Broadband electromagnetic wave absorbing material with transparent-flexible-self-repairing synergistic characteristic, preparation method and application

Abstract

The invention belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a broadband electromagnetic wave absorbing material with a transparent-flexible-self-repairing synergistic characteristic, a preparation method and application. The method comprises the following steps: respectively drying and dewatering PCL, IPDH, IPDI, DBTDL and DMF (Dimethyl Formamide); then PCL is stirred and heated, dibutyltin dilaurate and IPDI are added, and a polyurethane prepolymer is obtained; s2, adding DMF and IPDH into the polyurethane prepolymer obtained in the step S1, continuously stirring to obtain a mixed solution A, transferring the mixed solution A into a mold, and drying to obtain a transparent polyurethane elastomer; s3, 1-butyl-3-methylimidazole bis (trifluoromethanesulfonyl) imide salt is added into the polyurethane prepolymer, DNF and IPDH are added and stirred, a mixed solution B is obtained, the mixed solution B is transferred into a mold, and the broadband electromagnetic wave absorbing material with the transparent-flexible-self-repairing synergistic characteristic is obtained.

Description

Technical Field

[0001] The present invention belongs to the technical field of electromagnetic wave absorbing materials, and particularly relates to a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic characteristics, a preparation method and an application thereof. Background Art

[0002] With the rapid development of the information age, the development of electronic devices has become increasingly rapid. Emerging electronic devices such as flexible transparent touch screens, displays, soft robots, electronic skins, and human-machine interfaces have been widely used in various fields. Although these advancements have brought new conveniences to all aspects of life, they have also brought potential electromagnetic pollution, posing new challenges to current electromagnetic protection materials. It is not only required to achieve the electromagnetic wave protection ability of transparent electronic devices and visual observation fields, but also to contribute to the assembly and integration of other transparent flexible electronic components. Therefore, there is an urgent need to develop new transparent flexible, high mechanical strength, and strong service performance electromagnetic wave absorbing materials. However, despite the great progress that has been made, designing absorbers that meet transparency, stretchability, service performance, and electromagnetic wave absorption still faces huge challenges.

[0003] In addition to broadband electromagnetic wave absorption performance, transparent flexible electromagnetic wave absorbers should also meet high transmittance and mechanical strength in the visible light range. Moreover, due to the long service life of electromagnetic wave absorbers, good service and self-healing performance are also crucial. However, traditional electromagnetic wave absorbing fillers such as metals and metal oxides, carbon materials, and conductive polymers are usually opaque. After being added to an elastomeric substrate, the uneven dispersion of the fillers often leads to light scattering and reduces optical transparency. In addition, due to the high extinction coefficient of the fillers, a high filler content will further reduce transparency. At the same time, introducing fillers will disrupt the original molecular chain structure of the elastomer, reducing elasticity and mechanical strength and damaging the durability of the material. Therefore, it is difficult to simultaneously possess transparency, stretchability, and repair ability using traditional electromagnetic wave fillers.

[0004] Ionic liquids (ILs) are a new type of multifunctional solvents and soft materials with unique physical and chemical properties, including a wide liquid range, inherent ionic conductivity, excellent electrochemical stability, and high transparency, and are widely used as electrolytes. At the same time, ILs have a higher dielectric loss ability in the microwave frequency band compared with ordinary polymer materials. Therefore, an ionogel made by fixing ILs in a cross-linked solid matrix can have skin-like soft, tough, and long-term reliable characteristics, with good transparency and mechanical properties. At the same time, using a reparable polyurethane as a cross-linked network is promising to achieve an electromagnetic wave absorber with transparent flexibility, self-healing, and strong electromagnetic absorption ability. Summary of the Invention

[0005] Aiming at the problems in the prior art that the existing electromagnetic wave absorbing materials have low transparency and cannot be applied to flexible transparent electronic devices and visual observation fields; and the problem of low IL loading when preparing conductive ionic gels in existing research; and the problem of difficulty in maintaining the mechanical properties of ionic gels at high IL loading in existing research; and the problem that the wave absorption performance of existing transparent electromagnetic wave absorbing materials decreases after various wear and damages in practical applications.

[0006] The present invention designs a transparent electromagnetic wave absorbing gel, which has high transparency, high elongation at break, strong self-healing ability, and can effectively absorb electromagnetic waves in the X-band. The transparent ionic gel is synthesized by hydrogen bond array cross-linked network polyurethane loaded with IL. The preparation process of this gel is simple, adopting a two-step in-situ polymerization method. IL is tightly combined with the polymer network through hydrogen bond interaction, and it has good stability. The effective absorption bandwidth of this ionic gel can cover the entire X-band, and the minimum reflection loss can reach -35.39 dB. At the same time, it shows visible light transmittance and ultra-high tensile properties (1306.11%). Due to the reversibility of the hydrogen bond array, the ionic gel also shows excellent repair ability and can be effectively repaired under heating conditions. Finally, the present invention realizes a multifunctional integrated wave absorbing material that combines transparency, high elongation at break, self-repair function and electromagnetic wave absorption.

[0007] The present invention provides a preparation method of a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic characteristics, including the following steps:

[0008] S1: Dry and remove water from PCL, IPDH, IPDI, DBTDL and DMF respectively; then stir and heat PCL, add dibutyltin dilaurate and IPDI to obtain a polyurethane prepolymer;

[0009] S2: Add the polyurethane prepolymer obtained in S1 to DMF and IPDH, continue to stir to obtain a mixed solution A, transfer the mixed solution A to a mold, and dry it to obtain a transparent polyurethane elastomer;

[0010] S3: Add 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt to the polyurethane prepolymer, then add DNF and IPDH and stir to obtain a mixed solution B, transfer the mixed solution B to a mold to obtain an electromagnetic wave absorbing material with transparent, flexible and self-healing characteristics at the same time.

[0011] Further, the time of the drying and water removal process in S1 is 24 h, and the temperature of the drying and water removal process is 100 °C. Among them, IPDI, DBTDL and DMF are dried by molecular sieve, and PCL and IPDH are dried in a vacuum drying oven. The gas atmosphere during the drying and water removal process is N 2 .

[0012] Further, the heating temperature in S1 is 80°C, and the stirring duration is 30 min to 3 h.

[0013] Further, the mass ratio of PCL, dibutyltin dilaurate, and IPDI described in S1 is 4.5:1.

[0014] Further, the stirring time in S2 is 24 h, the drying temperature is 50 - 80°C; the drying time is 12 h, and the mass ratio of the DMF solution and IPDH described in S2 is 130:1.

[0015] Further, the mass fraction of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide in S3 is 70% - 80%, the stirring duration is 6 h to 12 h, and the drying temperature is 50 - 80°C.

[0016] A broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic properties, the electromagnetic wave absorbing material is a polyurethane substrate, and the ionic liquid is cross-linked on the polyurethane molecular chain through a hydrogen bond array. The electromagnetic wave absorbing material is a high-content ionic liquid with a hydrogen bond array cross-linked and loaded on the polyurethane.

[0017] An application of a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic properties, the electromagnetic wave absorbing material is used in the preparation of flexible transparent touch screens, displays, soft robots, electronic skins, and human-machine interfaces.

[0018] Beneficial effects

[0019] Through the preparation method of a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic properties provided by the present invention, by synthesizing a transparent polyurethane containing a hydrogen bond array as the polymer skeleton of the ion gel, the preparation of the ion gel is realized through in-situ polymerization, and the preparation of a high-loading ion gel is realized. When the IL loading amount is 90%, the basic mechanical characteristics of the polyurethane can still be maintained, and an elongation at break of 1306.11% and a breaking strength of 0.635 MPa can be achieved.

[0020] Through the broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic properties provided by the present invention, the self-healing polyurethane synthesized provides the healing ability for the ion gel, solves the problem that the electromagnetic wave absorption performance of the transparent flexible electromagnetic wave absorbing material decreases after various wear and tear damages in practical applications. Different proportions of ion gels can achieve high transparency while achieving more than 95% repair of the electromagnetic wave absorption performance at 60°C for 12 h after being cut.

[0021] Through the preparation method of a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic characteristics provided by the present invention, the ionic gel developed in the present invention is distributed in the polyurethane molecular skeleton at ratios of 70%, 80%, and 90% with 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([BMIM][TFSI]) as the filler. Among them, PU-IL-90 can achieve effective absorption in the entire frequency band in the X band, and realizes a minimum reflection loss of -35.39 dB at 3.7 mm, achieving the multifunctional design of a transparent flexible self-healing electromagnetic wave absorbing elastomer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention, and thus should not be regarded as limiting the scope. For those of ordinary skill in the art, other related drawings can also be obtained based on these drawings without creative efforts. In the drawings:

[0023] Figure 1 It is the synthetic route diagram of the multiple hydrogen bond polyurethane of the present invention;

[0024] Figure 2 It is the optical photo, microscopic schematic diagram of the designed ionic gel of the present invention, and the detailed structural schematic diagram of the PU molecular chain;

[0025] Figures 3 to 11 It is the dielectric property diagram of the PU-IL-X transparent flexible wave-absorbing film of the present invention;

[0026] Figures 12 to 19 It is the electromagnetic wave absorption property diagram of the PU-IL-X transparent flexible wave-absorbing film of the present invention;

[0027] Figure 20 It is the mechanical property diagram of the PU of the present invention;

[0028] Figures 21 to 23 It is the mechanical property diagram of the ionic gel of the present invention;

[0029] Figure 24 It is the mechanical self-healing property diagram of the ionic gel of the present invention;

[0030] Figures 25 to 33 It is the wave absorption self-healing property diagram of the ionic gel of the present invention;

[0031] Figure 34 It is the reflection loss self-healing property diagram of the ionic gel of the present invention;

[0032] Figure 35 It is the diagram of the change in the binding energy between PU molecular chains after inserting IL of the present invention. Detailed implementation mode

[0033] The following will combine Examples 1-3 of the present invention and the attached Figures 1 to 35 , and clearly and completely describe the technical solutions 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 work belong to the scope of protection of the present invention.

[0034] The present invention provides a preparation method of a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic characteristics, including the following steps:

[0035] S1: PCL and IPDH are dried in a vacuum drying oven at 100 °C for more than 24 h to remove water. IPDI, DBTDL, and DMF are dehydrated with molecular sieve for 24 h, and N is continuously introduced during the dehydration process 2 to exclude the moisture in the system; Weigh 12 g of PCL and add it to a clean three-necked flask, continuously stir and heat to 80 °C, and continuously stir in an N 2 atmosphere for 30 min. After the PCL is completely melted, 60 mg of dibutyltin dilaurate (DBTDL) and 2.7 g of IPDI are added to the reaction system, and then continuously stirred at 80 °C for 3 h to obtain a transparent viscous prepolymer;

[0036] S2: After cooling the reaction system of S1 to room temperature, add 100 ml of DMF solution, then add 1.19 g of IPDH, stir at room temperature for more than 24 h to obtain a transparent viscous solution, transfer the solution to a silica gel mold, dry it in a forced-air drying oven at 50 °C for 12 h, and then dry it in a vacuum oven at 80 °C for 12 h to obtain a transparent polyurethane elastomer;

[0037] S3: Add 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt with a mass fraction of X% to the corresponding volume of the polyurethane prepolymer system, add 100 ml of DMF solution and stir at room temperature for 6 h, then add 1.19 g of IPDH into the system, stir at room temperature for 12 h to obtain a uniform transparent solution, then transfer the solution to a silica gel mold, dry it in a forced-air drying oven at 50 °C for 12 h, and then dry it in a vacuum oven at 80 °C for 12 h to obtain an electromagnetic absorption material with transparent flexible self-healing characteristics.

[0038] It is named PU-IL-X (X = 70-90, X represents the mass fraction of IL relative to the ion gel).

[0039] Example 1

[0040] S1: Dehydrate PCL and IPDH in a vacuum drying oven at 100 °C for more than 24 h. Dehydrate IPDI, DBTDL, and DMF using molecular sieve for 24 h, and continuously introduce N 2 to exclude moisture from the system; Weigh 12 g of PCL and add it to a clean three-necked flask. Continuously stir and heat to 80 °C, and continuously stir in an N 2 atmosphere for 30 min. After PCL completely melts, add 60 mg of dibutyltin dilaurate (DBTDL) and 2.7 g of IPDI to the reaction system, and then continuously stir at 80 °C for 3 h to obtain a transparent viscous prepolymer;

[0041] S2: After cooling the reaction system in S1 to room temperature, add 100 ml of DMF solution, then add 1.19 g of IPDH, and stir at room temperature for more than 24 h to obtain a transparent viscous solution. Transfer the solution to a silica gel mold, dry it in a forced-air drying oven at 50 °C for 12 h, and then dry it in a vacuum oven at 80 °C for 12 h to obtain a transparent polyurethane elastomer;

[0042] S3: Add 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide salt with a mass fraction of 70% to the corresponding volume of the polyurethane prepolymer system. Add 100 ml of DMF solution at room temperature and stir for 6 h, then add 1.19 g of IPDH into the system and stir at room temperature for 12 h to obtain a uniform transparent solution. Then transfer the solution to a silica gel mold, dry it in a forced-air drying oven at 50 °C for 12 h, and then dry it in a vacuum oven at 80 °C for 12 h to obtain an electromagnetic absorption material with transparent, flexible, and self-healing properties.

[0043] Name it PU-IL-70.

[0044] Example 2

[0045] S1: Dehydrate PCL and IPDH in a vacuum drying oven at 100 °C for more than 24 h. Dehydrate IPDI, DBTDL, and DMF using molecular sieve for 24 h, and continuously introduce N 2 to exclude moisture from the system; Weigh 12 g of PCL and add it to a clean three-necked flask. Continuously stir and heat to 80 °C, and continuously stir in an N 2 atmosphere for 30 min. After PCL completely melts, add 60 mg of dibutyltin dilaurate (DBTDL) and 2.7 g of IPDI to the reaction system, and then continuously stir at 80 °C for 3 h to obtain a transparent viscous prepolymer;

[0046] S2: After the reaction system of S1 was cooled to room temperature, 100 ml of DMF solution was added, and then 1.19 g of IPDH was added, and stirred at room temperature for more than 24 hours to obtain a transparent viscous solution. The solution was transferred to a silica gel mold, dried in a blast drying oven at 50°C for 12 hours, and then dried in a vacuum oven at 80°C for 12 hours to obtain a transparent polyurethane elastomer;

[0047] S3: Add 80% mass fraction of 1-butyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt to the corresponding volume of polyurethane prepolymer system, add 100 ml of DMF solution and stir for 6 hours at room temperature, then add 1.19 g of IPDH into the system, stir at room temperature for 12 hours to obtain a uniform transparent solution, then transfer the solution to a silica gel mold, dry it at 50°C in a forced air drying oven for 12 hours, and then dry it at 80°C in a vacuum oven for 12 hours to obtain an electromagnetic absorption material with transparent, flexible and self-healing properties.

[0048] It was named PU-IL-80.

[0049] Example 3

[0050] S1: Dry PCL and IPDH in a vacuum oven at 100°C for more than 24 hours to remove water, and use IPDI, DBTDL and DMF The molecular sieve was used to remove water for 24 h, and N was continuously introduced during the removal process. 2 Remove moisture from the system; weigh 12 g of PCL and add it to a clean three-necked flask, continue stirring and heat to 80 °C under N 2 The mixture was stirred for 30 min in the atmosphere. After PCL was completely melted, 60 mg of dibutyltin dilaurate (DBTDL) and 2.7 g of IPDI were added to the reaction system. The mixture was then stirred for 3 h at 80 °C to obtain a transparent and viscous prepolymer.

[0051] S2: After the reaction system of S1 was cooled to room temperature, 100 ml of DMF solution was added, and then 1.19 g of IPDH was added, and stirred at room temperature for more than 24 hours to obtain a transparent viscous solution. The solution was transferred to a silica gel mold, dried in a blast drying oven at 50°C for 12 hours, and then dried in a vacuum oven at 80°C for 12 hours to obtain a transparent polyurethane elastomer;

[0052] S3: Add 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide with a mass fraction of 90% into the corresponding volume of the polyurethane prepolymer system. Add 100 ml of DMF solution at room temperature and stir for 6 h. Then add 1.19 g of IPDH into the system and stir at room temperature for 12 h to obtain a uniform transparent solution. Subsequently, transfer the solution to a silica gel mold and dry it in a forced-air drying oven at 50 °C for 12 h, and then dry it in a vacuum oven at 80 °C for 12 h to obtain an electromagnetic absorption material with both transparent flexible self-healing properties.

[0053] Name it PU-IL-90.

[0054] Perform performance tests on the above-mentioned polyurethane-based transparent flexible self-healing electromagnetic wave absorption material. Using the waveguide method, perform tests using a vector network analyzer to test the dielectric constant and reflection loss performance of the ion gel, and prepare the elastomer into a rectangular test piece for testing. Use a small material testing machine to perform the mechanical property test of the elastomer, and cut the sample into dumbbell-shaped specimens using a cutter. Use a UV-visible spectrophotometer to test the light transmittance of the sample.

[0055] Combined with Figure 1 , the synthesis route of polyurethane can be obtained. First, hydroxyl-terminated PCL (HO-PCL-OH) reacts with IPDI to synthesize isocyanate group-terminated PCL (NCO-PCL-OCN) as a prepolymer. Subsequently, add IPDH into the system, and react the isocyanate group and hydrazide group to form an acyl semicarbazide group. The feed molar ratio of PCL, IPDI, and IPDH is 1:2:1. Among them, PCL serves as the soft segment to provide resilience and flexibility to the system, and IPDI and IPDH serve as the hard segments to make the elastomer exhibit high tensile strength. During the entire reaction process, cross-linking does not occur through molecular bonds, but the urethane and acyl semicarbazide groups form a hydrogen bond array through stacking to provide similar cross-linking characteristics to the system, and macroscopically exhibit good transparency and self-healing properties.

[0056] Combined with Figure 2 , Figure 2 (a) is the optical photo and microscopic schematic diagram of the designed ion gel. It can be obtained that the ion gel with a thickness of 2 mm can achieve a transmittance of at least 92.8% in the visible light range. IL consists of [[BMIM]] + and [[TFSI]] - and is distributed in the free space between the hard segment and the soft segment and is loaded on the polyurethane through hydrogen bond interaction. Figure 2(b) is a detailed structural schematic diagram of the PU molecular chain, and potential hydrogen bond donors and acceptors on the PU molecular chain can also be obtained. After adding [BMIM][TFSI] to PU, in-situ polymerization is carried out, and the cross-linked elastomer successfully loads [BMIM][TFSI] to form a transparent, homogeneous and stable ion gel. [BMIM][TFSI] is distributed in the free space where the polyurethane hard segments and soft segments are separated from each other in the form of ion pairs and is loaded on the molecular chain through hydrogen bond interactions. As Figure 2 (a) The digital photos show that the ion gel is defect-free and highly transparent. The ultraviolet-visible light transmission spectrum indicates that the transmittance of the ion gel with a thickness of 0.2 mm can reach 96.74% at 550 nm. This high transparency indicates that PCL in the polyurethane mainly shows an amorphous state, and the introduction of asymmetric IPDI and multiple hydrogen bond arrays further inhibits the crystallization of PCL segments. At the same time, the high transparency can also indirectly show that IL is successfully and uniformly loaded into PU without changing the crystallization morphology and molecular structure of PU. Figure 2 (b) shows the potential hydrogen bond donors and acceptors on the PU molecular chain. A large number of hydrogen bond sites are connected on one side, providing conditions for the formation of hydrogen bond arrays and the binding of IL.

[0057] Combined with Figures 3 to 5 , they are the detailed dielectric constants of PU-IL-70, PU-IL-80, and PU-IL-90 respectively; Figures 6 to 8 is the two-dimensional reflection loss of the ion gel; Figures 9 to 11 is the cole-cole curve of the ion gel. The relative complex permittivity (ε r = ε′ - jε”) and relative complex permeability (μr = μ′ - jμ”) of the PU-IL flexible transparent self-healing electromagnetic wave absorbing elastomer in the frequency range of 8 - 12 GHz were measured using a vector network analyzer as Figures 3 to 11 shown. In addition, the imaginary part of the permittivity ε″ shows an upward trend in the frequency range of 8 - 12 GHz. With the increase of the IL content, the values of ε' and ε″ of PU-IL increase significantly, and PU-IL-90 shows the largest ε″ value. This is because with the increase of the IL content, the distance between PU molecular chains increases, and the conductive regions overlap with each other, resulting in the expansion of the conductive network and an increase in the electron transport path. On the one hand, this indicates that the composite of IL and PU effectively regulates the ε″ of the system, which has an impact on the impedance matching performance of the system; on the other hand, it also proves that the conductive loss ability of the composite system to electromagnetic waves has been significantly improved. tanδ ε value is an important parameter for evaluating the dielectric loss ability of microwave absorbing materials to incident electromagnetic waves. By calculating tanδ ε , the dielectric loss intensity of the material to incident electromagnetic waves was evaluated, and it can be seen that tanδ ε gradually increases with the increase of the IL content.Figures 6 to 8 The two-dimensional reflection loss of PU-IL was calculated. It can be seen that the effective absorption bandwidth (EAB) in the range of 8 - 12 GHz gradually broadens with the increase of IL content. The EAB of PU-IL-70 is only 1.48 GHz, while the EAB of PU-IL-80 increases to 3.62 GHz. PU-IL-90 realizes effective absorption in the entire X-band frequency range, and also reaches the strongest reflection loss of -35.39 dB when the reflection loss is 3.7 mm. Therefore, for the PU-IL elastomer, the absorption and attenuation of incident electromagnetic waves are mainly adjusted by changing the IL content to control the dielectric loss.

[0058] Combined with Figures 12 to 14 , they are the three-dimensional reflection losses of PU-IL-70, PU-IL-80, and PU-IL-90 respectively; Figures 15 to 17 , they are the variation of the reflection loss of the ion gel with thickness respectively; Figure 18 is the attenuation constant of the ion gel, Figure 19 is the variation of the dielectric constant of the ion gel.

[0059] Combined with Figure 20 , Figure 20 a is the stress-strain curve of uniaxial tension of PU, Figure 20 b is the maximum tensile strength and toughness of PU; Figure 20 c is the stress data in 500 cycles of 100% deformation tensile cycling; Figure 20 d is the stress-strain curve of 500% strain cyclic loading-unloading; the mechanical properties of the PU elastomer were measured by a tensile test, and the tensile speed was 50 mm / min at room temperature using a small universal testing machine -1 . The stress-strain curve of PU is as Figure 20 shown in a. The tensile strength is 63.2 MPa and the fracture strain is 787.4%, corresponding to an extremely high toughness of 157.39 MJ / m -3 . As Figure 20 shown in c, PU was subjected to 500 cycles of 100% deformation tensile cycling. It can be observed that although the tensile stress gradually decreases with the increase of the number of cycles, the degree of decrease is only 12.21%, indicating the good durability of PU as an elastomer. As Figure 20 shown in d, the cyclic loading-unloading curve of the PU elastomer at 500% strain was measured to study the elastic and rebound properties of the polyurethane. In the first loading-unloading cycle, a hysteresis energy of 31.7 MJ / m -3 appeared. When the second cycle was immediately carried out, a residual strain of 70.46% was observed, indicating the good elasticity of the PU elastomer. After waiting for 120 min at room temperature, the residual strain and the hysteresis area basically disappeared, and the elastomer completely recovered, indicating its good rebound performance. Figure 6The same tensile tests were carried out on the ionogel PU-IL. As the IL content increased, the tensile strength of the ionogel decreased significantly, from 5.51 MPa to 2.16 MPa and then to 0.635 MPa for PU-IL-90; the fracture strain increased gradually, from 1025% to 1306%. This indicates that as the IL content increases, the larger the number of ILs inserted between the PU molecular chains, the greater the distance between the PU molecular chains, the increase in polymer flexibility, showing lower tensile strength and higher fracture length. However, PU-IL can still maintain in the MPa level at high loadings, indicating that the introduction of IL plays a plasticizing role, being tightly loaded on the PU backbone through hydrogen bond interactions, effectively regulating the mechanical properties of the ionogel. At the same time, the mechanical properties of the synthesized PU-IL ionogel are at a high level among the currently known related gels.

[0060] Combined with Figures 21 to 23 , Figure 21 are the stress-strain curves of PU-IL-70, PU-IL-80, and PU-IL-90; Figure 22 are the maximum tensile strength and toughness of the ionogel; Figure 23 are the stress data of PU-IL-70 during 500 cycles of 100% deformation tensile cycling; The PU-IL-X was cut with a cutter in the middle and then closely butted together. After heat treatment at 60 °C for different times, the mechanical properties of the samples were tested on a universal testing machine, as Figures 21 to 23 shown

[0061] Combined with Figure 24 , Figure 24 a is the stress-strain curve of PU-IL-70 after cutting at 60 °C as a function of time; Figure 24 b is the stress-strain curve of PU-IL-80 after cutting at 60 °C as a function of time; Figure 24 c is the stress-strain curve of PU-IL-90 after cutting at 60 °C as a function of time; Figure 24 d is the self-healing efficiency of the ionogel.

[0062] The self-healing property of polymers is inversely proportional to their mechanical strength. When the mechanical strength of the sample is higher, the repair of the sample is more difficult. This is because the molecular chains are in a state of constant motion. When the binding energy between the molecular chains is stronger, the movement of the molecular chains is slower, and the mutual diffusion between the molecular chains and the reconstruction of the hydrogen bond cross-linking network are more difficult. When the molecular chains are damaged, the energy required to return to the original state is higher, so the self-healing efficiency is low. By calculating the self-healing efficiency of the PU-IL-X samples through the above formula, we get Figure 24d. Therefore, when the content of IL increases, the self-healing efficiency of the sample gradually increases with time. When calculating the self-healing efficiency at 60 °C through the above formula, all samples can reach more than 95%. Compared with the self-healing efficiency of only 25% of PU, it shows that the healing ability is significantly increased, verifying the plasticizing effect of IL and also indicating the good self-healing ability of PU-IL. This good self-healing performance benefits from the reversibility of the hydrogen bond array crosslinking. When the material is damaged, the local hydrogen bonds break reversibly, absorb energy and prevent crack propagation. After the external force is removed, the broken hydrogen bonds spontaneously reform under the drive of thermal motion, restoring the structural integrity of the material. This dynamic property enables the self-healing process to be completed at room temperature with relatively low external energy.

[0063] Combined with Figures 25 to 33 , Figures 25 to 27 Figure 7 shows the real part, imaginary part of the dielectric and the tangent of the loss angle of PU-IL-70 after cutting as a function of time at 60 °C; Figures 28 to 30 Figure 8 shows the real part, imaginary part of the dielectric and the tangent of the loss angle of PU-IL-80 after cutting as a function of time at 60 °C; Figures 31 to 33 Figure 9 shows the real part, imaginary part of the dielectric and the tangent of the loss angle of PU-IL-90 after cutting as a function of time at 60 °C.

[0064] During the entire self-healing process, ε' shows a downward trend with the increase of the self-healing time, being lower than that of the sample before self-healing.

[0065] Combined with Figure 34 , Figure 34 a, Figure 34 b, Figure 34 c shows the reflection loss of PU-IL-70, PU-IL-80 and PU-IL-90 after cutting as a function of time at 60 °C.

[0066] The binding energy between hydrogen-bonded aggregates is calculated as the energy difference between hydrogen-bonded ASC and urethane groups and the individual monomers:

[0067] ΔE H = E AB - E A - E B

[0068] The conformational optimization and binding energy calculation of hydrogen-bonded aggregates were carried out without considering the solvation effect. All conformational optimizations and energy calculations were completed using the Dmol3 module in Materials Studio software. The study adopted the density functional theory (DFT) method, used the gradient correction (GGA) PW91 correlation function proposed by Perdew-Wang, and selected the double numerical plus polarization (DNP) basis set. The convergence threshold parameters in the optimization process were set as: energy 2.7×10 -4eV, gradient Displacement Through DFT calculations, we successfully obtained the binding energy of the hydrogen-bonded aggregates. The specific results are as Figure 10 shown. When one molecule of IL was inserted, the original hydrogen bonds between PU molecular chains were broken, and new hydrogen-bonding interactions were formed between IL and PU. During this process, the binding energy of the system decreased, from -0.05274 Ha to -0.04981 Ha, a decrease of 5.56%. The change in the tensile strength of the ion gel formed by introducing IL into PU can be verified by DFT simulation.

[0069] Through a broadband electromagnetic wave absorbing material, preparation method and application with transparent-flexible-self-healing synergistic characteristics provided by the present invention, the specific innovation points and innovativeness are reflected in the following aspects:

[0070] First, a transparent ion gel design with a large-capacity ionic liquid loading is realized by forming a new multiple hydrogen-bond cross-linked network array between polyurethane and ionic liquid. When the IL loading is 90%, the basic mechanical characteristics of polyurethane can still be maintained, and an elongation at break of 1306.11% and a breaking strength of 0.635 MPa can be achieved, reflecting the innovation in the design of the present invention: an ion gel is prepared by cross-linking ionic liquid and polyurethane molecular chains through a hydrogen-bond array

[0071] Second, compared with traditional electromagnetic wave absorbing materials, using an ion gel as an absorbing material can achieve a light transmittance of 95.7% at 550 nm, and full-band effective absorption in the X-band and a minimum reflection loss of -35.39 dB;

[0072] Third, the self-healing polyurethane synthesized by this method provides the ion gel with healing ability, which can solve the problem that the electromagnetic wave absorption performance of the transparent flexible electromagnetic wave absorbing material decreases after various wear and tear damages in practical applications. Ion gels with different ratios can achieve high transparency while achieving more than 95% repair of both mechanical properties and electromagnetic wave absorption performance at 60 °C for 12 h after being cut, reflecting the innovation in performance of the present invention. No material in the prior art can achieve an integrated design of transparency, self-healing and electromagnetic wave absorption.

[0073] Finally, regarding the design of the ionic gel in this patent: The polymer substrate in this article uses a polyurethane substrate, and the polyurethane chain has abundant hydrogen bond binding sites. The gel is prepared by an in-situ polymerization method. An ionic liquid is added during the cross-linking of polyurethane. The ionic liquid is cross-linked to the polyurethane molecular chain through a hydrogen bond array during this process. At the same time, through this method, a high content of ionic liquid can be cross-linked by the hydrogen bond array and loaded on the polyurethane. (The ionic liquid content of the present invention is 50% - 90%, preferably 70% - 90%). While achieving high transparency, high electrical conductivity, high electromagnetic wave absorption ability, and high elongation at break are realized. The flexible transparent self-healing electromagnetic wave absorbing material prepared by the present invention can achieve an integrated design of flexibility, transparency, self-healing, and electromagnetic wave absorption, making up for the poor transparency of the previous electromagnetic wave absorbing materials. The disadvantages of the transparent electromagnetic wave absorbing material with poor service performance (without self-healing performance) are a breakthrough innovation in technology as an electromagnetic wave absorbing material.

[0074] In summary

[0075] The most important innovation lies in simultaneously having the characteristics of being transparent, self-healing, and electromagnetic wave absorbing. Due to the simultaneous design of the transparent matrix, wave-absorbing unit, and dynamic repair network, the requirements for interfacial compatibility and dispersion uniformity are extremely high. Integrating these three properties into one material has always been a research difficulty in the current field of electromagnetic wave absorption. This requires both the absorbing filler to be evenly and stably distributed in the dynamic self-healing system and to provide good wave-absorbing and self-healing characteristics, and the three properties should not interfere with each other.

[0076] The reason why the present invention can achieve these three characteristics simultaneously is that the ionic liquid has high ionic loss while having high transparency, which can provide electromagnetic wave loss ability and is added to the polyurethane system; at the same time, the polyurethane chain has abundant hydrogen bond binding sites. The gel is prepared by an in-situ polymerization method. An ionic liquid is added during the cross-linking of polyurethane. The ionic liquid is cross-linked to the polyurethane molecular chain through a hydrogen bond array during this process. Through this method, a high content of ionic liquid cross-linked by the hydrogen bond array can be loaded on the polyurethane to achieve high transparency while achieving high electrical conductivity and high electromagnetic wave absorption ability. At the same time, in this method, the ionic liquid plays a plasticizing role in the system and does not damage the polyurethane molecular structure and mechanical properties. When damage occurs, it can promote the self-healing process of the material through the high ionic loss characteristics of the ionic liquid. Therefore, the obtained polyurethane-ionic liquid multiple hydrogen bond cross-linked system realizes the characteristics of high transparency, high self-healing efficiency, and electromagnetic wave absorption ability being compatible. This system breaks through the performance boundaries of traditional materials. Traditional materials usually only focus on a single function (such as transparent conductive glass is only used for electromagnetic shielding), while this design breaks the inherent contradiction between "transparent-wave absorbing" and "durable-self-healing" and opens up a new direction for multifunctional integration.

Claims

1. A method for preparing a broadband electromagnetic wave absorbing material with transparent-flexible-self-repairing synergistic characteristics, characterized in that: The following steps are involved: S1: drying PCL, IPDH, IPDI, DBTDL and DMF to remove water respectively; then stirring and heating PCL, adding dibutyltin dilaurate and IPDI to obtain a polyurethane prepolymer; S2: adding DMF and IPDH to the polyurethane prepolymer obtained in S1 and continuing to stir to obtain a mixed solution A, transferring the mixed solution A to a mold, and drying to obtain a transparent polyurethane elastomer; S3: Add 1-butyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt to the polyurethane prepolymer, then add DNF and IPDH and stir to obtain a mixed solution B, transfer the mixed solution B to a mold, and obtain a broadband electromagnetic wave absorbing material with transparent-flexible-self-healing synergistic properties.

2. The method for preparing a broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic characteristics according to claim 1, characterized in that: The drying and dehydration process described in S1 takes 24 hours and the temperature of the drying and dehydration process is 100°C. The PCL and IPDH were dried in a vacuum oven. The atmosphere during the drying process was N 2。 3. The method for preparing a broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic characteristics according to claim 1, characterized in that: The heating temperature described in S1 is 80° C., and the stirring time is 30 min to 3 h.

4. The method for preparing a broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic characteristics according to claim 1, characterized in that: The mass ratio of PCL to dibutyltin dilaurate and IPDI described in S1 is 4.5:

1.

5. The method for preparing a broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic characteristics according to claim 1, characterized in that: The stirring time described in S2 is 24 hours, the drying temperature is 50-80°C; the drying time is 12 hours, and the mass ratio of the DMF solution and IPDH described in S2 is 130:

1.

6. The method for preparing a broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic characteristics according to claim 1, characterized in that: The mass fraction of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt described in S3 is 70% to 80%, the stirring time is 6h to 12h, and the drying temperature is 50 to 80°C.

7. A broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic characteristics obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The electromagnetic wave absorbing material is a polyurethane substrate, and the ionic liquid is cross-linked on the polyurethane molecular chain through a hydrogen bond array. The electromagnetic wave absorbing material is a structure in which a high-content ionic liquid is loaded on the polyurethane through a hydrogen bond array cross-linked.

8. The use of a broadband electromagnetic wave absorbing material having transparent-flexible-self-repairing synergistic properties according to claim 7, characterized in that: The electromagnetic wave absorbing material is used in preparing flexible transparent touch screens, displays, soft robots, electronic skins, and human-machine interfaces.

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