchable temperature-sensitive color-changing film device according to claim 8 on a standard heating table, changing the temperature of the standard heating table, and photographing the color-changing film device at different temperatures with a camera to obtain photos of the color-changing film at different temperatures in the color-changing film device; Extract the color information of the color-changing film in the photo, and convert the RGB values into CIE1931 chromaticity coordinate values (x, y) through Equation (A) and Equation (B); x = (0.4124R + 0.3576G + 0.1805B) / (0.6443R + 1.192G + 1.2032B), Equation (A); y = (0.2126R + 0.7152G + 0.0722B) / (0.6443R + 1.192G + 1.2032B), Equation (B); wherein, the color information is the average intensity of each channel of R, G, and B; Establish the relationship between color and temperature by three-dimensional curve fitting using the CIE1931 chromaticity coordinate values (x, y) of the color-changing film and the corresponding temperature, so that any (x, y) coordinate value corresponds to the temperature value; Use the RGB channel intensity values in the photos of 6 color temperature calibration colors in two color temperature environments to establish the linear calibration curves of the corresponding R, G, and B color channels; Under unknown color temperature, place the stretchable temperature-sensitive color-changing film device described in Claim 8 on the three-dimensional surface to be measured, take a photo with a camera, import the picture of the color-changing film area into the MATLAB program for image processing, traverse each pixel of the picture, substitute the R, G, and B channel intensity values of each pixel into the linear calibration curves of the R, G, and B color channels to obtain the corresponding R, G, and B channel intensity values under the known color temperature, and output the picture after color temperature calibration; Process the picture after color temperature calibration with the MATLAB program, traverse each pixel of the picture, convert the R, G, and B channel intensity values of each pixel into CIE1931 chromaticity coordinate values (x, y) according to Equation (A) and Equation (B), calculate the comparison between the chromaticity coordinate values (x, y) of each pixel and the three-dimensional fitting curve to obtain the nearest distance point, and the temperature value corresponding to the nearest distance point is the temperature of this area, and finally output the visual three-dimensional surface temperature field image.

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