Visible-infrared-microwave multi-band mechanically regulated mxene nanocomposite chiral liquid crystal photonic crystal flexible film and preparation method and application thereof

Abstract

The application discloses a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film and a preparation method and application thereof, and the preparation method comprises the following steps: step 1, preparing a chiral liquid crystal photonic crystal flexible film; step 2, coating an optically transparent polymer solution with an isocyanate functional group on the chiral liquid crystal photonic crystal flexible film obtained in step 1, and irradiating the same with ultraviolet light to cause second-step crosslinking, so that a modified liquid crystal film is obtained; and step 3, coating a MXene nanosheet dispersion liquid on the modified liquid crystal film obtained in step 2, so that a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film is obtained. According to the application, a visible light band cyclic color change and an infrared band force-induced variable infrared emissivity can be realized by applying a small force, and electromagnetic shielding in a microwave band can be realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of photonic crystals, 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

[0002] Camouflage is an important topic in the field of optics, as it provides a means of evading danger. Some animals exhibit camouflage skills in nature by evolving a series of defensive color patterns, including fixed and adaptive body colors. The limitations of animals' fixed body colors are obvious, as the colors 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 in the dermal layer iridophores; cephalopods such as octopuses can reflect variable wavelengths of visible and near-infrared light through the synergistic action of iridophores and chromatophores, achieving a wide range of skin color changes and stealth effects.

[0003] Bionic intelligent camouflage technology overcomes the limitations of traditional static camouflage, breaking through the traditional camouflage ideas and modes in terms of material use and control methods. When the background environment changes, the camouflage target can make continuous responses according to the background information, and autonomously realize the fusion matching of the target and background photoelectric characteristics. It has the advantages of strong adaptability, good concealment, fast response speed, etc., and has wide application prospects in the fields of military camouflage, reconnaissance and surveillance systems, and stealth aircraft, and can be used in privacy protection and other aspects in civilian fields.

[0004] Inspired by natural organisms, the preparation of chameleon materials with bionic camouflage function has become a research hotspot. How to develop bionic intelligent chameleon materials that can realize color change and stealth in the visible and infrared spectral range and related technologies is a key scientific problem 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, have good external field responsiveness and synergistic effect, and can realize high-throughput preparation of large-area flexible films through long-range ordered self-assembly of molecules. The introduction of chiral molecules into main-chain nematic liquid crystal materials can self-assemble into 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, such chiral liquid crystal materials not only can selectively reflect circularly polarized light, but also can sensitively respond to changes in stress, heat, electricity, light, humidity and other stimuli, showing dynamic regulation of structural color, and have wide application prospects in the fields of color-changing camouflage, information encryption, tunable lasers and the like.

[0005] However, these chiral liquid crystal systems mainly focus on the color change control in the visible 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

[0006] The purpose of the present application is to provide a visible-infrared-microwave multi-band mechanical regulation MXene nanocomposite chiral liquid crystal photonic crystal flexible film and a preparation method to solve the problems that the stimulus-responsive color-changing chiral liquid crystals in the prior art only realize structural color change in the visible light band and cannot simultaneously regulate infrared radiation in the infrared band and electromagnetic shielding in the microwave band.

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

[0008] The technical scheme adopted to achieve the purpose of the present application is as follows:

[0009] A preparation method of a visible-infrared-microwave multi-band mechanical regulation MXene nanocomposite chiral liquid crystal photonic crystal flexible film, comprising the following steps:

[0010] Step 1: uniformly mix a monofunctional polymerizable liquid crystal monomer, a bifunctional polymerizable liquid crystal monomer, a chain extender, a crosslinking agent, a chiral agent, and a photoinitiator in a predetermined ratio to prepare a polymerizable chiral liquid crystal precursor, wherein the functionality is acryloyloxy; pour the prepared chiral liquid crystal precursor into a previously prepared mold, and form a long-range ordered three-dimensional blue phase photonic crystal or a one-dimensional cholesteric phase photonic crystal by self-assembly of the liquid crystal monomer at a specific temperature through heat preservation, and finally, perform in-situ photopolymerization reaction using ultraviolet light to obtain a chiral liquid crystal photonic crystal flexible film;

[0011] Step 2: coat an optically transparent polymer solution with isocyanate functional groups onto the chiral liquid crystal photonic crystal flexible film obtained in step 1, and then irradiate the chiral liquid crystal photonic crystal flexible film with ultraviolet light to cause a second crosslinking, so as to ensure the combination of the polymer and the chiral liquid crystal photonic crystal flexible film, and obtain a modified liquid crystal film with isocyanate functional groups;

[0012] Step 3, coating the MXene nanosheet dispersion liquid onto the modified liquid crystal film obtained in step 2, or partially coating the modified liquid crystal film obtained in step 2, in the coating area, the isocyanate functional group and the hydroxyl group in the MXene nanosheet are chemically crosslinked, to obtain an ultra-thin transparent conductive MXene nano-structured film; then remove the mold to obtain the MXene nano-composite chiral liquid crystal photonic crystal flexible film composed of polymer, chiral liquid crystal photonic crystal and MXene nano-structured film.

[0013] In the above technical solution, in step 1, the mass fraction ratio of monofunctional polymerizable liquid crystal monomer, difunctional polymerizable liquid crystal monomer, chain extender, crosslinking agent, chiral agent and 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 25-180℃, 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, CH3.

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

[0019]

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

[0021] X=H, Cl, F, CH3.

[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 dimercapto monomers, including but not limited to one or more of 2,2-(ethylenedioxy)diethyl mercaptan, 1,3-propanedithiol and 1,6-hexanedithiol;

[0024] The crosslinking agent is selected from one or more of a trimercaptan monomer and a tetramercaptan monomer, including but not limited to 3-mercaptopropionic acid-2-ethyl-2-[(3-mercapto-1-oxopropoxy)methyl]-1,3-propanediyl (TTMP), pentaerythritol tetra(3-mercaptopropionate) (PETMP);

[0025] The photoinitiator is an ultraviolet photoinitiator having an optical absorption capacity in the range of 250-420 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), 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone (I-2959).

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

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

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

[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, and the glass substrate is cleaned by ultrasonic cleaning in ethanol and deionized water, preferably, the length of the glass substrate is 10-1000 mm, the flexible frame is adhered to the surface of the glass substrate using adhesive, the adhesive is modified acrylate adhesive, epoxy resin adhesive, polyvinyl acetal adhesive, alpha-cyanoacrylic acid ethyl ester, etc., and 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 groups 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 ultrathin MXene nanosheet includes but is not limited to Ti3C2T x , Ti2CTx Ti4N3T x Ti3CNT x Cr2TiC2T x Mo2CT x Mo2TiC2T x Mo2Ti2C3T x Nb2CT x or V2CT x The lateral size of the ultra-thin MXene nanosheet is 100 nm-10 mu m;

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

[0033] The MXene nanostructure film is obtained by scraping, dropping, spinning or pulling, and the thickness is 20 nm-1 mu m;

[0034] The prepared MXene nanolayer has a thickness of 2 nm-1 mu m.

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

[0036] The visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film has visible-infrared-microwave compatible dynamic regulation performance, and by controlling the regulation degree, reversible structural color change can be realized in the visible light band, dynamic on-demand regulation of infrared emissivity can be realized in the infrared band, and dynamic regulation of electromagnetic shielding signals can also be realized.

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

[0038] Another aspect of the present application provides the 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 biomimetic skin, the infrared camouflage is a mechanochromic infrared emissivity infrared camouflage, the area without coating MXene nanosheet dispersion liquid and the area coated with MXene nanosheet dispersion liquid present different colors under visible light irradiation, during the stretching process, the colors tend to be consistent, and after the morphology is restored, the colors are restored to the colors before stretching; in addition, under the condition of heating at 40-55 DEG C, the area without coating MXene nanosheet dispersion liquid and the area coated with MXene nanosheet dispersion liquid also present different colors, during the stretching process, the colors tend to be consistent, and after the morphology is restored, the colors are restored to the colors before stretching.

[0039] Compared with the prior art, the present application has the following advantages:

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

[0041] 2. The MXene nanocomposite chiral liquid crystal photonic crystal flexible film of the present application enhances the interface bonding between different functional layers by introducing a molecular anchoring layer capable of chemical cross-linking at the interface, improves the mechanical properties and processability of the flexible film, and 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 application configures the crack morphology of the surface by mechanical stretching, which adjusts the direct transmission / reflection and scattering behavior of infrared light. BRIEF DESCRIPTION OF DRAWINGS

[0043] Figure 1 It is a schematic diagram for the preparation process of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film.

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

[0045] Figure 3 It is the reflection spectrum corresponding to different components of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film.

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

[0047] Figure 5 Comparison of electromagnetic shielding performance of MXene nanocomposite chiral liquid crystal photonic flexible film, chiral liquid crystal photonic flexible film and pure MXene nanomaterial.

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

[0049] Figure 7 Force-induced stretching of MXene nanocomposite chiral liquid crystal photonic flexible film (a) color change and (b) corresponding reflectance spectrum.

[0050] Figure 8 Force-induced stretching of MXene nanocomposite chiral liquid crystal photonic flexible film (a) temperature change (observation under infrared camera) and (b) corresponding stretching temperature change.

[0051] Figure 9 Force-induced stretching of MXene nanocomposite chiral liquid crystal photonic flexible film (a) infrared reflectance change and (b) infrared emissivity change.

[0052] Figure 10 Force-induced stretching of MXene-CLCE flexible film (a) stretching schematic diagram, (b) scanning electron microscope (SEM) and (c) 3D surface profiler image.

[0053] Figure 11 Force-induced stretching of MXene nanocomposite chiral liquid crystal photonic flexible film corresponding electromagnetic shielding performance change.

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

[0055] The application will be further described below in conjunction with specific examples. It should be understood that the specific examples described herein are intended to explain the application and are not intended to limit the application.

[0056] Example 1

[0057] A preparation method of a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film, comprising the following steps:

[0058] Step 1, weigh 630 mg of RM257 and 29 mg of LC756 (4.5 wt%) and dissolve them in 400 mg of toluene solvent, heat at 80°C to completely dissolve the monomers. After cooling to room temperature, add 155 mg of EDDET, 36.7 mg of PETMP and 4 mg of Irg651. Add 180 mg of diluted DPA solution (toluene:DPA=50:1), stir the mixed solution at room temperature for 5 min to mix uniformly, and then place it in a vacuum drying box to degas. Then pour the precursor onto a polytetrafluoroethylene mold, place it in a fume hood at room temperature for 24 h, and after the toluene solvent is completely volatilized, finally irradiate it under 20 mW / cm 2 of ultraviolet light for 600 s for curing 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 hydrochloric acid (HCl) solution and stir for 10 min, then slowly add 2 g of Ti3AlC2 powder, react at 50°C for 36 h, centrifuge the reaction product with deionized water until pH≥6, and re-disperse the precipitate into deionized water, centrifuge at 3000 rpm for 15 min, and then centrifuge the collected supernatant at 9800 rpm for 10 min. The obtained sludge-like precipitate is the synthesized ultra-thin MXene nanosheet (the average lateral size of the nanosheet is 1.5 μm). Disperse the ultra-thin MXene nanosheet into dimethyl sulfoxide (DMSO) to prepare ultra-thin MXene nanosheet dispersions with different concentrations (5 mg / mL -1 , 10 mg / mL -1 , 15 mg / mL -1 , 20 mg / mL -1 .

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

[0061] Step 4, 1 ml of ultrathin MXene nanosheet dispersion was taken with a pipette and coated onto the modified liquid crystal film obtained in step 3, and rotated at a speed of 500 rpm for 1 min, a total of 30 times of spin coating. During the coating process, the isocyanate functional group and the hydroxyl group in the MXene nanosheet chemically crosslinked. Then the flexible film was placed on a hot stage and heated at 50°C to dry the flexible film quickly, obtaining the Mxene-CLCE flexible film. The preparation process is shown in Figure 1 .

[0062] The structural formula of the reactants used in this example is shown below:

[0063]

[0064] Figure 2 The microstructure of the MXene-CLCE flexible film under SEM can be seen from the figure. The interface between the double-layer structure is tightly combined. The MXene layer in the upper layer is tightly stacked, and the lower CLCE layer also has obvious layer texture.

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

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

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

[0068] Figure 6 Comparison of (a) visible light transmittance, (b) infrared emissivity and (c) electromagnetic shielding performance of MXene-CLCE flexible films with different thickness of MXene layers. It can be seen that, Figure 6 In (a), the optical transmittance of MXene-CLCE flexible film, the transmittance of MXene-CLCE flexible film with MXene layer thickness of 33.7 nm is 79% at a wavelength of 550 nm, and the transmittance gradually decreases with the increase of the number of stacked layers, and the transmittance remains at 21% when the MXene layer is stacked to 196.9 nm. The infrared emissivity of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film is also closely related to the thickness of MXene, from Figure 6 As can be seen in (b), when the thickness of MXene is 33.7 nm, the average infrared emissivity of the film is 63%, and when the thickness of MXene is 196.9 nm, the average infrared emissivity of the film is 22%. From Figure 6 As can be seen in (b), with the gradual increase of the thickness of MXene, the infrared emissivity of the MXene-CLCE flexible film slows down, and after the thickness of MXene reaches 107.6 nm, a clear slowing trend appears. Next, Figure 6 (c) shows the change of EMI total 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 thickness of MXene is 33.7 nm, the average EMI SET of the MXene nanocomposite chiral liquid crystal photonic crystal flexible film is 3.5 dB, which provides ≈25% shielding for incident electromagnetic waves. When the thickness of MXene layer is 196.9 nm, the EMI shielding effectiveness increases rapidly with the increase of the number of stacked layers, reaching 29.5 dB, which can attenuate 99% of electromagnetic waves.

[0069] Example 2

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

[0071] Step 1, 720 mg of C6M and 29 mg of LC756 were weighed and dissolved in 600 mg of dichloroethane solvent, and heated at 80°C to completely dissolve the monomers. After cooling to room temperature, 90.2 mg of 1,6-hexanedithiol, 99.65 mg of TTMP and 4 mg of Irg1173 were added. 180 mg of diluted n-hexylamine solution (dichloroethane:n-hexylamine = 50:1) was added, and the mixed solution was stirred at room temperature for 5 min to mix uniformly, and then placed in a vacuum drying box to degas. Then the precursor was poured onto the ionogel network, and placed in a fume hood at room temperature for 24 h. Finally, the CLCE chiral liquid crystal photonic crystal flexible film was obtained by irradiation under 5 mW / cm 2 of ultraviolet light for 600 s for curing.

[0072] Step 2, 3.2 g of lithium fluoride (LiF) was added to 40 mL of 9 mol L -1 of hydrochloric acid (HCl) solution and stirred for 10 min, then 2 g of Ti3AlC2 powder was slowly added, and the reaction was carried out at 50°C for 36 h. The reaction product was washed by centrifugation with deionized water until pH≥6, and the precipitate was re-dispersed in deionized water, centrifuged at 3000 rpm for 15 min, and then the collected supernatant was centrifuged at 9800 rpm for 10 min. The obtained muddy precipitate was the synthesized ultra-thin MXene nanosheet (the average lateral size of the nanosheet was 1.5 μm). The ultra-thin MXene nanosheet was dispersed in dimethyl sulfoxide (DMSO) to prepare ultra-thin MXene nanosheet dispersions with different concentrations (5 mg mL -1 , 10 mg mL -1 , 15 mg mL -1 , 20 mg mL -1 .

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

[0074] Step 4, 1 ml of ultra-thin MXene nanosheet dispersion was taken with a pipette and sprayed onto the modified liquid crystal film obtained in step 3, and the spraying was repeated 3-5 times. During the coating process, the isocyanate functional group chemically reacted with the hydroxyl group in the MXene nanosheet. Then the flexible film was placed on a hot stage and heated at 50°C to dry quickly, to obtain the MXene-CLCE flexible film.

[0075] The reflection wavelength of the MXene-CLCE flexible film during stretching was measured by an optical fiber spectrometer, and the dynamic color change was recorded by a camera; the color change and temperature change of the MXene-CLCE flexible film during stretching were recorded by an infrared camera; the infrared reflectivity change of the MXene-CLCE flexible film under stretching was tested by an infrared spectrometer, and the corresponding change of the infrared emissivity was calculated; the change of the electromagnetic shielding performance of the MXene-CLCE flexible film during stretching was tested by a vector analyzer.

[0076] The structural formula of the reactant used in the embodiment is as follows:

[0077]

[0078] Figure 7 For the color change and the reflection spectrum of the MXene-CLCE flexible film during stretching, it can be found from the figure that during the stretching process, the MXene-CLCE flexible film shows dynamic color change, gradually changing from red to green and then to blue, and the corresponding reflection spectrum gradually shows blue shift, and the reflection peak wavelength changes from 645 nm at the initial stage to 466 nm at 120% strain.

[0079] Figure 8 For the temperature change (observation under the infrared camera) and the stretching temperature change corresponding to different temperature hot tables of the MXene-CLCE flexible film during force-induced stretching, (a) the hot table heating temperature is 50℃, (b) the hot table heating temperature is 40℃, 45℃, 50℃ and 55℃, it can be seen from the figure that during the stretching process, the MXene-CLCE flexible film shows dynamic color change when observed by an infrared camera, indicating that the temperature gradually increases with the stretching. Figure (b) uses data to illustrate this point, as the stretching gradually increases, the surface temperature of the flexible film gradually increases. And the higher the hot table temperature, the greater the temperature difference generated by stretching, and when the hot table temperature is 55℃, the surface temperature difference of the flexible film is maximum, which is 17℃.

[0080] Figure 9 For the infrared reflectivity change and the infrared emissivity change of the MXene-CLCE flexible film during force-induced stretching, it can be seen that as the stretching gradually increases, the infrared reflectivity of the flexible film gradually decreases from 0.68 to 0.42, and the infrared emissivity gradually increases from 0.32 to 0.58.

[0081] Figure 10The corresponding (a) tensile diagram, (b) scanning electron microscope (SEM) and (c) 3D surface profiler images of the MXene-CLCE flexible film force-induced stretching can be seen that as the tensile strength gradually increases, the surface cracks of the MXene-CLCE flexible film gradually increase, and when the tensile slightly increases to a certain extent, the MXene becomes isolated sheet due to the difference in tensile modulus between MXene and CLCE. When the surface of the MXene-CLCE flexible film is flat (0%), the infrared radiation is blocked under the edge of the flexible film by MXene, which shows that the infrared reflectivity of the MXene-CLCE flexible film is as high as 0.68, and the infrared emissivity is 0.32. As the stretching gradually proceeds, the surface cracks of the MXene-CLCE flexible film gradually increase, and when the stretching increases to 120%, the infrared reflectivity of the flexible film decreases to 0.42, and the infrared emissivity increases to 0.58, indicating that the crack generation of the MXene-CLCE flexible film can adjust the transmission, absorption and reflection of infrared light.

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

[0083] Example 3

[0084] A preparation method of a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film, comprising the following steps:

[0085] Step 1, weigh 630 mg of RM257 and 29 mg of LC756 and dissolve them in 500 mg of toluene solvent, heat at 80°C to completely dissolve the monomers. After cooling to room temperature, add 155 mg of EDDET, 36.7 mg of PETMP and 4 mg of Irg 651. Add 180 mg of diluted DPA solution (toluene:DPA=50:1), stir the mixed solution at room temperature for 5 min to make it uniform, and then place it in a vacuum drying box to degas. Then pour the precursor into a polytetrafluoroethylene mold, place it in a fume hood at room temperature for 8 h, use an octopus pattern for masking, and irradiate it under 20 mW / cm 2 of ultraviolet light for 200 s for pre-crosslinking, and then place it in an oven. After the toluene solvent is completely volatilized, irradiate it under 20 mW / cm 2 of ultraviolet light for 600 s for curing to obtain a CLCE cholesteric liquid crystal elastomer with an octopus pattern.

[0086] Step 2, add 3.2 g of lithium fluoride (LiF) to 40 mL of 9 mol / L-1 The 2 g of Ti3AlC2 powder was slowly added into the stirring HCl solution, and the reaction was carried out at 50 °C for 36 h. The reaction product was washed by centrifugation with deionized water until the pH was greater than or equal to 6. The precipitate was re-dispersed in deionized water, and centrifuged at 3000 rpm for 15 min. The supernatant was collected and centrifuged at 9800 rpm for 10 min. The obtained sludge-like precipitate was the synthesized ultrathin MXene nanosheets (the average lateral size of the nanosheets was 1.5 pm). The ultrathin MXene nanosheets were dispersed in deionized water to prepare ultrathin MXene nanosheet aqueous dispersions with different concentrations (5 mg mL -1 , 10 mg mL -1 , 15 mg mL -1 , 20 mg mL -1 ).

[0087] Step 3: 1 ml of (trans) ethylene diisocyanate polymer solution was taken with a pipette and spin-coated on the cholesteric cholesteric phase liquid crystal elastomer flexible film at a rotation speed of 800 rpm for 1 min. Subsequently, the cholesteric liquid crystal photonic crystal flexible film was subjected to second cross-linking by UV light irradiation to obtain a modified liquid crystal film.

[0088] Step 4: An octopus pattern was pasted on the modified liquid crystal film that had been secondarily cured by UV light using a tape (the octopus pattern part was not pasted with the tape, and the rest was pasted with the tape). Then, 1 ml of ultrathin MXene nanosheet dispersion was taken with a pipette and coated on the secondarily UV-cured modified liquid crystal film, and then spin-coated at a rotation speed of 500 rpm for 1 min, for a total of 30 times. Then, the flexible film was placed on a hot stage and heated at 50 °C to dry the flexible film quickly, to obtain an MXene-CLCE flexible film with an octopus pattern (the octopus pattern part was cross-linked with the MXene layer, and the rest was not cross-linked).

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

[0090]

[0091] Figure 12The (a) biomimetic color-changing camouflage skin and (b) infrared stealth effect of the MXene-CLCE flexible film. It can be seen that during the force-induced stretching of the MXene-CLCE flexible film, the color of the octopus pattern gradually becomes consistent with the color of the surrounding CLCE flexible film part with uncrosslinked MXene, realizing the biomimetic color-changing camouflage effect in the visible light region, because the area with octopus pattern is photocured earlier and has a lower crosslinking degree than the area without octopus pattern. The unique low mid-infrared emissivity of MXene can significantly reduce the mid-infrared radiation of the target object, thereby effectively blocking the capture of infrared radiation signals by the infrared thermal imager. When the MXene-CLCE flexible film with an octopus pattern is placed on a hot table, it can be seen from the infrared thermal imager that as the stretching gradually proceeds, the color of the octopus pattern gradually blends into the surrounding environment, realizing the effect of infrared stealth.

[0092] The above only describes the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled persons in the art, several improvements and refinements can be made without departing from the principles of the present application, and these improvements and refinements should also be considered within the protection scope of the present application.

Claims

1. A method for preparing a visible-infrared-microwave multi-band mechanically regulated MXene nanocomposite chiral liquid crystal photonic crystal flexible film, characterized in that, The method comprises the following steps: Step 1, a single functionality polymerizable liquid crystal monomer, a double functionality polymerizable liquid crystal monomer, a chain extender, a crosslinking agent, a chiral agent and a photoinitiator are mixed in a preset ratio to prepare a polymerizable chiral liquid crystal precursor, the functionality is acryloyloxy; the prepared chiral liquid crystal precursor is poured into a prepared mold, and a long-range ordered three-dimensional blue phase photonic crystal or a one-dimensional cholesteric phase photonic crystal is formed by self-assembly of the liquid crystal monomer under a specific temperature; finally, in-situ photopolymerization is performed by using ultraviolet light to obtain a chiral liquid crystal photonic crystal flexible film; Step 2, an optically transparent polymer solution with an isocyanate functional group is coated on the chiral liquid crystal photonic crystal flexible film obtained in step 1, and then the chiral liquid crystal photonic crystal flexible film is irradiated by using ultraviolet light to cause a second crosslinking, so that the polymer and the chiral liquid crystal photonic crystal flexible film are combined to obtain a modified liquid crystal film with an isocyanate functional group; Step 3, a MXene nanosheet dispersion solution is coated on the modified liquid crystal film obtained in step 2, or is partially coated on the modified liquid crystal film obtained in step 2, in the coated area, the isocyanate functional group and the hydroxyl group in the MXene nanosheet are chemically crosslinked to obtain an ultra-thin transparent conductive MXene nanostructure film; then the mold is removed to obtain the MXene nanocomposite chiral liquid crystal photonic crystal flexible film composed of the polymer, the chiral liquid crystal photonic crystal and the MXene nanostructure film.

2. The production method according to claim 1, wherein In step 1, the mass ratio of the single functionality polymerizable liquid crystal monomer, the double functionality 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 ℃~180 ℃, and the single functionality liquid crystal monomer is one or more of the following: ； The double functionality liquid crystal monomer is one or more of the following: ； The chiral agent is LC756, R5011, S5011, R811, S811, R1011, S1011, CB15 or C15; The chain extender is selected from dimercapto monomers, and is one or more of 2,2-((ethylenedioxy)diethyl sulfide, 1,3-propanedithiol and 1,6-hexanedithiol; The crosslinking agent is selected from one or more of trimercapto monomers and tetramercapto monomers, and the crosslinking agent is 3-mercaptopropionic acid-2-ethyl-2-[(3-mercapto-1-oxopropoxy) methyl]-1,3-propanediol or tetra(3-mercaptopropionic acid) pentaerythritol ester; The photoinitiator is an ultraviolet photoinitiator having an optical absorption capacity in the range of 250~420 nm, and the photoinitiator is one or more of benzoin dimethyl ether, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-2-methyl-1-phenyl-1-propanone and 2-hydroxy-4-(2-hydroxyethoxy)-2-methylpropiophenone.

3. The production method according to claim 1, wherein The ratio of the total moles of acryloyloxy groups of the monofunctional polymerizable liquid crystal monomer, the difunctional polymerizable liquid crystal monomer and the chiral agent to the total moles of mercapto groups of the chain extender and the crosslinker in step 1 is 1:1-11:10; the molar ratio of the crosslinker to the chain extender is 1:19-1:

4.

4. The production method according to claim 1, wherein In step 1, the self-assembly reaction temperature is 15-35°C, and the reaction time is 18-36 h.

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

6. The production method according to claim 1, wherein In step 1, the mold includes a glass substrate and a flexible frame, the glass substrate is square in shape, is cleaned by ultrasonic cleaning in ethanol and deionized water, the length of the glass substrate is 10-1000 mm, the flexible frame is adhered to the surface of the glass substrate using glue, the glue is modified acrylic adhesive, epoxy resin glue, polyvinyl acetal glue or alpha-cyanoacrylic acid ethyl ester, and the flexible frame is rubber, silicone rubber, TPU, TPE or soft PVC.

7. The production method according to claim 1, wherein In step 2, the optically transparent polymer with isocyanate functional groups is trans-vinyl diisocyanate, 1,4-but-2-ene-diol diisocyanate, toluene diisocyanate or methyl methacrylate 2-isocyanate ethyl ester.

8. The production method according to claim 1, wherein In step 3, the ultrathin MXene nanosheet is Ti3C2T x , Ti2CT x , Ti4N3T x , Ti3CNT x , Cr2TiC2T x , Mo2CT x , Mo2TiC2T x , Mo2Ti2C3T x , Nb2CT x or V2CT x , and the lateral size of the ultrathin MXene nanosheet is 100 nm ~ 10 μm. The concentration of the MXene nanoplatelet dispersion liquid is 1 mg mL -1 ~ 20 mg mL -1 ; The MXene nanostructured film is obtained by scraping, dropping, spinning or pulling, and has a thickness of 20 nm-1 μm. The prepared MXene nanolayer has a thickness of 2 nm-1 μm.

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

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

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