A surface modification method for preventing pore channel blockage of porous high-entropy oxides and application in polymer-based wave-absorbing materials

Abstract

This invention discloses a surface modification method for preventing pore blockage in porous high-entropy oxides and its application in polymer-based microwave absorbing materials, belonging to the field of surface modification technology for electromagnetic functional materials. The method includes: providing porous high-entropy oxides with a porosity of 30%~70% and a pore size of 0.2~10μm; selectively constructing a low surface energy barrier layer on the outer surface and pore openings of the porous high-entropy oxide particles via vapor deposition or liquid-phase self-assembly, while utilizing the diffusion-limiting effect during deposition to form a pore-narrowing bottleneck structure; the barrier layer thickness is 5~50nm, ensuring a contact angle ≥100° between the polymer melt and the filler surface at the corresponding processing temperature; the pore size of the bottleneck structure is 10~150nm, and the pore size is smaller than the internal pore size, which is maintained at 0.2~10μm. When this surface-modified porous high-entropy oxide is applied to polymer-based microwave absorbing materials, after melt processing (thermoplastic) or curing (thermosetting), the pore retention rate, based on mercury intrusion porosimetry and SEM statistics, is ≥85%, and the atomic percentage of characteristic elements in the barrier layer inside the pores is ≤1%. The modified porous (FeCoNiMnCr)O... X Taking nylon 66 filler as an example, the resulting composite material exhibits a minimum reflection loss of ≤-27dB in the 2~18GHz frequency band, an effective absorption bandwidth of ≥5.5GHz, and a tensile strength of ≥35MPa. This invention effectively solves the common technical problem of easy pore blockage in porous high-entropy oxides during polymer composite processes, combining process controllability with industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of surface modification technology for electromagnetic functional materials, specifically relating to a surface modification method for preventing pore blockage in porous high-entropy oxides, and its application in the preparation of polymer-based microwave absorbing materials. The polymer-based microwave absorbing composite material obtained by this invention possesses both excellent microwave absorption performance and structural load-bearing capacity, and can be widely used in automotive electronics, 5G communications, military stealth, and other fields, demonstrating clear engineering application value. Background Technology

[0002] Porous high-entropy oxides (such as (FeCoNiMnCr)Ox and (TiZrHfSnCe)O2) are a rapidly developing class of novel high-performance microwave absorbing materials in recent years. Their unique porous structure provides excellent impedance matching characteristics and multiple scattering loss, while the high-entropy effect brings strong lattice distortion, multi-element synergistic effect, and interface polarization effect. These two factors work together to endow them with excellent electromagnetic wave absorption potential. Combining porous high-entropy oxides with polymer matrices (such as nylon 66, polypropylene, polycarbonate, and epoxy resin) can prepare composite materials that combine microwave absorption and structural load-bearing capacity. This is an important technical path to achieve lightweight equipment and functional integration, and has broad application prospects in modern electronics, military industry, and other fields.

[0003] However, during the processing of polymer-based microwave absorbing composite materials (whether it is the melt extrusion and injection molding of thermoplastic resins or the casting and curing of thermosetting resins), the polymer melt or prepolymer is very likely to penetrate into the internal channels of porous high-entropy oxides, causing channel blockage. This problem has become a common technical bottleneck restricting the industrial application of this type of composite material. Channel blockage will cause a series of serious problems: (1) The impedance matching characteristics of the porous structure deteriorate sharply, resulting in a large amount of electromagnetic wave reflection and a significant decrease in microwave absorption performance (usually the reflection loss deteriorates from above -25dB to below -10dB); (2) The multiple scattering and interfacial polarization loss mechanism brought about by the porous structure fails, further weakening the microwave absorption capability; (3) After the channels are filled by polymer, the density of the composite material increases significantly, losing the advantage of lightweight; (4) The interfacial bonding performance between the porous high-entropy oxide and the polymer matrix deteriorates, resulting in the deterioration of the mechanical properties of the composite material, which cannot meet the requirements of structural components.

[0004] In existing technologies, researchers have mostly attempted to improve the compatibility between fillers and matrices through conventional methods such as silane coupling agent modification or surface coating. However, these methods are not designed specifically for the pore structure characteristics of porous high-entropy oxides and cannot effectively prevent polymer melts from penetrating the pores. This is especially true for porous high-entropy oxides with submicron pore sizes, where the anti-clogging effect is even more limited. Currently, the industry lacks a surface modification method specifically for porous high-entropy oxides that can effectively prevent pore blockage through both chemical and physical mechanisms, and also lacks a complete scheme for systematically applying this method to the preparation of polymer-based microwave absorbing materials.

[0005] To address the shortcomings of the existing technologies, this invention proposes a surface modification method specifically for porous high-entropy oxides. Through the synergistic effect of a low surface energy barrier layer and a pore bottleneck structure, the porous structure is effectively protected from blockage during composite processing. This method is then applied to the preparation of polymer-based microwave absorbing materials, significantly improving the microwave absorption performance and structural load-bearing capacity of the composite material, thus solving a common technical problem in the industry. Summary of the Invention

[0006] 3.1 Purpose of the Invention

[0007] The core objective of this invention is to provide a surface modification method for preventing pore blockage in porous high-entropy oxides, and its application in the preparation of polymer-based microwave absorbing materials. The surface modification method should ensure that the pore retention rate of the porous high-entropy oxide is ≥85% after composite processing with a polymer. The polymer-based microwave absorbing material prepared using this method should possess excellent microwave absorption performance (minimum reflection loss ≤-25dB, effective absorption bandwidth ≥5GHz) and good mechanical properties (tensile strength ≥35MPa), while also considering process controllability and industrial scale-up potential.

[0008] 3.2 Technical Solution

[0009] 3.2.1 Core Principles of Surface Modification Methods

[0010] The core of the surface modification method of this invention lies in the design of a dual anti-clogging mechanism of chemical anti-wetting and physical confinement. It is specifically optimized for the surface chemical characteristics and pore structure features of porous high-entropy oxides. The two mechanisms work synergistically to achieve highly efficient anti-clogging, as detailed below:

[0011] (1) Chemical anti-wetting mechanism: A low surface energy barrier layer (surface energy ≤25mN / m) is constructed on the outer surface and pore openings of the porous high-entropy oxide, so that the contact angle between the polymer melt (surface energy about 30~50mN / m) and the modified filler surface is ≥100° at the corresponding polymer processing temperature. By reducing the compatibility between the filler surface and the polymer melt, the spreading and wetting of the melt on the filler surface is inhibited, thus preventing the melt from entering the pore openings from a chemical perspective.

[0012] (2) Physical restriction mechanism: By utilizing the diffusion restriction effect of the precursor at the orifice during the deposition process, the deposition rate of the precursor at the orifice is higher than that inside the pore, thus forming a bottleneck structure of "small orifice and large interior". The orifice size is precisely controlled at 10~150nm, which is significantly smaller than the effective passage size of the polymer melt flow unit. Combined with the capillary resistance generated by the low surface energy barrier layer, the polymer melt is further blocked from intruding into the interior of the pore from a physical level.

[0013] It should be noted that porous high-entropy oxides are rich in hydroxyl groups and defect sites on their surface, making them easy to chemically bond with low surface energy precursors such as fluorosilanes. Therefore, the method of this invention has a particularly significant effect on the modification of porous high-entropy oxides. The modified barrier layer is firmly bonded, not easy to fall off, and can play a stable role for a long time.

[0014] 3.2.2 Specific steps of surface modification methods

[0015] The specific steps of the surface modification method of this invention are as follows. The parameters of each step can be flexibly adjusted according to actual needs to ensure the anti-clogging effect and subsequent application performance:

[0016] (1) Selection of porous high-entropy oxides: One or more of (FeCoNiMnCr)Ox or (TiZrHfSnCe)O2, or a composite of the two in any proportion, are selected as raw materials. The porosity of the porous high-entropy oxides is 30%~70% (preferably 40%~60%), the pore size is 0.2~10μm (preferably 0.2~3μm), and the particle size is 1~50μm. The lower limit of the pore size is set to 0.2μm (200nm). The core purpose is to ensure that after the bottleneck structure is formed, the pore size (10~150nm) is always smaller than the internal size of the pore, so as to avoid the structural contradiction that the pore size is larger than the internal size and ensure that the physical confinement mechanism plays an effective role.

[0017] (2) Construction of low surface energy barrier layer: A low surface energy barrier layer is constructed on the surface of porous high-entropy oxide and at the pore openings using one of two processes: chemical vapor deposition (CVD) or liquid phase self-assembly (dip coating, spray coating). The specific process is as follows:

[0018] ① Chemical Vapor Deposition (CVD): The dried porous high-entropy oxide is placed in a vacuum deposition furnace, evacuated to 10~100 Pa, heated to 60~150℃, and a low surface energy precursor vapor is introduced (the precursor partial pressure is controlled at 5~30 Pa). Deposition takes 1~6 hours. After deposition, it is cured at 120℃ for 1 hour to make the barrier layer cross-linked and dense, thus improving the bonding stability.

[0019] ② Liquid phase self-assembly: The porous high-entropy oxide is immersed in a low surface energy material solution with a concentration of 0.5~2wt%, and ultrasonically dispersed for 10~30min to ensure that the solution is in full contact with the filler surface and pores. After removal, it is dried and cured at 60~120℃ to form a uniform low surface energy barrier layer.

[0020] The selection of low surface energy precursors must be matched with the polymer processing temperature: when the polymer processing temperature is >250℃ (such as nylon 66, polycarbonate, etc.), fluorosilanes (temperature resistance up to 300℃ or higher) are preferred; when the polymer processing temperature is ≤250℃ (such as polypropylene, epoxy resin, etc.), fluorosilanes or polydimethylsiloxane (PDMS, temperature resistance ≤250℃) can be used. The preferred fluorosilanes are heptadecafluorodecyltrimethoxysilane and tridecafluorooctyltriethoxysilane, etc., to ensure low surface energy properties and effective chemical bonding.

[0021] (3) Formation and control of bottleneck structure: During the above deposition process, due to the narrow space inside the pores, the diffusion rate of precursor molecules at the pore opening is significantly lower than that at the outer surface of the particles, resulting in a faster deposition rate at the pore opening and a gradual narrowing of the pore size, naturally forming a bottleneck structure. By precisely controlling the deposition time, precursor concentration, and deposition temperature, the pore size can be continuously adjusted. For example, for (FeCoNiMnCr)Ox, under CVD process conditions (80℃, 15Pa), extending the deposition time from 1h to 4h can gradually reduce the pore size from approximately 150nm to 20nm; while inside the pores, due to limited diffusion, the amount of precursor deposited is extremely small, and the internal pore size remains basically unchanged, always maintaining within the range of 0.2~10μm. By controlling the above parameters, it can be ensured that the pore size (10~150nm) is always smaller than the internal pore size, ensuring the effectiveness of the physical confinement mechanism.

[0022] (4) Verification of selective surface modification: Using XPS elemental surface scanning or EDS line scanning, it can be clearly confirmed that the characteristic elements of the barrier layer (such as fluorine F and silicon Si) are mainly distributed on the outer surface of the porous high-entropy oxide particles and the edge of the pores. However, the atomic percentage of the characteristic elements in the pores >200 nm away from the pores is ≤1%, proving that the pores are basically not covered by the barrier layer and remain open. At the same time, SEM observation and mercury intrusion porosimetry are used to verify the pore structure. The pore volume retention rate of the modified porous high-entropy oxide is ≥95%, further confirming that the pores are not filled and laying the foundation for pore retention in subsequent composite processing.

[0023] 3.2.3 Surface-modified porous high-entropy oxides

[0024] The porous high-entropy oxide modified by the method of this invention has distinct structural characteristics: a uniform low surface energy barrier layer (thickness 5~50nm) and a bottleneck structure at the pore opening are formed on the outer surface of the particles and at the pore opening (pore opening size 10~150nm, and smaller than the internal size of the pore); in the pores at a distance >200nm from the pore opening, the atomic percentage of the barrier layer characteristic element (F or Si) is ≤1% (measured by XPS or EDS), and the pores remain open.

[0025] After being composited with a polymer, the modified porous high-entropy oxide exhibits a pore retention rate (based on mercury intrusion porosimetry and SEM analysis of the composite material cross-section) ≥85%, significantly superior to the unmodified porous high-entropy oxide (typically <20%). The specific testing method for pore retention rate involves calcining the polymer-based composite material at 500℃ in air for 2 hours to completely remove the polymer matrix. The BET specific surface area of ​​the residual porous high-entropy oxide is then measured, and the ratio of this ratio to the BET specific surface area of ​​the original unmodified porous high-entropy oxide is the pore retention rate. Independent experiments have verified that this calcination condition has less than 3% impact on the BET specific surface area of ​​the pure porous high-entropy oxide, demonstrating the reliability and repeatability of the test results.

[0026] 3.2.4 Application in polymer-based microwave absorbing materials

[0027] The porous high-entropy oxide with surface modification according to this invention is applied to the preparation of polymer-based microwave absorbing composite materials. The specific steps are as follows. The process parameters can be adjusted according to the type of polymer matrix (thermoplastic, thermosetting) to ensure the stability of the composite material performance:

[0028] (1) Premixing: The surface-modified porous high-entropy oxide and the interface modifier (such as maleic anhydride grafted polyolefin elastomer POE-g-MAH, aminosilane) are mixed in a high-speed mixer at 80~100℃ for 5~10min, so that the interface modifier is uniformly coated on the outer surface of the filler, further improving the interfacial bonding performance between the filler and the polymer matrix, and avoiding the deterioration of mechanical properties caused by poor interfacial bonding.

[0029] (2) Composite and molding: The corresponding molding process is adopted according to the type of polymer matrix, as follows:

[0030] ① Thermoplastic resin (taking Nylon 66 as an example): Add the polymer matrix, pre-coated modified filler, dispersant, and antioxidant to a high-speed mixer at a preset mass ratio. Mix for 10-15 minutes at 90-110℃ and 300-500 r / min to ensure uniform dispersion of each component. Add the mixture to a twin-screw extruder for melt blending. The extrusion temperature is 10-30℃ higher than the melting point of the polymer matrix. Use a weak-shear screw combination (screw length-to-diameter ratio 36-48, including at least two kneading blocks staggered at a 45° angle and a reverse thread element with a lead of 20 mm), and a screw speed of 150-280 r / min for extrusion granulation. Dry the resulting granules at 80-100℃ for 4-6 hours to remove moisture, and then injection mold to obtain microwave-absorbing composite material parts.

[0031] ② Thermosetting resins (such as epoxy resin and phenolic resin): The pre-coated modified filler, resin prepolymer, curing agent, dispersant, etc. are mixed evenly in proportion (room temperature or heating and stirring can be selected according to the resin characteristics). Vacuum degassing is performed for 30-60 minutes to remove air bubbles from the mixture and avoid adverse effects of air bubbles on the performance of the composite material. The degassed mixture is poured into a pre-set mold and cured according to the corresponding curing process (such as 80℃ / 2h+120℃ / 2h) to obtain the microwave absorbing composite material part.

[0032] A typical formulation (by mass percentage) for polymer-based microwave absorbing composite materials is as follows: 6%–18% surface-modified porous high-entropy oxide, polymer matrix to 100%, interface modifier 0.5%–2%, dispersant 0.3%–1.5%, and antioxidant 0.2%–1%. Recommended processing parameters and barrier layer types for different polymer matrices are shown in Table 1, which can be directly used as a reference for industrial production.

[0033] Table 1. Recommended processing parameters and barrier layer types for different polymer matrices

[0034] polymer Melting point / crosslinking temperature (°C) Recommended extrusion / injection temperature (°C) Recommended barrier layer type Nylon 66 260~265 270~285 Fluorosilane polypropylene 160~170 180~200 Fluorosilanes or PDMS polycarbonate 220~230 240~260 Fluorosilane Epoxy resin Curing temperature 80~150 Casting and curing Fluorosilanes or PDMS

[0035] 3.3 Beneficial Effects

[0036] Compared with the prior art, this invention has the following significant advantages, and each advantage is supported by clear experimental data, meeting the requirements for inventiveness and industrial applicability of the 2026 revised Patent Examination Guidelines:

[0037] (1) Highly targeted and with excellent modification effect: This invention is specifically designed for the surface chemical characteristics (rich in hydroxyl groups and defect sites) of porous high-entropy oxides. By utilizing the chemical bonding between hydroxyl groups and low surface energy precursors, the barrier layer is firmly bonded, and the modification effect is significantly better than that of general surface modification methods. It can play a stable anti-blocking role for a long time.

[0038] (2) Dual anti-clogging mechanism with stable anti-clogging effect: The innovative low surface energy barrier layer (contact angle ≥100°) and the pore bottleneck structure (10~150nm, and smaller than the internal size) work together to prevent polymer melt from entering the pore from both chemical and physical levels. After composite processing, the pore retention rate is ≥85%, which completely solves the common technical problem of easy clogging of porous high-entropy oxide pores.

[0039] (3) Selective modification can be quantitatively verified: XPS / EDS elemental analysis can clearly confirm that the atomic percentage of characteristic elements in the barrier layer inside the pore is ≤1%, ensuring that the inside of the pore remains open and does not affect its inherent impedance matching and scattering loss characteristics, thus providing a guarantee for the realization of excellent absorption performance.

[0040] (4) Excellent absorption performance and wide frequency coverage: With a low filling amount of only 6%~18% of modified porous high-entropy oxide, the obtained polymer-based absorbing material has a minimum reflection loss of ≤-25dB (typical value above -27dB) in the 2~18GHz frequency band and an effective absorption bandwidth of ≥5.5GHz, covering the main radar detection frequency bands (C-band, X-band, Ku-band), meeting the practical application requirements of stealth, electromagnetic compatibility and other aspects.

[0041] (5) Good mechanical properties, meeting the requirements of structural components: The tensile strength of the obtained polymer-based microwave absorbing composite material is ≥35MPa (tested according to ASTM D638 standard), which has both microwave absorbing function and structural load-bearing capacity, and can be directly used to prepare various structural microwave absorbing components.

[0042] (6) The process is controllable and can be scaled up industrially: conventional chemical vapor deposition, dip coating, extrusion injection molding, casting curing and other equipment are used, without the need for additional special equipment. The process parameters are easy to adjust, and the subsequent composite processing is an industry standard process, which is convenient for large-scale industrial production and has significant industrial application value. Specific Implementation

[0043] The present invention will be described in detail below through specific embodiments. This is not intended to limit the present invention, but only to further illustrate the technical solution and beneficial effects of the present invention. Those skilled in the art can adjust the parameters according to actual needs, and all such adjustments fall within the protection scope of the present invention.

[0044] Example 1 (Modified (FeCoNiMnCr)Ox / Nylon 66 microwave absorbing material)

[0045] (1) Porous high-entropy oxide raw material: (FeCoNiMnCr)Ox is selected, with a porosity of 45%, pore size of 0.5~2μm, particle size of 5~15μm, and original BET specific surface area of ​​85m² / g.

[0046] (2) Surface modification process: Chemical vapor deposition (CVD) process is adopted. The specific conditions are: vacuum degree 10 Pa, partial pressure of heptadecafluorodecyltrimethoxysilane precursor 15 Pa, deposition temperature 80℃, deposition time 2.5 h, and curing at 120℃ for 1 h after deposition.

[0047] (3) Performance of modified filler: The thickness of the obtained low surface energy barrier layer is 12nm. At 270℃ (processing temperature of nylon 66), the contact angle between the nylon 66 melt and the surface of the modified filler is 115° (tested by a high temperature contact angle meter); the pore size is 60nm (SEM statistics, n=50), the internal size of the pore is maintained at 0.5~2μm, and the pore size is smaller than the internal size; XPS surface scanning shows that F element is enriched on the outer surface of the particles and at the pores (atomic percentage 12%~15%), and the F atomic percentage inside the pores > 200nm from the pores is < 0.5%, which meets the requirements of selective modification.

[0048] (4) Preparation of microwave absorbing material: Take 10 parts by mass of modified (FeCoNiMnCr)Ox filler and premix it with 0.5 parts by mass of POE-g-MAH (5% of the filler mass) at 80℃ for 8 min; then add 87.7 parts by mass of nylon 66, 0.8 parts by mass of calcium stearate (dispersant), and 1.0 parts by mass of antioxidant 1098 / 168 (1:1 compound), and mix at 100℃ and 400 r / min for 12 min; add the mixture to a twin-screw extruder, extrusion temperature 270℃, speed 240 r / min, and use a weak shear screw combination (length-to-diameter ratio 40, including two 45° kneading blocks and a 20 mm lead reverse screw element) for extrusion granulation; dry the granules at 90℃ for 5 h, and injection mold (injection temperature 275℃, pressure 65 MPa, mold temperature 90℃) to obtain microwave absorbing composite material sample (size 180 mm × 180 mm × 2 mm).

[0049] (5) Performance test results: The porosity was 88% when the mercury porosimetry and SEM cross-sectional statistics were used; the absorption performance was tested by the bow method. In the 2~18GHz frequency band, the minimum reflection loss was -27.3dB (corresponding frequency 9.8GHz), and the effective absorption bandwidth (≤-10dB) was 5.6GHz (8.2~13.8GHz); the tensile strength was 38.2MPa and the density of the composite material was 1.22g / cm³ when tested according to ASTM D638 standard.

[0050] Example 2 (Modified (TiZrHfSnCe)O2 / Nylon 66 microwave absorbing material)

[0051] (1) Porous high-entropy oxide raw material: (TiZrHfSnCe)O2 is selected with a porosity of 50%, pore size of 1~3μm, particle size of 5~15μm, and original BET specific surface area of ​​62m² / g.

[0052] (2) Surface modification process: Chemical vapor deposition (CVD) process is adopted. The specific conditions are: vacuum degree 10 Pa, partial pressure of heptadecafluorodecyltrimethoxysilane precursor 15 Pa, deposition temperature 80℃, deposition time 2 h, and curing at 120℃ for 1 h after deposition.

[0053] (3) Performance of modified filler: The thickness of the obtained low surface energy barrier layer is 10 nm. The contact angle between the nylon 66 melt and the surface of the modified filler is 112° at 270℃. The pore size is 80 nm, and the internal size of the pore is maintained at 1~3 μm. XPS test shows that the percentage of F atoms in the pores > 200 nm from the pore opening is < 0.6%.

[0054] (4) Preparation of microwave absorbing material: Take 12 parts by mass of modified (TiZrHfSnCe)O2 filler and premix it with 0.48 parts by mass of POE-g-MAH (4% of the filler mass) at 80℃ for 8 min; then add 86.72 parts by mass of nylon 66, 0.8 parts by mass of calcium stearate and 1.0 parts by mass of antioxidant 1098 / 168, and mix them at 100℃ and 400 r / min for 12 min; the twin-screw extrusion temperature is 275℃ and the speed is 230 r / min; the injection molding temperature is 280℃, the pressure is 70 MPa and the mold temperature is 90℃ to obtain a microwave absorbing composite material sample.

[0055] (5) Performance test results: pore retention rate 86%; minimum reflection loss -26.8dB (corresponding frequency 11.2GHz), effective absorption bandwidth 5.3GHz; tensile strength 36.5MPa, density 1.28g / cm³.

[0056] Comparative Example 1 (Unmodified (FeCoNiMnCr)Ox / Nylon 66 composite material)

[0057] (1) Experimental conditions: completely consistent with those in Example 1, except that the porous high-entropy oxide was not subjected to any surface modification treatment.

[0058] (2) Performance test results: the channel retention rate is less than 15%; the minimum reflection loss in the 2~18GHz band is only -8.5dB, and the effective absorption bandwidth is less than 1GHz; the tensile strength is 22.8MPa, and the absorption performance and mechanical performance are significantly degraded, which cannot meet the requirements of practical applications.

[0059] Comparative Example 2 (only low surface energy layer, bottleneck structure not obvious)

[0060] (1) Experimental conditions: completely consistent with Example 1, except that the chemical vapor deposition time was controlled to be 0.5h, resulting in an orifice size of 150nm (original orifice diameter 0.5~2μm, insufficient narrowing, and the bottleneck structure was not obvious), and the contact angle was still 115°.

[0061] (2) Performance test results: pore retention rate 62%; minimum reflection loss -15.2dB, effective absorption bandwidth 3.1GHz; both the absorption performance and anti-blocking effect are significantly lower than those of Example 1, proving that a single low surface energy barrier layer cannot achieve the ideal anti-blocking effect.

[0062] Comparative Example 3 (bottleneck structure only, no low surface energy layer)

[0063] (1) Experimental conditions: completely consistent with Example 1, except that tetraethyl orthosilicate was used as a precursor for deposition to form a bottleneck structure with a pore size of 60 nm, but no low surface energy barrier layer was formed, and the contact angle of the filler surface was about 40° (similar to the unmodified surface).

[0064] (2) Performance test results: channel retention rate 45%; minimum reflection loss -11.3dB, effective absorption bandwidth 1.8GHz; both the anti-blocking effect and the absorption performance are poor, proving that a single bottleneck structure cannot effectively prevent polymer melt from entering the channel, and a dual anti-blocking mechanism is indispensable. Experimental examples (mechanism verification data)

[0065] To further verify the anti-clogging mechanism, parameter control rules, and performance advantages of the surface modification method of the present invention, the following series of experiments were conducted. All experiments were based on Example 1, with only a single variable changed to ensure the scientific validity and reliability of the experimental data.

[0066] 5.1 Orifice Size Adjustment Experiment

[0067] Using the chemical vapor deposition (CVD) conditions of Example 1, only the deposition time was changed, and the orifice size was statistically analyzed by SEM (n=50). The test results are shown in Table 2, clarifying the control law of orifice size.

[0068] Table 2. Deposition time and average orifice size

[0069] Deposition time (h) Average orifice size (nm) Internal dimensions of the hole (μm) Contact angle (°) 0.5 150 0.5~2 115 1.0 110 0.5~2 115 2.0 75 0.5~2 115 2.5 60 0.5~2 115 3.0 35 0.5~2 115 4.0 20 0.5~2 115

[0070] Experimental results analysis: By adjusting the deposition time, the pore size can be precisely controlled within the range of 20~150nm, and the internal pore size remains consistently between 0.5~2μm. The pore size is always smaller than the internal size (≥500nm), proving that this invention can achieve precise fabrication of the pore bottleneck structure through simple parameter adjustment, meeting different anti-clogging requirements. Simultaneously, the contact angle remains consistently at 115°, indicating that the deposition time has no significant impact on the surface properties of the low surface energy barrier layer, ensuring the stable functioning of the chemical anti-wetting mechanism.

[0071] 5.2 Experiment on the Correspondence between Orifice Size and Channel Retention Rate

[0072] Modified (FeCoNiMnCr)Ox fillers with different pore sizes were prepared using different deposition times. Nylon 66 composite materials were prepared according to the composite process in Example 1. The pore retention rate was statistically analyzed by mercury intrusion porosimetry and SEM, and the microwave absorption performance was tested to explore the influence of pore size on the anti-clogging effect and microwave absorption performance. The results are shown in Table 3.

[0073] Table 3. Deposition time, pore retention rate, and minimum reflection loss

[0074] Deposition time (h) Channel retention rate (%) Minimum reflection loss (dB) 0.5 62 -15.2 1.0 73 -18.6 2.0 82 -23.4 2.5 88 -27.3 3.0 89 -26.8 4.0 87 -25.9

[0075] Experimental results analysis: When the aperture size decreased from 150 nm to 60 nm, the channel retention rate gradually increased from 62% to 88%, and the minimum reflection loss increased from -15.2 dB to -27.3 dB. This indicates that moderate narrowing of the bottleneck structure (aperture size 60~75 nm) can significantly enhance the physical confinement effect and improve the anti-blocking and absorption performance. When the aperture size was further reduced to below 35 nm, the channel retention rate tended to stabilize (87%~89%), but the reflection loss decreased slightly. The reason for this is that excessive narrowing of the aperture may affect the efficiency of electromagnetic waves entering the channel to some extent, resulting in a slight decrease in scattering loss. Therefore, it is preferable to control the aperture size within the range of 35~100 nm to achieve the best balance between anti-blocking effect and absorption performance. This data further confirms that the present invention can achieve precise control of the aperture size by adjusting the deposition parameters, which directly affects the anti-blocking effect and absorption performance.

[0076] 5.3 Contact Angle Test Experiment

[0077] Using a high-temperature contact angle meter, the contact angles of unmodified porous high-entropy oxide, the modified filler of Example 1, and the PDMS modified filler (Example 3, not listed separately) were tested at different polymer processing temperatures to verify the chemical anti-wetting effect of the low surface energy barrier layer. The results are shown in Table 4.

[0078] Table 4. Contact Angle Test Results

[0079] filler surface Contact angle (°) of Nylon 66 melt (270℃) Contact angle (°) of PP melt (190℃) PC melt (250℃) contact angle (°) Contact angle (°) of epoxy prepolymer (80℃) Unmodified 28 24 30 35 Example 1 (Fluorosilane Modification) 115 112 114 118 Example 3 (PDMS Modification) 98 (Tends to decompose) 110 96 105

[0080] Analysis of experimental results: The contact angles of the unmodified porous high-entropy oxide surfaces were all below 35°, making it easy for polymer melts to spread and wet the surfaces, and then penetrate the pores. After modification with fluorosilane in Example 1, the contact angles were all ≥112°, which met the requirements of this invention and could effectively inhibit melt wetting. When the PDMS modification was at a processing temperature ≤250°, the contact angle was ≥105°, and the anti-wetting effect was good. However, at 270° (the processing temperature of Nylon 66), the contact angle dropped to 98°, and PDMS showed a tendency to decompose. Therefore, it is clear that PDMS is only suitable for polymer systems with a processing temperature ≤250°, which further verifies the rationality of the selection of low surface energy barrier layer materials.

[0081] 5.4 XPS / EDS Elemental Analysis Experiment

[0082] Using the modified (FeCoNiMnCr)Ox from Example 1 as a sample, the distribution of element F (a characteristic element of the fluorosilane barrier layer) was analyzed by XPS surface scanning to verify the selective modification effect. The results are shown in Table 5.

[0083] Table 5. Distribution of F element in Example 1

[0084] Test location F atomic percentage (at%) outer surface of particles 13.2 Orifice edge (10nm from the edge) 8.5 Inside the pore (more than 200 nm from the pore opening) 0.4 Unmodified particle surface 0.1

[0085] Experimental results analysis: F element is mainly distributed on the outer surface of the particles and the edge of the pores, with atomic percentages of 13.2% and 8.5%, respectively, proving that the low surface energy barrier layer is mainly constructed on the surface and pores; while in the pores more than 200 nm away from the pores, the F atomic percentage is only 0.4%, far below the requirement of ≤1%, confirming that the pores are basically not covered by the barrier layer and remain open, further verifying the effectiveness of the selective modification of the present invention.

[0086] 5.5 Comparison Experiment of BET Specific Surface Area Retention Rate

[0087] Taking the (FeCoNiMnCr)Ox / Nylon 66 system as an example, the BET specific surface area retention rate of Comparative Examples 1 and 1-3 was compared to further verify the pore retention effect. The results are shown in Table 6.

[0088] Table 6. Channel Retention Rate

[0089] sample Original BET (m² / g) BET (m² / g) after compounding Retention rate (%) Example 1 (Dual Modification) 85 75 88 Comparative Example 1 (Unmodified) 85 12 14 Comparative Example 2 (low surface energy only) 85 53 62 Comparative Example 3 (bottleneck only) 85 38 45

[0090] Experimental Description: The BET test method after composite formation involves calcining the composite material at 500℃ in air for 2 hours to remove the polymer matrix, and then taking the residual porous high-entropy oxide for BET testing. Independent experiments verified that this calcination condition has only a -2.5% effect (85→82.9 m² / g) on ​​the BET specific surface area of ​​pure (FeCoNiMnCr)Ox, which is negligible, and the test results are reliable.

[0091] Analysis of experimental results: The BET specific surface area retention rate of Example 1 was as high as 88%, proving that the dual anti-blocking mechanism effectively protected the pore structure; while the retention rates of Comparative Examples 1 to 3 were significantly lower than those of Example 1, with the retention rate of the unmodified sample being only 14%, further confirming the superiority of the dual anti-blocking mechanism of the present invention and the limitations of the single anti-blocking mechanism.

[0092] 5.6 Comparison Experiment of Absorption Performance

[0093] The reflection loss of the composite materials of each embodiment and comparative example was tested in the 2-18 GHz frequency band using the bow method. The thickness of all samples was 2.0 mm to ensure consistent test conditions. The results are shown in Table 7.

[0094] Table 7. Comparison of Absorption Performance

[0095] sample Minimum reflection loss (dB) Effective bandwidth (≤-10dB, GHz) Example 1 -27.3 5.6 Example 2 -26.8 5.3 Comparative Example 1 -8.5 <1 Comparative Example 2 -15.2 3.1 Comparative Example 3 -11.3 1.8

[0096] As can be seen from the above results, the absorption performance of each embodiment of the present invention is significantly better than that of the comparative example, and the specific analysis is as follows.

[0097] First, the dual anti-blocking design of this invention significantly improves microwave absorption performance. Comparing Example 1 and Comparative Example 1, it can be seen that the porous high-entropy oxide (Comparative Example 1) without any surface modification, after being melt-blended with nylon 66, has its pores completely filled by the polymer, resulting in severely deteriorated impedance matching, a minimum reflection loss of only -8.5dB, and an effective bandwidth of less than 1GHz, essentially losing its microwave absorption function. However, Example 1, after being treated with the surface modification method of this invention, exhibits a high pore retention rate of 88% due to the dual anti-blocking effect of the low surface energy barrier layer and the pore bottleneck structure, achieving good impedance matching, a minimum reflection loss of -27.3dB, and an effective bandwidth of 5.6GHz, resulting in a microwave absorption performance improvement of more than 3 times. Example 2 also demonstrates excellent microwave absorption performance, with a minimum reflection loss of -26.1dB and an effective bandwidth of 5.2GHz.

[0098] Second, the synergistic effect of the dual anti-blocking mechanism is significantly better than any single mechanism. Comparing Example 1 with Comparative Examples 2 and 3, it is clear that neither single mechanism in the dual anti-blocking mechanism can achieve the desired effect. Comparative Example 2 only has a low surface energy barrier layer without a significant pore bottleneck structure (pore size is similar to the internal size, approximately 0.5 μm). Although the contact angle is still 115°, the pore size is too large to effectively block the intrusion of nylon 66 molecular chains, resulting in a pore retention rate of only 62%, a minimum reflection loss of -15.2 dB, and an effective bandwidth of 3.1 GHz. Comparative Example 3 only has a pore bottleneck structure (pore size 60 nm) without a low surface energy barrier layer (contact angle approximately 40°). Although the pore size is small enough, due to the lack of chemical anti-wetting effect, the polymer melt can still enter the pores through capillary action, resulting in a pore retention rate of only 45%, a minimum reflection loss of -11.3 dB, and an effective bandwidth of only 1.8 GHz. The above comparison fully demonstrates that the synergistic effect of the low surface energy barrier layer and the orifice bottleneck structure is indispensable. Only when both exist simultaneously can the best anti-blocking effect and wave absorption performance be achieved.

[0099] Third, the present invention exhibits excellent performance in various high-entropy oxide systems. A comparison of Examples 1 and 2 shows that both high-entropy oxides with different compositions achieve excellent microwave absorption performance. The (FeCoNiMnCr)Ox system (Example 1) has a minimum reflection loss of -27.3 dB and an effective bandwidth of 5.6 GHz; the (TiZrHfSnCe)O2 system (Example 2) has a minimum reflection loss of -26.1 dB and an effective bandwidth of 5.2 GHz. Both exhibit similar performance and meet the requirements for structural microwave absorbing materials, allowing selection based on specific application scenarios and requirements for dielectric properties, density, etc.

[0100] Fourth, the absorption performance of this invention far surpasses that of the unmodified system, reaching the level required for engineering applications. Comparative Example 1 has a minimum reflection loss of only -8.5 dB, meaning that only about 86% of the electromagnetic waves are absorbed, with about 14% still reflected, failing to meet the practical requirements of stealth or electromagnetic compatibility. In contrast, Examples 1 and 2 of this invention achieve minimum reflection losses of -27.3 dB and -26.1 dB, respectively, corresponding to absorption rates of 99.8% and 99.75%. The effective bandwidths with reflection losses ≤ -10 dB reach 5.6 GHz and 5.2 GHz, respectively, covering the main frequency bands for radar detection (C-band, X-band, Ku-band), fully meeting the performance requirements of structural absorbing materials in fields such as automotive electronics, 5G communication, and military stealth.

[0101] In summary, this invention successfully solves the technical problem of pore blockage in polymer melting of porous high-entropy oxides through a dual anti-blocking design of a low surface energy barrier layer and a pore bottleneck structure. The resulting composite material achieves broadband strong absorption in the 2~18GHz frequency band, and its wave absorption performance is significantly better than that of the unmodified system and the single-mechanism modified system, which has clear engineering application value. Industrial Application Examples

[0102] Taking the modified porous (FeCoNiMnCr)Ox / Nylon 66 microwave absorbing composite material of Example 1 as an example, an automotive electronic control unit (ECU) housing (wall thickness 2mm) was prepared by injection molding. Testing showed that the housing exhibited an average electromagnetic wave reflection loss of ≤-22dB in the 2~18GHz frequency band, effectively shielding against external electromagnetic interference. Its mechanical properties met automotive industry standards (tensile strength ≥35MPa, notched impact strength ≥6kJ / m²), and it reduced weight by approximately 40% compared to traditional metal housings. Taking the modified (TiZrHfSnCe)O2 / Nylon 66 microwave absorbing composite material of Example 2 as an example, it can be used to prepare 5G communication equipment housings, possessing both microwave absorption capabilities and excellent thermal stability (heat distortion temperature 135℃). This material can also be used in drone fuselage structural components, etc.

Claims

1. A surface modification method for preventing pore blockage in porous high-entropy oxides, characterized in that, Includes the following steps: (a) Providing a porous high-entropy oxide, wherein the porous high-entropy oxide has a porosity of 30% to 70% and a pore size of 0.2 to 10 μm; (b) By using vapor deposition or liquid self-assembly process, a low surface energy barrier layer is selectively constructed on the outer surface of the porous high entropy oxide particles and at the pore openings. At the same time, the diffusion restriction effect of the precursor at the pore openings during the deposition process is utilized to form a bottleneck structure with the pore opening size smaller than the pore internal size. (c) The thickness of the low surface energy barrier layer is 5~50nm, and the low surface energy barrier layer makes the contact angle between the target polymer melt and the surface of the modified filler ≥100° at the corresponding polymer processing temperature. (d) The aperture size of the pore bottleneck structure is 10~150nm, and the aperture size is smaller than the internal size of the pore. The internal size of the pore is consistent with the pore size range of the porous high-entropy oxide in step (a), which is 0.2~10μm.

2. The method according to claim 1, characterized in that, The porous high-entropy oxide is one or more of (FeCoNiMnCr)Ox or (TiZrHfSnCe)O2, or a composite of the two in any proportion.

3. The method according to claim 1, characterized in that, The material of the low surface energy barrier layer is selectively selected according to the polymer processing temperature: when the polymer processing temperature is >250℃, fluorosilane is selected; when the polymer processing temperature is ≤250℃, fluorosilane or polydimethylsiloxane (PDMS) is selected.

4. The method according to claim 1, characterized in that, The vapor deposition is chemical vapor deposition, and the deposition conditions are: pressure 10~100Pa, precursor partial pressure 5~30Pa, temperature 60~150℃, and time 1~6h; the liquid phase self-assembly is dip coating or spray coating, the concentration of the solution used is 0.5~2wt%, and the coating is cured at 60~120℃ for 1~4h.

5. The method according to claim 1, characterized in that, By adjusting the vapor deposition time or the solution concentration of liquid phase self-assembly, the pore size can be continuously adjusted within the range of 10~150nm, and the pore size is always smaller than the internal size of the pore.

6. A surface-modified porous high-entropy oxide prepared by the method according to any one of claims 1-5, characterized in that, The outer surface and pores of the porous high-entropy oxide have a low surface energy barrier layer and a pore bottleneck structure, and the atomic percentage of the characteristic element of the barrier layer inside the pores at a distance >200 nm from the pores is ≤1%; the characteristic element is fluorine (F) or silicon (Si), determined by XPS or EDS.

7. The application of the method according to any one of claims 1-5 in the preparation of polymer-based microwave absorbing materials, characterized in that, The porous high-entropy oxide obtained by the surface modification method is mixed with a polymer matrix and molded to prepare a polymer-based microwave absorbing composite material that prevents pore blockage. The molding method is as follows: for thermoplastic resins, melt processing is used; for thermosetting resins, casting or molding curing is used, and the thermosetting system needs to be vacuum degassing before molding.

8. The application according to claim 7, characterized in that, The polymer matrix is ​​a thermoplastic resin or a thermosetting resin; the thermoplastic resin is nylon 66; the thermosetting resin is one or more of epoxy resin and phenolic resin.

9. The application according to claim 7, characterized in that, In the polymer-based microwave absorbing composite material, the mass fraction of each component is as follows: 6%~18% of surface-modified porous high-entropy oxide, nylon 66 matrix to make up to 100%, interface modifier 0.5%~2%, dispersant 0.3%~1.5%, and antioxidant 0.2%~1%; the interface modifier is maleic anhydride grafted polyolefin elastomer (POE-g-MAH) or aminosilane; the dispersant is calcium stearate or ethylene bis-stearamide; and the antioxidant is a compound of hindered phenols and phosphites.

10. The application according to claim 7 or 9, characterized in that, According to ASTM D638 standard, the tensile strength of the polymer-based microwave absorbing composite material is ≥35MPa.