Preparation of carbon fiber / liquid crystal composite material based on structural color

Abstract

The invention discloses preparation of a carbon fiber / liquid crystal composite material based on structural color, and belongs to the technical field of functional composite materials. The composite material is of a'carbon fiber-cholesteric phase liquid crystal-PDMS 'sandwich structure and is prepared by taking T700-12k carbon fiber as a substrate, 31.2 wt% cholesteric phase thermochromic liquid crystal as a functional layer and PDMS 184 as a packaging layer through carbon fiber pretreatment, liquid crystal blade coating and crosslinking and PDMS coating and curing. The material has thermochromism and electrochromism functions, 0.5 s fast active color control is achieved by means of the carbon fiber Joule heating effect, stray light is eliminated through the black substrate, durability is improved through the PDMS layer, and the mechanical property is excellent. The preparation process is simple and convenient, large-scale production is easy, and the material can be applied to the fields of temperature display, intelligent textiles and optical camouflage, can also be made into intelligent color developing fabrics and temperature visualization devices, and has wide application prospects.

Description

Technical Field

[0001] This invention belongs to the field of functional composite materials technology, specifically relating to the preparation of carbon fiber / liquid crystal composite materials based on structural color. Background Technology

[0002] Color-responsive materials have significant application value in fields such as smart textiles, temperature displays, and optical camouflage. Color changes are mainly divided into chemical colors and structural colors. Chemical colors are prone to fading and have poor weather resistance, while structural colors are generated based on the interference, refraction, and scattering of light by the microstructure of the material, and have advantages such as wide color gamut, high saturation, and resistance to fading.

[0003] Cholesteric liquid crystals, as typical structural color materials, exhibit color changes dependent on alterations in molecular helical spacing, following Bragg's law. They can display a variety of colors under different external stimuli, making them an ideal choice for intelligent color-changing materials. However, cholesteric liquid crystals possess circular dichroism, selectively reflecting only specific wavelengths of light while transmitting the rest. Their color rendering effect heavily depends on the substrate's absorption capacity of the transmitted light; ordinary substrates are prone to background stray light interference, leading to blurred colors. Furthermore, traditional cholesteric liquid crystal materials passively respond to ambient temperature changes, making active and rapid color control difficult. Additionally, the liquid crystal layer is susceptible to moisture corrosion and failure when directly exposed, resulting in insufficient durability and limiting the expansion of its practical applications.

[0004] Carbon fiber, as a high-performance material, possesses high mechanical strength, excellent corrosion resistance, and thermal stability, and is widely used in aerospace, automotive, and energy storage fields. With the increasing demand for multifunctional materials, single mechanical properties are no longer sufficient for practical applications. Imbuing it with optical response capabilities while maintaining its mechanical advantages has become an important development direction. Carbon fiber itself is black and can effectively absorb excess transmitted light, theoretically making it an ideal substrate for cholesteric liquid crystals, improving color rendering. Simultaneously, carbon fiber has good electrical conductivity, and its Joule heating effect allows for active temperature control, providing possibilities for active color control of cholesteric liquid crystals. However, currently, there are no mature solutions for effectively integrating cholesteric liquid crystals with carbon fiber, addressing technical challenges such as interface bonding, liquid crystal layer protection, and active color control, which limits the research and application of this type of multifunctional composite material. Summary of the Invention

[0005] Technical issues Cholesteric liquid crystals are susceptible to interference from stray light from ordinary substrates, resulting in poor color rendering. They are also mostly passive temperature-responsive, making it difficult to achieve active and rapid color control. In addition, the liquid crystal layer is easily corroded by moisture and has insufficient durability. Furthermore, there are stability issues with the interfacial bonding between cholesteric liquid crystals and carbon fibers.

[0006] Technical solution To address the aforementioned technical problems, this invention provides a carbon fiber / liquid crystal composite material based on structural color, its preparation method, and its application. By constructing a "carbon fiber-cholesterol-PDMS" sandwich structure, a synergistic improvement in color rendering performance (thermochromic and electrochromic), active color control capability, and durability is achieved, resulting in a cholesterol-PDMS / carbon fiber composite system with clear color rendering, strong stability, active color control capability, and excellent durability.

[0007] The first objective of this invention is to provide a carbon fiber / liquid crystal composite material based on structural color, wherein the carbon fiber / liquid crystal composite material comprises, from bottom to top, a substrate, a functional layer, and an encapsulation and protective layer; the substrate is carbon fiber, the functional layer is cholesteric thermochromic liquid crystal, and the encapsulation and protective layer is polydimethylsiloxane.

[0008] In one embodiment of the present invention, the thickness of the substrate is 0.1~0.15mm; the thickness of the functional layer is 1-2.5mm; and the thickness of the encapsulation protective layer is 0.5~1.5mm.

[0009] Preferably, the thickness of the functional layer is 1-1.5 mm; most preferably, the thickness is 1-1.25 mm.

[0010] Preferably, the thickness of the encapsulation protective layer is 1~1.25mm.

[0011] In one embodiment of the present invention, the carbon fiber is T700-12k type carbon fiber; the small gaps in the bundled carbon fiber structure can effectively achieve structural physical bonding with the uncured liquid crystal, and its black properties can effectively absorb transmitted light and eliminate background stray light interference.

[0012] A second objective of this invention is to provide a method for preparing the above-mentioned carbon fiber / liquid crystal composite material based on structural color, the method comprising the following steps: (1) The cholesteric phase thermochromic liquid crystal is uniformly coated on the surface of carbon fiber and allowed to crosslink statically until the liquid crystal layer is completely dry and presents a stable natural color, thus obtaining a carbon fiber substrate loaded with liquid crystal layer. (2) Mix the polydimethylsiloxane prepolymer and the curing agent evenly, stir and disperse evenly, let stand to degas, remove the bubbles, and then coat it evenly on the surface of the liquid crystal layer of the carbon fiber substrate loaded with liquid crystal layer. Then heat and cure to obtain carbon fiber / liquid crystal composite material based on structural color.

[0013] In one embodiment of the present invention, the carbon fiber needs to be ultrasonically cleaned in anhydrous ethanol and acetone systems for 0.5 to 2 hours respectively, and the surface of the carbon fiber is treated with dielectric barrier discharge plasma. The plasma treatment conditions are: in an air atmosphere, first treat at 1200 to 1400V for 4 to 6 times, then treat at 1500 to 1600V for 4 to 6 times, and the treatment speed is 10 to 20 mm / s.

[0014] In one embodiment of the present invention, the coating speed of the cholesteric phase thermochromic liquid crystal is 5-15 mm / min; the thickness of the liquid crystal layer is 1-2.5 mm.

[0015] Preferably, the thickness of the liquid crystal layer is 1 mm. At this thickness, the composite material exhibits optimal bending fracture strength, strong resistance to large deformations, and is not easily broken.

[0016] In one embodiment of the present invention, the temperature for static crosslinking is 20~30°C and the time is 5~10h.

[0017] In one embodiment of the present invention, the polydimethylsiloxane prepolymer is Dow Corning PDMS 184.

[0018] In one embodiment of the present invention, the curing agent is Dow Corning Sylgard 184 (CURING AGENT).

[0019] In one embodiment of the present invention, the mass ratio of polydimethylsiloxane prepolymer to curing agent is 5~15:1.

[0020] In one embodiment of the present invention, the heating and curing temperature is 50~60℃ and the time is 2~5h.

[0021] The third objective of this invention is to provide applications of the aforementioned carbon fiber / liquid crystal composite material based on structural color, specifically in the fields of temperature display, smart textiles, and optical camouflage.

[0022] The fourth objective of this invention is to provide a smart color-changing fabric, which is woven or composited from the above-mentioned carbon fiber / liquid crystal composite material based on structural color. The color can be changed by temperature or voltage regulation, and it is suitable for smart clothing, decorative fabrics and other scenarios.

[0023] The fifth objective of this invention is to provide a temperature visualization device, the core functional component of which is the aforementioned carbon fiber / liquid crystal composite material based on structural color. By observing the correspondence between material color changes and temperature, the device enables visual indication of temperature and can be applied to fields such as industrial monitoring and medical assistance.

[0024] The sixth objective of this invention is to provide a method for improving the color stability and active color control performance of cholesteric liquid crystal matrix composites. The method uses carbon fiber as a black substrate and PDMS as an encapsulation protective layer. A "carbon fiber-cholesteric liquid crystal-PDMS" sandwich structure is constructed by a scraping method. Active color control is achieved by utilizing the Joule heating effect of carbon fiber. The specific preparation steps include the above (1) and (2).

[0025] Beneficial effects 1. This invention uses black T700-12k carbon fiber as a substrate, which can efficiently absorb excess transmitted light from cholesteric liquid crystals, completely eliminate the interference of background stray light on color development, make the structural color selectively reflected by the liquid crystal more vivid and saturated, and have a concentrated and single reflection peak, thus greatly improving the color development effect and stability of the composite material.

[0026] 2. This invention utilizes the excellent electrical conductivity and Joule heating effect of carbon fiber to precisely change the material temperature by adjusting the applied voltage, thereby achieving active and rapid color control. The active color control response time is only 0.5s, which is far superior to the traditional passive temperature response method. Moreover, the color change is continuously adjustable, expanding the application scenarios of the material.

[0027] 3. This invention uses PDMS 184 as a packaging protective layer, which has good hydrophobicity and protective properties. It can effectively prevent the liquid crystal layer from dissolving in water and failing due to external environmental corrosion, while not affecting the optical color rendering effect of the material. This allows the composite material to maintain stable performance after long-term use, significantly improving durability.

[0028] 4. By optimizing the thickness of the liquid crystal layer, this invention enables the composite material to have good bending performance and resistance to large deformation. The resistance change rate is small after 150 bends, which can meet the needs of subsequent processing such as weaving and molding. It is suitable for flexible application scenarios such as smart fabrics. Moreover, the material has stable performance in 100 yellow-purple reversible color conversion cycles and has a long service life.

[0029] 5. This invention uses a coating method to prepare composite materials. The overall operation is simple, the required cost is low, no complicated production equipment is needed, the process is highly controllable, the coating thickness and uniformity can be stably controlled, and it is easy to achieve large-scale and industrialized production, thus possessing good industrial transformation value. Attached Figure Description

[0030] Figure 1 The diagram shows the process flow chart (A), composite material structure and color change principle (B), and selective reflection principle of cholesteric liquid crystal and substrate coordination (C) for Example 1.

[0031] Figure 2The color diagram (A) corresponding to the color-changing thermo-electric coupling of the carbon fiber / liquid crystal composite material based on structural color in Example 1 and the CIE diagram (B) of the color pairs of the composite material at 23, 26, and 29°C are shown.

[0032] Figure 3 This is a graph showing the change in reflection wavelength of the carbon fiber / liquid crystal composite material based on structural color as a function of voltage in Example 1.

[0033] Figure 4 Optical photograph (A) and infrared photograph (B) of the carbon fiber / liquid crystal composite material based on structural color as a temperature display device in Example 1.

[0034] Figure 5 The image shows the effect of using carbon fiber / liquid crystal composite material based on structural color as a smart display device in Example 1. Detailed Implementation

[0035] The preferred embodiments of the present invention are described below. It should be understood that the embodiments are for better explanation of the present invention and are not intended to limit the present invention.

[0036] Test methods 1. Characterization of microstructure and chemical properties: The sandwich structure morphology and interfacial bonding state of the composite material "carbon fiber-liquid crystal-PDMS" were observed using a low-magnification electron microscope; Fourier transform infrared spectroscopy (Nicolet IS10) was used to analyze the chemical bonding state of each component in the composite material; and X-ray diffraction (D2 PHASER) with Cu Kα radiation was used to characterize the crystal structure of the composite material.

[0037] 2. Thermal stability test: Thermogravimetric analysis (Q550, TA Instruments) was performed under nitrogen atmosphere with an initial sample mass of approximately 140 mg, a temperature range of 50-800℃, and a heating rate of 10℃ / min. The thermal decomposition curves and characteristic decomposition temperatures of the composite materials were recorded.

[0038] 3. Mechanical property testing: A universal testing machine (3385H) was used to perform bending tests on composite materials with different liquid crystal layer thicknesses (1 mm, 1.5 mm, 2 mm, 2.5 mm), and the bending stiffness data were recorded. Each group of samples was tested 5 times, and the average value and standard deviation were taken.

[0039] 4. Durability test: The water contact angle of the composite material surface was measured using a contact angle meter (OCA50, Dataphysics), and the change in contact angle over 120 min was observed. 1 mL of pure water was added to the surface of the PTC composite material and the liquid crystal / carbon fiber sample without encapsulated PDMS (control group), and the color development performance was observed after standing for 120 min.

[0040] 5. Color performance test: The reflectance and absorptivity in the 400-700nm wavelength range were tested using a computer colorimeter (Data Color 650) under D65 artificial daylight (6500K). Color changes were measured using the CIE Lab system with color difference ΔE*ab (color difference meter: 3nhNR200) ​​to evaluate color saturation and stability.

[0041] 6. Active color rendering performance test: Power supply (DC, LW) Different voltages were applied to the K305D fiber to observe the thermochromic phenomenon induced by different voltages. An infrared thermal imager (FLIR E54) was used to record the temperature change process, measuring the voltage and temperature required to achieve a specific color. Within the range of 20-50℃, the material's color change was recorded every 5℃. A computer colorimeter (Data Color650) was used to simultaneously test the corresponding color and reflection wavelength to analyze the color change pattern.

[0042] Raw materials used in the examples: Carbon fiber: T700-12k model, purchased from Toray Industries, Japan; Cholesteric phase thermochromic liquid crystal (TLC): purchased from Shenzhen Qiansebian Pigment Co., Ltd.; Polydimethylsiloxane prepolymer PDMS 184 and matching curing agent SYLGARD 184 (CURING AGENT): purchased from Dow Corning Incorporated, USA.

[0043] Example 1 A method for preparing carbon fiber / liquid crystal composite material based on structural color includes the following steps: (1) Cut T700-12k carbon fiber (thickness 0.1~0.15mm) into 10cm×5cm sheets. Before composite, the carbon fiber needs to be ultrasonically cleaned in anhydrous ethanol and acetone systems for 1h respectively, and the surface of the carbon fiber is treated with dielectric barrier discharge plasma. It is treated five times at 1300v and five times at 1500v in air atmosphere. The treatment speed is 15mm / s. After that, it is placed in a ventilated place at 25℃ to dry for later use. (2) The cholesteric phase thermochromic liquid crystal was uniformly coated onto the pretreated carbon fiber surface using a scraper. The scraping speed was set to 10 mm / s, and the thickness of the liquid crystal layer was controlled to be 1 mm. The sample was placed in a 25°C environment for static crosslinking for 6 h until the liquid crystal layer was completely dry and showed a stable initial yellow color. (3) Weigh PDMS 184 and curing agent at a mass ratio of 10:1, place them in a beaker, and stir at 300 r / min for 1 h on a magnetic stirrer to ensure uniform mixing; then place the mixture in a vacuum drying oven for 2 h to completely remove internal bubbles, and then use a scraping method to uniformly coat the degassed PDMS mixture onto the surface of the liquid crystal layer, controlling the PDMS coating thickness to be 1 mm; (4) The sample was placed in a 50°C oven for 2 hours to cure. After being taken out, it was naturally cooled to room temperature to obtain a carbon fiber / liquid crystal composite material based on structural color.

[0044] The obtained composite material was subjected to performance testing, and the test results are as follows: Table 1 shows the color and infrared thermal imaging temperature corresponding to the input voltage of the carbon fiber / liquid crystal composite material (hereinafter referred to as PTC) based on structural color. It can be seen that the color of the TLC layer is in a one-to-one correspondence with the surface temperature of the device, and the color change is continuous. Multiple colors can be adjusted by controlling the input voltage.

[0045] Table 1

[0046] Example 2 The thickness of the liquid crystal layer in step 2 of Example 1 was adjusted to 1.5 mm, 2 mm, and 2.5 mm, respectively. The other raw materials and process parameters were completely consistent with those in Example 1. Three sets of composite materials with different liquid crystal layer thicknesses were prepared for comparative testing of mechanical properties and color rendering performance.

[0047] The obtained composite fibers were subjected to performance tests, and the test results are as follows: Table 2

[0048] Example 3 The carbon fiber black substrate in Example 1 was replaced with cotton substrates of different colors (red, green, blue, white, orange-red, grass green, sky blue), while the other raw materials and process parameters remained unchanged. Liquid crystal / PDMS composite materials with different colored substrates were prepared for color rendering effect comparison tests.

[0049] The obtained composite material was subjected to performance testing, and the test results are as follows: Table 3

[0050] Example 4 The PDMS encapsulation process in steps 3 and 4 of Example 1 is omitted, while the remaining raw materials and process parameters remain unchanged, resulting in a composite material composed only of carbon fiber and liquid crystal layer, which is used for durability comparison testing.

[0051] The obtained composite material was subjected to performance testing, and the test results are as follows: Table 4

[0052] Comparative Example 1 The carbon fiber substrate in Example 1 was replaced with a black conductive nylon fabric substrate, while the other raw materials and process parameters remained unchanged, to prepare a cholesteric liquid crystal composite material for comparative testing of active color control performance.

[0053] The obtained composite material was subjected to performance testing, and the test results are as follows: Table 5

[0054] Comparative Example 2 The thickness of the PDMS layer in the composite material in Example 1 was replaced with 2 mm, while the other raw materials and process parameters remained unchanged, to prepare a cholesteric liquid crystal composite material for color performance comparison testing.

[0055] Table 6

[0056] Example 5 The composite material of Example 1 is used as a sensitive temperature display device and as a visual temperature indication device.

[0057] The results are as follows Figure 4 As can be seen, in a temperature gradient environment, the material color distribution perfectly matches the infrared thermal imaging image, accurately reflecting regional temperature differences. Using the composite material from Example 1 as the core functional component, along with a voltage regulation module, a temperature calibration module, and a display panel, a temperature visualization device is assembled. This device can intuitively indicate the ambient temperature within a range of 20-30℃ through material color changes, with a temperature resolution of ±0.5℃ and a response time of 0.5 s. It is suitable for scenarios such as temperature monitoring of industrial equipment and auxiliary body temperature indication in medical settings.

[0058] Example 6 The composite material of Example 1 is used as a touch visualization device for intelligent display.

[0059] The results are as follows Figure 5It can be seen that by applying a voltage of 0.8V to the composite material, clear numbers "1, 2, 3" and letters "J, N" can be quickly written on its surface. The writing response time is 0.3s and the pattern retention time is ≥30s, which meets the requirements of touch visualization display.

[0060] The above embodiments are only preferred embodiments of the present invention. In practical applications, parameters such as carbon fiber size, liquid crystal layer thickness, PDMS coating thickness and applied voltage range can be adjusted according to specific needs, and all of these fall within the protection scope of the present invention.

Claims

1. A carbon fiber / liquid crystal composite material based on structural color, characterized in that, The carbon fiber / liquid crystal composite material consists of a substrate, a functional layer, and an encapsulation and protective layer from bottom to top; the substrate is carbon fiber, the functional layer is cholesteric thermochromic liquid crystal, and the encapsulation and protective layer is polydimethylsiloxane. The carbon fiber is T700-12k type carbon fiber; the thickness of the substrate is 0.1~0.15mm; the thickness of the functional layer is 1-2.5mm; and the thickness of the encapsulation protective layer is 0.5~1.5mm.

2. The carbon fiber / liquid crystal composite material according to claim 1, characterized in that, The thickness of the functional layer is 1-1.25 mm.

3. The carbon fiber / liquid crystal composite material according to claim 1, characterized in that, The thickness of the encapsulation protective layer is 1~1.25mm.

4. The method for preparing carbon fiber / liquid crystal composite material based on structural color according to any one of claims 1 to 3, characterized in that, The preparation method includes the following steps: (1) The cholesteric phase thermochromic liquid crystal is uniformly coated on the surface of carbon fiber and allowed to crosslink statically until the liquid crystal layer is completely dry and presents a stable natural color, thus obtaining a carbon fiber substrate loaded with liquid crystal layer. (2) Mix the polydimethylsiloxane prepolymer and the curing agent evenly, stir and disperse evenly, let stand to degas, remove the bubbles, and then coat it evenly on the surface of the liquid crystal layer of the carbon fiber substrate loaded with liquid crystal layer. Then heat and cure to obtain carbon fiber / liquid crystal composite material based on structural color. Carbon fibers were ultrasonically cleaned in anhydrous ethanol and acetone systems for 0.5 to 2 hours respectively, and the surface of the carbon fibers was treated with dielectric barrier discharge plasma. The plasma treatment conditions were as follows: in an air atmosphere, the carbon fibers were treated at 1200 to 1400V for 4 to 6 times, and then at 1500 to 1600V for 4 to 6 times, with a treatment speed of 10 to 20 mm / s.

5. The preparation method according to claim 4, characterized in that, The coating speed of the liquid crystal is 5~15mm / min.

6. The preparation method according to claim 4, characterized in that, The temperature for static crosslinking is 20~30℃, and the time is 5~10h.

7. The preparation method according to claim 4, characterized in that, The polydimethylsiloxane prepolymer is Dow Corning PDMS 184; the curing agent is Dow Corning SYLGARD 184.

8. The preparation method according to claim 4, characterized in that, The mass ratio of polydimethylsiloxane prepolymer to curing agent is 5~15:

1.

9. The preparation method according to claim 4, characterized in that, The curing temperature is 50~60℃, and the time is 2~5h.

10. The application of the carbon fiber / liquid crystal composite material based on structural color as described in any one of claims 1 to 3 in the fields of temperature display, smart textiles and optical camouflage.

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