Color-changeable material based on dye liquid crystal technology and application thereof

Abstract

The invention relates to the field of intelligent materials, and discloses a variable color material based on a dye liquid crystal technology and application of the variable color material, and the variable color material is formed by compounding a main nematic phase liquid crystal, a chiral dopant and a functional anthraquinone dye with a specific structure according to a predetermined mass percentage. When an electric field is not applied, the chiral dopant induces the liquid crystal and the dye molecules to form a spiral ordered structure, and the structure shows a strong absorption characteristic on incident light, so that the material is in a low-reflectivity dark-color heat absorption state. When an electric field is applied, the liquid crystal and the dye molecules synergistically respond, the long axes of the liquid crystal and the dye molecules are rearranged in the direction of the electric field, an original spiral structure is damaged, and the material is converted into a high-reflectivity light-color low-heat-absorption state. Through on-off of an electric field, rapid and reversible switching between the two states can be realized, so that efficient cooperative regulation and control of the optical reflectivity and the heat absorption performance of the material are achieved.

Description

Technical Field

[0001] This invention relates to the field of smart materials, specifically to a color-changing material based on dye liquid crystal technology and its applications. Background Technology

[0002] Materials with tunable optical and thermal properties have broad application prospects in fields such as building energy conservation, intelligent transportation, and information display. By actively changing the color, reflectivity, or absorptivity of materials, dynamic management of light and heat radiation can be achieved to adapt to different environmental conditions or functional requirements.

[0003] Currently, the main technical solutions for controlling the optical properties of materials include electrochromic technology, thermochromic technology, and liquid crystal technology. Electrochromic technology alters the transmission or reflection spectrum of a material by applying an electric field to drive the insertion and extraction of ions within the material; however, this process typically has a slow response speed and requires improvement in cycling stability. Liquid crystal technology uses an external electric field to change the orientation of liquid crystal molecules, thereby modulating the polarization, phase, or scattering of light, and has been widely used in display devices. Regarding the control of thermal properties, existing technologies mainly rely on low-emissivity coatings or phase-change energy storage materials. The thermal parameters of these materials are usually static and cannot be actively adjusted according to changes in the external environment.

[0004] In existing technologies, achieving active and coordinated control of both optical appearance and thermal performance simultaneously typically requires integrating different functional units. For example, this involves physically bonding an electrically controlled color-changing layer with a separate thermal insulation or heat dissipation layer. This multi-layered composite structure not only increases the overall thickness, weight, and manufacturing cost of the device but also leads to decreased reliability due to material incompatibility and suboptimal interface bonding between functional layers. Furthermore, existing single-material systems exhibit weak correlation between changes in their optical state and thermal radiation characteristics under an electric field, making it difficult to achieve effective control of color and thermal management simultaneously over a wide range, thus failing to meet the demands of high-performance applications. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a color-changing material based on dye liquid crystal technology and its application, which solves the problems in existing technologies that require multi-layer composite structures to achieve dynamic control of optical and thermal properties simultaneously, as well as the low correlation between optical state and thermal properties in single material systems, making it difficult to achieve efficient synergistic changes.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solution: a color-changing material based on dye liquid crystal technology and its application.

[0007] The first aspect of this invention provides a color-changing material based on dye-liquid crystal technology, the color-changing material being composed of the following components by mass percentage:

[0008] Main liquid crystal material: 88.0%-98.0%;

[0009] Functional anthraquinone dyes: 1.5%-2.5%;

[0010] Chiral dopant: 0.2%-0.4%;

[0011] The main liquid crystal material is composed of 4-cyano-4'-pentylbiphenyl and 4-cyano-4'-heptylbiphenyl, with a mass ratio between the two ranging from 65.0:33.0 to 75.0:23.0.

[0012] In the technical solution provided by this invention, the working mechanism is as follows: the chiral dopant induces the host liquid crystal material to spontaneously form a periodic helical structure under low electric field or no electric field conditions, and the structure produces Bragg reflection of incident light of a specific wavelength; at the same time, the functional anthraquinone dye molecules are arranged in an orderly manner along the long axis of the host liquid crystal molecules, and produce anisotropic absorption of incident light.

[0013] When the orientation of liquid crystal molecules is changed by an external electric field, the orientation of dye molecules also changes accordingly. This allows for the simultaneous and synergistic modulation of the material's Bragg reflection intensity and anisotropic absorption intensity, enabling controllable transformation of the material's optical and thermal properties.

[0014] In one specific embodiment, the functional anthraquinone dye is prepared by reacting 1,4-diaminoanthraquinone and 4-n-butylphenylboronic acid as raw materials at a reaction temperature of 80-90°C for 18-24 hours under the condition of tetrakis(triphenylphosphine)palladium(0) as catalyst.

[0015] In one specific embodiment, the chiral dopant is (S)-4-(2-methylbutyl)-4'-cyanobiphenyl.

[0016] In one specific embodiment, the color-changing material is sealed within a liquid crystal cell. The liquid crystal cell is composed of two flexible substrates, each with an ITO conductive layer and a polyimide alignment layer on its inner side.

[0017] In one specific embodiment, the polyimide orientation layer is prepared by: polymerizing pyromellitic dianhydride and 4,4'-diaminodiphenyl ether in an N-methyl-2-pyrrolidone solvent to generate a polyamic acid precursor; subsequently, the polyamic acid precursor is subjected to thermal imidization treatment at a temperature of 280-300°C for 1-1.5 hours to form the polyimide orientation layer.

[0018] In one specific embodiment, the polyimide orientation layer is subjected to unidirectional friction treatment, and the friction directions of the polyimide orientation layers on the two flexible substrates are arranged in antiparallel directions at 180°.

[0019] In one specific embodiment, the process parameters for the unidirectional friction treatment are: the rotation speed of the friction roller is set to 200-400 rpm, and the indentation depth is set to 0.3-0.5 mm.

[0020] In one specific embodiment, the two flexible substrates are separated by microsphere spacers with a particle size of 4.0-6.0 μm to control the thickness of the liquid crystal cell.

[0021] A second aspect of this invention provides an application of the aforementioned color-changing material in an intelligent color-changing vehicle body system. This application achieves dynamic adjustment of the vehicle body color by applying AC square wave voltages with different root-mean-square values ​​to the color-changing material. The frequency of the AC square wave voltage is set to 0.8-1.5 kHz.

[0022] When a root mean square voltage of 18.0-25.0V is applied, the main liquid crystal molecules and functional anthraquinone dye molecules are arranged almost perpendicular to the substrate along the direction of the electric field. At this time, the material's absorption of light and Bragg reflection are at their lowest levels, making the car body appear light-colored and highly reflective.

[0023] When a root mean square voltage of 0-4.0V is applied, the main liquid crystal material forms a regular helical structure, and the functional anthraquinone dye molecules are arranged in a helical pattern accordingly. At this time, the material's absorption of light and Bragg reflection are at their highest levels, making the car body appear in a dark, high-absorption state.

[0024] In one specific implementation, the application of the root mean square voltage is determined based on environmental parameters detected by the vehicle-mounted sensors. Specifically, when the external light intensity is detected to be greater than 60,000 Lux and the ambient temperature is greater than 25°C, the control system applies a root mean square voltage of 18.0-25.0V to the color-changing material; when the external light intensity is detected to be greater than 40,000 Lux and the ambient temperature is less than 10°C, the control system applies a root mean square voltage of 0-4.0V to the color-changing material.

[0025] This invention provides a color-changing material based on dye-liquid crystal technology and its applications. It has the following beneficial effects:

[0026] 1. This invention combines a specific ratio of host liquid crystal material, chiral dopant, and functional anthraquinone dye, and uses electric fields of different intensities to control their molecular orientation, enabling the color-changing material to reversibly switch between a dark high-absorption state and a light high-reflection state, thereby achieving synchronous dynamic control of the material's optical appearance and thermal radiation absorption / reflection characteristics.

[0027] 2. This invention introduces a specific functional anthraquinone dye into the host liquid crystal. The anisotropic absorption characteristics of the dye molecules work synergistically with the Bragg reflection characteristics of the host liquid crystal material, so that a single material layer can simultaneously possess both color adjustment and thermal management functions, simplifying the device structure required to achieve the composite function.

[0028] 3. This invention pre-orients liquid crystal molecules by using a polyimide alignment layer that has undergone unidirectional friction treatment, and applies an AC square wave driving signal with a specific frequency and voltage range. This ensures that liquid crystal and dye molecules can undergo stable and uniform transitions between well-defined alignment states, providing a physical basis for achieving automated and precise control based on environmental parameters. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to embodiments, comparative examples, and test examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] Main ingredients:

[0031] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0032] 4-Cyano-4'-pentylbiphenyl, CAS No.: 40817-08-1;

[0033] 4-Cyano-4'-Heptylbiphenyl, CAS No.: 41122-71-8;

[0034] (S)-4-(2-methylbutyl)-4'-cyanobiphenyl, CAS No.: 59137-36-9;

[0035] 1,4-Diaminoanthraquinone, CAS No.: 128-95-0;

[0036] 4-Butylphenylboronic acid, CAS No.: 145240-28-4;

[0037] Tetra(triphenylphosphine)palladium(0), CAS No.: 14221-01-3;

[0038] Pyromellitic dianhydride, CAS No.: 89-32-7;

[0039] 4,4'-Diaminodiphenyl ether, CAS No.: 101-80-4;

[0040] N-Methyl-2-pyrrolidone, CAS No.: 872-50-4.

[0041] Examples 1-3:

[0042] Example 1:

[0043] Preparation of polyimide orientation agent solution:

[0044] In a 500 mL three-necked flask equipped with a mechanical stirrer, nitrogen inlet and outlet pipes, and a condenser, 20.0 g (0.1 mol) of 4,4'-diaminodiphenyl ether and 350 mL of anhydrous N-methyl-2-pyrrolidone were added. The mixture was stirred at room temperature until completely dissolved. The reaction system was placed in an ice-water bath at 0–5 °C, and 21.8 g (0.1 mol) of pyromellitic dianhydride was slowly added in batches over 45 minutes, maintaining the system temperature below 10 °C. After the addition was complete, the ice bath was removed, and the reaction was stirred continuously at room temperature (20–25 °C) for 10 hours to obtain a polyamic acid precursor solution. The obtained solution was diluted with N-methyl-2-pyrrolidone to adjust its solids mass fraction to 3.0%, and then filtered for later use.

[0045] Synthesis of functional anthraquinone dyes:

[0046] Under nitrogen protection, 1,4-diaminoanthraquinone (23.8 g, 0.1 mol), anhydrous potassium carbonate (27.6 g, 0.2 mol), and N,N-dimethylformamide were added sequentially to a 250 mL three-necked flask. The mixture was heated to 80 °C, and then a solution of N,N-dimethylformamide containing 17.8 g, 0.1 mol of 4-n-butylphenylboronic acid and 1.15 g, 1 mol% tetrakis(triphenylphosphine)palladium(0) (1.15 g, 1 mol%) was slowly added dropwise. After the addition was complete, the reaction mixture was stirred at this temperature for 18 hours. After the reaction was completed, the system was cooled to room temperature, and the reaction solution was poured into water to precipitate a solid precipitate. The precipitate was collected by vacuum filtration and washed sequentially with deionized water and ethanol. The crude product was purified by silica gel column chromatography to obtain the target functional anthraquinone dye.

[0047] Preparation of color-changing liquid crystal mixtures:

[0048] Weigh each component precisely according to the following mass:

[0049] 4-Cyano-4'-pentylbiphenyl: 65.22g;

[0050] 4-Cyano-4'-Heptylbiphenyl: 33.08g;

[0051] Functional anthraquinone dye prepared in the synthesis of functional anthraquinone dyes: 1.50 g;

[0052] (S)-4-(2-methylbutyl)-4'-cyanobiphenyl: 0.20g.

[0053] Add all weighed components to a clean brown sample vial. Place the vial on a magnetic stirrer, set the temperature to 80°C, and stir at 300 rpm for 3 hours. Then, transfer the vial to a vacuum drying oven and degas it at 60°C for 1 hour. After degassing, allow it to cool naturally to room temperature under a nitrogen atmosphere and seal it for later use.

[0054] Fabrication of color-changing devices:

[0055] Cut a PET flexible substrate with an ITO conductive layer pre-coated on its surface into a predetermined size, place it in acetone, isopropanol and deionized water in sequence, ultrasonically clean each for 10 minutes, remove it and blow it dry with high-purity nitrogen gas, and then put it in an oven at 110°C to dry for 30 minutes.

[0056] The prepared PI solution was spin-coated onto a clean ITO substrate at 2500 rpm for 40 seconds using a spin coating method. The coated substrate was then pre-baked on a hot plate at 80°C for 10 minutes. Afterward, it was transferred to a nitrogen atmosphere furnace and the temperature was programmed to 280°C for thermal imidization treatment for 1 hour.

[0057] After the substrate has cooled to room temperature, a friction machine with a cloth roller is used to perform unidirectional friction treatment on the surface of the PI alignment layer. The speed of the friction roller is set to 200 rpm and the pressing depth is controlled at 0.3 mm.

[0058] 4.0 μm silica microspheres were dispersed in anhydrous ethanol and sprayed evenly onto the surface of a rub-treated substrate. UV-curable sealant was applied to the edge region of another treated substrate using screen printing, with injection ports pre-drilled. The two substrates were then aligned and stacked with the rubbing directions antiparallel at 180°. The laminate was placed in a press and pressed under 0.1 MPa pressure, while a 365 nm UV lamp was used at 60 mW / cm². 2 Irradiate the sealant with light intensity for 90 seconds to fully cure it and form a hollow liquid crystal cell.

[0059] The prepared empty liquid crystal cell was placed in a vacuum of less than 10. -3In a vacuum chamber of Pa, the prepared dye-liquid crystal mixture was injected into the cell at a temperature of 70°C using capillary action. After injection, the injection port was sealed with UV-curable adhesive and then cured again under the same UV irradiation conditions to obtain the color-changing device of Example 1.

[0060] Example 2:

[0061] Preparation of polyimide orientation agent solution:

[0062] 4,4'-Diaminodiphenyl ether (20.0 g, 0.1 mol) was dissolved in 350 mL of anhydrous N-methyl-2-pyrrolidone. In an ice-water bath at 0–5 °C, pyromellitic dianhydride (21.8 g, 0.1 mol) was slowly added in portions over approximately 52 minutes, maintaining the system temperature below 10 °C. After the addition was complete, the ice bath was removed, and the reaction was allowed to proceed with stirring at room temperature (20–25 °C) for 11 hours to obtain a polyamic acid precursor solution. The resulting solution was diluted with N-methyl-2-pyrrolidone to adjust its solids content to 4.0%, and then filtered for later use.

[0063] Synthesis of functional anthraquinone dyes:

[0064] Under nitrogen protection, 1,4-diaminoanthraquinone (23.8 g, 0.1 mol), anhydrous potassium carbonate (27.6 g, 0.2 mol), and N,N-dimethylformamide were added sequentially to a reaction vessel. The mixture was heated to 85°C, and then a solution of N,N-dimethylformamide containing 17.8 g, 0.1 mol of 4-n-butylphenylboronic acid and 1.15 g, 1 mol% tetrakis(triphenylphosphine)palladium(0) (1.15 g, 1 mol%) was slowly added dropwise. After the addition was complete, the reaction mixture was stirred at this temperature for 21 hours. After the reaction was completed, the product was post-processed and purified using the same method as in Example 1 to obtain the target functional anthraquinone dye.

[0065] Preparation of color-changing liquid crystal mixtures:

[0066] Weigh each component precisely according to the following mass:

[0067] 4-Cyano-4'-pentylbiphenyl: 69.79g;

[0068] 4-Cyano-4'-Heptylbiphenyl: 27.91g;

[0069] Synthesis of functional anthraquinone dyes: 2.00 g;

[0070] (S)-4-(2-methylbutyl)-4'-cyanobiphenyl: 0.30g.

[0071] Add all weighed components to a clean brown sample vial. Place the vial on a magnetic stirrer, set the temperature to 85°C, and stir at 400 rpm for 3.5 hours. Then, transfer the vial to a vacuum drying oven and degas it at 65°C for 1.5 hours. After degassing, allow it to cool naturally to room temperature under a nitrogen atmosphere and seal it for later use.

[0072] Fabrication of color-changing devices:

[0073] Cut a PET flexible substrate with an ITO conductive layer pre-coated on its surface into a predetermined size, place it in acetone, isopropanol and deionized water in sequence, and ultrasonically clean each for 12 minutes. After taking it out, blow it dry with high-purity nitrogen gas and put it in an oven at 115°C to dry for 30 minutes.

[0074] The prepared PI solution was spin-coated onto a clean ITO substrate at 3000 rpm for 50 seconds using a spin coating method. The coated substrate was then pre-baked on a hot plate at 85°C for 12 minutes. Afterward, it was transferred to a nitrogen atmosphere furnace and the temperature was programmed to 290°C for thermal imidization treatment for 75 minutes.

[0075] After the substrate has cooled to room temperature, a friction machine with a cloth roller is used to perform unidirectional friction treatment on the surface of the PI alignment layer. The speed of the friction roller is set to 300 rpm and the pressing depth is controlled at 0.4 mm.

[0076] 5.0 μm silica microspheres were dispersed in anhydrous ethanol and uniformly distributed onto the surface of a rub-treated substrate by spraying. UV-curable sealant was applied to the edge region of another treated substrate using screen printing, with injection ports pre-drilled. The two substrates were then aligned and stacked with the rubbing directions antiparallel at 180°. The laminate was placed in a press and pressed under a pressure of 0.15 MPa, while simultaneously using a 365 nm UV lamp at 70 mW / cm². 2 Irradiate the sealant with light intensity for 105 seconds to fully cure it and form a hollow liquid crystal cell.

[0077] The prepared empty liquid crystal cell was placed in a vacuum of less than 10. -3 In a vacuum chamber of Pa, the prepared dye-liquid crystal mixture was injected into the cell at 75°C using capillary action. After injection, the injection port was sealed with UV-curable adhesive and then cured again under the same UV irradiation conditions to obtain the color-changing device of Example 2.

[0078] Example 3:

[0079] Preparation of polyimide orientation agent solution:

[0080] 4,4'-Diaminodiphenyl ether (20.0 g, 0.1 mol) was dissolved in 350 mL of anhydrous N-methyl-2-pyrrolidone. In an ice-water bath at 0–5 °C, pyromellitic dianhydride (21.8 g, 0.1 mol) was slowly added in portions over approximately 60 minutes, maintaining the system temperature below 10 °C. After the addition was complete, the ice bath was removed, and the reaction was stirred continuously at room temperature (20–25 °C) for 12 hours to obtain a polyamic acid precursor solution. The resulting solution was diluted with N-methyl-2-pyrrolidone to adjust its solids content to 5.0%, and then filtered for later use.

[0081] Synthesis of functional anthraquinone dyes:

[0082] Under nitrogen protection, 1,4-diaminoanthraquinone (23.8 g, 0.1 mol), anhydrous potassium carbonate (27.6 g, 0.2 mol), and N,N-dimethylformamide were added sequentially to a reaction vessel. The mixture was heated to 90 °C, and then a solution of N,N-dimethylformamide containing 17.8 g, 0.1 mol of 4-n-butylphenylboronic acid and 1.15 g, 1 mol% tetrakis(triphenylphosphine)palladium(0) (1.15 g, 1 mol%) was slowly added dropwise. After the addition was complete, the reaction mixture was stirred continuously at this temperature for 24 hours. After the reaction was completed, the product was post-processed and purified according to the same method as in Example 1 to obtain the target functional anthraquinone dye.

[0083] Preparation of color-changing liquid crystal mixtures:

[0084] Weigh each component precisely according to the following mass:

[0085] 4-Cyano-4'-pentylbiphenyl: 74.31g;

[0086] 4-Cyano-4'-Heptylbiphenyl: 22.79g;

[0087] Functional anthraquinone dye prepared in the synthesis of functional anthraquinone dyes: 2.50 g;

[0088] (S)-4-(2-methylbutyl)-4'-cyanobiphenyl: 0.40g.

[0089] Add all weighed components to a clean brown sample vial. Place the vial on a magnetic stirrer, set the temperature to 90°C, and stir at 500 rpm for 4 hours. Then, transfer the vial to a vacuum drying oven and degas it at 70°C for 2 hours. After degassing, allow it to cool naturally to room temperature under a nitrogen atmosphere and seal it for later use.

[0090] Fabrication of color-changing devices:

[0091] Cut a PET flexible substrate with an ITO conductive layer pre-coated on its surface into a predetermined size, and place it in acetone, isopropanol and deionized water in sequence. Clean each substrate with ultrasonic cleaner for 15 minutes. After cleaning, remove the substrate and blow it dry with high-purity nitrogen gas. Then, dry it in an oven at 120°C for 30 minutes.

[0092] The prepared PI solution was spin-coated onto a clean ITO substrate at 3500 rpm for 60 seconds using a spin coating method. The coated substrate was then pre-baked on a hot plate at 90°C for 15 minutes. Afterward, it was transferred to a nitrogen atmosphere furnace and the temperature was programmed to rise to 300°C for thermal imidization treatment for 1.5 hours.

[0093] After the substrate has cooled to room temperature, a friction machine with a cloth roller is used to perform unidirectional friction treatment on the surface of the PI alignment layer. The speed of the friction roller is set to 400 rpm and the pressing depth is controlled at 0.5 mm.

[0094] 6.0 μm silica microspheres were dispersed in anhydrous ethanol and sprayed evenly onto the surface of a rub-treated substrate. UV-curable sealant was applied to the edge region of another treated substrate using screen printing, with injection ports pre-drilled. The two substrates were then aligned and stacked with the rubbing directions antiparallel at 180°. The laminate was placed in a press and pressed under 0.2 MPa pressure, while a 365 nm UV lamp was used at 80 mW / cm². 2 Irradiate the sealant with light intensity for 120 seconds to fully cure it and form a hollow liquid crystal cell.

[0095] The prepared empty liquid crystal cell was placed in a vacuum of less than 10. -3 In a vacuum chamber of Pa, the prepared dye-liquid crystal mixture was injected into the cell at 80°C using capillary action. After injection, the injection port was sealed with UV-curable adhesive and then cured again under the same UV irradiation conditions to obtain the color-changing device of Example 3.

[0096] Comparative Examples 1-2:

[0097] Comparative Example 1:

[0098] Compared with Example 2, the difference lies in that, in the preparation of the color-changing liquid crystal mixture, the mass percentage of the added functional anthraquinone dye is adjusted to 0.5%, and the mass of the main liquid crystal material is adjusted accordingly to make the total of all components 100%. The remaining raw materials, proportions, and preparation steps are exactly the same as in Example 2.

[0099] Comparative Example 2:

[0100] Compared to Example 2, the difference lies in that, in the preparation of the color-changing liquid crystal mixture, the functional anthraquinone dye synthesized in this invention is replaced with an equal mass of a commercially available conventional black dichroic dye mixture. All other raw materials, proportions, and preparation steps are exactly the same as in Example 2.

[0101] Test Example 1-2:

[0102] Test Example 1:

[0103] Test method:

[0104] The color-changing device samples prepared in Examples 1-3 and Comparative Examples 1-2 were fixed on an optical testing bracket with their surfaces perpendicular to the incident light beam. The testing system consisted of a xenon lamp source, a function signal generator, a high-voltage amplifier, and a visible light spectrometer equipped with an integrating sphere. The function signal generator was used to generate an AC square wave signal with a frequency of 1.0 kHz, which was amplified by the high-voltage amplifier and applied to the ITO electrodes at both ends of the device under test.

[0105] The testing steps are as follows:

[0106] Without applying a voltage (0 Vrms) to the device, the device surface was illuminated perpendicularly by parallel light emitted from a xenon lamp source. The total reflectance of the device at a wavelength of 550 nm was measured and recorded using a spectrometer, denoted as the dark-state reflectance. ).

[0107] An AC square wave voltage with a root mean square value of 25.0V was applied to the device. After the optical state of the device stabilized, its total reflectance at a wavelength of 550nm was measured and recorded again under the same conditions, and denoted as the light-colored reflectance. ).

[0108] According to the formula The contrast ratio (CR) of the calculation device is calculated.

[0109] Repeat the above measurement three times for each sample, and take the average value as the result.

[0110] Test results:

[0111] The electro-optic response performance test results of each embodiment and comparative example are recorded in Table 1.

[0112] Table 1. Electro-optic response performance test results of each embodiment and comparative example

[0113] sample Dark-state reflectivity (%) Light color reflectance (%) Contrast Ratio (CR) Example 1 12.3 65.8 5.35 Example 2 10.9 68.2 6.26 Example 3 11.5 66.7 5.80 Comparative Example 1 35.6 69.1 1.94 Comparative Example 2 21.8 55.3 2.54

[0114] Table 1 shows that the samples in Examples 1-3 all exhibited reflectivity below 13% at 0 Vrms, while at 25.0 Vrms they all exhibited reflectivity above 65%, with calculated contrast ratios greater than 5.0. This is because, in the zero-field state, the chiral dopant induces the host liquid crystal molecules to form a periodic helical structure, and the functional anthraquinone dye molecules synthesized in this invention are also arranged in an orderly manner along this helical structure. This composite structure simultaneously produces Bragg reflection and anisotropic absorption of the dye on the incident light, resulting in the material exhibiting a low-reflectivity, dark color. When a high voltage of 25.0 Vrms is applied, both the liquid crystal molecules and the dye molecules rearrange along the electric field direction, perpendicular to the substrate surface. At this point, the absorption and reflection of light by the system are at their lowest levels, causing the material to exhibit a high-reflectivity, light-colored color.

[0115] In contrast, Comparative Example 1, due to the concentration of the functional anthraquinone dye being less than 1.5%, exhibited insufficient molecular absorption under zero electric field, failing to effectively suppress light reflection. Its dark-state reflectance reached as high as 35.6%, resulting in a calculated contrast ratio below 2.0. Comparative Example 2 used a conventional dichroic dye, whose molecular structure's compatibility and synergistic alignment with the host liquid crystal material were inferior to the specific functional anthraquinone dye synthesized in this invention. Consequently, its absorption efficiency under zero electric field and its transmittance under high electric field were both inferior to Examples 1-3, resulting in a contrast ratio below 3.0.

[0116] The test results confirm that by combining functional anthraquinone dyes with specific structures in a mass percentage range of 1.5% to 2.5% with the host liquid crystal material, and combining this with chiral dopant, the internal helical structure and dye molecule orientation of the material can undergo synergistic changes when an electric field is applied and not applied. This synergistic change results in significant differences in the material's light absorption and reflection properties, thereby achieving high contrast.

[0117] Test Example 2:

[0118] Test method:

[0119] The color-changing device samples prepared in Examples 1-3 and Comparative Examples 1-2 were placed in a heat-insulated test chamber with a blackened interior. A quartz window was provided at the top of the test chamber to allow external light source illumination. A xenon lamp with adjustable power (equipped with an AM1.5G filter) was used as a simulated solar light source, with its light path perpendicular to the sample surface. The output light power density was calibrated to 1000 W / m² at the sample surface. 2 A type K thermocouple is fitted tightly to the center of the back of the sample to monitor the sample temperature in real time, which is then recorded by a data acquisition instrument. Before testing, the ambient temperature inside the test chamber is stabilized at 20.0℃.

[0120] The testing steps are as follows:

[0121] Heating mode test:

[0122] No voltage is applied to the device (0Vrms). The simulated sunlight source is turned on to irradiate the sample, while the data acquisition instrument records the temperature on the back of the sample at a frequency of 1Hz. Irradiation continues for 600 seconds, and the stable temperature at the 600th second is recorded as the stable temperature in heating mode. ).

[0123] Cooling mode test:

[0124] Turn off the light source and allow the sample to cool completely to 20.0℃. Apply an AC square wave voltage with a root mean square value of 25.0V and a frequency of 1.0kHz to the device. Turn on the simulated sunlight source and irradiate the sample under the same illumination conditions. Record the stable temperature after 600 seconds, and denote it as the cooling mode stable temperature. ).

[0125] Temperature difference range calculation:

[0126] According to the formula Calculate the temperature difference range of the device.

[0127] Repeat the above test for each sample to ensure that the initial conditions are consistent.

[0128] Test results:

[0129] The thermal management performance test results of each embodiment and comparative example are recorded in Table 2.

[0130] Table 2. Thermal management performance test results of each embodiment and comparative example

[0131] sample Heating mode stabilizes temperature (°C) Cooling mode stabilizes temperature (°C) Temperature difference range ΔT (°C) Example 1 52.8 39.1 13.7 Example 2 54.1 38.3 15.8 Example 3 53.5 38.6 14.9 Comparative Example 1 43.1 39.5 3.6 Comparative Example 2 48.2 42.3 5.9

[0132] Table 2 shows that the samples in Examples 1-3 all exhibited a temperature difference range exceeding 13°C. In heating mode (0 Vrms), the material is in its dark state. The helical structure of the chiral liquid crystal and the orderly arrangement of the functional anthraquinone dye molecules work together to achieve a high absorption rate of the simulated solar spectrum, effectively converting light energy into heat energy and raising the temperature of the back side of the device to above 52°C. In cooling mode (25.0 Vrms), the material switches to its light state. The liquid crystal and dye molecules align along the electric field direction. In this state, the absorption of light by the material is suppressed while the reflectivity is high, reducing heat accumulation and maintaining the temperature of the back side of the device below 40°C.

[0133] The temperature difference range of Comparative Example 1 was only 3.6℃, ​​mainly due to the excessively low concentration of the functional anthraquinone dye. This resulted in insufficient total absorbance of the material in heating mode, making it unable to efficiently convert incident light energy into heat energy. Its stable temperature in heating mode was only 43.1℃, with no significant difference from the temperature in cooling mode. The temperature difference range of Comparative Example 2 was also only 5.9℃. This was because the conventional dye used had a weak synergistic effect with the liquid crystal host material in terms of molecular structure, resulting in insufficient absorption in heating mode. At the same time, some residual absorption still existed in cooling mode, weakening the difference in thermal performance between the two states.

[0134] The above test results confirm that the technical solution of this invention achieves reversible control of the material's thermal properties by compounding a functional anthraquinone dye with a specific structure with the host liquid crystal within a preset concentration range, and by using an electric field to drive the material to switch between a strongly absorbing helical state and a strongly reflective vertical orientation state. This mechanism, in which a change in molecular arrangement directly causes a significant change in macroscopic thermal properties, is the basis for obtaining a wide temperature range.

Claims

1. A color-changing material based on dye-liquid crystal technology, characterized in that, The color-changing material is composed of the following components by mass percentage: Main liquid crystal material: 88.0%-98.0%; Functional anthraquinone dyes: 1.5%-2.5%; Chiral dopant: 0.2%-0.4%; The main liquid crystal material is composed of 4-cyano-4'-pentylbiphenyl and 4-cyano-4'-heptylbiphenyl, with a mass ratio between the two ranging from 65.0:33.0 to 75.0:23.

0.

2. The color-changing material based on dye-liquid crystal technology according to claim 1, characterized in that, The functional anthraquinone dye is prepared by reacting 1,4-diaminoanthraquinone and 4-n-butylphenylboronic acid at 80-90°C for 18-24 hours with tetrakis(triphenylphosphine)palladium(0) as a catalyst.

3. The color-changing material based on dye-liquid crystal technology according to claim 1, characterized in that, The chiral dopant is (S)-4-(2-methylbutyl)-4'-cyanobiphenyl.

4. A color-changing material based on dye-liquid crystal technology according to claim 3, characterized in that, The color-changing material is sealed in a liquid crystal cell, which is composed of two flexible substrates. The inner sides of the two flexible substrates are provided with an ITO conductive layer and a polyimide alignment layer.

5. A color-changing material based on dye-liquid crystal technology according to claim 4, characterized in that, The polyimide orientation layer is prepared by polymerizing pyromellitic dianhydride and 4,4'-diaminodiphenyl ether in N-methyl-2-pyrrolidone solvent to generate a polyamic acid precursor, followed by thermal imidization treatment at 280-300℃ for 1-1.5 hours.

6. A color-changing material based on dye-liquid crystal technology according to claim 4, characterized in that, The polyimide orientation layer is subjected to unidirectional friction treatment, and the friction directions of the polyimide orientation layers on the two flexible substrates are arranged in antiparallel directions at 180°.

7. A color-changing material based on dye-liquid crystal technology according to claim 6, characterized in that, The process parameters for the unidirectional friction treatment are: the friction roller speed is 200-400 rpm, and the pressing depth is 0.3-0.5 mm.

8. A color-changing material based on dye-liquid crystal technology according to claim 4, characterized in that, The two flexible substrates are separated by microsphere spacers with a particle size of 4.0-6.0 μm.

9. An application for preparing the color-changing material based on dye liquid crystal technology according to any one of claims 1-8, wherein dynamic adjustment of vehicle body color is achieved by applying AC square wave voltages with different root mean square values ​​to the color-changing material; The frequency of the AC square wave voltage is 0.8-1.5kHz; When a root mean square voltage of 18.0-25.0V is applied, the car body exhibits a light-colored, highly reflective appearance. When a root mean square voltage of 0-4.0V is applied, the vehicle body exhibits a dark, high-absorption state.

10. The application of a color-changing material based on dye-liquid crystal technology according to claim 5, characterized in that, The applied root mean square voltage is based on environmental parameters detected by onboard sensors: When the external light intensity is detected to be greater than 60,000 Lux and the ambient temperature is greater than 25°C, a root mean square voltage of 18.0-25.0V is applied. When the external light intensity is detected to be greater than 40,000 Lux and the ambient temperature is less than 10°C, a root mean square voltage of 0-4.0V is applied.