A recyclable and reshaped transparent intelligent microwave absorbing material, its preparation method and application

Abstract

The present invention discloses a recyclable and remoldable transparent intelligent microwave absorbing material, its preparation method and application, belonging to the field of novel electromagnetic protection materials. In the present invention, a polymer matrix material is dissolved in a solvent, and then an appropriate amount of ionic liquid and vanadium dioxide nanoparticles are added thereto and mixed uniformly. Then, the mixed solution is poured into a mold, and after drying, hot pressing is carried out to obtain the recyclable and remoldable transparent intelligent microwave absorbing material. The recyclable and remoldable transparent intelligent microwave absorbing material not only can be recycled and remolded, has economic value and environmental protection significance, but also has good transparency, excellent high temperature resistance, as well as intelligent microwave absorption and color change properties, and has high application value in military or civilian transparent electromagnetic protection fields such as fighter cockpit glass, warship portholes and transparent electromagnetic shielding rooms.

Description

Technical Field

[0001] The present invention belongs to the field of novel electromagnetic shielding materials, relates to wave-absorbing materials, and particularly relates to a recyclable and reshaping transparent intelligent wave-absorbing material, a preparation method thereof, and an application thereof. Background Art

[0002] In the military aspect, the rapid development of modern electronic communication technologies and radar detection systems has greatly improved the ability to search for and track targets in war, and the threats faced by traditional combat weapons have become increasingly serious. As an effective means to improve the survival and penetration capabilities of weapon systems, stealth technology has received great attention from countries around the world. In the civilian aspect, with the wide application of electromagnetic waves in fields such as electronic communication, Internet of Things, radio, and medical, the problem of electromagnetic pollution has become increasingly serious. On the one hand, electromagnetic interference can damage the normal operation of electronic communication and electronic devices; on the other hand, dense electromagnetic waves can cause interference and damage to the human body. Wave-absorbing materials have been favored by various countries because they can effectively attenuate electromagnetic waves and play an irreplaceable role in both military and civilian fields. In order to meet the relevant requirements of wave-absorbing materials in military and civilian fields and enable them to meet the application needs in military equipment such as warships and military fighter jets, as well as scenarios such as radio frequency identification systems and electronic toll collection systems (ETC), wave-absorbing materials need to meet the performance requirements of "thin thickness, light weight, large absorption bandwidth, and high absorption intensity", while also taking into account a certain optical transmittance. In addition, with the current development of radar detection technology towards multi-band coverage and multi-mode detection, military targets with fixed absorption spectra face the risk of being identified by enemy radars. Realizing the dynamic regulation of the target absorption spectrum and the integration of wave-absorbing and wave-transmitting materials is an important development direction for future intelligent wave-absorbing materials.

[0003] Traditional wave-absorbing materials use solid fillers such as graphene, carbon nanotubes, and magnetic powders as wave-absorbing agents. The fillers have poor dispersibility in the matrix, making it difficult to achieve uniform mixing, and the optical transmittance is relatively low. At the same time, magnetic powder fillers such as ferrites have a high density and large dosage, making it difficult to meet the requirements of light weight and high efficiency. In addition, solid filler-based materials are often discarded into the natural environment for degradation or directly destroyed after use or being phased out. Such methods not only cause a great waste of resources, but also require several months or even years for natural degradation to re-enter the cycle. Excessive accumulation will also have a serious impact on the environment and life, increasing the environmental burden, which does not conform to the rapid update speed of electronic products and the environmental protection concept of transient electronics. Moreover, wave-absorbing materials designed with solid fillers are often a static wave-absorbing method, that is, once prepared, their structures cannot be changed anymore, resulting in the fixation of their electromagnetic properties such as frequency response and wave-absorbing intensity, and they cannot be applied to military equipment that requires dynamic regulation of the target absorption spectrum.

[0004] Ionic liquids are molten salts composed entirely of anions and cations, which can be well-compatible with matrix materials. Moreover, the ionic conductivity of ionic liquids has good responsiveness in the microwave band and excellent wave absorption performance. For example, the composite material of ionic gel / metal material prepared by using ionic gel as the solid matrix material and metal material as the conductive filler in the patent with the publication number of CN112029047A has good electromagnetic shielding effect, but it still has high hardness, is opaque, and once formed, its shape cannot be changed. It not only cannot be recycled after use, but also is prone to structural damage when subjected to large deformations, unable to maintain the cyclic stability of its wave absorption performance, and also unable to withstand large tensile stresses, thus being restricted in applications on non-planar surfaces (such as cylinders and cones). At the same time, its electromagnetic characteristics are fixed and it does not have a dynamic regulation function. The patent with the publication number of CN102349364A incorporates ionic liquids into a polymer network to prepare a gel, and disperses an electromagnetic wave suppressor into the gel to obtain a gel-like composition capable of shielding electromagnetic waves. Although it has a certain degree of flexibility, its shape cannot be changed after forming, and the product is opaque and its electromagnetic characteristics are fixed, so it cannot be applied to objects that require stealth and dynamic regulation of the target absorption spectrum, etc.

[0005] Therefore, there is an urgent need in the art to develop new transparent intelligent electromagnetic protection materials that are easy to recycle. These materials not only have excellent electromagnetic wave absorption performance, but can also be recycled, and can achieve switchable wave absorption / transmission and dynamic adjustment of wave absorption intensity and wave absorption performance in different frequency bands, so as to meet the different needs of various application scenarios and be further applied to military and civilian transparent electromagnetic protection fields such as fighter cockpit glass, warship portholes, and transparent electromagnetic shielding rooms. Summary of the Invention

[0006] Aiming at the problems existing in the background technology, the present invention proposes a recyclable and reshaped transparent intelligent wave-absorbing material, its preparation method and application. This material is simple to prepare, not only has excellent recyclable and reshaped properties, but also has switchable wave absorption / transmission and dynamic adjustment of wave absorption intensity and wave absorption performance in different frequency bands, and can be applied to a variety of application scenarios.

[0007] In order to achieve the above object, the technical solution of the present invention is realized as follows:

[0008] A preparation method of a recyclable and reshapable transparent intelligent microwave absorbing material, using ionic liquid and vanadium dioxide nanoparticles as fillers and polymer as matrix, and through dissolution, drying and hot pressing, the recyclable and reshapable transparent intelligent microwave absorbing material is prepared, wherein the mass percentage content of the ionic liquid is 10 - 50%, the mass percentage content of the vanadium dioxide nanoparticles is 2 - 20%, and the balance is polymer. Vanadium dioxide is a typical thermally induced phase change intelligent material. When the temperature reaches its phase change temperature, it transforms from semiconductor to metal phase. Therefore, by using temperature change, the dynamic regulation of its conductivity can be realized; in addition, the conductivity of both ionic conductors and electronic conductors is a function of temperature. By using the variation of the conductivity of ionic liquid (ionic conductor) and vanadium dioxide (electronic conductor) with temperature, the active and reversible regulation of the dielectric constant within a multi - frequency band range can be achieved, and further the reversible intelligent regulation of the microwave absorbing performance can be realized.

[0009] Preferably, the ionic liquid consists of a cation and an anion, wherein the cation is any one of imidazole - type cations, pyrrole - type cations, quaternary phosphonium cations, quaternary ammonium cations and pyridine - type cations, and the anion is any one of halogens, oxygen - containing acid radicals and fluorine - containing acid radicals anions.

[0010] More preferably, the ionic liquid is any one of 1 - ethyl - 3 - methylimidazolium tetrafluoroborate, 1 - butyl - 1 - methylpyrrolidinium bromide, 1 - butylpyridinium acetate, tributylethylphosphonium tetrafluoroborate, 1 - octyl - 3 - methylimidazolium nitrate and 1 - hexyl - 3 - methylimidazolium hydrogen sulfate.

[0011] Preferably, the phase change temperature of the vanadium dioxide nanoparticles is 68 °C, and the particle size range is 30 - 100 nm.

[0012] Preferably, the polymer includes but is not limited to any one of polyvinylidene fluoride (PVDF), polymethyl methacrylate (PMMA), polystyrene (PS), polyvinylidene fluoride - hexafluoropropylene (PVDF - HFP) and polyimide (PI).

[0013] Preferably, the preparation method of the above - mentioned recyclable and reshapable transparent intelligent microwave absorbing material includes the following steps:

[0014] (1) Raw material premixing: Weigh ionic liquid, vanadium dioxide nanoparticles and polymer according to the ratio, dissolve the polymer in a solvent to obtain a polymer solution, and then add the ionic liquid and vanadium dioxide nanoparticles into the polymer solution and mix evenly to obtain a premixed solution;

[0015] (2) Film - forming treatment: Pour the premixed solution in step (1) into a mold, and then heat to evaporate the solvent to form an ionic liquid / vanadium dioxide / polymer film;

[0016] (3) Hot pressing forming: Place the ionic liquid / vanadium dioxide / polymer film obtained in step (2) into a mold for hot pressing forming to obtain a recyclable and remoldable transparent intelligent wave-absorbing material. Among them, the polymer matrix can effectively encapsulate the ionic liquid and nano-vanadium dioxide and will not leak even when pressed by a heavy object.

[0017] More preferably, in the step (1), the mass-volume ratio of the polymer to the solvent is 1 g:(2~15) mL; the solvent is an aprotic polar solvent, and the aprotic polar solvent includes but is not limited to any one or several of N-methylpyrrolidone, N,N-dimethylformamide, acetone, and dichloromethane.

[0018] More preferably, in the step (2), the heating temperature is 30~120 °C and the time is 2~48 h; in the step (3), the hot pressing temperature is 160~300 °C and the time is 10~50 min.

[0019] The present invention also includes the recyclable and remoldable transparent intelligent wave-absorbing material prepared by the above method.

[0020] The present invention also includes the application of the above recyclable and remoldable transparent intelligent wave-absorbing material in military and civilian transparent electromagnetic protection equipment.

[0021] The beneficial effects of the present invention:

[0022] 1. The wave-absorbing material in the present invention can be recycled. In the present invention, by utilizing the solubility of the polymer in the solvent, the recycled ionic liquid / vanadium dioxide / polymer wave-absorbing material is placed back into the solvent again. Under heating conditions, the polymer and the ionic liquid are redissolved in the solvent, and after evaporating the solvent again, a composite material is obtained by hot pressing. High-temperature tests show that the composite material after secondary forming still has excellent wave-absorbing performance, and the wave-absorbing performance is basically the same as that of the initial test ( Figure 4 ), indicating that the recyclable and remoldable transparent intelligent wave-absorbing material of the present invention has excellent recycling and reuse characteristics.

[0023] 2. The wave-absorbing material in the present invention can be recycled and remolded. In the present invention, the recycled recyclable and remoldable transparent intelligent wave-absorbing material is placed into the solvent. Under heating conditions, the polymer and the ionic liquid are redissolved in the solvent, and the solvent can be evaporated for secondary forming. In this process, the mass percentage of the filler (ionic liquid and nano-vanadium dioxide) and the polymer can be readjusted during the dissolution stage ( Figure 7 ) or other components can be added ( Figure 5 ), so as to realize the composition optimization, recycling and remolding of the material and the redesign of its wave-absorbing intensity and effective frequency band range.

[0024] 3. The recyclable and reshaped microwave absorbing material in the present invention has good transparency. Ionic liquids, as liquid microwave absorbing agents, have excellent transparency compared to solid microwave absorbing agents. The microwave absorbing material prepared by combining ionic liquids with vanadium dioxide nanoparticles and polymers in the present invention has good transparency at room temperature ( Figure 8 , 10 ) and is almost colorless. Military glass microwave absorbing materials not only need to meet the requirements of "thin thickness, light weight, wide absorption frequency band, and high absorption intensity", but also need to have excellent optical transmittance so that they can exhibit transparent characteristics under visible light. The microwave absorbing material prepared in the present invention is expected to be applied to the preparation of fighter cockpit glass and warship portholes in the military field to achieve complete stealth of military equipment when facing radar. At the same time, with the development of modern civil information and communication technology, it can also be applied to scenarios with high requirements for the optical and electromagnetic properties of microwave absorbing materials, such as transparent electromagnetic shielding rooms.

[0025] 4. The recyclable and reshaped transparent microwave absorbing material in the present invention can absorb microwaves and change color intelligently. First, the material realizes the flexible transformation between wave transmission and absorption at different temperatures and different frequency bands. For example, it is a wave-transmitting material at room temperature of 25 °C and an absorbing material at 140 °C, with an absorption performance of up to -48 dB and an effective bandwidth covering the entire X band ( Figure 11 ); or at an ambient temperature of 120 °C, it is a wave-transmitting material at 8.2 - 8.6 GHz and 11.4 - 12.4 GHz, and an absorbing material at 8.6 - 11.4 GHz ( Figure 12 ). Second, the material also realizes the intelligent regulation of the absorption frequency band under temperature changes. For example, when the ambient temperature is 110 °C, the effective absorption frequency band of the material is 9.2 - 12.2 GHz, and when the ambient temperature is 120 °C, the effective absorption frequency band of the material is 8.6 - 11.4 GHz ( Figure 12 ). Introducing vanadium dioxide nanoparticles into ionic liquid / polymer can realize intelligent microwave absorption and color change while maintaining its transparency. Electrically, vanadium dioxide undergoes a transformation from semiconductor to metallic state during phase change, which is characterized by a huge change in conductivity. Using this feature, dynamic reversible transformation of absorption intensity, absorption frequency band, and absorption to shielding can be achieved (as shown in Figure 12 ), realizing intelligent microwave absorption; optically, this material has a high transmittance at low temperatures, allowing sunlight to enter, and a low transmittance at high temperatures, blocking sunlight from entering. Therefore, the material can change color intelligently under temperature changes ( Figure 8 and Figure 9 ). Using this feature, it is possible to automatically adjust the indoor temperature of automobiles, buildings, spacecraft, etc. while meeting the absorption performance, thereby achieving intelligent utilization of solar energy and saving the earth's energy.

[0026] 5. The recyclable and remoldable transparent intelligent microwave absorbing material in the present invention has excellent high-temperature resistance and repeatability. Ionic liquids are ionic compounds composed entirely of cations and anions, with good electrical conductivity and thermal stability, and the decomposition temperature can reach above 300 °C. It can be seen from the TG diagram that the recyclable and remoldable transparent intelligent microwave absorbing material has good thermal stability, and only loses 2% of its weight at 330 °C( Figure 15 ). After the recyclable and remoldable transparent intelligent microwave absorbing material is cycled 10 times, the microwave absorption performance at 140 °C can still reach -26 dB, and the reversibility and repeatability are remarkable( Figure 14 ).

[0027] 6. The recyclable and remoldable transparent intelligent microwave absorbing material in the present invention is environmentally friendly and has economic value. After use, it is recycled and reused. On the one hand, it can reduce the impact of excessive accumulation on the environment and life, and reduce the environmental burden; on the other hand, it can reduce resource waste and increase economic value. Description of the Drawings

[0028] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0029] Figure 1 It is the SEM diagram of vanadium dioxide nanowires in the present invention.

[0030] Figure 2 It is a picture of the recyclable and remoldable transparent intelligent microwave absorbing material prepared in Example 1 after being pressed by a heavy object.

[0031] Figure 3 It is the microwave absorption performance of the recyclable and remoldable transparent intelligent microwave absorbing material prepared for the first time in Example 1.

[0032] Figure 4 It is the microwave absorption performance of the recyclable and remoldable transparent intelligent microwave absorbing material prepared for the second time in Example 2.

[0033] Figure 5 It is the microwave absorption performance of the recyclable and remoldable transparent intelligent microwave absorbing material recycled and remolded in Example 3.

[0034] Figure 6 It is an optical photo of the recyclable and remoldable transparent intelligent microwave absorbing material recycled and remolded in Example 4.

[0035] Figure 7 It is the microwave absorption performance of the recyclable and remoldable transparent intelligent microwave absorbing material recycled and remolded in Example 4.

[0036] Figure 8 Optical photograph of the recyclable and reshaping transparent intelligent microwave absorbing material at room temperature in Example 5.

[0037] Figure 9 Optical photograph of the recyclable and reshaping transparent intelligent microwave absorbing material at 90 °C in Example 5.

[0038] Figure 10 Optical photograph of the transparency of the recyclable and reshaping transparent intelligent microwave absorbing material in Example 6.

[0039] Figure 11 Microwave absorption performance of the recyclable and reshaping transparent intelligent microwave absorbing material in Example 7.

[0040] Figure 12 Microwave absorption performance of the recyclable and reshaping transparent intelligent microwave absorbing material in Example 8.

[0041] Figure 13 Initial microwave absorption performance of the recyclable and reshaping transparent intelligent microwave absorbing material in Example 9.

[0042] Figure 14 Microwave absorption performance of the recyclable and reshaping transparent intelligent microwave absorbing material after 10 cycles in Example 9.

[0043] Figure 15 TG diagram of the recyclable and reshaping transparent intelligent microwave absorbing material in Example 9. Detailed implementation manners

[0044] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0045] The polymers used in the present invention refer to transparent and thermoplastic polymers, including but not limited to any one of polyvinylidene fluoride, polymethyl methacrylate, polystyrene, polyvinylidene fluoride - hexafluoropropylene, and polyimide.

[0046] The phase transition temperature of the vanadium dioxide nanoparticles used in the present invention is 68 °C, and the particle size range is 30 nm to 100 nm. Its SEM diagram is as Figure 1 shown.

[0047] The ionic liquids, vanadium dioxide nanoparticles, and polymers used in the present invention are all commercially available.

[0048] Example 1

[0049] In this example, 1-ethyl-3-methylimidazolium tetrafluoroborate is used to prepare a recyclable and reshaped transparent intelligent microwave absorbing material (where the mass percentage content of 1-ethyl-3-methylimidazolium tetrafluoroborate is 40%), and the steps are as follows:

[0050] (1) Place 20 g of PVDF powder in 140 mL of NMP solution, heat and stir to dissolve it completely, then add 13.3 g of 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid and 1 g of vanadium dioxide nanoparticles and mix evenly to obtain a premixed solution;

[0051] (2) Pour the premixed solution into a mold, and heat it at 80 °C for 48 h to completely evaporate the solvent NMP, forming an ionic liquid / vanadium dioxide / PVDF film;

[0052] (3) Place the ionic liquid / vanadium dioxide / PVDF film in a mold, and hot press it at 200 °C for 30 min to obtain an ionic liquid / vanadium dioxide / PVDF composite material, which is the recyclable and reshaped transparent intelligent microwave absorbing material.

[0053] Figure 2 This is a picture of the recyclable and reshaped transparent intelligent microwave absorbing material prepared in this example being pressed by a 2 Kg heavy object. It can be seen that when the recyclable and reshaped transparent intelligent microwave absorbing material is pressed by the heavy object, the ionic liquid in it does not leak, indicating that the polymer matrix of the present invention can effectively encapsulate the ionic liquid.

[0054] The microwave absorption performance of the recyclable and reshaped transparent intelligent microwave absorbing material is tested using a vector network analyzer, and the results are as Figure 3 shown. When the environmental temperature is 140 °C, the microwave absorption performance can reach -48 dB (able to absorb 99.99% of the electromagnetic wave energy), and the effective bandwidth can cover the entire X-band (the frequency band range with a reflection loss less than -10 dB).

[0055] Example 2

[0056] In this example, by utilizing the dissolvable characteristics of the polymer in the solvent, the recyclable and reshaped transparent intelligent microwave absorbing material of Example 1 is recycled and a recyclable and reshaped transparent intelligent microwave absorbing material is prepared again, and the steps are as follows:

[0057] (1) Place the recyclable and reshaped transparent intelligent microwave absorbing material of Example 1 back into the solvent NMP. Under heating conditions, the polymer PVDF, vanadium dioxide nanoparticles, and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are redissolved in the solvent NMP to obtain a premixed solution;

[0058] (2) Pour the premixed solution into a mold, and heat it at 120 °C for 2 h to completely evaporate the solvent NMP, forming an ionic liquid / vanadium dioxide / PVDF film;

[0059] (3) Place the ionic liquid / vanadium dioxide / PVDF film in a mold and hot press it at 210 °C for 30 min to obtain a recyclable and reshaped transparent intelligent microwave absorbing material.

[0060] Use a vector network analyzer to test the microwave absorption performance of the second-prepared recyclable and reshaped transparent intelligent microwave absorbing material. The results are as Figure 4 shown. When the ambient temperature is 160 °C, the microwave absorption performance can reach -43 dB, and the effective bandwidth can cover the entire X-band. Moreover, the microwave absorption performance is almost exactly the same as that tested during the first preparation (Example 1), indicating that the recyclable and reshaped transparent intelligent microwave absorbing material has excellent recycling and reusability.

[0061] Example 3

[0062] In this example, by utilizing the solubility characteristics of the polymer in the solvent, the recyclable and reshaped transparent intelligent microwave absorbing material of Example 1 was recycled and a new recyclable and reshaped transparent intelligent microwave absorbing material was prepared. The steps are as follows:

[0063] (1) Place the recyclable and reshaped transparent intelligent microwave absorbing material of Example 1 back into the solvent dichloromethane. Under heating conditions, the polymer PVDF, nano-vanadium dioxide, and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are redissolved in the solvent dichloromethane to obtain a premixed solution. Add 6.7 g of lithium salt (LiCl) to the premixed solution and mix evenly;

[0064] (2) Pour the lithium salt-added premixed solution into a mold and heat it at 35 °C for 24 h to completely evaporate the solvent dichloromethane, forming a lithium salt-added ionic liquid / vanadium dioxide / PVDF film;

[0065] (3) Place the lithium salt-added ionic liquid / vanadium dioxide / PVDF film in a mold and hot press it at 180 °C for 40 min to obtain a recycled and reshaped recyclable and reshaped transparent intelligent microwave absorbing material.

[0066] After recycling the recyclable and reshaped transparent intelligent microwave absorbing material of Example 1 in this example, a lithium salt (LiCl) was added for secondary forming to prepare a recyclable and reshaped transparent intelligent microwave absorbing material. Use a vector network analyzer to test the microwave absorption performance of the reshaped recyclable and reshaped transparent intelligent microwave absorbing material. The results are as Figure 5 shown. Adding lithium salt can increase the ion concentration, introduce the multiple polarization mechanism of ions and more ionic conductivity to effectively regulate the microwave absorption frequency band. When the ambient temperature is as high as 200 °C, the microwave absorption performance can still reach -27 dB (able to absorb 99% of electromagnetic wave energy), realizing the controllable performance of the microwave absorbing composite material.

[0067] Example 4

[0068] In this embodiment, the soluble property of the polymer in the solvent is utilized, and at the same time, the mass percentages of the fillers (ionic liquid and vanadium dioxide nanoparticles) and the polymer are readjusted. The multiple polarization losses of the ionic liquid and the conductive losses of the ions are used to regulate the wave absorption performance. The recyclable and reshaping transparent intelligent wave-absorbing material of Example 1 is recycled and remanufactured into a recyclable and reshaping transparent intelligent wave-absorbing material. The steps are as follows:

[0069] (1) The recyclable and reshaping transparent intelligent wave-absorbing material of Example 1 is placed back into the solvent DMF. Under heating conditions, the polymer PVDF, vanadium dioxide nanoparticles, and 1-ethyl-3-methylimidazolium tetrafluoroborate ionic liquid are redissolved in the solvent DMF. Then, 6.7 g of tetraethylammonium trifluoroacetate ionic liquid is added thereto and mixed evenly to prepare a premixed solution with an ionic liquid mass percentage content of 50%.

[0070] (2) The premixed solution is poured into a mold and heated at 60 °C for 24 h to completely evaporate the solvent DMF, forming an ionic liquid / vanadium dioxide / PVDF film.

[0071] (3) The ionic liquid / vanadium dioxide / PVDF film is placed in a mold and hot-pressed at 250 °C for 10 min to obtain a recyclable and reshaping transparent intelligent wave-absorbing material.

[0072] In this embodiment, after recycling the recyclable and reshaping transparent intelligent wave-absorbing material of Example 1, the mass percentages of the fillers (ionic liquid and vanadium dioxide nanoparticles) and the polymer are readjusted. The optical photograph of the recyclable and reshaping transparent intelligent wave-absorbing material prepared by secondary molding is as Figure 6 shown. It can be seen from the figure that the material has extremely high transparency.

[0073] The wave absorption performance of the recycled and reshaped recyclable and reshaping transparent intelligent wave-absorbing material is tested using a vector network analyzer. The results are as Figure 7 shown. When the environmental temperature is 140 °C, the wave absorption performance of this wave-absorbing material can reach -47 dB, and the effective bandwidth can almost cover the entire X band. Compared with the directly reshaped recyclable and reshaping transparent intelligent wave-absorbing material (Example 2), the wave absorption intensity is significantly improved, realizing the recycling and reshaping of the composite material and the redesign of the wave absorption intensity.

[0074] Example 5

[0075] In this embodiment, 1-butyl-1-methylpyrrolidinium bromide is used to prepare a recyclable and reshaping transparent intelligent wave-absorbing material (where the mass percentage content of 1-butyl-1-methylpyrrolidinium bromide is 10%). The steps are as follows:

[0076] (1) Place 20 g of PI powder in 150 mL of acetone solution, heat and stir to dissolve it completely, then add 2.5 g of 1-butyl-1-methylpyrrolidinium bromide ionic liquid and 1 g of vanadium dioxide nanometer and mix evenly to obtain a premixed solution;

[0077] (2) Pour the premixed solution into a mold, heat at 100 °C for 48 h to completely evaporate the acetone solution, and form an ionic liquid / vanadium dioxide / PI film;

[0078] (3) Place the ionic liquid / vanadium dioxide / PI film in a mold, hot press at 300 °C for 50 min to obtain a recyclable and reshaped transparent intelligent microwave absorbing material.

[0079] The optical photograph of the recyclable and reshaped transparent intelligent microwave absorbing material prepared in this example at room temperature is as Figure 8 shown. It can be seen from the figure that the recyclable and reshaped transparent intelligent microwave absorbing material has obvious transparency at room temperature. Therefore, it is expected to be used in fighter cockpit glass, warship portholes, etc. to achieve complete stealth of military equipment against radar, and can also be used in scenarios with high requirements for the optical and electromagnetic properties of microwave absorbing materials such as transparent electromagnetic shielding rooms.

[0080] The optical photograph of the recyclable and reshaped transparent intelligent microwave absorbing material placed on a heating table when the temperature rises to 90 °C is as Figure 9 shown. It can be seen that the color of the material deepens at 90 °C, realizing intelligent color change under temperature change. Utilizing this feature, while meeting the microwave absorbing performance, it can automatically adjust the indoor temperature of automobiles, buildings, spacecraft, etc., so as to achieve intelligent utilization of solar energy and save the earth's energy.

[0081] Example 6

[0082] Prepare a recyclable and reshaped transparent intelligent microwave absorbing material (where the mass percentage content of vanadium dioxide nanometer is 2%) in this example. The steps are as follows:

[0083] (1) Place 20 g of PMMA powder in 200 mL of dichloromethane solution, heat and stir to dissolve it completely, then add 0.5 g of vanadium dioxide nanometer and 0.2 g of 1-butylpyridine acetate ionic liquid and mix evenly to obtain a premixed solution;

[0084] (2) Pour the premixed solution into a mold, heat at 30 °C for 25 h to completely evaporate the dichloromethane solution, and form an ionic liquid / vanadium dioxide / PMMA film;

[0085] (3) Place the ionic liquid / vanadium dioxide / PMMA film in a mold, hot press at 160 °C for 30 min to obtain a recyclable and reshaped transparent intelligent microwave absorbing material.

[0086] The optical photograph of the recyclable and remoldable transparent intelligent microwave absorbing material prepared in this example is as follows Figure 10 shown. It can be seen from the figure that the recyclable and remoldable transparent intelligent microwave absorbing material also has good transparency.

[0087] Example 7

[0088] In this example, tributylethylphosphonium tetrafluoroborate is used to prepare a recyclable and remoldable transparent intelligent microwave absorbing material (where the mass percentage content of tributylethylphosphonium tetrafluoroborate is 50%), and the steps are as follows:

[0089] (1) Place 40 g of PS powder in a mixed solution of 600 mL of DMF and acetone, heat and stir to fully dissolve it, then add 40 g of tributylethylphosphonium tetrafluoroborate ionic liquid and 1.5 g of vanadium dioxide nanoparticles and mix evenly to obtain a premixed solution;

[0090] (2) Pour the premixed solution into a mold, and heat it at 100 °C for 30 h to completely evaporate the solvents DMF and acetone, forming an ionic liquid / vanadium dioxide / PS film;

[0091] (3) Place the ionic liquid / vanadium dioxide / PS film in a mold and hot press it at 220 °C for 30 min to obtain a recyclable and remoldable transparent intelligent microwave absorbing material.

[0092] Use a vector network analyzer to test the microwave absorption performance of the recyclable and remoldable transparent intelligent microwave absorbing material. The results are as follows Figure 11 shown. At room temperature (25 °C), the recyclable and remoldable transparent intelligent microwave absorbing material is a wave-transparent material; when the environmental temperature is 140 °C, the recyclable and remoldable transparent intelligent microwave absorbing material is a microwave absorbing material, and its microwave absorption performance can reach -48 dB, and the effective bandwidth can cover the entire X band, realizing the switchable microwave absorption / wave transmission and the intelligent regulation of microwave absorption intensity.

[0093] Example 8

[0094] In this example, a recyclable and remoldable transparent intelligent microwave absorbing material is prepared (where the mass percentage content of vanadium dioxide nanoparticles is 20%), and the steps are as follows:

[0095] (1) Place 20 g of PMMA powder in 100 mL of acetone solution, heat and stir to fully dissolve it, then add 5 g of vanadium dioxide nanoparticles and 1 g of 1-octyl-3-methylimidazolium nitrate ionic liquid and mix evenly to obtain a premixed solution;

[0096] (2) Pour the premixed solution into a mold, and heat it at 120 °C for 12 h to completely evaporate the acetone solution, forming a vanadium dioxide / ionic liquid / PMMA film;

[0097] (3) Place the vanadium dioxide / ionic liquid / PMMA film in a mold and hot press it at 180 °C for 20 min to obtain a recyclable and reshaped transparent intelligent microwave absorption material.

[0098] Use a vector network analyzer to test the microwave absorption performance of the sample, and the results are as Figure 12 shown. When the environmental temperature is 110 °C, the effective microwave absorption frequency band is 9.2 - 12.2 GHz. When the environmental temperature is 120 °C, the effective microwave absorption frequency band is 8.6 - 11.4 GHz, realizing effective regulation of the microwave absorption frequency band. In addition, when the environmental temperature is 120 °C, it is a wave-transparent material at 8.2 - 8.6 GHz and 11.4 - 12.4 GHz, and a microwave absorption material at 8.6 - 11.4 GHz, realizing the integration of microwave absorption and wave transmission of the composite material.

[0099] Example 9

[0100] In this example, 1-hexyl-3-methylimidazolium hydrogensulfate is used to prepare a recyclable and reshaped transparent intelligent microwave absorption material (where the mass percentage content of 1-hexyl-3-methylimidazolium hydrogensulfate is 50%), and the steps are as follows:

[0101] (1) Place 40 g of PVDF-HFP powder in 80 mL of DMF solution, heat and stir to dissolve it completely, then add 40 g of 1-hexyl-3-methylimidazolium hydrogensulfate ionic liquid and 2 g of nanometer vanadium dioxide and mix evenly to obtain a premixed solution;

[0102] (2) Pour the premixed solution into a mold and heat it at 120 °C for 20 h to completely evaporate the solvent DMF, forming an ionic liquid / vanadium dioxide / PVDF-HFP film;

[0103] (3) Place the ionic liquid / vanadium dioxide / PVDF-HFP film in a mold and hot press it at 210 °C for 30 min to obtain a recyclable and reshaped transparent intelligent microwave absorption material.

[0104] Use a vector network analyzer to test the microwave absorption performance of the recyclable and reshaped transparent intelligent microwave absorption material, and the results are as Figure 13 shown. When the environmental temperature is 140 °C, its microwave absorption performance can reach -30 dB.

[0105] Conduct a cyclic test on the recyclable and reshaped transparent intelligent microwave absorption material. When cycling 10 times, the microwave absorption performance is as Figure 14 shown. When the environmental temperature is 140 °C, the microwave absorption performance can still reach -26 dB, indicating that the recyclable and reshaped transparent intelligent microwave absorption material has excellent reversibility and repeatability.

[0106] Conduct a temperature resistance test on the recyclable and reshaped transparent intelligent microwave absorption material, and the test results are as Figure 15As shown, the material only loses 2% of its weight at 330 °C, indicating that the recyclable, reshapable, transparent and intelligent microwave absorption material has good high-temperature stability.

[0107] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A preparation method of a recyclable and remoldable transparent intelligent microwave absorbing material, characterized in that: A recyclable and remoldable transparent intelligent wave-absorbing material is prepared by using an ionic liquid and vanadium dioxide nanoparticles as fillers and a polymer as a matrix through dissolution, drying, and hot pressing. The mass percentage content of the ionic liquid is 10 - 50%, the mass percentage content of the vanadium dioxide nanoparticles is 2 - 20%, and the balance is the polymer; The ionic liquid is any one of 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-butyl-1-methylpyrrolidinium bromide, 1-butylpyridinium acetate, tributylethylphosphonium tetrafluoroborate, 1-octyl-3-methylimidazolium nitrate, and 1-hexyl-3-methylimidazolium hydrogen sulfate; The phase transition temperature of the vanadium dioxide nanoparticles is 68 °C, and the particle size range is 30 - 100 nm; The polymer is any one of polyvinylidene fluoride, polymethyl methacrylate, polystyrene, polyvinylidene fluoride - hexafluoropropylene, and polyimide.

2. The preparation method of the recyclable and remoldable transparent intelligent microwave absorbing material according to claim 1, characterized in that, It includes the following steps: (1) Raw material premixing: Weigh the ionic liquid, vanadium dioxide nanoparticles, and polymer according to the ratio. Dissolve the polymer in a solvent to obtain a polymer solution, and then add the ionic liquid and vanadium dioxide nanoparticles to the polymer solution and mix evenly to obtain a premixed solution; (2) Film-forming treatment: Pour the premixed solution from step (1) into a mold, and then heat to evaporate the solvent to form an ionic liquid / vanadium dioxide / polymer film; (3) Hot pressing and molding: Place the ionic liquid / vanadium dioxide / polymer film from step (2) in a mold and hot press it to obtain a recyclable and remoldable transparent intelligent wave-absorbing material.

3. The preparation method of the recyclable and remoldable transparent intelligent microwave absorbing material according to claim 2, characterized in that: In step (1), the mass-volume ratio of the polymer to the solvent is 1 g:(2 - 15) mL; the solvent is an aprotic polar solvent, and the aprotic polar solvent is any one or several of N-methylpyrrolidone, N,N-dimethylformamide, acetone, and dichloromethane.

4. The preparation method of the recyclable and remoldable transparent intelligent microwave absorbing material according to claim 3, characterized in that: In step (2), the heating temperature is 30 - 120 °C and the time is 2 - 48 h; in step (3), the hot pressing temperature is 160 - 300 °C and the time is 10 - 50 min.

5. A preparation method of a recyclable and remoldable transparent intelligent microwave absorbing material, characterized in that, It includes the following steps: (1) Place 20 g of PMMA powder in 200 mL of dichloromethane solution, heat and stir to dissolve it completely, then add 0.5 g of vanadium dioxide nanoparticles and 0.2 g of 1-butylpyridinium acetate ionic liquid and mix evenly to obtain a premixed solution; (2) Pour the premixed solution into a mold, and heat at 30 °C for 25 h to completely evaporate the dichloromethane solution to form an ionic liquid / vanadium dioxide / PMMA film; (3) Place the ionic liquid / vanadium dioxide / PMMA film in a mold, hot press at 160 °C for 30 min to obtain a recyclable and remoldable transparent intelligent wave-absorbing material.

6. A preparation method of a recyclable and remoldable transparent intelligent microwave absorbing material, characterized in that, It includes the following steps: (1) Place 40 g of PS powder in a mixed solution of 600 mL of DMF and acetone, heat and stir to dissolve it completely, then add 40 g of tributylethylphosphonium tetrafluoroborate ionic liquid and 1.5 g of vanadium dioxide nanoparticles and mix evenly to obtain a premixed solution; (2) Pour the premixed solution into a mold, and heat at 100 °C for 30 h to completely evaporate the solvents DMF and acetone to form an ionic liquid / vanadium dioxide / PS film; (3) Place the ionic liquid / vanadium dioxide / PS film in a mold and hot press it at 220 °C for 30 min to obtain a recyclable and reshaped transparent intelligent microwave absorption material.

7. A preparation method of a recyclable and remoldable transparent intelligent microwave absorbing material, characterized in that, The steps include: (1) Place 20 g of PMMA powder in 100 mL of acetone solution, heat and stir to fully dissolve it, then add 5 g of vanadium dioxide nanoparticles and 1 g of 1-octyl-3-methylimidazolium nitrate ionic liquid and mix evenly to obtain a premixed solution; (2) Pour the premixed solution into a mold and heat it at 120 °C for 12 h to completely evaporate the acetone solution, forming a vanadium dioxide / ionic liquid / PMMA film; (3) Place the vanadium dioxide / ionic liquid / PMMA film in a mold and hot press it at 180 °C for 20 min to obtain a recyclable and reshaped transparent intelligent microwave absorption material.

8. A recyclable and remoldable transparent intelligent microwave absorbing material prepared by the method according to any one of claims 1-7.

9. Application of the recyclable and remoldable transparent intelligent microwave absorbing material according to claim 8 in the fields of military and civilian transparent electromagnetic protection.

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