Visible-infrared-microwave multiband mechanically regulated MXene nano-composite chiral liquid crystal photonic crystal flexible film as well as preparation method and application thereof

Abstract

The invention discloses a visible-infrared-microwave multiband mechanically regulated MXene nano-composite chiral liquid crystal photonic crystal flexible film as well as a preparation method and application thereof. The preparation method comprises the following steps: step 1, preparing a chiral liquid crystal photonic crystal flexible film; 2, coating the chiral liquid crystal photonic crystal flexible film obtained in the step 1 with an optically transparent polymer solution with an isocyanate functional group, and performing second-step crosslinking by using ultraviolet irradiation to obtain a modified liquid crystal film; 3, the modified liquid crystal film obtained in the step 2 is coated with the MXene nanosheet dispersion liquid, and the visible-infrared-microwave multi-band mechanically-regulated MXene nano-composite chiral liquid crystal photonic crystal flexible film is obtained.The cyclic color change of the visible light band and the force-induced infrared emissivity change of the infrared band can be achieved by applying small force, and the mechanical regulation of the visible-infrared-microwave multi-band mechanically-regulated MXene nano-composite chiral liquid crystal photonic crystal flexible film is achieved. And electromagnetic shielding of a microwave band can be realized.

Description

Technical Field

[0001] The present invention relates to the technical field of photonic crystals, and in particular to a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film and a preparation method thereof. Background Art

[0002] Camouflage is an important topic in the field of optics because it provides a means of avoiding danger. Some animals in nature display camouflage skills by evolving a range of defensive color patterns, including fixed and adaptive body colors. The limitations of animals with fixed body colors are obvious, as the color cannot adapt to the changing background during movement. In contrast, chameleons can quickly change their body color by actively adjusting the lattice of guanine nanocrystals within the iridocytes of the dermis; cephalopods such as octopuses can reflect variable wavelengths of visible and near-infrared light through the synergistic action of iridocytes and pigment cells to achieve a wide range of skin color changes and stealth effects.

[0003] Bionic intelligent camouflage technology overcomes the limitations of traditional static camouflage and breaks through traditional camouflage ideas and models in terms of material use and control methods. When the background environment changes, the camouflaged target can respond continuously according to the background information and autonomously achieve the fusion and matching of the target and background optoelectronic characteristics. It has the advantages of strong adaptability, good concealment, and fast response speed. It has broad application prospects in military camouflage, reconnaissance and surveillance systems, and stealth aircraft. It can also be used in the civilian field for privacy protection.

[0004] Inspired by natural organisms, the preparation of color-changing materials with bionic camouflage functions has become a hot topic in research. How to develop bionic intelligent color-changing materials and related technologies that can achieve color-changing invisibility in the visible light and infrared spectrum is a key scientific issue in this field. Among many material systems, liquid crystal materials can change their molecular orientation, phase structure and macroscopic properties under the stimulation of external environments such as electricity, heat and magnetism. They have good external field responsiveness and synergistic effects, and can achieve high-throughput preparation of large-area flexible films through long-range orderly self-assembly of molecules. Introducing chiral molecules into main-chain nematic liquid crystal materials can self-assemble to form chiral soft photonic crystals with periodic nanostructures, such as one-dimensional cholesteric liquid crystal elastomers and three-dimensional blue phase liquid crystals. Due to their inherent liquid crystal properties, this type of chiral liquid crystal material can not only selectively reflect circularly polarized light, but also sensitively respond to changes in force, heat, electricity, light, humidity and other stimuli, showing dynamic regulation of structural color, and has broad application prospects in the fields of color-changing camouflage, information encryption, tunable lasers, etc.

[0005] However, these chiral liquid crystal systems mainly focus on the color change control in the visible light region, and there is little research on camouflage in the infrared region. Based on this, integrating dynamic visible color change performance with emerging infrared camouflage strategies into an adaptive multi-spectral mechanical optical system will undoubtedly promote the rapid development of advanced chiral liquid crystal materials and provide great opportunities for many emerging fields, including intelligent multi-spectral camouflage technology, energy conversion buildings, and personal protection. Summary of the invention

[0006] The purpose of the present invention is to provide a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film and a preparation method thereof, in order to address the problem that the stimulus-responsive color-changing chiral liquid crystals in the prior art are limited to realizing structural color changes in the visible light band, and cannot take into account the infrared radiation regulation in the infrared band and the electromagnetic shielding regulation in the microwave band.

[0007] Another object of the present invention is to provide an application of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film.

[0008] The technical solution adopted to achieve the purpose of the present invention is:

[0009] A method for preparing a visible-infrared-microwave multi-band mechanically controlled MXene nanocomposite chiral liquid crystal photonic crystal flexible film comprises the following steps:

[0010] Step 1, uniformly mixing a monofunctional polymerizable liquid crystal monomer, a difunctional polymerizable liquid crystal monomer, a chain extender, a crosslinking agent, a chiral agent, and a photoinitiator according to a preset ratio to prepare a polymerizable chiral liquid crystal precursor, wherein the functionality is acryloyloxy; uniformly pouring the prepared chiral liquid crystal precursor into a mold prepared in advance, and allowing the liquid crystal monomer to self-assemble to form a long-range ordered three-dimensional blue phase photonic crystal or a one-dimensional cholesteric phase photonic crystal by keeping it warm at a specific temperature; finally, using ultraviolet light to perform an in-situ photopolymerization reaction to obtain a chiral liquid crystal photonic crystal flexible film;

[0011] Step 2, coating an optically transparent polymer solution with isocyanate functional groups on the chiral liquid crystal photonic crystal flexible film obtained in step 1, and then irradiating the chiral liquid crystal photonic crystal flexible film with ultraviolet light to cause a second step of crosslinking to ensure that the polymer is completely combined with the chiral liquid crystal photonic crystal flexible film, thereby obtaining a modified liquid crystal film with isocyanate functional groups;

[0012] Step 3, coating the MXene nanosheet dispersion on the modified liquid crystal film obtained in step 2, or partially coating it on the modified liquid crystal film obtained in step 2, in the coated area, the isocyanate functional groups and the hydroxyl groups in the MXene nanosheets are chemically cross-linked to obtain an ultra-thin, transparent and conductive MXene nanostructure film; then remove the mold to obtain the MXene nanocomposite chiral liquid crystal photonic crystal flexible film composed of a polymer, a chiral liquid crystal photonic crystal and a MXene nanostructure film.

[0013] In the above technical solution, in step 1, the mass fraction ratio of the monofunctional polymerizable liquid crystal monomer, the difunctional polymerizable liquid crystal monomer, the chain extender, the crosslinking agent, the chiral agent, and the photoinitiator is (0.0-45.0):(60.0-95.0):(15.0-35.0):(0.5-15.0):(0.5-8.0):(0.5-2.0);

[0014] The liquid crystal phase transition temperature of the liquid crystal monomer is 25° C. to 180° C. Preferably, the monofunctional liquid crystal monomer is one or more of the following:

[0015]

[0016] Wherein, n=2~13, m=1~12,

[0017] x=H、Cl、F、CH 3 .

[0018] The dual monofunctional liquid crystal monomer is one or more of the following:

[0019]

[0020] Wherein, n=2~13, m=1~12,

[0021] X=H、Cl、F、CH 3 .;

[0022] The chiral agent includes but is not limited to LC756, R5011, S5011, R811, S811, R1011, S1011, CB15, C15;

[0023] The chain extender is selected from dithiol monomers, including but not limited to one or more of 2,2-(ethylenedioxy)diethylmercaptan, 1,3-propanedithiol and 1,6-hexanedithiol;

[0024] The crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers, including but not limited to 3-mercaptopropionic acid-2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]-1,3-propanediol (TTMP) and tetrakis(3-mercaptopropionic acid) pentaerythritol ester (PETMP);

[0025] The photoinitiator is an ultraviolet photoinitiator having light absorption ability in the range of 250 to 420 nm. Preferably, the photoinitiator is one or more of benzoin dimethyl ether (I-651), 1-hydroxycyclohexyl phenyl ketone (I-184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (I-1173), and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (I-2959).

[0026] In the above technical solution, the ratio of the total molar amount of the monofunctional polymerizable liquid crystal monomer, the difunctional polymerizable liquid crystal monomer and the acryloxy group of the chiral agent to the total molar amount of the thiol group of the chain extender and the cross-linking agent is 1:1 to 11:10; the molar ratio of the cross-linking agent to the chain extender is 1:19 to 1:4.

[0027] In the above technical solution, in step 1, the reaction temperature of the self-assembly is 15°C to 35°C, and the reaction time is 18 to 36 hours.

[0028] In the above technical solution, in step 1, the light source for the in-situ photopolymerization reaction is a UV light source with a wavelength of 254 to 520 nm and a light intensity of 5 to 200 mW / cm 2 , the polymerization time is 60s~1800s.

[0029] In the above technical solution, in step 1, the mold includes a glass substrate and a flexible frame. The shape of the glass substrate is rectangular, square or other shapes. When cleaning, it is ultrasonically cleaned in ethanol and deionized water. Preferably, the length of the glass substrate is 10 mm to 1000 mm. The flexible frame is glued to the surface of the glass substrate with glue. The glue is modified acrylic adhesive, epoxy resin glue, polyvinyl acetal glue, α-cyanoacrylate ethyl, etc. The flexible frame is rubber, silicone rubber, TPU, TPE or soft PVC.

[0030] In the above technical solution, in step 2, the optically transparent polymer with isocyanate functional group includes but is not limited to (trans) ethylene diisocyanate, 1,4-but-2-ene-diol diisocyanate, toluene diisocyanate, or 2-isocyanatoethyl methacrylate.

[0031] In the above technical solution, in step 3, the ultra-thin MXene nanosheets include but are not limited to Ti 3 C 2T x 、Ti 2 CT x 、Ti 4 N 3 T x 、Ti 3 CNT x Cr 2 TiC 2 T x 、Mo 2 CT x 、Mo 2 TiC 2 T x 、Mo 2 Ti 2 C 3 T x , Nb 2 CT x or V 2 CT x , the lateral size of the ultrathin MXene nanosheet is 100nm~10μm;

[0032] The concentration of the MXene nanosheet dispersion was 1 mg mL -1 ~20mg mL -1 ;

[0033] The MXene nanostructured film is obtained by scraping, dripping, spin coating or pulling, and has a thickness of 20 nm to 1 μm;

[0034] The thickness of the prepared MXene nanolayer is 2nm to 1μm.

[0035] Another aspect of the present invention also includes a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film obtained by the preparation method.

[0036] The MXene nanocomposite chiral liquid crystal photonic crystal flexible film with visible-infrared-microwave multi-band mechanical regulation has visible-infrared-microwave compatible dynamic regulation performance. By controlling the degree of regulation, it can not only achieve reversible structural color changes in the visible light band, but also achieve dynamic on-demand regulation of infrared emissivity in the infrared band, and also achieve dynamic regulation of electromagnetic shielding signals.

[0037] The visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film can be dynamically controlled by electric field, humidity, light intensity and mechanical force.

[0038] Another aspect of the present invention provides an application of the visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film. The multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film can be used in color-changing devices, infrared camouflage and microwave electromagnetic shielding. Preferably, the color-changing device is a mechanochromic bionic skin, and the infrared camouflage is a mechanochromic infrared emissivity infrared camouflage. The area not coated with the MXene nanosheet dispersion and the area coated with the MXene nanosheet dispersion show different colors under visible light irradiation. During the stretching process, the colors tend to be consistent, and after the shape is restored, the colors are restored to the colors before stretching. In addition, when heated at 40 to 55° C. and observed under an infrared camera, the area not coated with the MXene nanosheet dispersion and the area coated with the MXene nanosheet dispersion also show different colors. During the stretching process, the colors tend to be consistent, and after the shape is restored, the colors are restored to the colors before stretching.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] 1. The multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film of the present invention cleverly combines the mechanochromic properties of chiral liquid crystals with the excellent conductivity and unique low mid-infrared emissivity of two-dimensional MXene nanomaterials. By applying a small force, cyclic color change in the visible light band and mechanochromic infrared emissivity in the infrared band can be achieved, and electromagnetic shielding in the microwave band can be achieved.

[0041] 2. The MXene nanocomposite chiral liquid crystal photonic crystal flexible film of the present invention enhances the interfacial bonding between different functional layers by introducing a molecular anchoring layer capable of chemical cross-linking at the interface, thereby improving the mechanical properties and processability of the flexible film, which is beneficial to the large-scale production and multi-scenario application of the flexible film.

[0042] 3. The MXene nanocomposite chiral liquid crystal photonic crystal flexible film of the present invention is configured with surface crack morphology by mechanical stretching, and this morphological evolution regulates the direct transmission / reflection and scattering behavior of infrared light. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 Schematic diagram of the preparation process of MXene nanocomposite chiral liquid crystal photonic crystal flexible film.

[0044] Figure 2 This is the morphology of the cross-section of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film.

[0045] Figure 3 The reflection spectra corresponding to different components of MXene nanocomposite chiral liquid crystal photonic crystal flexible film.

[0046] Figure 4 Comparison of infrared emissivity of MXene nanocomposite chiral liquid crystal photonic crystal flexible film, chiral liquid crystal photonic crystal flexible film and pure MXene nanomaterials.

[0047] Figure 5 This is a comparison of the electromagnetic shielding properties of MXene nanocomposite chiral liquid crystal photonic crystal flexible film, chiral liquid crystal photonic crystal flexible film and pure MXene nanomaterials.

[0048] Figure 6 Comparison of (a) visible light transmittance, (b) infrared emissivity, and (c) electromagnetic shielding performance of MXene layers with different thicknesses in MXene nanocomposite chiral liquid crystal photonic crystal flexible films.

[0049] Figure 7 (a) Color change and corresponding (b) reflection spectrum of MXene nanocomposite chiral liquid crystal photonic crystal flexible film induced by stretching.

[0050] Figure 8 Figure 3. (a) Temperature change during force-induced stretching of MXene nanocomposite chiral liquid crystal photonic crystal flexible film (observed under infrared camera) and (b) stretching temperature change corresponding to hot stages at different temperatures.

[0051] Fig. 9 Figure 2. (a) Change in infrared reflectivity and (b) change in infrared emissivity of MXene nanocomposite chiral liquid crystal photonic crystal flexible film induced by stretching.

[0052] Fig.10 (a) Schematic diagram of stretching, (b) scanning electron microscope (SEM), and (c) 3D surface profiler images corresponding to the mechanical stretching of MXene-CLCE flexible film.

[0053] Fig.11 The changes in electromagnetic shielding performance corresponding to the force-induced stretching of MXene nanocomposite chiral liquid crystal photonic crystal flexible films.

[0054] Fig.12 (a) Bionic color-changing camouflage skin and (b) infrared stealth effect of MXene nanocomposite chiral liquid crystal photonic crystal flexible film. DETAILED DESCRIPTION

[0055] The present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0056] Example 1

[0057] A method for preparing a visible-infrared-microwave multi-band mechanically controlled MXene nanocomposite chiral liquid crystal photonic crystal flexible film comprises the following steps:

[0058] Step 1, weigh 630mg RM257 and 29mg LC756 (4.5wt%) and dissolve them in 400mg toluene solvent, and heat at 80°C to completely dissolve the monomers. After cooling to room temperature, add 155mg EDDET, 36.7mg PETMP and 4mg Irg651. Add 180mg diluted DPA solution (toluene: DPA = 50:1), stir the mixed solution at room temperature for 5min to mix it evenly, and then place it in a vacuum drying oven for degassing. Then pour the precursor onto a polytetrafluoroethylene mold and place it in a fume hood at room temperature for 24h. After the toluene solvent evaporates completely, finally at 20mW / cm 2 The film was cured under ultraviolet light for 600 s to obtain a CLCE chiral liquid crystal photonic crystal flexible film.

[0059] Step 2: Add 3.2 g of lithium fluoride (LiF) to 40 mL of 9 mol L -1 Stir in hydrochloric acid (HCl) solution for 10 min, then slowly add 2 g Ti 3 AlC 2 The powder was placed at 50°C for 36 hours. The reaction product was washed by centrifugation with deionized water until the pH was ≥ 6. The precipitate was redispersed in deionized water and centrifuged at 3000 rpm for 15 minutes. The collected supernatant was centrifuged at 9800 rpm for 10 minutes. The resulting sludge-like precipitate was the synthesized ultrathin MXene nanosheets (the average lateral size of the nanosheets was 1.5 μm). The ultrathin MXene nanosheets were dispersed in dimethyl sulfoxide (DMSO) to prepare different concentrations (5 mg mL -1 , 10mg mL -1 , 15mg mL -1 , 20mg mL -1 ) of ultrathin MXene nanosheet dispersion.

[0060] Step 3, use a pipette to draw 1 ml of 2-isocyanatoethyl methacrylate (2-ICEMA) polymer solution on the CLCE chiral liquid crystal photonic crystal flexible film obtained in step 1 and rotate it at a speed of 500 rpm for 1 minute, then use ultraviolet light to irradiate it to cause the second step of cross-linking to obtain a modified liquid crystal film.

[0061] Step 4: Use a pipette to absorb 1 ml of ultra-thin MXene nanosheet dispersion and apply it to the modified liquid crystal film obtained in step 3. Spin at 500 rpm for 1 min, and spin-coat 30 times in total. During the coating process, the isocyanate functional groups and the hydroxyl groups in the MXene nanosheets are chemically cross-linked. Then, the flexible film is placed on a hot plate and heated at 50°C to quickly dry the flexible film to obtain a MXene-CLCE flexible film. The preparation process is shown in the figure below. Figure 1 shown.

[0062] The structural formula of the reactants used in this example is as follows:

[0063]

[0064] Figure 2 This is the microstructure of the MXene-CLCE flexible film under SEM. It can be seen from the figure that the interface of the double-layer structure is tightly bonded, the upper MXene layer is stacked very tightly, and the lower CLCE also has an obvious layered texture.

[0065] Figure 3 The color changes of the chiral agents in different components of the MXene-CLCE flexible film. It can be seen from the figure that with the gradual increase of the addition of chiral agents (4.5wt%, 5.5wt%, 6.5wt%), the color of the flexible film gradually shifts to blue, and the reflection peak wavelength changes from the initial 652nm to 465nm.

[0066] Figure 4 The figure shows the infrared emissivity comparison of MXene-CLCE flexible film, CLCE chiral liquid crystal photonic crystal flexible film and pure MXene nanomaterial. It can be seen that the infrared emissivity of CLCE chiral liquid crystal photonic crystal flexible film is 0.87, the infrared emissivity of pure MXene nanomaterial is 0.2, and the emissivity of MXene-CLCE flexible film is between the two, which is 0.34.

[0067] Figure 5 The electromagnetic shielding performance of MXene-CLCE flexible film, CLCE chiral liquid crystal photonic crystal flexible film and pure MXene nanomaterials is compared. It can be seen that the CLCE chiral liquid crystal photonic crystal flexible film has basically no electromagnetic shielding performance, and the electromagnetic shielding performance of pure MXene nanomaterials is SE T 28.2dB, SE R 10.46dB, SE A The electromagnetic shielding performance of MXene-CLCE flexible film is 17.74dB. T 18.4dB, SE R 6.58dB, SE A It is 11.82dB.

[0068] Figure 6 Comparison of (a) visible light transmittance, (b) infrared emissivity, and (c) electromagnetic shielding performance of MXene layers of different thicknesses in MXene-CLCE flexible films. It can be seen that Figure 6 (a) is the optical transmittance of the MXene-CLCE flexible film. The transmittance of the MXene-CLCE flexible film with a MXene layer thickness of 33.7nm at a wavelength of 550nm is 79%. The transmittance gradually decreases with the increase in the number of stacked layers. When the MXene layer of 196.9nm is stacked, the transmittance remains at 21%. The infrared emissivity of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film is also closely related to the thickness of the MXene. Figure 6 It can be seen from (b) that when the MXene thickness is 33.7nm, the average infrared emissivity of the film is 63%, while when the MXene thickness is 196.9nm, the average infrared emissivity of the film is 22%. Figure 6 It is not difficult to see in (b) that as the thickness of MXene gradually increases, the rate of decrease of the infrared emissivity of the MXene-CLCE flexible film slows down, and after the MXene thickness reaches 107.6nm, there is an obvious slowing trend. Next, Figure 6 (c) shows the variation of the total EMI shielding effectiveness of several multilayer MXene-CLCE flexible films with the thickness of MXene in the frequency range of 8.2 to 12.4 GHz. It can be seen that the EMI shielding effectiveness can also be adjusted according to the thickness of MXene. When the MXene thickness is 33.7nm, the average EMI SET of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film is 3.5dB, providing ≈25% shielding for the incident electromagnetic waves. When the thickness of the MXene layer is 196.9nm, the EMI shielding effectiveness increases rapidly with the increase in the number of stacking, reaching 29.5dB, which can attenuate 99% of electromagnetic waves.

[0069] Example 2

[0070] A method for preparing a visible-infrared-microwave multi-band mechanically controlled MXene nanocomposite chiral liquid crystal photonic crystal flexible film comprises the following steps:

[0071] Step 1, weigh 720mg C6M and 29mg LC756 and dissolve them in 600mg dichloroethane solvent, and heat at 80°C to completely dissolve the monomers. After cooling to room temperature, add 90.2mg 1,6-hexanedithiol, 99.65mg TTMP and 4mg Irg1173. Add 180mg diluted n-hexylamine solution (dichloroethane: n-hexylamine = 50:1), stir the mixed solution at room temperature for 5min to mix it evenly, and then place it in a vacuum drying oven for degassing. Then pour the precursor onto the ion gel network and place it in a fume hood at room temperature for 24h. Finally, at 5mW / cm 2 The CLCE chiral liquid crystal photonic crystal flexible film was obtained by irradiating it under ultraviolet light for 600s for curing.

[0072] Step 2: Add 3.2 g of lithium fluoride (LiF) to 40 mL of 9 mol L -1 Stir in hydrochloric acid (HCl) solution for 10 min, then slowly add 2 g Ti 3 AlC 2 The powder was placed at 50°C for 36 hours. The reaction product was washed by centrifugation with deionized water until the pH was ≥ 6. The precipitate was redispersed in deionized water and centrifuged at 3000 rpm for 15 minutes. The collected supernatant was centrifuged at 9800 rpm for 10 minutes. The resulting sludge-like precipitate was the synthesized ultrathin MXene nanosheets (the average lateral size of the nanosheets was 1.5 μm). The ultrathin MXene nanosheets were dispersed in dimethyl sulfoxide (DMSO) to prepare different concentrations (5 mg mL -1 ,10mg mL -1 ,15mg mL -1 ,20mg mL -1 ) of ultrathin MXene nanosheet dispersion.

[0073] Step 3, use a pipette to draw 1 ml of 1,4-but-2-ene-diol diisocyanate polymer solution on the chiral cholesteric liquid crystal elastomer flexible film at a speed of 500 rpm for 1 minute, and then use ultraviolet light to cause the second step of cross-linking to obtain a modified liquid crystal film.

[0074] Step 4: Use a pipette to absorb 1 ml of ultra-thin MXene nanosheet dispersion and spray it onto the modified liquid crystal film obtained in step 3. Repeat the spraying 3-5 times. During the coating process, the isocyanate functional group reacts chemically with the hydroxyl group in the MXene nanosheet. Then, place the flexible film on a hot table and heat it at 50°C to quickly dry the flexible film to obtain a MXene-CLCE flexible film.

[0075] An optical fiber spectrometer was used to measure the reflection wavelength of the MXene-CLCE flexible film during the stretching process, and its dynamic color changes were recorded by a camera. An infrared camera was used to record the color changes and temperature changes of the MXene-CLCE flexible film during the stretching process. An infrared spectrometer was used to test the changes in the infrared reflectivity of the MXene-CLCE flexible film under stretching, and the corresponding changes in its infrared emissivity were calculated. A vector analyzer was used to test the changes in the electromagnetic shielding properties of the MXene-CLCE flexible film during the stretching process.

[0076] The structural formula of the reactants used in this example is as follows:

[0077]

[0078] Figure 7 (a) Color change and (b) reflection spectrum of MXene-CLCE flexible film during stretching. It can be found that during the stretching process, the MXene-CLCE flexible film shows dynamic color change, gradually changing from red to green and then to blue. Its corresponding reflection spectrum gradually blue-shifts, and the reflection peak wavelength changes from 645nm at the initial time to 466nm at 120% strain.

[0079] Figure 8 Figure 1 shows the temperature change (a) of the MXene-CLCE flexible film during force-induced stretching (observed under an infrared camera) and the temperature change (b) of the stretching corresponding to hot stages at different temperatures. The heating temperature of the hot stage (a) is 50°C, and the heating temperature of the hot stage (b) is 40°C, 45°C, 50°C and 55°C. As can be seen from the figure, the MXene-CLCE flexible film shows dynamic color changes when observed with an infrared camera during the stretching process, indicating that its temperature gradually increases with stretching. Figure (b) illustrates this point using data. As the stretching gradually increases, the surface temperature of the flexible film gradually increases. The higher the temperature of the hot stage, the greater the temperature difference caused by the stretching. When the hot stage temperature is 55°C, the maximum temperature difference on the surface of the flexible film is 17°C.

[0080] Fig. 9 Figure 3 (a) Change in infrared reflectivity and (b) change in infrared emissivity of MXene-CLCE flexible film under force-induced stretching. It can be seen that as the stretching gradually increases, the infrared reflectivity of the flexible film gradually decreases from the initial 0.68 to 0.42, and the infrared emissivity gradually increases from the initial 0.32 to 0.58.

[0081] Fig.10(a) Schematic diagram of the stretching, (b) scanning electron microscope (SEM), and (c) 3D surface profiler images corresponding to the mechanical stretching of the MXene-CLCE flexible film. It can be seen that as the tensile strength gradually increases, the surface cracks of the MXene-CLCE flexible film gradually increase, and when the stretching increases slightly to a certain extent, due to the difference in the tensile modulus between MXene and CLCE, the MXene becomes an isolated sheet. When the surface of the MXene-CLCE flexible film is flat (0%), the infrared radiation at this time is blocked by MXene under the flexible film, which is manifested as the infrared reflectivity of the MXene-CLCE flexible film is as high as 0.68, and its infrared emissivity is 0.32. As the stretching progresses, the surface cracks of the MXene-CLCE flexible film gradually increase. When the stretching degree increases to 120%, the infrared reflectivity of the flexible film decreases to 0.42, and its infrared emissivity increases to 0.58, indicating that the crack formation of the MXene-CLCE flexible film can regulate the transmission, absorption and reflection of infrared light.

[0082] Fig.11 The change in electromagnetic shielding performance of the MXene-CLCE flexible film corresponding to the force-induced stretching. As can be seen from the figure, as the stretching gradually increases, the electromagnetic shielding performance of the flexible film decreases rapidly, from the initial 21dB to almost 0.

[0083] Example 3

[0084] A method for preparing a visible-infrared-microwave multi-band mechanically controlled MXene nanocomposite chiral liquid crystal photonic crystal flexible film comprises the following steps:

[0085] Step 1, weigh 630mg RM257 and 29mg LC756 and dissolve them in 500mg toluene solvent, and heat at 80℃ to completely dissolve the monomers. After cooling to room temperature, add 155mg EDDET, 36.7mg PETMP and 4mg Irg 651. Add 180mg diluted DPA solution (toluene: DPA = 50:1), stir the mixed solution at room temperature for 5min to mix it evenly, and then place it in a vacuum drying oven for degassing. Then pour the precursor on a polytetrafluoroethylene mold, place it in a fume hood at room temperature for 8h, use an octopus pattern for masking, and hold it at 20mW / cm 2 The samples were irradiated with ultraviolet light for 200 s for pre-crosslinking, and then placed in an oven. After the toluene solvent evaporated completely, the samples were heated at 20 mW / cm 2 The resulting film was cured under ultraviolet light for 600 s to obtain a cholesteric liquid crystal elastomer with CLCE having an octopus pattern.

[0086] Step 2: Add 3.2 g of lithium fluoride (LiF) to 40 mL of 9 mol L-1 Stir in hydrochloric acid (HCl) solution for 10 min, then slowly add 2 g Ti 3 AlC 2 The powder was placed at 50 ° C for 36 hours. The reaction product was centrifuged and washed with deionized water until the pH was ≥ 6. The precipitate was redispersed in deionized water and centrifuged at 3000 rpm for 15 minutes. The collected supernatant was centrifuged at 9800 rpm for 10 minutes. The resulting sludge-like precipitate was the synthesized ultrathin MXene nanosheets (the average lateral size of the nanosheets was 1.5 μm). The ultrathin MXene nanosheets were dispersed in deionized water to prepare different concentrations (5 mg mL -1 ,10mgmL -1 ,15mg mL -1 ,20mg mL -1 ) of ultrathin MXene nanosheets in water.

[0087] Step 3, use a pipette to draw 1 ml of (trans) ethylene diisocyanate polymer solution on the chiral cholesteric liquid crystal elastomer flexible film and rotate it at a speed of 800 rpm for 1 minute, then use ultraviolet light to irradiate the chiral liquid crystal photonic crystal flexible film to cause a second step of crosslinking to obtain a modified liquid crystal film.

[0088] Step 4, use tape to stick an octopus pattern on the modified liquid crystal film that has been UV-cured for the second time (the octopus pattern part is not taped, and the rest is taped), then use a pipette to absorb 1 ml of ultrathin MXene nanosheet dispersion, and apply it to the modified liquid crystal film that has been UV-cured for the second time, and then rotate at 500 rpm for 1 min, for a total of 30 spin coatings, and then put the flexible film on a hot stage and heat it at 50°C to quickly dry the flexible film to obtain a MXene-CLCE flexible film with an octopus pattern (the octopus pattern part cross-links the MXene layer, and the rest is not cross-linked).

[0089] The structural formula of the reactants used in this example is as follows:

[0090]

[0091] Fig.12The (a) bionic color-changing camouflage skin and (b) infrared stealth effect of MXene-CLCE flexible film. It can be seen that during the mechanical stretching of MXene-CLCE flexible film, the uncrosslinked MXene area is photocured earlier than the area with the octopus pattern and has a lower degree of crosslinking. Therefore, during the mechanical stretching of MXene-CLCE flexible film, as the stretching progresses, the color of the octopus pattern gradually becomes consistent with the color of the surrounding CLCE flexible film without crosslinked MXene, achieving the bionic color-changing camouflage effect in the visible light region; due to the unique low mid-infrared emissivity of MXene, the mid-infrared radiation of the target object can be significantly reduced, thereby effectively blocking the infrared thermal imager from capturing the infrared radiation signal. The MXene-CLCE flexible film with the octopus pattern is placed on the hot stage. It can be seen from the infrared thermal imager that as the stretching progresses, the color of the octopus pattern gradually blends into the surrounding environment, achieving the infrared stealth effect.

[0092] The above is only a preferred embodiment of the present invention. It should be pointed out that, for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a visible-infrared-microwave multi-band mechanically controlled MXene nanocomposite chiral liquid crystal photonic crystal flexible film, characterized in that: The following steps are involved: Step 1, uniformly mixing a monofunctional polymerizable liquid crystal monomer, a difunctional polymerizable liquid crystal monomer, a chain extender, a crosslinking agent, a chiral agent, and a photoinitiator according to a preset ratio to prepare a polymerizable chiral liquid crystal precursor, wherein the functionality is acryloyloxy; uniformly pouring the prepared chiral liquid crystal precursor into a mold prepared in advance, and allowing the liquid crystal monomer to self-assemble to form a long-range ordered three-dimensional blue phase photonic crystal or a one-dimensional cholesteric phase photonic crystal by keeping it warm at a specific temperature; finally, using ultraviolet light to perform an in-situ photopolymerization reaction to obtain a chiral liquid crystal photonic crystal flexible film; Step 2, coating an optically transparent polymer solution with isocyanate functional groups on the chiral liquid crystal photonic crystal flexible film obtained in step 1, and then irradiating the chiral liquid crystal photonic crystal flexible film with ultraviolet light to cause a second step of crosslinking to ensure that the polymer is completely combined with the chiral liquid crystal photonic crystal flexible film, thereby obtaining a modified liquid crystal film with isocyanate functional groups; Step 3, coating the MXene nanosheet dispersion on the modified liquid crystal film obtained in step 2, or partially coating it on the modified liquid crystal film obtained in step 2, in the coated area, the isocyanate functional groups and the hydroxyl groups in the MXene nanosheets are chemically cross-linked to obtain an ultra-thin, transparent and conductive MXene nanostructure film; then remove the mold to obtain the MXene nanocomposite chiral liquid crystal photonic crystal flexible film composed of a polymer, a chiral liquid crystal photonic crystal and a MXene nanostructure film.

2. The preparation method according to claim 1, characterized in that In the step 1, the mass fraction ratio of the monofunctional polymerizable liquid crystal monomer, the difunctional polymerizable liquid crystal monomer, the chain extender, the crosslinking agent, the chiral agent, and the photoinitiator is (0.0-45.0):(60.0-95.0):(15.0-35.0):(0.5-15.0):(0.5-8.0):(0.5-2.0); The liquid crystal phase transition temperature of the liquid crystal monomer is 25° C. to 180° C. Preferably, the monofunctional liquid crystal monomer is one or more of the following: Wherein, n=2~13, m=1~12, X=H、Cl、F、CH3. The dual monofunctional liquid crystal monomer is one or more of the following: Wherein, n=2~13, m=1~12, X=H、Cl、F、CH3.; The chiral agent includes but is not limited to LC756, R5011, S5011, R811, S811, R1011, S1011, CB15, C15; The chain extender is selected from dithiol monomers, including but not limited to one or more of 2,2-(ethylenedioxy)diethylmercaptan, 1,3-propanedithiol and 1,6-hexanedithiol; The crosslinking agent is selected from one or more of trithiol monomers and tetrathiol monomers, including but not limited to 3-mercaptopropionic acid-2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]-1,3-propanediol (TTMP) and tetrakis(3-mercaptopropionic acid) pentaerythritol ester (PETMP); The photoinitiator is an ultraviolet photoinitiator having light absorption ability in the range of 250 to 420 nm. Preferably, the photoinitiator is one or more of benzoin dimethyl ether (I-651), 1-hydroxycyclohexyl phenyl ketone (I-184), 2-hydroxy-2-methyl-1-phenyl-1-propanone (I-1173), and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (I-2959).

3. The preparation method according to claim 1, characterized in that: In the step 1, the ratio of the total molar amount of the monofunctional polymerizable liquid crystal monomer, the difunctional polymerizable liquid crystal monomer and the acryloxy group of the chiral agent to the total molar amount of the thiol group of the chain extender and the cross-linking agent is 1:1 to 11:10; the molar ratio of the cross-linking agent to the chain extender is 1:19 to 1:

4.

4. The preparation method according to claim 1, characterized in that: In the step 1, the reaction temperature of the self-assembly is 15° C. to 35° C., and the reaction time is 18 to 36 hours.

5. The preparation method according to claim 1, characterized in that: In step 1, the light source for the in-situ photopolymerization reaction is a UV light source with a wavelength of 254 to 520 nm and a light intensity of 5 to 200 mW / cm 2 , the polymerization time is 60s~1800s.

6. The preparation method according to claim 1, characterized in that: In the step 1, the mold includes a glass substrate and a flexible frame. The shape of the glass substrate is rectangular, square or other shapes. When cleaning, it is placed in ethanol and deionized water for ultrasonic cleaning. Preferably, the length of the glass substrate is 10 mm to 1000 mm. The flexible frame is glued to the surface of the glass substrate with glue. The glue is modified acrylic adhesive, epoxy resin glue, polyvinyl acetal glue, α-cyanoacrylate ethyl, etc. The flexible frame is rubber, silicone rubber, TPU, TPE or soft PVC.

7. The preparation method according to claim 1, characterized in that: In step 2, the optically transparent polymer with isocyanate functional groups includes, but is not limited to, (trans)ethylene diisocyanate, 1,4-but-2-ene-diol diisocyanate, toluene diisocyanate, or 2-isocyanatoethyl methacrylate.

8. The preparation method according to claim 1, characterized in that: In step 3, the ultrathin MXene nanosheets include but are not limited to Ti3C2T x 、Ti2CT x 、Ti4N3T x 、Ti3CNT x 、Cr2TiC2T x 、Mo2CT x 、Mo2TiC2T x 、Mo2Ti2C3T x 、Nb2CT x or V2CT x , the lateral size of the ultrathin MXene nanosheet is 100nm~10μm; The concentration of the MXene nanosheet dispersion was 1 mg mL -1 ~20 mg mL -1 ; The MXene nanostructured film is obtained by scraping, dripping, spin coating or pulling, and has a thickness of 20 nm to 1 μm; The thickness of the prepared MXene nanolayer is 2nm to 1μm.

9. A visible-infrared-microwave multi-band mechanically controlled MXene nanocomposite chiral liquid crystal photonic crystal flexible film obtained by the preparation method as described in any one of claims 1 to 8.

10. Application of the visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film as described in claim 9 in color-changing devices, infrared camouflage and microwave electromagnetic shielding.

Images