Fluorine-modified super-hydrophobic low-dielectric aerogel composite material and preparation method thereof

Abstract

The invention relates to a fluorine-modified super-hydrophobic low-dielectric aerogel composite material and a preparation method thereof, belongs to the field of functional composite materials, and solves at least one of the problems of dielectric property deterioration of traditional aerogel in a high-humidity environment, high framework brittleness caused by fluorine modification, insufficient mechanical strength and heat insulation efficiency, easiness in structure collapse and the like. The invention relates to a preparation method of a fluorine-modified super-hydrophobic low-dielectric aerogel composite material. The preparation method comprises the following steps: preparing precursor sol; injecting the precursor sol into the polyimide foam skeleton to form a gel complex; and sequentially carrying out solvent replacement and normal-pressure drying on the gel complex. The prepared aerogel composite material has hydrophobicity, low dielectric loss and dielectric constant and good mechanical strength, and keeps excellent dielectric stability and moisture absorption resistance in a high-temperature and high-humidity environment.

Description

Technical Field

[0001] This invention relates to the field of functional composite materials technology, and in particular to a fluorine-modified superhydrophobic low-dielectric electrogel composite material and its preparation method. Background Technology

[0002] In modern aerospace and high-frequency communication fields, radar radomes and other wave-transparent structural components face the challenges of harsh all-weather service environments, especially under conditions of high humidity, condensation, and rain erosion. Although traditional porous organosilicon aerogels have a certain degree of hydrophobicity, their abundant nanopores are prone to water molecule adsorption and capillary condensation. Given the extremely high dielectric constant and high loss of water, even a small amount of moisture absorption can lead to severe "wet dielectric failure" of the material. Existing surface coatings are prone to peeling and failure under high-speed airflow. Traditional bulk fluorine modification technology often disrupts the continuity of the siloxane skeleton due to the large steric hindrance effect of long-chain fluorine groups, resulting in a significant decrease in the material's mechanical strength and a significant increase in brittleness, making it difficult to meet the requirements of load-bearing structures. Therefore, there is an urgent need to develop a wave-transparent composite material that combines bulk superhydrophobicity, excellent resistance to humid heat and dielectric stability, and high mechanical strength to meet the needs of precise signal transmission under complex weather conditions. Summary of the Invention

[0003] Based on the above analysis, the present invention aims to provide a fluorine-modified superhydrophobic low-dielectric gel composite material and its preparation method, in order to solve at least one of the following problems: the dielectric properties of traditional aerogels deteriorate in high humidity environments, the brittleness of the skeleton caused by fluorine modification, insufficient mechanical strength and thermal insulation efficiency, and easy structural collapse.

[0004] The objective of this invention is achieved through the following technical solution: This invention provides a method for preparing a fluorine-modified superhydrophobic low-dielectric electrogel composite material, comprising the following steps: S1. Preparation of precursor sol: The precursor sol is obtained by co-hydrolysis and polycondensation reaction of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) dissolved in water in a first organic solvent under the catalysis of an alkaline catalyst. S2. The precursor sol is injected into the polyimide foam skeleton, and then a gelation reaction is carried out to allow the organosilicon molecular chains in the precursor sol to grow and cross-link in situ on the surface of the polyimide foam skeleton, forming a gel composite with an interpenetrating network coupled with a micron skeleton and fluorine-modified nanoaerogel. S3. The gel composite is subjected to solvent replacement and atmospheric pressure drying in sequence to obtain the fluorine-modified superhydrophobic low dielectric electrogel composite material.

[0005] Furthermore, the molar ratio of isobutyltrimethoxysilane IBTMS, dimethyldimethoxysilane DMDMS, perfluorooctyltriethoxysilane PFOTES to vinyltriethoxysilane VTES is (3~6):1:(0.1~0.5):0.5.

[0006] Furthermore, the solid content of the precursor sol is 10~30 wt.%; and / or, The bulk density of the polyimide foam skeleton is 0.05~0.30 g / cm³. 3 .

[0007] Furthermore, the temperature in the co-hydrolysis-condensation reaction is controlled at 23~27℃; and / or, The stirring rate in the co-hydrolysis condensation reaction is 400~700 rpm.

[0008] Furthermore, after the co-hydrolysis and polycondensation reaction is completed, the resulting precursor sol is subjected to ultrasonic homogenization, degassing, and filtration in sequence. The parameters of the ultrasonic homogenization process include: ultrasonic frequency of 20~30kHz, peak power of 200~600W, and processing time of 10~60min.

[0009] Furthermore, the gelation is static gelation, which includes the following steps: (1) Degassing stage at room temperature: let stand at 20-25℃ for 1-2 hours; (2) Programmed temperature rise stage: The temperature rises from room temperature to the target gel temperature at a rate of 1~5℃ / min, where the target gel temperature is 60~90℃; (3) Constant temperature gelation stage: gelation is completed by keeping the temperature at the target gelation temperature for 12~48h.

[0010] Furthermore, the alkaline catalyst is tetramethylammonium hydroxide; and / or, The amount of alkaline catalyst added is 0.1-1.0 wt.% of the total mass of the reaction mixture, where the total mass of the reaction mixture refers to the sum of the masses of isobutyltrimethoxysilane IBTMS, dimethyldimethoxysilane DMDMS, perfluorooctyltriethoxysilane PFOTES, vinyltriethoxysilane VTES, water, and the first organic solvent.

[0011] Furthermore, in step S1, the molar ratio of water to alkoxy groups is 0.4 to 1.0, and the alkoxy groups include methoxy groups in IBTMS and DMDMS, and ethoxy groups in PFOTES and VTES.

[0012] Furthermore, in step S3, the atmospheric pressure drying includes: Air drying stage: The gel composite after solvent replacement is heated from room temperature to a first target temperature at a first heating rate, and held at the first target temperature for a first holding time. Heat treatment stage: Continue to heat from the first target temperature to the second target temperature at a second heating rate, and maintain the second target temperature for a second holding time; The first heating rate and the second heating rate are each independently 5-15℃ / h; the first target temperature is 70-90℃; the second target temperature is 180-220℃; and the first holding time and the second holding time are each independently 4-12h.

[0013] This invention provides a fluorine-modified superhydrophobic low-dielectric electrogel composite material, prepared by the aforementioned method. The properties of the fluorine-modified superhydrophobic low-dielectric electrogel composite material are as follows: water contact angle ≥150° at room temperature, roll-off angle ≤10°; density 0.13~0.28 g / cm³. 3 The dielectric constant at room temperature is ≤1.45, and the dielectric loss is ≤0.0032. The humid heat resistance is as follows: after being placed in an environment with a relative humidity of 95% and a temperature of 60℃ for 48 hours, the dielectric constant change rate of the fluorine-modified superhydrophobic low dielectric electrogel composite material is ≤2.96%, and the moisture absorption rate is ≤1.35%.

[0014] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: (1) To address the problem of “dielectric performance deterioration under high humidity conditions”, perfluorooctyltriethoxysilane (PFOTES) is introduced as a low-polarity hydrophobic unit to participate in co-hydrolysis condensation. Its long-chain perfluoroalkyl group has extremely low surface energy and electronic polarizability. During the condensation process, it is connected to the organosilicon network through Si-O-Si bonds and forms a low-polarity fluorocarbon shield on the material bulk and pore surface. This low-polarity fluorocarbon shield fundamentally blocks the adsorption and condensation of highly polar water molecules in the pores through the principle of surface energy minimization and capillary effect suppression, thereby avoiding “wet dielectric failure” caused by the high dielectric constant and high loss factor of water. It endows the material bulk with superhydrophobic properties and extremely low intrinsic dielectric loss, effectively preventing moisture from damaging the dielectric properties.

[0015] (2) To address the problem of "high brittleness of aerogels caused by traditional fluorine modification", dimethyldimethoxysilane (DMDMS) was introduced as a flexible stress dissipation unit, which was then used in situ for ternary controlled co-condensation with rigid unit IBTMS and low surface energy unit PFOTES. The dimethylsiloxane segments contained in DMDMS have excellent molecular flexibility and low rotational barrier, and act as "molecular hinges" in the solidified network. When the introduction of long-chain fluorine groups causes local stress concentration in the network, the flexible segments of DMDMS effectively dissipate internal stress through conformational transformation and entropic elastic retraction, achieving "flexible compensation for steric hindrance effect". Thus, while maintaining the superhydrophobic properties of high fluorine content, the spatial continuity and mechanical toughness of the silicon-oxygen network are maintained.

[0016] (3) To address the problem of insufficient mechanical strength and thermal insulation efficiency, polyimide foam was selected as the macroscopic reinforcing skeleton. An in-situ gelation process was used to react the precursor sol within the foam pores to generate fluorine-modified nano-aerogels, forming a bicontinuous interpenetrating network of "micron-sized polyimide foam skeleton / fluorine-modified nano-organic silica aerogels". The polyimide foam skeleton was used to bear the macroscopic mechanical load, and a ternary synergistic design method was adopted at the molecular level: "low-polarization fluorocarbon shielding (PFOTES) - flexible steric hindrance compensation (DMDMS) - rigid skeleton support (IBTMS)". The flexible segments of DMDMS effectively offset the internal stress introduced by the fluorocarbon chains, alleviating network embrittlement; IBTMS was used to construct a rigid silica skeleton and provide structural stability to the network, achieving skeleton toughening under high fluorine content, thereby significantly improving the mechanical properties and environmental adaptability of the composite material. Furthermore, the in-situ generated fluorine-modified nano-aerogels, due to their extremely high porosity and nanoscale pore walls, effectively inhibited the thermal motion of gas molecules and solid-state heat conduction, endowing them with excellent thermal insulation performance.

[0017] (4) To address the problem of structural collapse in traditional aerogel composites, this invention injects a precursor sol into polyimide foam and performs in-situ gelation, allowing the organosilicon network to grow and crosslink in situ on the surface and within the pores of the foam skeleton, forming a bicontinuous interpenetrating network structure of "micron-sized polyimide foam skeleton / fluorine-modified nano-organosilicon aerogel". This structure effectively suppresses the drying shrinkage and stress collapse of the aerogel network, resulting in better structural stability. For example, see... Figures 2-4 The composite material obtained in the embodiments of the present invention has no structural collapse and good structural integrity.

[0018] (5) In some preferred embodiments, by limiting the molar ratio range of silane precursors (IBTMS, DMDMS, PFOTES, VTES), the precise ratio and synergistic effect between rigid units, flexible units, low surface energy units and crosslinking units are achieved. While ensuring the superhydrophobicity of fluorine modification, the mechanical toughness, structural continuity and low dielectric properties of the network are effectively balanced, and the performance degradation caused by excessive single component (such as increased brittleness, decreased hydrophobicity or increased dielectric loss) is avoided.

[0019] (6) In some preferred embodiments, by controlling the solid content of the precursor sol and the bulk density of the polyimide foam skeleton, the ratio of organic phase, skeleton phase and pore phase in the composite material is precisely controlled, thereby optimizing the synergistic relationship between its dielectric properties, mechanical strength and thermal insulation efficiency while ensuring the superhydrophobicity, lightweight and structural integrity of the material.

[0020] (7) In some preferred embodiments, by controlling the stirring rate and temperature range during the co-hydrolysis and polycondensation process, the uniformity and controllability of the reaction system are ensured, the full hydrolysis and orderly polycondensation of the precursor are promoted, which is conducive to the formation of a uniform organosilicon network with few defects, laying the foundation for subsequent gelation and the stability of the final performance.

[0021] (8) In some preferred embodiments, by performing ultrasonic homogenization, degassing and filtration on the precursor sol, bubbles and unreacted agglomerates in the precursor sol are effectively eliminated, improving the uniformity, stability and injectability of the sol, thereby reducing structural defects in the final composite material and ensuring overall performance stability and uniformity.

[0022] (9) In some preferred embodiments, a gentle and controllable gelation process is achieved by adopting a staged (room temperature degassing, programmed temperature rise, and isothermal gelation) static gelation process, which is conducive to the uniform growth of the organosilicon network in the polyimide skeleton and the formation of a stable interpenetrating structure, avoiding stress concentration and structural inhomogeneity caused by rapid gelation.

[0023] (10) In some preferred embodiments, by selecting tetramethylammonium hydroxide as an alkaline catalyst and controlling the amount of alkaline catalyst added, a suitable and stable catalytic environment is provided, ensuring the high efficiency and controllability of the ternary co-hydrolysis polycondensation reaction, which helps to form a siloxane network with moderate crosslinking degree and complete structure, while avoiding the adverse effects of catalyst residue on the dielectric properties of the material.

[0024] (11) In some preferred embodiments, by controlling the molar ratio of water to total alkoxy groups, the degree of hydrolysis reaction is precisely controlled, which ensures sufficient hydrolysis to generate the necessary silanols for polycondensation and crosslinking, while avoiding excessive hydrolysis that leads to excessively rapid gelation or phase separation, thereby obtaining a precursor sol with uniform structure and stable performance.

[0025] (12) In some preferred embodiments, by designing an atmospheric pressure drying process that includes an air-drying stage and a multi-stage heat treatment, the nanoporous structure of the material is gradually solidified and stabilized while the solvent is gently removed, effectively suppressing shrinkage and collapse during the drying process, so that the material can obtain low density, heat resistance and excellent comprehensive performance without supercritical drying (especially in all-weather service environment, when the moisture content increases, it can still maintain excellent dielectric and mechanical properties).

[0026] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0027] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts. Figure 1 This is a schematic flowchart of the preparation method of the fluorine-modified superhydrophobic low-dielectric electrogel composite material provided in the embodiments of the present invention; Figure 2 Macroscopic images of fluorine-modified superhydrophobic low-dielectric electrogel composite materials obtained by the preparation method provided in the embodiments of the present invention; Figure 3 SEM image of the fluorine-modified superhydrophobic low-dielectric electrogel composite material obtained by the preparation method provided in the embodiments of the present invention; wherein, part B is a polyimide foam skeleton; Figure 4 for Figure 3 SEM image of the aerogel after magnification of part A in the middle. Detailed Implementation

[0028] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0029] In a first aspect, the present invention provides a method for preparing a fluorine-modified superhydrophobic low-dielectric electrogel composite material, comprising the following steps: S1. Preparation of precursor sol: The precursor sol is obtained by co-hydrolysis and polycondensation reaction of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) dissolved in water in a first organic solvent under the catalysis of an alkaline catalyst. S2. The precursor sol is injected into the polyimide foam skeleton, and then a gelation reaction is carried out to allow the organosilicon molecular chains in the precursor sol to grow and cross-link in situ on the surface of the polyimide foam skeleton, forming a gel composite with an interpenetrating network coupled with a micron skeleton and fluorine-modified nanoaerogel. S3. The gel composite is subjected to solvent replacement and atmospheric pressure drying in sequence to obtain the fluorine-modified superhydrophobic low dielectric electrogel composite material.

[0030] Compared with existing technologies, this invention solves the problems of dielectric performance failure of traditional aerogels in high humidity environments and increased brittleness of the skeleton caused by fluorine modification by constructing a ternary molecular network of "fluorocarbon shielding-rigid-flexible synergy" and a "micro-nano double continuous interpenetrating structure". The resulting aerogel composite material has hydrophobicity, low dielectric loss and dielectric constant, good mechanical strength, and maintains excellent dielectric stability and moisture resistance in high temperature and high humidity environments.

[0031] The core of this invention lies in abandoning the traditional hygroscopic hydrophilic formulation or the brittle simple fluorine-modified formulation, and using the rigid unit isobutyltrimethoxysilane (IBTMS), the flexible unit dimethyldimethoxysilane (DMDMS) and the low surface energy unit perfluorooctyltriethoxysilane (PFOTES) for in-situ ternary controlled co-condensation to form an organosilicon precursor sol with fluorocarbon chain modification.

[0032] 1. Low-polarization fluorocarbon shielding: Utilizing the extremely low surface energy and electronic polarizability of the long-chain fluorocarbon groups of PFOTES, the material is endowed with superhydrophobic properties and extremely low intrinsic dielectric loss, fundamentally blocking the adsorption and condensation of water molecules in the pores and preventing wet dielectric failure.

[0033] 2. Flexible compensation for steric hindrance: To address the problem that the large steric hindrance of long-chain fluorine groups can easily disrupt network continuity and lead to brittleness, the flexible segments of DMDMS (D unit) are used as "molecular hinges" to effectively alleviate the internal stress caused by the introduction of fluorocarbon chains, thus maintaining the mechanical toughness of the skeleton while maintaining a high fluorine content.

[0034] 3. Multi-level network reinforcement and anchoring: Using polyimide foam as a macroscopic reinforcing skeleton, organosilicon precursor sol is injected into the polyimide foam skeleton to construct an interpenetrating network coupled with micron skeleton and nano aerogel, which synergistically improves mechanical strength and environmental adaptability.

[0035] Specifically, the molar ratio of isobutyltrimethoxysilane IBTMS, dimethyldimethoxysilane DMDMS, perfluorooctyltriethoxysilane PFOTES to vinyltriethoxysilane VTES is (3~6):1:(0.1~0.5):0.5.

[0036] For example, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is (3, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0):1:(0.1, 0.15, 0.20, 0.25, 0.3, 0.4, 0.5):0.5.

[0037] Preferably, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is (3~5):1:(0.1~0.3):0.5.

[0038] Specifically, the solid content of the precursor sol is 10~30 wt.%.

[0039] For example, the solid content of the precursor sol is 10 wt.%, 12 wt.%, 15 wt.%, 17 wt.%, 20 wt.%, 22 wt.%, 25 wt.%, 27 wt.%, or 30 wt.%.

[0040] Specifically, in the preparation of the precursor sol, the mass ratio of the sum of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) to the mass of the first organic solvent is 0.1139:1 to 0.4691:1, corresponding to a solid content of 10~30 wt.% in the precursor sol.

[0041] For example, the mass ratio of the sum of the masses of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) to the mass of the first organic solvent is 0.15:1, 0.20:1, 0.25:1, 0.30:1, 0.35:1, 0.4:1, and 0.45:1.

[0042] Preferably, the ratio of the total mass of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) to the mass of the first organic solvent is 0.1830:1 to 0.3571:1, corresponding to a solid content of 15 to 25 wt.% in the precursor sol.

[0043] Specifically, the molar ratio of water to alkoxy groups is controlled at 0.4-1.0, and the alkoxy groups include methoxy groups in IBTMS and DMDMS, and ethoxy groups in PFOTES and VTES.

[0044] For example, the molar ratio of water to alkoxy groups is 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, or 1.0; preferably, the molar ratio of water to alkoxy groups is 0.6 to 0.8.

[0045] Specifically, the alkaline catalyst is tetramethylammonium hydroxide (TMAH).

[0046] Specifically, the amount of alkaline catalyst added is 0.1-1.0 wt.% of the total mass of the reaction mixture, where the total mass of the reaction mixture refers to the sum of the masses of isobutyltrimethoxysilane IBTMS, dimethyldimethoxysilane DMDMS, perfluorooctyltriethoxysilane PFOTES, vinyltriethoxysilane VTES, water, and the first organic solvent.

[0047] For example, the amount of alkaline catalyst added is 0.1 wt.%, 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, or 1.0 wt.% of the total mass of the reaction mixture; preferably 0.2 wt.% to 0.4 wt.%.

[0048] Specifically, the bulk density of the polyimide foam is 0.05~0.30 g / cm³. 3 Preferably, the concentration is 0.08~0.12 g / cm³. 3 .

[0049] Preferably, the polyimide foam has an open cell ratio of ≥80% and an average pore size of 50~1000μm. More preferably, the polyimide foam has an open cell ratio of ≥85%, for example, 85~90%, and an average pore size of 100~500μm.

[0050] Preferably, the polyimide foam has a modulus of 3~8 MPa, a strength of 0.1~0.3 MPa, and a glass transition temperature of 300~380℃.

[0051] Specifically, the temperature during the co-hydrolysis and polycondensation process is controlled at 23~27℃. Preferably, the temperature during the co-hydrolysis and polycondensation process is controlled at 24~26℃, for example, 25℃; the temperature fluctuation is controlled within ±2℃.

[0052] Specifically, the stirring rate during the co-hydrolysis and polycondensation process is 400~700 rpm, for example, 500 rpm or 600 rpm.

[0053] In some embodiments, the preparation of the precursor sol includes the following steps: S11. System initialization: Isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), vinyltriethoxysilane (VTES), water, and the first organic solvent are mixed evenly to form a stable initial reaction system. S12. The alkaline catalyst is pre-dissolved in a second organic solvent to prepare a catalyst dilution solution. Under continuous stirring and temperature control, the catalyst dilution solution is added dropwise to the initial reaction system in batches, and the pH value of the reaction system is maintained at 8-11.

[0054] Specifically, the mass concentration of the catalyst dilution solution is 20-30 wt.%, for example 22 wt.%, 24 wt.%, 26 wt.%, 28 wt.%, or 30 wt.%.

[0055] Specifically, in the preparation of the precursor sol, the pH value of the reaction system is controlled (8~11) by controlling the interval time between each batch and / or the dropping rate. The interval time between each batch is 5-10 min, and the dropping rate is controlled at 0.05-0.10 mL / s.

[0056] Specifically, in step S11, isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) are weighed and dissolved in a first organic solvent to prepare a solution of 10-60 wt.% (e.g., 20 wt.%, 30 wt.%, 40 wt.%, 50 wt.%). Water (preferably deionized water) is then added, and the mixture is thoroughly mixed under continuous stirring. Preferably, the stirring speed is 400-700 rpm, for example, 500 rpm.

[0057] In step S11, to ensure more uniform mixing, the mixture is first magnetically stirred at 400-700 rpm for at least 10 minutes, then placed in an ultrasonic cleaner and ultrasonically dispersed at 200-600W for at least 30 minutes to ensure uniform distribution of the reactants and form a stable and uniform initial reaction system. Preferably, in step S11, the temperature is controlled at 23-27°C during the mixing process.

[0058] For example, in step S1, the first organic solvent and the second organic solvent are each independently selected from at least one of anhydrous ethanol, isopropanol, n-propanol, and ethylene glycol monomethyl ether. Preferably, the first organic solvent and the second organic solvent are of the same type.

[0059] Preferably, after the co-hydrolysis and condensation reaction is completed, the obtained precursor sol is subjected to ultrasonic homogenization, degassing and filtration in sequence to improve the uniform dispersion and reactivity of the precursor sol, reduce the bubble content, remove gel clumps, and better ensure the stability and injectability of the precursor sol during injection.

[0060] Specifically, the ultrasonic homogenization process employs a probe-type or tank-type ultrasonic device. The parameters for the ultrasonic homogenization process include: an ultrasonic frequency of 20–30 kHz, a peak power of 200–600 W, and a processing time of 10–60 min. For example, the ultrasonic frequencies are 22 kHz, 24 kHz, 26 kHz, and 28 kHz; the peak powers are 250 W, 300 W, 350 W, 400 W, 450 W, 500 W, and 550 W; and the processing times are 10 min, 20 min, 25 min, 30 min, 40 min, and 50 min.

[0061] Preferably, in the ultrasonic homogenization process, a pulse working mode is used and a cooling circuit is used to control the processing temperature to ≤35℃.

[0062] Specifically, the pore size of the filter is 5~50μm.

[0063] Preferably, the ultrasonic frequency is 24~26kHz, the peak power is 300~500W, and the processing time is 20~30min.

[0064] Preferably, the duty cycle of the pulse working mode is 40% to 60%.

[0065] Preferably, the degassing process is carried out under a vacuum of ≤-0.1MPa for 5~30 minutes.

[0066] Preferably, the cooling circuit adopts a circulating water cooling system to control the temperature at 25~30℃.

[0067] Preferably, the filter uses a multi-layer stainless steel filter screen, and the filter screen pore size can be selected as 50μm, 25μm, 10μm, or 5μm.

[0068] Preferably, in step S2, the polyimide foam is pretreated before injection, and the pretreatment method is plasma treatment or surfactant soaking. The parameters of the plasma treatment satisfy the following relationship: C1 = (P × t1) / (ρ × V), where C1 is 500~1000; where P: plasma power, in W; t1: treatment time, in min; ρ: bulk density of polyimide foam, in g / cm³. 3 V: Volume of the polyimide foam being treated, in cm³ 3 ; The surfactant is an aqueous solution of sodium dodecyl sulfate, and satisfies the following relationship: C2 = (ω × t2) / (ρ × V), where C2 is 0.5~5; where ω: concentration of the sodium dodecyl sulfate aqueous solution, in wt.%; t2: treatment time, in min; ρ: bulk density of the polyimide foam, in g / cm³. 3 V: Volume of the polyimide foam being treated, in cm³ 3 .

[0069] Specifically, the parameters of the plasma treatment include: plasma power P of 100~300W; working gas is a mixture of helium and oxygen, with a helium to oxygen volume ratio of 100:0.5~100:2; total gas flow rate of 10~30 SLM; and treatment distance of 5~15mm. Preferably, the plasma treatment employs an atmospheric pressure plasma jet method. Preferably, the plasma treatment uses a dynamic scanning method with a scanning speed of 1~20mm / s.

[0070] Specifically, the parameters for soaking the surfactant include: the concentration ω of the sodium dodecyl sulfate aqueous solution is 0.1~5 wt.%, for example, 0.5 wt.%, 1.0 wt.%, 2.0 wt.%, 3.0 wt.%, 4.0 wt.%.

[0071] Specifically, the pretreatment temperature is 15~35℃, for example 25℃. The surface energy of the pretreated polyimide foam is increased to 50~70mN / m.

[0072] Specifically, the injection in step S2 employs a resin transfer molding process, and specifically includes the following steps: S21. Before injection, the polyimide foam is evacuated to an absolute pressure ≤50mbar; S22. Under an injection pressure of 0.05~0.5MPa, the precursor sol is injected into the polyimide foam at an injection rate of 5~50mL / min for a time of 10~30min. S23. After injection, maintain pressure for 5-60 minutes.

[0073] Specifically, the holding pressure is controlled between 0.1 and 0.3 MPa. Holding pressure promotes interfacial wetting between the silicone precursor sol and the polyimide foam skeleton and reduces local voids. In terms of mechanical properties, sufficient interfacial wetting enhances the interfacial bonding strength between the aerogel and the foam skeleton, and improves the structural integrity of the material by eliminating local voids. In terms of functional properties, uniform interfacial bonding reduces dielectric polarization while maintaining the continuity of the nanoporous structure and thermal insulation performance.

[0074] For example, in step S22, the injection pressure is 0.05 MPa, 0.10 MPa, 0.15 MPa, 0.2 MPa, 0.25 MPa, 0.3 MPa, 0.4 MPa, or 0.5 MPa. A constant flow pump is used to control the injection rate; the injection rate is 5 mL / min, 10 mL / min, 15 mL / min, 20 mL / min, 25 mL / min, 30 mL / min, 40 mL / min, or 50 mL / min; the injection time is 10 min, 15 min, 18 min, 20 min, 22 min, 25 min, or 30 min.

[0075] Preferably, in step S22, the injection pressure is 0.1~0.3MPa; the injection rate is 10~30mL / min; and the injection time is 15~25min.

[0076] Preferably, the injection process is performed in an alternating cycle of liquid injection and pressure assistance (vacuum-pressure alternating pulse mode). During the pressure assistance process, liquid injection is stopped, and the pressure assistance adopts one of the following two methods: (1) Vacuuming-decompression cycle: Perform 1-3 cycles, each cycle including: Vacuuming procedure: Reduce the system pressure to ≤-0.08MPa (gauge pressure) and maintain it for 3~10min; Decompression procedure: Restore the system pressure to the injection pressure and maintain it for 3-10 minutes; (2) Continuous negative pressure treatment: Perform 1-3 continuous negative pressure treatments, each treatment including: Reduce the system pressure to -0.08 to -0.1 MPa (gauge pressure) and maintain it for 5 to 15 minutes, then restore the system pressure to the injection pressure.

[0077] It should be noted that the present invention uses a vacuum-pressure alternating pulse process to inject the precursor sol into the polyimide foam skeleton to achieve deep and uniform impregnation. This helps to overcome the capillary resistance of high-viscosity fluorinated sol in micron-sized pores, realize the saturation filling of deep closed pores and small pores of the foam by the precursor, eliminate macroscopic defects at the interface, and thus improve the interfacial bonding strength between the aerogel phase and the foam skeleton.

[0078] Specifically, the gelation is static gelation, and the static gelation process employs a segmented temperature control program, including the following steps: (1) Degassing stage at room temperature: let stand at 20-25℃ for 1-2 hours; (2) Programmed temperature rise stage: The temperature rises from room temperature to the target gel temperature at a rate of 1~5℃ / min, wherein the target gel temperature is 60~90℃, preferably 70~80℃; (3) Constant temperature gelation stage: gelation is completed by keeping the temperature at the target gelation temperature for 12 to 48 hours, preferably 24 to 36 hours.

[0079] For example, the gelation process is carried out under the protection of dry air or inert gas; preferably, the temperature fluctuation in the reactor (preferably a closed reactor) used for gelation is controlled within ±2°C.

[0080] Preferably, an external field-assisted treatment is applied during the gelation stage. By introducing specific physical energy (mechanical or thermal energy), the sol-gel process is actively intervened at the molecular and mesoscopic scales, guiding the formation of a stable structure with stronger interfacial bonding and better nanopores, thereby further improving the overall performance. The external field-assisted treatment is selected from any of the following: (a) A slight external load of 0.1~1.0 kPa; (b) Alternating stress with a frequency of 0.01 to 1.0 Hz and a stress amplitude of 0.5 to 5.0 kPa; (c) Periodic thermal shock treatment with a temperature difference of 5~20℃ and a cycle of 5~15min.

[0081] For example, the slight external load is applied by a precision ballast platform or a pneumatic thin-film loading device, which can achieve a uniform micro-pressure of 0.1-1.0 kPa without damaging the sol-gel structure.

[0082] For example, the alternating stress is applied by a low-frequency dynamic loader or a servo reciprocating loading device to achieve a periodic light load disturbance of 0.01-1Hz.

[0083] For example, the periodic thermal shock is achieved by a programmable thermal cycle reactor or a Peltier temperature control device, which forms a periodic temperature difference of 5 to 20°C through an automatic heating and cooling program.

[0084] Preferably, the external field auxiliary treatment is applied in the middle to late stage of the isothermal gelation stage and lasts for no less than 1 / 3 of the total gelation time.

[0085] Specifically, during the gelation process, the inert gas is nitrogen or argon, and the gas flow rate is controlled at 0.5~2.0 L / min.

[0086] Specifically, in step S3, the solvent replacement process employs at least one combination of the following technical features: (1) The replacement solvent is ethanol with a water content ≤1wt%; (2) The number of replacements is ≥3 times; each replacement lasts 2~6 hours; preferably 3~4 hours; (3) The volume / mass ratio of solvent volume to gel mass in a single replacement is (2~10) mL:1g; preferably (3~5) mL:1g.

[0087] (4) The residual moisture content in the gel at the end of the replacement process is ≤0.5wt%.

[0088] For example, the replacement process employs any of the following operating modes to improve replacement efficiency: (a) Static stirring mode: The stirring speed is controlled at 100~300 rpm; (b) Circulating flow mode: The replacement solvent circulates outside the gel at a flow rate of 0.2~0.8 L / min.

[0089] Specifically, the replacement process is carried out under a negative pressure of -0.05 to -0.09 MPa.

[0090] Specifically, the temperature during the replacement process is controlled at 20-40℃, preferably 25-35℃.

[0091] It is understood that the residual moisture content is determined using the Karl Fischer method or an equivalent method.

[0092] It should be noted that by controlling the parameters of the gelation process, it is beneficial to form a continuous and uniform three-dimensional organosilicon network from the organosilicon precursor sol, which makes the microstructure of the composite material uniform and stable, thereby obtaining better dielectric properties, hydrophobicity, mechanical properties, and lightweight and thermal insulation properties.

[0093] Specifically, in step S3, the atmospheric pressure drying includes: (1) Air drying stage: The gel composite after solvent replacement is heated from room temperature to a first target temperature at a first heating rate, and kept at the first target temperature for a first holding time; (2) Heat treatment stage: Continue to heat from the first target temperature to the second target temperature at the second heating rate, and maintain the second heat treatment time at the second target temperature; The first heating rate and the second heating rate are each independently 5-15℃ / h, for example 5℃ / h, 8℃ / h, 10℃ / h, 12℃ / h, and 15℃ / h; the first target temperature is 70-90℃, the second target temperature is 180-220℃, and the first and second holding times are each independently 4-12h, for example 4h, 6h, 8h, 10h, and 12h.

[0094] It should be noted that, in the atmospheric pressure drying process, this invention actively guides the gel network to gradually release internal stress during the drying process by controlling the temperature history of air drying (70-90℃) and heat treatment (180-220℃) in stages. This constructs a stress relaxation-type segmented atmospheric pressure drying process, achieving synergistic control of solvent evaporation rate and skeleton rebound stress. Compared with traditional rapid drying, this process effectively suppresses the shrinkage and collapse of the fluorine-modified gel skeleton by slowly releasing capillary tension, ensuring the integrity of the internal nanoporous structure of the material, thereby obtaining lower thermal conductivity and superior dielectric properties.

[0095] Preferably, the first heating rate is 8~12℃ / h; and / or, the second heating rate is 5~10℃ / h.

[0096] Preferably, the first heat preservation time is 6 to 10 hours; and / or, the second heat preservation time is 4 to 6 hours.

[0097] Preferably, during the air-drying and heat-treatment stages, mechanical assistance is applied to the gel composite to relieve drying stress, the mechanical assistance including placing the gel composite on a rotating platform at 200-400 rpm or applying a gentle airflow of 0.1-0.5 kPa to it.

[0098] Secondly, the present invention provides a fluorine-modified superhydrophobic low-dielectric electrogel composite material, which is prepared by the preparation method described in the first aspect.

[0099] Specifically, the fluorine-modified superhydrophobic low-dielectric electrogel composite material possesses a ternary molecular network of "fluorocarbon shielding-rigid-flexible synergy" and a "micro-nano double continuous interpenetrating structure". The "micro-nano double continuous interpenetrating structure" refers to an interpenetrating network structure in which a micron-sized polyimide skeleton is coupled with fluorine-modified nano-aerogel.

[0100] The fluorine-modified superhydrophobic low-dielectric electrogel composite material prepared in the embodiments of the present invention exhibits excellent comprehensive properties: (a) Hydrophobicity: Water contact angle ≥150° and roll-off angle ≤10° at room temperature; (b) Density is 0.13~0.28 g / cm³ 3 It exhibits obvious lightweight characteristics; (c) The thermal conductivity at room temperature is 0.028~0.040 W / (m·K), which provides good thermal insulation performance; (d) The compressive strength is 0.21~0.85MPa, exhibiting good mechanical bearing capacity; (e) In terms of dielectric properties, the dielectric constant at room temperature is ≤1.45, and further, the dielectric constant at room temperature is ≤1.35; the dielectric loss at room temperature is ≤0.0032; the dielectric constant in the wet state is ≤1.46, and the dielectric loss in the wet state is ≤0.0038. (f) Moisture and heat resistance: After being placed in an environment with a relative humidity of 95% and a temperature of 60°C for 48 hours, the dielectric constant change rate of the fluorine-modified superhydrophobic low dielectric gel composite material is ≤2.96%, and further, the dielectric constant change rate is ≤2.0%; the moisture absorption rate is ≤1.35%, and further, the moisture absorption rate is ≤1.0%.

[0101] The above performance parameters comprehensively demonstrate that the fluorine-modified superhydrophobic low-dielectric electrogel composite material obtained by the method of this invention has bulk superhydrophobicity, extremely low dielectric loss, excellent mechanical strength, and excellent dielectric stability and moisture resistance under high temperature and high humidity environments. It effectively solves the problems of moisture absorption failure of traditional aerogels under high temperature and humidity environments and the high mechanical brittleness of fluorine-modified materials. It has broad application prospects in all-weather aerospace radar radomes and shipborne radar transparent windows.

[0102] In this invention, the fluorine-modified superhydrophobic low-dielectric electrogel composite material, compared with traditional aerogels or surface coating protective materials, maintains low density and excellent dry-state dielectric properties while significantly improving the dielectric stability and mechanical integrity of the material under high humidity, condensation, and rain erosion environments by constructing a "Ternary Synergistic Network of IBTMS-DMDMS-PFOTES". The prepared material has advantages such as a contact angle ≥150°, extremely low moisture absorption, and no deterioration of wet-state dielectric loss under high temperature, high humidity, and water immersion environments, and can be widely used in key structural components such as all-weather aerospace radar radomes and shipborne radar transparent windows.

[0103] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and comparative examples.

[0104] Example 1 This embodiment provides a method for preparing a fluorine-modified superhydrophobic low-dielectric electrogel composite material, including the following steps: S1. Preparation of precursor sol: The precursor sol is obtained by co-hydrolysis and polycondensation reaction of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) dissolved in water in anhydrous ethanol (the first organic solvent) under the catalysis of tetramethylammonium hydroxide (TMAH) (alkaline catalyst); In this embodiment, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the molar ratio of water to alkoxy groups is 0.7, the dosage of tetramethylammonium hydroxide (TMAH) is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of IBTMS, DMDMS, PFOTES, and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2629:1, and the prepared precursor sol has a solid content of 20 wt.% and is a fluorinated ternary synergistic precursor sol. The specific preparation process is as follows: S11. System initialization: Isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), vinyltriethoxysilane (VTES), water, and the first organic solvent are mixed evenly to form a stable initial reaction system. Weigh 35.7g of IBTMS, 6.0g of DMDMS, 5.1g of PFOTES, and 4.8g of VTES and dissolve them in 196.3g of anhydrous ethanol. Then add 10.1g of deionized water. At a temperature controlled at 25℃±2℃, first stir magnetically at 500rpm for 10min, then place in an ultrasonic cleaner and ultrasonically disperse at 300W for 30min to achieve thorough mixing.

[0105] S12. Dissolve 0.77g of tetramethylammonium hydroxide in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25wt.%. Under continuous stirring at 500rpm and temperature control at 25℃±2℃, add the catalyst dilution solution dropwise to the reaction system in batches. By controlling the interval between each batch and / or the dropping rate, the pH value of the reaction system is maintained at 9.5±0.2; the interval between each batch is 5min, and the dropping rate is controlled at 0.05-0.10 mL / s. After the hydrolysis and condensation reactions are completed in step S12, the obtained organosilicon precursor sol is subjected to ultrasonic homogenization treatment using a probe-type ultrasonic device. The parameters of the ultrasonic homogenization treatment include: ultrasonic frequency of 25kHz, peak power of 400W, and treatment time of 30min. During the ultrasonic homogenization treatment, a pulse working mode is adopted and the treatment temperature is controlled to be ≤35℃ with the help of a cooling circuit. After the ultrasonic homogenization treatment, the organosilicon precursor sol is degassed under a vacuum of ≤-0.1MPa for 10min. The degassed organosilicon precursor sol is then filtered through a 10μm filter to obtain an organosilicon precursor sol with a solid content of 20wt.%.

[0106] S2. The organosilicon precursor sol is injected into the polyimide foam skeleton, and then a gelation reaction is carried out to form a three-dimensional organosilicon network structure in the polyimide foam skeleton, thereby obtaining a gel composite. S20. Pretreatment of the polyimide foam: Selecting a density ρ of 0.10 g / cm³. 3 The porosity is 85-90%, the average pore size is 250 μm, and the volume is 120 cm³. 3 The polyimide foam was pretreated at room temperature using an atmospheric pressure plasma surface treatment device for t1=30min, with plasma power P=200W; C1=(P×t1) / (ρ×V)=(200×30) / (0.1×120)=500.

[0107] S21. Before injection, the pretreated polyimide foam is evacuated to an absolute pressure ≤50mbar. S22. Under an injection pressure of 0.1 MPa, the organosilicon precursor sol is injected into the pretreated polyimide foam at an injection rate of 20 mL / min for 15 min. S23. After injection, maintain pressure at 0.1 MPa for 5 minutes.

[0108] S24. After pressure holding, static gelation is performed; the static gelation process adopts a segmented temperature control program, specifically including the following steps: (1) Room temperature degassing stage: let stand at room temperature (20-25℃) for 1 hour; (2) Programmed heating stage: The temperature is increased from room temperature to 75°C at a heating rate of 5°C / min; (3) Constant temperature gelation stage: gelation is completed by keeping the temperature at 75℃±2℃ for 24 hours.

[0109] S3. The gel composite is subjected to solvent replacement and atmospheric pressure drying in sequence to obtain the low dielectric organosilicon aerogel composite material. The parameters for the solvent replacement process include: the replacement solvent is ethanol with a water content ≤1 wt%, the number of replacements is 3, each replacement lasts for 3 hours, the volume / mass ratio of solvent volume to gel mass in a single replacement is 3 mL:1 g, and the residual water content in the gel at the end of the replacement is ≤0.5 wt%. The atmospheric pressure drying includes the following steps: (1) Drying stage: The gel composite after solvent replacement is heated from room temperature to the first target temperature of 80°C at a first heating rate of 10°C / h, and kept at the first target temperature for a first holding time of 8h. (2) Heat treatment stage: Continue to heat from 80°C to the second target temperature of 200°C at the second heating rate of 8°C / h, and maintain the second heat preservation time of 4h at the second target temperature to obtain the fluorine modified superhydrophobic low dielectric electrogel composite material.

[0110] Example 2 This embodiment is the same as Example 1, except that in step S1, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.5:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2618:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 12.8 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 226.5 g of anhydrous ethanol, and then 10.7 g of deionized water is added. In step S12, 0.89 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0111] Example 3 This embodiment is the same as Example 1, except that in step S1, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.1:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2634:1, and the prepared precursor sol has a solid content of 20 wt.% fluorinated ternary synergistic precursor sol; specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 2.6 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 186.4 g of anhydrous ethanol, and then 10.0 g of deionized water is added. In step S12, 0.74 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0112] Example 4 This embodiment is the same as Example 1, except that in step S1, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 3:1:0.2:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2630:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 26.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 162.0 g of anhydrous ethanol, and then 8.3 g of deionized water is added. In step S12, 0.64 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0113] Example 5 This embodiment is the same as Example 1, except that in step S1, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 6:1:0.2:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2632:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 53.5 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 263.7 g of anhydrous ethanol, and then 13.9 g of deionized water is added. In step S12, 1.0 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0114] Example 6 This embodiment is the same as Example 1, except that in step S1, a precursor sol with a solid content of 15 wt.% is prepared; the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, and the mass ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.1830:1. The prepared precursor sol has a solid content of 15 wt.% and is a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 282.0 g of anhydrous ethanol, and then 10.1 g of deionized water is added. In step S12, 1.0 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0115] Example 7 This embodiment is the same as Example 1, except that in step S1, a precursor sol with a solid content of 25 wt.% is prepared; the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, and the mass ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.3571:1. The prepared precursor sol has a solid content of 25 wt.% and is a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 144.5 g of anhydrous ethanol, and then 10.1 g of deionized water is added. In step S12, 0.62 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0116] Example 8 This embodiment is the same as Example 1, except that in step S1, a precursor sol with a solid content of 30 wt.% is prepared; the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, and the mass ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.4691:1. The prepared precursor sol has a solid content of 30 wt.% and is a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 110.0 g of anhydrous ethanol, and then 10.1 g of deionized water is added. In step S12, 0.52 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0117] Example 9 This embodiment is the same as Example 1, except that in step S1, a precursor sol with a solid content of 10 wt.% is prepared; the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the molar ratio of water to alkoxy group is 0.7, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, and the mass ratio of the sum of the masses of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.1139:1. The prepared precursor sol has a solid content of 10 wt.% and is a fluorinated ternary synergistic precursor sol. Specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 453.0 g of anhydrous ethanol, and then 10.1 g of deionized water is added. In step S12, 1.54 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0118] Example 10 This embodiment is the same as Embodiment 1, except that a density ρ of 0.05 g / cm³ is selected. 3 The porosity is 80-83%, the average pore size is 1000 μm, and the volume is 240 cm³. 3 Polyimide foam.

[0119] Example 11 This embodiment is the same as Embodiment 1, except that a density ρ of 0.20 g / cm³ is selected. 3The porosity is 80-83%, the average pore size is 50 μm, and the volume is 60 cm³. 3 Polyimide foam.

[0120] Example 12 This embodiment is the same as Embodiment 1, except that a density ρ of 0.10 g / cm³ is selected. 3 The porosity is 85-90%, the average pore size is 300 μm, and the volume is 90 cm³. 3 Polyimide foam.

[0121] Example 13 This embodiment is the same as Example 1, except that the molar ratio of water to alkoxy groups is 1.0; specifically, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the mass ratio of the sum of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2745:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol; specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 188.0 g of anhydrous ethanol, and then 14.5 g of deionized water is added. In step S12, 0.76 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0122] Example 14 This embodiment is the same as Example 1, except that the molar ratio of water to alkoxy groups is 0.4; specifically, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the mass ratio of the sum of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2542:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol; specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 203.0 g of anhydrous ethanol, and then 5.8 g of deionized water is added. In step S12, 0.78 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0123] Example 15 This embodiment is the same as Example 1, except that the amount of tetramethylammonium hydroxide (TMAH) added is 0.1% of the total mass of the reaction mixture; specifically, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the amount of tetramethylammonium hydroxide (TMAH) added is 0.1 wt.% of the total mass of the reaction mixture, the mass ratio of the sum of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2629:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol; specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 196.3 g of anhydrous ethanol, and then 10.1 g of deionized water is added. In step S12, 0.26 g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25 wt.%.

[0124] Example 16 This embodiment is the same as Example 1, except that the amount of tetramethylammonium hydroxide (TMAH) added is 1.0% of the total mass of the reaction mixture; specifically, the molar ratio of IBTMS:DMDMS:PFOTES:VTES is 4:1:0.2:0.5, the amount of tetramethylammonium hydroxide (TMAH) added is 1.0 wt.% of the total mass of the reaction mixture, the mass ratio of the sum of IBTMS, DMDMS, PFOTES and VTES to the mass of anhydrous ethanol (the first organic solvent) is 0.2629:1, and the solid content of the prepared precursor sol is 20 wt.% of a fluorinated ternary synergistic precursor sol; specifically, in step S11, 35.7 g of IBTMS, 6.0 g of DMDMS, 5.1 g of PFOTES and 4.8 g of VTES are weighed and dissolved in 196.3 g of anhydrous ethanol, and then 10.1 g of deionized water is added. In step S12, 2.58g of tetramethylammonium hydroxide is pre-dissolved in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25wt.%.

[0125] Example 17 This embodiment is the same as Embodiment 1, except that in step S12, the temperature is controlled at 35℃±2℃, the interval between each batch is 1min, and the dropping rate is controlled at 0.5 mL / s.

[0126] Example 18 This embodiment is the same as Embodiment 1, except that in step S22, the organosilicon precursor sol is injected into the pretreated polyimide foam at an injection pressure of 0.5 MPa and an injection rate of 50 mL / min for 10 min.

[0127] Example 19 This embodiment is the same as Embodiment 1, except that the polyimide foam is not pretreated before injection and is directly injected; and in step S22, there is no pressure holding after injection.

[0128] Example 20 This embodiment is the same as Embodiment 1, except for the atmospheric pressure drying stage: (1) Air drying stage: The gel composite after solvent replacement is heated from room temperature to the first target temperature of 80°C at a first heating rate of 15°C / h, and kept at the first target temperature for a first holding time of 4h. (2) Heat treatment stage: Continue to heat from 80°C to the second target temperature of 200°C at the second heating rate of 15°C / h, and maintain the second heat treatment time of 12h at the second target temperature.

[0129] Comparative Example 1 This comparative example is the same as Example 1, except that perfluorooctyltriethoxysilane (PFOTES) is not added to the precursor sol preparation; specifically, Specifically, the molar ratio of IBTMS:DMDMS:VTES is 4:1:0.5, the dosage of tetramethylammonium hydroxide (TMAH) is 0.3 wt.% of the total mass of the reaction mixture, the mass ratio of the sum of IBTMS, DMDMS, and VTES to anhydrous ethanol (the first organic solvent) is 0.2703:1, and the solid content of the prepared precursor sol is 20 wt.%. The specific preparation process is as follows: S11. System initialization: Isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), vinyltriethoxysilane (VTES), water, and the first organic solvent are mixed evenly to form a stable initial reaction system. Weigh 35.7g of IBTMS, 6.0g of DMDMS, and 4.8g of VTES and dissolve them in 172.0g of anhydrous ethanol. Then add 9.8g of deionized water. At a temperature controlled at 25℃±2℃, first stir magnetically at 500rpm for 10min, then place in an ultrasonic cleaner and ultrasonically disperse at 300W for 30min to achieve thorough mixing.

[0130] S12. Dissolve 0.69g of tetramethylammonium hydroxide in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25wt.%. Under continuous stirring at 500rpm and temperature control at 25℃±2℃, add the catalyst dilution solution dropwise to the reaction system in batches. By controlling the interval between each batch and / or the dropping rate, the pH value of the reaction system is maintained at 9.5±0.2. The interval between each batch is 5min, and the dropping rate is controlled at 0.05-0.10 mL / s.

[0131] Comparative Example 2 This comparative example is the same as Example 1, except that IBTMS is not added in the precursor sol preparation; specifically, the molar ratio of DMDMS:PFOTES:VTES is 1:0.2:0.5, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of DMDMS, PFOTES, and VTES to the mass of anhydrous ethanol is 0.2446:1, and the solid content of the prepared precursor sol is 20 wt.%; the specific preparation process is as follows: S11. System initialization: Dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), vinyltriethoxysilane (VTES), water, and the first organic solvent are mixed evenly to form a stable initial reaction system. Weigh 6.0g of DMDMS, 5.1g of PFOTES, and 4.8g of VTES and dissolve them in 65.0g of anhydrous ethanol. Then add 2.6g of deionized water. At a temperature controlled at 25℃±2℃, first stir magnetically at 500rpm for 10min, then place in an ultrasonic cleaner and ultrasonically disperse at 300W for 30min to achieve thorough mixing.

[0132] S12. Dissolve 0.25g of tetramethylammonium hydroxide in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25wt.%. Under continuous stirring at 500rpm and temperature control at 25℃±2℃, add the catalyst dilution solution dropwise to the reaction system in batches. By controlling the interval between each batch and / or the dropping rate, the pH value of the reaction system is maintained at 9.5±0.2. The interval between each batch is 5min, and the dropping rate is controlled at 0.05-0.10 mL / s.

[0133] Comparative Example 3 This comparative example is the same as Example 1, except that DMDMS is not added in the precursor sol preparation; specifically, the molar ratio of IBTMS:PFOTES:VTES is 4:0.2:0.5, the amount of tetramethylammonium hydroxide (TMAH) added is 0.3 wt.% of the total mass of the reaction mixture, the ratio of the sum of the masses of IBTMS, PFOTES, and VTES to the mass of anhydrous ethanol is 0.2606:1, and the solid content of the prepared precursor sol is 20 wt.%; the specific preparation process is as follows: S11. System initialization: Isobutyltrimethoxysilane (IBTMS), perfluorooctyltriethoxysilane (PFOTES), vinyltriethoxysilane (VTES), water, and the first organic solvent are mixed evenly to form a stable initial reaction system. Weigh 35.7g of IBTMS, 5.1g of PFOTES, and 4.8g of VTES and dissolve them in 175.0g of anhydrous ethanol. Then add 8.9g of deionized water. At a temperature controlled at 25℃±2℃, first stir magnetically at 500rpm for 10min, then place in an ultrasonic cleaner and ultrasonically disperse at 300W for 30min to achieve thorough mixing.

[0134] S12. Dissolve 0.69g of tetramethylammonium hydroxide in anhydrous ethanol to prepare a catalyst dilution solution with a mass concentration of 25wt.%. Under continuous stirring at 500rpm and temperature control at 25℃±2℃, add the catalyst dilution solution dropwise to the reaction system in batches. By controlling the interval between each batch and / or the dropping rate, the pH value of the reaction system is maintained at 9.5±0.2. The interval between each batch is 5min, and the dropping rate is controlled at 0.05-0.10 mL / s.

[0135] Tables 1 and 2 summarize the properties of the fluorine-modified superhydrophobic low-dielectric electrogel composites prepared in Examples 1-20 and the composites obtained in Comparative Examples 1-3. Density was tested according to GB / T 5486-2008, and thermal conductivity was tested according to GB / T 10295-2008. The surface water contact angle was tested using a contact angle meter according to GB / T 30693-2014 (test solution was deionized water, droplet volume 5 μL). Moisture absorption was determined by gravimetric method according to GB / T 1034-2008 (test conditions: relative humidity 95%, temperature 60℃, percentage mass increase calculated after 48 hours of storage). Dielectric constant and dielectric loss were measured at 10 GHz (X-band) according to GB / T 1409-2006. Compressive strength was tested according to GJB 10246.2-2021. The wet dielectric properties were tested under the following conditions: relative humidity 95%, temperature 60℃, and measured at 10GHz (X-band) after being placed for 48 hours.

[0136] Table 1: Test results of dielectric properties and dielectric stability under damp heat

[0137] Table 2: Test results of hydrophobicity, density, thermal conductivity and mechanical strength

[0138] The sodium dodecyl sulfate used was product 151-21-3 purchased from Huayuan.com.

[0139] The isobutyltrimethoxysilane used was product 18395-30-7 purchased from Huayuan.com.

[0140] The dimethyldimethoxysilane used was product 1112-39-6 purchased from Huayuan.com.

[0141] The perfluorooctyltriethoxysilane used was product 51851-37-7 purchased from Huayuan.com.

[0142] The vinyltriethoxysilane used was product 78-08-0 purchased from Huayuan.com.

[0143] The anhydrous ethanol used was product 64-17-5 purchased from Huayuan.com.

[0144] The tetramethylammonium hydroxide used was product 10424-65-4 purchased from Huayuan.com. Other reagents, methods, instruments, and equipment were conventional in the art. Unless otherwise specified, all reagents and materials used in the above examples were commercially available.

[0145] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a fluorine-modified superhydrophobic low-dielectric electrogel composite material, characterized in that, Includes the following steps: S1. Preparation of precursor sol: The precursor sol is obtained by co-hydrolysis and polycondensation reaction of isobutyltrimethoxysilane (IBTMS), dimethyldimethoxysilane (DMDMS), perfluorooctyltriethoxysilane (PFOTES), and vinyltriethoxysilane (VTES) dissolved in water in a first organic solvent under the catalysis of an alkaline catalyst. S2. The precursor sol is injected into the polyimide foam skeleton, and then a gelation reaction is carried out to allow the organosilicon molecular chains in the precursor sol to grow and cross-link in situ on the surface of the polyimide foam skeleton, forming a gel composite with an interpenetrating network coupled with a micron skeleton and fluorine-modified nanoaerogel. S3. The gel composite is subjected to solvent replacement and atmospheric pressure drying in sequence to obtain the fluorine-modified superhydrophobic low dielectric electrogel composite material.

2. The preparation method according to claim 1, characterized in that, The molar ratio of isobutyltrimethoxysilane IBTMS, dimethyldimethoxysilane DMDMS, perfluorooctyltriethoxysilane PFOTES to vinyltriethoxysilane VTES is (3~6):1:(0.1~0.5):0.

5.

3. The preparation method according to claim 1, characterized in that, The precursor sol has a solid content of 10~30 wt.%; and / or, The bulk density of the polyimide foam skeleton is 0.05~0.30 g / cm³. 3 .

4. The preparation method according to claim 1, characterized in that, The temperature during the co-hydrolysis-condensation reaction is controlled at 23~27℃; and / or, The stirring rate in the co-hydrolysis condensation reaction is 400~700 rpm.

5. The preparation method according to claim 1, characterized in that, After the co-hydrolysis and polycondensation reaction was completed, the resulting precursor sol was subjected to ultrasonic homogenization, degassing and filtration in sequence. The parameters of the ultrasonic homogenization process include: ultrasonic frequency of 20~30kHz, peak power of 200~600W, and processing time of 10~60min.

6. The preparation method according to claim 1, characterized in that, The gelation is static gelation, which includes the following steps: (1) Degassing stage at room temperature: let stand at 20-25℃ for 1-2 hours; (2) Programmed temperature rise stage: The temperature rises from room temperature to the target gel temperature at a rate of 1~5℃ / min, where the target gel temperature is 60~90℃; (3) Constant temperature gelation stage: gelation is completed by keeping the temperature at the target gelation temperature for 12~48h.

7. The preparation method according to claim 1, characterized in that, The alkaline catalyst is tetramethylammonium hydroxide; and / or, The amount of alkaline catalyst added is 0.1-1.0 wt.% of the total mass of the reaction mixture, where the total mass of the reaction mixture refers to the sum of the masses of isobutyltrimethoxysilane IBTMS, dimethyldimethoxysilane DMDMS, perfluorooctyltriethoxysilane PFOTES, vinyltriethoxysilane VTES, water, and the first organic solvent.

8. The preparation method according to claim 1, characterized in that, In step S1, the molar ratio of water to alkoxy groups is 0.4 to 1.0, and the alkoxy groups include methoxy groups in IBTMS and DMDMS, and ethoxy groups in PFOTES and VTES.

9. The preparation method according to claim 1, characterized in that, In step S3, the atmospheric pressure drying includes: Air drying stage: The gel composite after solvent replacement is heated from room temperature to a first target temperature at a first heating rate, and held at the first target temperature for a first holding time. Heat treatment stage: Continue to heat from the first target temperature to the second target temperature at a second heating rate, and maintain the second target temperature for a second holding time; The first heating rate and the second heating rate are each independently 5-15℃ / h; the first target temperature is 70-90℃; the second target temperature is 180-220℃; and the first holding time and the second holding time are each independently 4-12h.

10. A fluorine-modified superhydrophobic low-dielectric electrogel composite material, characterized in that, The fluorine-modified superhydrophobic low-dielectric electrogel composite material is prepared by the preparation method according to any one of claims 1 to 9; the properties of the composite material are as follows: water contact angle ≥150° at room temperature, roll-off angle ≤10°; density is 0.13~0.28 g / cm³. 3 The dielectric constant at room temperature is ≤1.45, and the dielectric loss is ≤0.0032. The humid heat resistance is as follows: after being placed in an environment with a relative humidity of 95% and a temperature of 60℃ for 48 hours, the dielectric constant change rate of the fluorine-modified superhydrophobic low dielectric electrogel composite material is ≤2.96%, and the moisture absorption rate is ≤1.35%.

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