Polymer composite aerogel metamaterial and preparation method and application thereof

Abstract

The present application relates to a kind of polymer composite aerogel super material and its preparation method and application, belong to aerogel technical field.The aerogel super material has three-dimensional porous network structure, the same structure layer of three-dimensional porous network structure simultaneously includes high modulus region and low modulus region, both in three-dimensional space with preset periodic pattern and / or non-periodic pattern distribution alternately.High modulus region is made of high modulus polyamide acid derived polyimide, forms three-dimensional connected reinforcing skeleton network;Low modulus region is made of low modulus polyamide acid derived polyimide, fills in the gap of reinforcing skeleton network and is co-continuous with skeleton network.Compared with prior art, the present application overcomes the defects that traditional aerogel is large, easy to pulverize and existing 3D printing aerogel is difficult to realize modulus differentiation distribution in single layer, so that material has the comprehensive performance advantages of high porosity, high-efficiency sound insulation, high energy absorption damping, light weight and heat insulation.

Description

Technical Field

[0001] This invention relates to the field of aerogel technology, and in particular to a polymer composite aerogel metamaterial, its preparation method, and its application. Background Technology

[0002] Aerogels are solid materials composed of micro-nano porous networks with ultra-high porosity (>90%). They are characterized by extremely low thermal conductivity, ultra-lightweight and high specific surface area. However, traditional aerogels, such as inorganic silicon-based aerogels, generally have inherent defects such as high brittleness, difficult molding and processing, and difficulty in integration.

[0003] Polymer-based aerogels, especially organic aerogels such as polyimide (PI), polyurethane (PUR), and cellulose, can significantly improve flexibility and mechanical strength while maintaining excellent thermal insulation and sound absorption properties, paving the way for a new generation of lightweight functional materials. However, there is an inherent physical contradiction between the high porosity and high strength of polymer-based aerogels. The nanoporous network structure of polymer aerogels inherently leads to low mechanical modulus and poor load-bearing capacity. On a macroscopic scale, they are usually soft and brittle, making them difficult to use as independent structural components to bear loads, which severely restricts their integrated application in high-performance equipment.

[0004] Metamaterials are novel composite materials that surpass the performance limits of natural materials by artificially designing microscopic structural units and their spatial arrangement, rather than relying solely on the intrinsic composition of the material. Through ingenious topological design of the material structure, extraordinary mechanical, acoustic, or thermal properties, such as negative Poisson's ratio, ultra-high specific stiffness / strength, and directional waveguide properties, can be regulated. Aerogel metamaterials maintain the porous network structure unique to aerogels at the microscale, while exhibiting a periodic or aperiodic topologically ordered arrangement at the macroscale, making them a typical example of advanced cross-scale composite materials. By adjusting their macroscopic geometry, the electromagnetic shielding or sound absorption properties of the material can be further controlled, achieving broadband, low-frequency, and highly efficient sound absorption.

[0005] For example, CN120923856A discloses an aerogel metamaterial capable of switching electromagnetic wave absorption and deflection beams. The preparation method requires pouring a mixed dispersion containing conductive / magnetic functional components and cellulose microfibers into a mold fabricated according to a set structure, followed by freeze-drying to obtain the metamaterial unit. However, the construction of this aerogel metamaterial largely relies on prefabricated molds with specific structures, resulting in low precision and difficulty in flexibly controlling the structure of the aerogel metamaterial. Furthermore, the use of prefabricated molds often only enables the preparation of aerogels with a single modulus, making it difficult to achieve differentiated modulus distribution within the aerogel metamaterial structure. This still cannot overcome the defects of low mechanical modulus and poor load-bearing capacity caused by the porous network structure of polymer aerogels. These defects severely restrict the development of aerogel metamaterials in terms of structural freedom and performance controllability.

[0006] Therefore, existing polymer-based aerogel materials cannot achieve precise partitioning and controllable composite of the internal modulus of aerogel materials, making it difficult to flexibly control the composition, shape, mechanical properties, and sound absorption properties of aerogel superstructure materials, and thus cannot achieve truly controllable molding of superstructure aerogel materials. Summary of the Invention

[0007] The purpose of this invention is to overcome at least one of the defects in the prior art by providing a polymer composite aerogel metamaterial, its preparation method, and its applications. Through synergistic innovation in material formulation, printing process, and structural design, this invention successfully achieves a programmable distribution of a high-modulus reinforcing phase and a low-modulus functional phase in three-dimensional space, and exhibits sound absorption performance far superior to that of single-modulus aerogel metamaterials in sound absorption performance tests.

[0008] The objective of this invention can be achieved through the following technical solutions: The first aspect of this invention provides a polymer composite aerogel metamaterial, wherein the aerogel metamaterial has a three-dimensional porous network structure, an overall porosity of 85%-98%, an average pore size of 10-200 μm, and an overall density of 0.05-0.20 g / cm³. 3 Its compression modulus is 4-20 MPa; The three-dimensional porous network structure contains both high-modulus and low-modulus regions within the same structural layer. These regions are distributed alternately in three-dimensional space in a preset periodic pattern and / or aperiodic pattern, and the ratio of their compressive modulus is not less than 2.5:1. The high-modulus region is composed of polyimide derived from high-modulus polyamic acid, forming a three-dimensionally connected reinforcing skeleton network; the low-modulus region is composed of polyimide derived from low-modulus polyamic acid, filling the gaps in the reinforcing skeleton network and co-continuous with the skeleton network.

[0009] Furthermore, the periodic pattern is any one or more of the following: periodic grid structure, hexagonal honeycomb structure, rhombus structure, and sinusoidal structure.

[0010] Furthermore, when the periodic pattern is a periodic grid structure, high-modulus regions and low-modulus regions are distributed alternately.

[0011] Furthermore, when the periodic pattern is a hexagonal honeycomb structure, the high-modulus region forms the honeycomb skeleton, and the low-modulus region fills the honeycomb skeleton, or the modulus distribution is exchanged.

[0012] Furthermore, when the periodic pattern is a rhombic structure, the high-modulus region forms a rhombic skeleton, and the low-modulus region fills the rhombic skeleton; or the low-modulus region forms a rhombic skeleton, and the high-modulus region fills the rhombic skeleton.

[0013] Furthermore, when the periodic pattern is a sinusoidal structure, the high-modulus region forms a sinusoidal skeleton, and the low-modulus region fills the sinusoidal skeleton; or the low-modulus region forms a sinusoidal skeleton, and the high-modulus region fills the sinusoidal skeleton.

[0014] Furthermore, the aperiodic pattern is a combination of at least two of the above-mentioned periodic patterns or other patterns.

[0015] A second aspect of this invention provides a method for preparing a polymer composite aerogel metamaterial, the method specifically comprising the following steps: S1: Prepare printable composite ink A and printable composite ink B; The printable composite ink A is composed of high-modulus polyamic acid, nanofillers, triethylamine and water, and the printable composite ink B is composed of low-modulus polyamic acid, nanofillers, triethylamine and water. S2: Load the two printable composite inks obtained in S1 into 3D printing barrels A and B respectively, and confirm the printing path by referring to the preset periodic pattern and / or non-periodic pattern. When the printer nozzle reaches the preset high modulus path coordinates, the control system switches to barrel A for printing; when the printer nozzle reaches the preset low modulus path coordinates, the control system switches to barrel B for printing; by switching barrel A and barrel B to print the high modulus area and the low modulus area respectively, a polymer composite hydrogel is finally printed. S3: The polymer composite hydrogel obtained in S2 is freeze-dried and thermal imidized to obtain the polymer composite aerogel metamaterial.

[0016] Further, in step S1, in the printable composite ink A, the mass concentration of the high modulus polyamic acid is 4~10wt%, the mass concentration of the nanofiller is 1~10wt%, and the amount of triethylamine added is 40%-80% of the molar amount of the anhydride groups in the high modulus polyamic acid.

[0017] Further, in step S1, in the printable composite ink B, the mass concentration of the low modulus polyamic acid is 4~10wt%, the mass concentration of the nanofiller is 1~10wt%, and the amount of triethylamine added is 40%-80% of the molar amount of anhydride groups in the low modulus polyamic acid.

[0018] Further, in step S1, the nanofiller is any one or more of polymer short fibers, carbon fibers, silicon carbide fibers, graphene oxide, glass fibers, and lithium saponite.

[0019] Further, in step S1, the high-modulus polyamic acid and low-modulus polyamic acid are prepared by the following method: under a protective gas atmosphere, a diamine and a diacid anhydride are dispersed in a polar aprotic solvent for polycondensation reaction to obtain a polyamic acid solution; the polyamic acid solution is precipitated in a poor solvent for solvent replacement, and after drying, polyamic acid is obtained.

[0020] Furthermore, the molar ratio of the diamine to the dicarboxylic anhydride is 1:0.94 to 1:1.04.

[0021] Furthermore, the reaction temperature of the polycondensation reaction is 0-25 °C.

[0022] Furthermore, the reaction time of the polycondensation reaction is 5-24 h.

[0023] Furthermore, the diamine used in the high-modulus polyamic acid is at least one or more of 4,4-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and p-phenylenediamine.

[0024] Furthermore, the diacid anhydride used in the high-modulus polyamic acid is at least one or more of pyromellitic anhydride, biphenyl anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride.

[0025] Furthermore, the diamine used in the low-modulus polyamic acid is a diamino-terminated polysiloxane.

[0026] Furthermore, the diacid anhydride used in the low-modulus polyamic acid is at least one or more of pyromellitic anhydride, biphenyl anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride.

[0027] Furthermore, the polar aprotic solvent is at least one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0028] Furthermore, the unsuitable solvent is at least one or more of water, acetone, ethanol, methanol, isopropanol, and n-hexane.

[0029] Furthermore, the drying process employs freeze drying at a temperature of -30 to -50 °C for 24 to 48 hours.

[0030] Furthermore, in step S2, the 3D printing speed is 1-12 mm / s. -1 .

[0031] Furthermore, in step S2, the air pressure for 3D printing is 100-700 kPa.

[0032] Furthermore, the pressure during printing of the high-modulus region is 600-700 kPa.

[0033] Furthermore, the pressure during printing of the low-modulus region is 200-400 kPa.

[0034] Furthermore, in step S2, the switching between material cylinder A and material cylinder B is achieved by an electromagnetic three-way valve connected to the front end of the nozzle, with a switching delay of no more than 0.1 seconds.

[0035] Furthermore, in step S3, the freeze-drying temperature is -30~50 ℃.

[0036] Furthermore, in step S3, the freeze-drying time is 24-48 h.

[0037] Furthermore, in step S3, the imidization treatment temperature is 250-300 °C.

[0038] Furthermore, in step S3, the imidization treatment time is 1-2 hours.

[0039] The third aspect of the present invention provides an application of a polymer composite aerogel metamaterial, wherein the polymer composite aerogel metamaterial is used to prepare any one of a buffer and vibration damping device, a sound absorbing device, and a heat insulation device, preferably a sound absorbing device.

[0040] Furthermore, the polymer composite aerogel metamaterial is used to prepare devices including but not limited to: internal buffer and vibration damping layers in smartphones or tablets, sound-absorbing and tuning components in headphones or in-ear headphones, lightweight sound and heat insulation composite layers for aircraft, high-speed rail or automobile interiors, and impact energy dissipation layers in wearable flexible protective equipment (such as knee pads and elbow pads).

[0041] Additive manufacturing (3D printing) technology can directly create three-dimensional objects with arbitrarily complex shapes or multi-component integrations from digital models by layer-by-layer material deposition, providing new possibilities for structural innovation and integrated molding of aerogel metamaterials. However, this process still faces several key challenges: First, the printing accuracy is relatively low, making it difficult to accurately mold complex aerogel metamaterials. Ideal printing requires the ink to solidify rapidly after extrusion to maintain the structural morphology, but the sol-gel process of aerogel precursors is usually slow. Before complete gelation, wet gel filaments are susceptible to flow, diffusion, and fusion due to gravity and surface tension, resulting in coarsened lines, loss of detail, and blurred interlayer interfaces. Second, in terms of multi-material integration, the interfacial bonding between heterogeneous materials is weak, seriously affecting the mechanical integrity and functional reliability of the overall structure.

[0042] In addition, existing methods for preparing multi-material aerogels by 3D printing mostly employ layer switching, that is, one layer is entirely made of hard material and the next layer is entirely made of soft material, or a static blending method in which two materials are premixed and then extruded, which makes it difficult to achieve a differentiated distribution of modulus within a single printed layer.

[0043] This invention innovatively switches between high and low modulus inks in real time during the printing process based on the nozzle coordinates (X, Y) according to a preset metamaterial structure model. This is achieved with a low-delay switching of ≤0.1 seconds using an electromagnetic three-way valve, along with high / low pressure zoned extrusion control. This coordinate-dependent 3D printing strategy allows for the distribution of high and low modulus regions within each printing filament and each printed layer in arbitrary periodic or non-periodic patterns. Ultimately, this enables diverse metamaterial structure designs and differentiated distribution of high and low modulus regions within the same structural layer.

[0044] Compared with the prior art, the present invention has the following technical advantages: (1) This invention, through the molecular structure design of high-modulus polyamic acid and low-modulus polyamic acid, combined with the coordinate-based same-layer switching printing strategy, enables the final polyimide aerogel metamaterial to simultaneously form a three-dimensional interconnected reinforcing skeleton network and a co-continuous flexible energy-dissipating matrix within the same structural layer. This allows the final polymer composite aerogel metamaterial to achieve a wide range of adjustable compressive modulus while maintaining high porosity. It overcomes the defects of traditional aerogels, such as high brittleness and easy powdering, as well as the difficulty of achieving modulus differentiation distribution in a single layer in existing 3D printed aerogels. This enables the material to maintain high porosity while possessing comprehensive performance advantages such as high-efficiency sound insulation, high-energy absorption and vibration reduction, lightweight and heat insulation.

[0045] (2) This invention innovatively switches between high and low modulus inks in real time according to the nozzle coordinates during the printing process based on a preset periodic or non-periodic structural model, and uses an electromagnetic three-way valve to achieve low-delay switching and high / low pressure zone extrusion control. This innovative printing strategy allows high and low modulus regions to be distributed in any periodic or non-periodic pattern within each printing filament and within each printing plane, achieving differentiated distribution of high and low modulus regions within the same structural layer.

[0046] (3) The present invention benefits from the synergistic microstructure of the composite of high modulus continuous skeleton and low modulus co-continuous matrix. The resulting polymer composite aerogel metamaterial exhibits sound absorption performance far superior to that of single modulus aerogel metamaterial in the sound absorption performance test. It also has the advantages of high efficiency sound insulation, high energy absorption and vibration reduction, lightweight and heat insulation. It can be used in the fields of electronic device buffering and vibration reduction, headphone sound absorption and tuning, vehicle sound insulation and heat insulation and wearable flexible protection. Attached Figure Description

[0047] Figure 1 The images show the infrared spectra of polyamic acids with different moduli in Example 1.

[0048] Figure 2 A schematic diagram (left), an optical photograph (middle), and a scanning electron microscope image (right) of the aerogel metamaterial prepared in Example 1.

[0049] Figure 3 This is a schematic diagram of the aerogel metamaterial prepared in Example 2.

[0050] Figure 4 An optical photograph of the aerogel material prepared in Comparative Example 1.

[0051] Figure 5 The sound absorption properties of the aerogel metamaterial prepared in Example 1 are shown. Detailed Implementation

[0052] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0053] Unless otherwise specified, the reagents, methods, instruments, and equipment used in this invention are conventional in the art. Unless otherwise specified, the reagents and materials used in the following examples are all commercially available.

[0054] Example 1: (1) Preparation of polyamic acid, a polyimide precursor with different moduli and structures: Under nitrogen protection, diaminodiphenyl ether (ODA, 0.01 mol, 2.002 g) and N,N-dimethylacetamide (DMAC, 31.52 g) were added sequentially to a three-necked round-bottom flask A. The mixture was mechanically stirred until BIA was completely dissolved. Then, biphenyl dicarboxylic anhydride (BPDA, 0.014 mol, 3.3190 g) was added, and the mixture was reacted at 25 °C for 24 h to obtain polyamic acid solution A, a precursor of high-modulus polyimide.

[0055] Under nitrogen protection, in a three-necked round-bottom flask A, diamino-terminated polysiloxane (PDMS, 0.01 mol, 10 g) and N,N-dimethylacetamide (DMAC, 81.26 g) were added sequentially. The mixture was mechanically stirred until the PDMS was completely dissolved. Then, biphenyl dicarboxylic anhydride (BPDA, 0.014 mol, 3.3190 g) was added, and the mixture was reacted at 25 °C for 24 h to obtain polyamic acid solution B, a precursor of low-modulus polyimide.

[0056] The above polyamic acid solutions were precipitated into ice water at 5 °C, washed with water for 24 h, transferred to a refrigeration cycler and frozen for 24 h, and then freeze-dried to obtain polyamic acid A and polyamic acid B, respectively.

[0057] Figure 1 The infrared spectra of high-modulus polyamic acid A and low-modulus polyamic acid B are shown. The low-modulus polyamic acid shows the characteristic absorption peak of Si-C, proving that the polysiloxane with diamino end-capped polysiloxane was successfully polymerized with dianhydride.

[0058] (2) Preparation of printable composite inks: Add 0.5g of polyamic acid A to 10ml of lithium saponite aqueous dispersion, add 0.25ml of triethylamine, and mechanically stir at room temperature to obtain polyamic acid / lithium saponite composite ink A.

[0059] The polyamic acid / lithium saponite composite ink B differs from composite ink A in that it uses the aforementioned polyamic acid B polymer. The lithium saponite aqueous dispersion contains 2 wt% solids.

[0060] (3) Preparation of polymer composite aerogel metamaterials: Printable composite ink A and printable composite ink B are loaded into barrels A and B of the 3D printer, respectively. The print head diameter is 0.4 mm, and the printing speed is 4 mm / s.

[0061] Based on the preset metamaterial structure model (in this embodiment, a periodic mesh structure is used, with high-modulus and low-modulus regions alternating in a checkerboard pattern, and each cell measuring 1.4 mm × 1.4 mm), the switching printing strategy is set: When the printing nozzle reaches the high-modulus region, the control system switches to barrel A, applies an air pressure of 650 kPa, and extrudes printable composite ink A. When the printing nozzle reaches the low-modulus region, the control system switches to barrel B, applies an air pressure of 300 kPa, and extrudes printable composite ink B. The switching between barrel A and barrel B is achieved through a solenoid three-way valve connected to the nozzle tip, with a switching delay controlled within 0.05 seconds. Printing layer by layer according to the above parameters yields a three-dimensional polymer composite hydrogel.

[0062] The printed polymer composite hydrogel was placed in a freeze dryer and freeze-dried at -40 °C for 36 h to obtain a polyamic acid composite aerogel. The aerogel was then placed in a muffle furnace and heated to 280 °C at a heating rate of 5 °C / min under nitrogen protection, and held at that temperature for 1.5 h for thermal imidization. After cooling with the furnace, the polymer composite aerogel metamaterial was obtained.

[0063] Figure 2 The images show a schematic diagram (left), an optical photograph (middle), and a SEM image (right) of the aerogel metamaterial prepared in this embodiment. As can be seen from the figures, the aerogel prepared in this embodiment has regular square shapes on a macroscopic scale, with dimensions of approximately 20 mm × 20 mm × 5 mm. Scanning electron microscopy observation shows that each cell exhibits a network structure composed of interwoven porous fibers, with a mesh size of approximately 1.3 mm × 1.3 mm and a fiber diameter of approximately 0.4 mm. The pore size of the aerogel matrix is ​​distributed in the range of 5–20 μm.

[0064] The calculated porosity of the polymer composite aerogel metamaterial obtained in this embodiment is 91%, and its density is 0.1 g / cm³. 3 .

[0065] The compressive modulus of the polymer composite aerogel metamaterial prepared in this embodiment was measured to be approximately 5 MPa using a universal testing machine.

[0066] Example 2: This embodiment is basically the same as Embodiment 1, except that: The preset structural model adopts, for example Figure 3 The hexagonal honeycomb structure shown (honeycomb side length 5 mm, wall thickness 0.7 mm) has black areas made of high-modulus polyimide and blank areas made of low-modulus polyimide.

[0067] The results showed that the polymer composite aerogel metamaterial prepared in this embodiment had a porosity of 93% and a density of 0.08 g / cm³. 3 Its compressive modulus is approximately 12 MPa.

[0068] Example 3: This embodiment is basically the same as Embodiment 1, except that: In the preparation of high-modulus polyamic acid, 2-(4-aminophenyl)-5-aminobenzimidazole (BIA) is selected as the diamine, and biphenyltetracarboxylic dianhydride (BPDA) is selected as the diacid anhydride; in the preparation of low-modulus polyamic acid, a diamine-terminated polysiloxane (number average molecular weight of about 2000 g / mol) is selected as the diamine, and 3,3',4,4'-benzophenone tetracarboxylic dianhydride (BTDA) is selected as the diacid anhydride.

[0069] The preset structural model adopts a hexagonal honeycomb structure (honeycomb side length 7 mm, wall thickness 0.5 mm), with high modulus regions forming the honeycomb walls and low modulus regions filling the honeycomb interior.

[0070] In the printing switching strategy, an air pressure of 700 kPa is applied to the high modulus region and an air pressure of 200 kPa is applied to the low modulus region.

[0071] The results showed that the porosity of the material obtained in this embodiment was 90%, and the density was 0.09 g / cm³. 3 Its compression modulus is approximately 8 MPa.

[0072] Comparative Example 1: This comparative example provides a simple high-modulus aerogel metamaterial, fabricated solely from composite ink A via 3D printing. The printed shape and structure are a mesh structure similar to that of Example 1, and the printing extrusion pressure is 700 kPa.

[0073] The results showed that the porosity of the material obtained in this embodiment was 94%, and the density was 0.075 g / cm³. 3 Its compression modulus is approximately 30 MPa.

[0074] Figure 4 An optical photograph of the aerogel material prepared in Comparative Example 1. Because a rheology modifier was added to the ink, the aerogel also has printability.

[0075] Comparative Example 2: This comparative example provides a simple low-modulus aerogel metamaterial, fabricated solely from composite ink B via 3D printing. The printed shape and structure are similar to a mesh structure in Example 1, and the printing extrusion pressure is 200 kPa.

[0076] The results showed that the porosity of the material obtained in this embodiment was 75%, and the density was 0.13 g / cm³. 3 Its compression modulus is approximately 200 kPa.

[0077] Based on the successful preparation of aerogel materials in the above embodiments and comparative examples, the present invention tests the sound absorption performance of the above aerogel samples.

[0078] The sound absorption coefficient was measured according to ISO 10534-2:1998 (GB / T 18696.2-2002) standard. The test temperature was 20 ℃, the humidity was 60%, the atmospheric pressure was 101325.0 Pa, the sound velocity was 343.237 m / s, and the air characteristic impedance was 412.568 Pa•s / m. The test frequency range was 63~6300 Hz. For the 63-1600 Hz test, the sample diameter was 100 mm, and for the 1600-6300 Hz test, the sample diameter was 30 mm, and the thickness was uniformly 10 mm.

[0079] Figure 5 The sound absorption coefficient of the aerogel metamaterial prepared in Example 1 is shown in the range of 0-6500 Hz. The test results show that the sound absorption coefficient of the aerogel metamaterial is greater than 0.8 in the high-frequency range, i.e., 2000-6500 Hz.

[0080] In contrast, the high-modulus aerogel prepared in Comparative Example 1 has a sound absorption coefficient of only 0.2 at 2000 Hz. Comparative Example 1 is composed of high-modulus polyimide aerogel, which has a rigid material structure. When sound waves are incident, the viscous flow resistance inside the material is extremely high, making it difficult for sound waves to penetrate into the material, thus resulting in a low sound absorption coefficient.

[0081] The low-modulus aerogel prepared in Comparative Example 2 showed a slight increase in sound absorption coefficient to 0.5 at 2000 Hz. Compared to Comparative Example 1, Comparative Example 2 exhibited a lower modulus, resulting in a softer material that allows sound waves to penetrate more easily and induce skeletal vibration, leading to increased viscous loss. The sound absorption coefficient of 0.5 is already considered optimal for traditional homogeneous porous materials. However, in the mid-frequency range of 2000 Hz, a single modulus cannot simultaneously satisfy both "low-frequency resonance" and "high-frequency attenuation," exhibiting an inherent dissipation bottleneck.

[0082] In the aerogel material sample prepared in Example 1 of this invention, a checkerboard distribution forms a large number of high- and low-modulus interfaces. At 2000 Hz, sound waves are strongly scattered when passing through these interfaces, resulting in a significant increase in sound path. Compared to the uniform low-modulus structure of Comparative Example 2, the effective acoustic path length of Example 1 increases by at least 2 to 3 times, leading to an exponential increase in viscous loss and thermal conductivity loss. In addition, the alternating arrangement of high-modulus and low-modulus regions constitutes a "local resonant unit," thereby further increasing the sound wave loss and ultimately exhibiting a sound absorption coefficient of not less than 0.8.

[0083] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A polymer composite aerogel metamaterial, characterized in that, The aerogel metamaterial has a three-dimensional porous network structure with an overall porosity of 85%-98%, an average pore size of 10-200 μm, and an overall density of 0.05-0.20 g / cm³. 3 Its compression modulus is 4-20 MPa; The three-dimensional porous network structure contains both high-modulus and low-modulus regions within the same structural layer. These regions are distributed alternately in three-dimensional space in a preset periodic pattern and / or aperiodic pattern, and the ratio of their compressive modulus is not less than 2.5:

1. The high-modulus region is composed of polyimide derived from high-modulus polyamic acid, forming a three-dimensionally connected reinforcing skeleton network; the low-modulus region is composed of polyimide derived from low-modulus polyamic acid, filling the gaps in the reinforcing skeleton network and co-continuous with the skeleton network.

2. The polymer composite aerogel metamaterial according to claim 1, characterized in that, The periodic pattern is any one or more of the following: periodic grid structure, hexagonal honeycomb structure, rhombus structure, and sinusoidal structure; When the periodic pattern is a periodic grid structure, high-modulus regions and low-modulus regions are distributed alternately; When the periodic pattern is a hexagonal honeycomb structure, the high modulus region is the honeycomb skeleton, and the low modulus region fills the honeycomb skeleton, or the modulus distribution is exchanged. When the periodic pattern is a rhombic structure, the high modulus region is a rhombic skeleton, and the low modulus region is filled in the rhombic skeleton; or the low modulus region is a rhombic skeleton, and the high modulus region is filled in the rhombic skeleton. When the periodic pattern is a sinusoidal structure, the high modulus region is a sinusoidal skeleton, and the low modulus region is filled in the sinusoidal skeleton; or the low modulus region is a sinusoidal skeleton, and the high modulus region is filled in the sinusoidal skeleton.

3. A method for preparing the polymer composite aerogel metamaterial according to any one of claims 1 or 2, characterized in that, The preparation method specifically includes the following steps: S1: Prepare printable composite ink A and printable composite ink B; The printable composite ink A is composed of high-modulus polyamic acid, nanofillers, triethylamine and water, and the printable composite ink B is composed of low-modulus polyamic acid, nanofillers, triethylamine and water. S2: Load the two printable composite inks obtained in S1 into 3D printing barrels A and B respectively, and confirm the printing path by referring to the preset periodic pattern and / or non-periodic pattern. When the printer nozzle reaches the preset high modulus path coordinates, the control system switches to barrel A for printing; when the printer nozzle reaches the preset low modulus path coordinates, the control system switches to barrel B for printing; by switching barrel A and barrel B to print the high modulus area and the low modulus area respectively, a polymer composite hydrogel is finally printed. S3: The polymer composite hydrogel obtained in S2 is freeze-dried and thermal imidized to obtain the polymer composite aerogel metamaterial.

4. The method for preparing the polymer composite aerogel metamaterial according to claim 3, characterized in that, In step S1, in the printable composite ink A, the mass concentration of the high-modulus polyamic acid is 4~10wt%, the mass concentration of the nanofiller is 1~10wt%, and the amount of triethylamine added is 40%-80% of the molar amount of anhydride groups in the high-modulus polyamic acid; In the printable composite ink B, the mass concentration of the low-modulus polyamic acid is 4~10wt%, the mass concentration of the nanofiller is 1~10wt%, and the amount of triethylamine added is 40%-80% of the molar amount of anhydride groups in the low-modulus polyamic acid; The nanofiller is any one or more of polymer short fibers, carbon fibers, silicon carbide fibers, graphene oxide, glass fibers, and lithium saponite.

5. The method for preparing the polymer composite aerogel metamaterial according to claim 3, characterized in that, In step S1, the high-modulus polyamic acid and low-modulus polyamic acid are prepared by the following method: Under a protective gas atmosphere, a diamine and a dicarboxylic acid anhydride are dispersed in a polar aprotic solvent for a polycondensation reaction to obtain a polyamic acid solution; the polyamic acid solution is then precipitated in a poor solvent for solvent displacement, and dried to obtain polyamic acid.

6. The method for preparing the polymer composite aerogel metamaterial according to claim 5, characterized in that, The molar ratio of the diamine to the diacid anhydride is 1:0.94-1:1.04; The reaction temperature for the polycondensation reaction is 0-25 ℃; The reaction time for the polycondensation reaction is 5-24 h.

7. The method for preparing the polymer composite aerogel metamaterial according to claim 5, characterized in that, The high-modulus polyamic acid uses a diamine selected from at least one or more of 4,4-diaminodiphenyl ether, 2-(4-aminophenyl)-5-aminobenzimidazole, and p-phenylenediamine. The high-modulus polyamic acid used is at least one or more of the following: pyromellitic anhydride, biphenyl anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride. The diamine used in the low-modulus polyamic acid is a diamino-terminated polysiloxane; The low-modulus polyamic acid used is at least one or more of the following: pyromellitic anhydride, biphenyl anhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and 2,3,3',4'-diphenyl ether tetracarboxylic dianhydride. The polar aprotic solvent is at least one or more of N-methylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide; The unsuitable solvent is at least one or more of water, acetone, ethanol, methanol, isopropanol, and n-hexane.

8. The method for preparing the polymer composite aerogel metamaterial according to claim 3, characterized in that, In step S2, the 3D printing speed is 1-12 mm / s. -1 The air pressure for 3D printing is 100-700 kPa; The printing pressure for the high modulus region is 600-700 kPa, and the printing pressure for the low modulus region is 200-400 kPa. The switching between material cylinder A and material cylinder B is achieved by a solenoid three-way valve connected to the front end of the nozzle, with a switching delay of no more than 0.1 seconds.

9. The method for preparing the polymer composite aerogel metamaterial according to claim 3, characterized in that, In step S3, the freeze-drying temperature is -30~50 ℃, and the freeze-drying time is 24-48 h; The imidization treatment is performed at a temperature of 250-300 °C for 1-2 h.

10. An application of the polymer composite aerogel metamaterial according to claim 1 or 2, characterized in that, The polymer composite aerogel metamaterial is used to prepare any one of the following: buffer and vibration damping devices, sound absorption devices, and heat insulation devices.

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