Flexible Janus structure silicon nitride / silicon dioxide nanofiber as well as preparation method and application thereof

Abstract

The invention relates to the technical field of wave-transparent materials, in particular to a flexible Janus structure silicon nitride / silicon dioxide nanofiber as well as a preparation method and application thereof. The preparation method provided by the invention comprises the following steps: preparing a silicon nitride precursor spinning solution and a silicon dioxide precursor spinning solution; performing side-by-side electrostatic spinning on the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution to obtain Janus structure silicon nitride / silicon dioxide precursor nanofibers; the Janus structure silicon nitride / silicon dioxide precursor nanofiber is sequentially subjected to drying, curing crosslinking and high-temperature pyrolysis, and the Janus structure silicon nitride / silicon dioxide nanofiber is obtained. The Janus structure silicon nitride / silicon dioxide nanofiber obtained by the invention forms a nanofiber membrane, and the nanofiber membrane has excellent flexibility and wave-transparent property and can have excellent properties of silicon nitride and silicon dioxide.

Description

Technical Field

[0001] This invention relates to the field of wave-transparent materials technology, and in particular to a flexible Janus structure silicon nitride / silica nanofiber, its preparation method, and its application. Background Technology

[0002] The applications of wave-transparent materials have expanded beyond the traditional aerospace field, extending to diverse scenarios such as communications, civilian use, and extreme environments. Their performance requirements are rapidly evolving towards multi-dimensional synergy, high-precision control, and green development. Wave-transparent nanofiber materials possess potential in the wave-transparent field due to nanoscale effects, but their current development still faces numerous challenges that urgently need to be addressed.

[0003] Silicon nitride (SiN) offers significant advantages as a microwave-transparent material. It boasts a low dielectric constant and low dielectric loss, enabling efficient electromagnetic wave transmission to meet the requirements of applications such as radar domes. Furthermore, it exhibits excellent high-temperature stability, high mechanical strength, and good thermal shock resistance and corrosion resistance, making it suitable for extreme environments such as aerospace. Chinese patent CN115974559A discloses a low thermal conductivity silicon nitride microwave-transparent ceramic material that achieves a reduction in thermal conductivity while maintaining the mechanical and dielectric properties of the ceramic.

[0004] Silica itself has an extremely low dielectric constant and minimal dielectric loss. The porous structure of nanofibers can further reduce the overall dielectric constant, making it closer to the dielectric properties of air. This results in minimal obstruction to electromagnetic wave transmission, especially in the high-frequency and wide-frequency domains, where it can meet the wave transmission requirements of high-precision radar, advanced communication antennas, and other applications.

[0005] Combining silicon nitride and silicon dioxide promises to yield high-performance wave-transparent materials that combine the excellent properties of both. However, combining the two using blending or core-shell structure designs does not result in materials that possess the superior properties of both silicon nitride and silicon dioxide. Furthermore, silicon nitride nanofibers currently suffer from high brittleness, a problem that remains to be addressed. Summary of the Invention

[0006] The purpose of this invention is to provide a flexible Janus-structured silicon nitride / silica nanofiber, its preparation method, and its application. The Janus-structured silicon nitride / silica nanofiber obtained by the preparation method of this invention has the properties of both silicon nitride and silicon dioxide, and also has good flexibility.

[0007] This invention provides a method for preparing flexible Janus-structured silicon nitride / silica nanofibers, comprising the following steps: A silicon nitride precursor spinning solution and a silica precursor spinning solution are prepared, wherein the silicon nitride precursor spinning solution comprises a silicon nitride precursor, a first spinning aid, a first organometallic salt, and a first organic solvent, and the silica precursor spinning solution comprises a silica precursor, a second spinning aid, a second organometallic salt, and a second organic solvent. The silicon nitride precursor spinning solution and the silica precursor spinning solution were electrospun side by side to obtain Janus-structured silicon nitride / silica precursor nanofibers. The Janus-structured silicon nitride / silica precursor nanofibers were sequentially dried, cured, crosslinked, and pyrolyzed at high temperature to obtain flexible Janus-structured silicon nitride / silica nanofibers.

[0008] Optionally, the silicon nitride precursor includes at least one of polycarbosilane, polysilazane, polyboronsilazane, and perhydropolysilazane, and the content of the silicon nitride precursor is 5-20 wt%.

[0009] Optionally, the first spinning aid includes at least one of polyacrylonitrile, polyvinylpyrrolidone, polycaprolactone, polyvinyl alcohol, and polyethylene oxide, and the content of the first spinning aid is 2-15 wt%; the first organometallic salt is at least one of organoferric salt, organonickel salt, organoaluminum salt, organozirconium salt, organotitanium salt, organoyttrium salt, organocopper salt, organozinc salt, and organolithium salt, and the content of the first organometallic salt is 2-8 wt%; the first organic solvent includes at least one of dichloroethane, dichloromethane, xylene, chloroform, toluene, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

[0010] Optionally, the silica precursor includes one of a silane coupling agent precursor and an inorganic silicate precursor, wherein the silane coupling agent precursor includes at least one of an epoxy silane, a methyl silane, and an amino silane, and the inorganic silicate precursor includes one of tetraethyl orthosilicate, tetrapropyl orthosilicate, and tetrabutyl orthosilicate, and the content of the silica precursor is 8-20 wt%.

[0011] Optionally, the second spinning aid includes at least one of polyvinyl acetate, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, and polyethylene oxide, and the content of the second spinning aid is 3-20 wt%; the second organometallic salt is at least one of organoiron salt, organonickel salt, organoaluminum salt, organozirconium salt, organotitanium salt, organoyttrium salt, organocopper salt, organozinc salt, and organolithium salt, and the content of the second organometallic salt is 2-10 wt%; the second organic solvent includes at least one of ethanol, methanol, isopropanol, acetone, butanol, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, and chloroform.

[0012] Optionally, the parameters of the side-by-side electrospinning include: a spinning voltage of 10-20 kV, a distance of 10-20 cm between the spinneret and the receiving plate, the same propulsion speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution, which is 0.01-0.03 mL / min, and the diameter of the two spinnerets of the side-by-side electrospinning needles is 0.7-0.9 mm.

[0013] Optionally, the curing and crosslinking are carried out in a protective atmosphere, the curing and crosslinking temperature is 200-600℃, the heating rate from room temperature to curing temperature is 5-15℃ / min, and the holding time after heating to curing temperature is 1-5 h.

[0014] Optionally, the high-temperature pyrolysis is carried out in a protective atmosphere, the temperature of the high-temperature pyrolysis is 1300-1700℃, the time is 3-8 h, and the rate of heating from room temperature to the temperature of the high-temperature pyrolysis is 10-25℃ / min.

[0015] The present invention also provides a flexible Janus-structured silicon nitride / silica nanofiber obtained by the preparation method described in any one of the above technical solutions.

[0016] This invention also provides the application of the flexible Janus structure silicon nitride / silica nanofibers described in the above technical solution as a wave-transparent material.

[0017] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes a side-by-side electrospinning method to prepare Janus-structured silicon nitride / silica precursor nanofibers from a silicon nitride precursor spinning solution containing organometallic salts and a silica precursor spinning solution. Further drying, curing, crosslinking, and high-temperature pyrolysis decompose the silicon nitride and silica precursors into silicon nitride and silica, respectively, resulting in flexible Janus-structured silicon nitride / silica nanofibers. The flexible Janus-structured silicon nitride / silica nanofibers obtained by this invention form nanofiber membranes. These nanofiber membranes exhibit excellent flexibility and wave transmission properties, and combine the superior properties of both silicon nitride and silica. Attached Figure Description

[0018] The above and other objects, features, and advantages of the present invention will be apparent from the following description of the preferred embodiments and drawings illustrating the gist of the invention and its use, wherein: Figure 1 This is a schematic diagram of a parallel electrospinning apparatus.

[0019] Figure 2This is a transmission electron microscope image of the flexible Janus structure silicon nitride / silica nanofibers obtained in Example 1.

[0020] Figure 3 The dielectric constant diagram is shown for the flexible Janus structure silicon nitride / silica nanofibers obtained in Example 1, tested at frequencies of 2-18 GHz.

[0021] Figure 4 This is a diagram illustrating the flexibility of the flexible Janus structure silicon nitride / silica nanofibers obtained in Example 1.

[0022] Figure 5 This is a diagram illustrating the brittleness of the Janus-structured silicon nitride / silica nanofibers obtained in Comparative Example 1. Detailed Implementation

[0023] The present invention will be described below through specific embodiments. Those skilled in the art will understand that the specific embodiments described below are for illustrative purposes only and do not limit the scope of the invention in any way. Furthermore, in the following embodiments, unless otherwise specified, the reagents and equipment used are commercially available. If specific processing conditions and methods are not explicitly described in the following embodiments, conditions and methods known in the art can be used for processing.

[0024] This invention provides a method for preparing flexible Janus-structured silicon nitride / silica nanofibers, comprising the following steps: A silicon nitride precursor spinning solution and a silica precursor spinning solution are prepared, wherein the silicon nitride precursor spinning solution comprises a silicon nitride precursor, a first spinning aid, a first organometallic salt, and a first organic solvent, and the silica precursor spinning solution comprises a silica precursor, a second spinning aid, a second organometallic salt, and a second organic solvent. The silicon nitride precursor spinning solution and the silica precursor spinning solution were electrospun side by side to obtain Janus-structured silicon nitride / silica precursor nanofibers. The Janus-structured silicon nitride / silica precursor nanofibers were sequentially dried, cured, crosslinked, and pyrolyzed at high temperature to obtain flexible Janus-structured silicon nitride / silica nanofibers.

[0025] This invention utilizes a parallel electrospinning method to prepare Janus-structured silicon nitride / silica precursor nanofibers from a silicon nitride precursor spinning solution containing organometallic salts and a silica precursor spinning solution. Further drying, curing, crosslinking, and high-temperature pyrolysis decompose the silicon nitride and silica precursors into silicon nitride and silica, respectively, while the organometallic salts are converted into metal carbide nanoparticles. This effectively fills the defects formed during the sintering stage of silicon nitride and silica, enabling the silicon nitride / silica nanofibers to exhibit excellent flexibility, thus obtaining flexible Janus-structured silicon nitride / silica nanofibers. This method is simple to operate and easy to implement, filling the gap in the field of preparing Janus-structured silicon nitride / silica nanofibers using side-by-side electrospinning. Furthermore, the nanofibers possess excellent properties such as flexibility, low dielectric constant, and low dielectric loss, overcoming the problem of high brittleness in silicon nitride nanofibers. The prepared nanofibers combine the properties of silicon nitride and silicon dioxide, effectively avoiding the performance limitations of single materials, and providing a new approach for the design of high-performance wave-transparent materials.

[0026] The present invention first prepares a silicon nitride precursor spinning solution and a silicon dioxide precursor spinning solution.

[0027] In some embodiments of the present invention, the silicon nitride precursor spinning solution includes a silicon nitride precursor, a first spinning aid, a first organometallic salt, and a first organic solvent.

[0028] In some embodiments of the present invention, the silicon nitride precursor includes at least one selected from polycarbosilane, polysilazane, polyboronsilazane, and perhydropolysilazane; the content of the silicon nitride precursor is 5-20 wt%, specifically 5 wt%, 10 wt%, 14 wt%, 15 wt%, 20 wt%, etc. In the present invention, the above-mentioned content can further ensure complete dissolution of the solute. If the content is too low, the final sample will contain too little silicon nitride, resulting in excessively fine silicon nitride-side fibers; if the content is too high, incomplete dissolution in the solution will occur, which is not conducive to spinning.

[0029] In some embodiments of the present invention, the first spinning aid includes at least one selected from polyacrylonitrile, polyvinylpyrrolidone, polycaprolactone, polyvinyl alcohol, and polyethylene oxide; the content of the first spinning aid is 2-15 wt%, specifically 5 wt%, 6 wt%, 8 wt%, 10 wt%, 15 wt%, etc. In the present invention, the above-mentioned first spinning aid facilitates the spinning of silicon nitride precursor into fibers, and successfully obtains the spinning solution of silicon nitride precursor. If the content of the spinning aid is too low, the overall entanglement of the spinning solution will be poor, and the precursor fibers obtained by spinning will easily form beads or even fail to be spun into fibers; if the content of the spinning aid is too high, it will lead to incomplete dissolution in the solvent.

[0030] In some embodiments of the present invention, the first organometallic salt is at least one selected from organoferric salt, organonickel salt, organoaluminum salt, organozirconium salt, organotitanium salt, organoyttrium salt, organocopper salt, organozinc salt, and organolithium salt. Specifically, it can be at least one selected from iron acetylacetonate, titanium isopropoxide, nickel acetylacetonate, aluminum acetylacetonate, zinc acetylacetonate, aluminum isopropoxide, yttrium acetylacetonate, and copper acetate. The content of the first organometallic salt is 2-8 wt%, specifically 5 wt%, 6 wt%, 8 wt%, etc. In the present invention, the addition of the first organometallic salt enables it to be converted into metal carbide nanoparticles during high-temperature calcination. These metal carbide nanoparticles can effectively fill the defects formed in silicon nitride during the sintering stage, ultimately allowing the nanofibers on the silicon nitride side to exhibit excellent flexibility.

[0031] In some embodiments of the present invention, the first organic solvent includes at least one of dichloroethane, dichloromethane, xylene, chloroform, toluene, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide. Specifically, it can be a mixed solvent of N,N-dimethylformamide and tetrahydrofuran in a volume ratio of 3:7, N,N-dimethylformamide, or a mixed solvent of dichloroethane and toluene in a volume ratio of 2:8.

[0032] In some embodiments of the present invention, the silica precursor spinning solution comprises a silica precursor, a second spinning aid, a second organometallic salt, and a second organic solvent. The silica precursor comprises one of a silane coupling agent precursor and an inorganic silicate precursor. The silane coupling agent precursor comprises at least one of an epoxy silane, a methyl silane, and an amino silane. The inorganic silicate precursor comprises one of tetraethyl orthosilicate, tetrapropyl orthosilicate, and tetrabutyl orthosilicate. The content of the silica precursor is 8-20 wt%, specifically 8 wt%, 12 wt%, 15 wt%, 20 wt%, etc. In the present invention, the above-mentioned content further ensures complete dissolution of the solute. Too low a content will result in insufficient silica in the final sample, leading to excessively fine fibers on the silica side; too high a content will result in incomplete dissolution in the solution, which is detrimental to spinning.

[0033] In some embodiments of the present invention, the second spinning aid includes at least one selected from polyvinyl acetate, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, and polyethylene oxide. The content of the second spinning aid is 3-20 wt%, specifically 5 wt%, 6 wt%, 9 wt%, 10 wt%, 15 wt%, 20 wt%, etc. In the present invention, the above-mentioned second spinning aid facilitates the spinning of silica precursor into fibers, and successfully obtains a spinning solution containing silica precursor. If the content is too low, the overall entanglement of the spinning solution will be poor, and the precursor fibers obtained by spinning will easily form beads or even fail to be spun into fibers. If the content of the spinning aid is too high, it will lead to incomplete dissolution in the solvent.

[0034] In some embodiments of the present invention, the second organometallic salt is at least one selected from organoferric salts, organonickel salts, organoaluminum salts, organozirconium salts, organotitanium salts, organoyttrium salts, organocopper salts, organozinc salts, and organolithium salts. Specifically, it can be at least one selected from yttrium acetylacetonate, copper acetate, aluminum isopropoxide, zinc acetylacetonate, iron acetylacetonate, titanium isopropoxide, nickel acetylacetonate, aluminum acetylacetonate, etc. The content of the second organometallic salt is 2-10 wt%, specifically 7 wt%, 5 wt%, 6 wt%, 10 wt%, etc. In the present invention, the addition of the second organometallic salt enables it to be converted into metal carbide nanoparticles during high-temperature calcination. These metal carbide nanoparticles can effectively fill the defects formed in silica during the sintering stage, ultimately allowing the nanofibers on the silica side to exhibit excellent flexibility.

[0035] In some embodiments of the present invention, the second organic solvent includes at least one of ethanol, methanol, isopropanol, acetone, butanol, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, and chloroform. Specifically, it can be ethanol, a mixed solvent of methanol and isopropanol in a volume ratio of 8:2, a mixed solvent of ethanol and acetone in a volume ratio of 3:7 and 2:8, butanol, etc.

[0036] This invention does not specify the particular method for preparing the silicon nitride precursor spinning solution and the silica precursor spinning solution, as long as a dissolved and uniformly mixed spinning solution is obtained. In the embodiments of this invention, the precursor and spinning aid are dissolved in the solvent by stirring.

[0037] After obtaining silicon nitride precursor spinning solution and silicon dioxide precursor spinning solution, the present invention performs parallel electrospinning of the silicon nitride precursor spinning solution and silicon dioxide precursor spinning solution to obtain Janus structure silicon nitride / silicon dioxide precursor nanofibers.

[0038] This invention does not specifically limit the particular operation method of the side-by-side electrospinning; conventional side-by-side electrospinning methods can be used. In the embodiments of this invention, the specific method used is as follows: Figure 1 The parallel electrospinning apparatus shown performs parallel electrospinning by adding the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution into two push syringes connected to the parallel electrospinning needles, respectively, to perform parallel electrospinning.

[0039] In some embodiments of the present invention, the parameters of the side-by-side electrospinning are as follows: the spinning voltage is 10-20 kV, specifically 10 kV, 16 kV, 18 kV, 20 kV, etc.; the distance from the spinneret to the receiving plate is 10-20 cm, specifically 14 cm, 16 cm, 18 cm, and 20 cm, etc.; the propulsion speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution is the same and is 0.01-0.03 mL / min, specifically 0.015 mL / min, 0.018 mL / min, 0.020 mL / min, 0.025 mL / min, etc.; the diameter of the two spinnerets of the side-by-side electrospinning needle is 0.7-0.9 mm, preferably 0.8 mm, and in the embodiments, the side-by-side electrospinning needle consists of two 21G flat-mouth stainless steel spinnerets. In this invention, the above parameters further ensure the successful acquisition of Janus-structured silicon nitride / silica precursor nanofibers, and the obtained Janus-structured silicon nitride / silica precursor nanofibers are deposited on the receiving plate to form a thin film (also referred to as thin-film form Janus-structured silicon nitride / silica precursor nanofibers, or Janus-structured silicon nitride / silica precursor nanofiber membrane). This invention does not specifically limit the side-by-side electrospinning time; those skilled in the art can select the side-by-side electrospinning time according to the desired thickness of the precursor nanofiber membrane. In the embodiments of the invention, the side-by-side electrospinning time is 6 hours.

[0040] After obtaining Janus-structured silicon nitride / silica precursor nanofibers, the present invention sequentially dries, cures, crosslinks, and pyrolyzes the Janus-structured silicon nitride / silica precursor nanofibers to obtain Janus-structured silicon nitride / silica nanofibers.

[0041] In some embodiments of the present invention, the drying is vacuum drying, and the temperature of the vacuum drying is 55-65°C, preferably 60°C; the time is based on drying to constant weight. In the embodiments of the present invention, the vacuum drying time is 1.5-2.5 h, preferably 2 h.

[0042] In some embodiments of the present invention, the curing and crosslinking are carried out in a protective atmosphere, and the curing and crosslinking temperature is 200-600℃, specifically 400℃, 500℃, 600℃, etc.; the heating rate from room temperature to curing temperature is 5-15℃ / min, specifically 5℃ / min, 8℃ / min, 10℃ / min, etc.; the holding time after heating to curing temperature is 1-5 h, specifically 2 h, 3 h, 4 h, etc. In this invention, the aforementioned temperature and time can further ensure complete curing of the precursor nanofibers. However, exceeding these parameters can lead to over-curing, causing microcracks inside the fiber and even resulting in the collapse of the final fiber structure. Conversely, below these parameters can lead to incomplete curing. Furthermore, excessively rapid heating rates can create a temperature gradient between the fiber surface and interior, causing the fiber surface to complete cross-linking first and form a dense "hard shell," while the internal cross-linking reaction lags behind and small molecules cannot escape, further exacerbating internal stress and ultimately leading to fiber expansion, cracking, or delamination. On the other hand, excessively slow heating rates can significantly prolong the curing cycle, reduce production efficiency, and increase production costs. On the other hand, excessively slow heating can prolong the holding time in the low-temperature stage, during which the precursor has not yet fully cross-linked, and small molecule volatiles will slowly and continuously escape, resulting in excessively high internal porosity and insufficient skeletal support in the fiber. Ultimately, this leads to fiber shrinkage, thinning, or even collapse, making it impossible to maintain the nanoscale diameter and continuous morphology.

[0043] In this invention, unless otherwise specified, the protective atmosphere refers to a reactive gas atmosphere, such as an inert gas (argon, etc.) or nitrogen.

[0044] In some embodiments of the present invention, the high-temperature pyrolysis is carried out in a protective atmosphere, and the temperature of the high-temperature pyrolysis is 1300-1700℃, specifically 1500℃, 1600℃, 1700℃, etc.; the time of the high-temperature pyrolysis is 3-8 h, specifically 3 h, 6 h, 7 h, 8 h, etc.; the rate of heating from room temperature to the temperature of the high-temperature pyrolysis is 10-25℃ / min, specifically 10℃ / min, 15℃ / min, 20℃ / min, etc. In the present invention, during the high-temperature pyrolysis process, the silicon nitride precursor and the silicon dioxide precursor decompose at high temperature, generating silicon nitride and silicon dioxide respectively, thereby obtaining Janus-structured silicon nitride / silica nanofibers. In the present invention, the above temperature and time can ensure that the silicon nitride precursor and the silicon dioxide precursor are fully pyrolyzed to form Janus-structured silicon nitride / silica nanofibers. Furthermore, since the Janus-structured silicon nitride / silica precursor nanofibers form a thin film on the receiving plate, the resulting Janus-structured silicon nitride / silica nanofibers are also in thin film form. In this invention, excessively rapid heating to high-temperature pyrolysis leads to uneven crystallization of the final ceramic material and significant thermal stress inside and outside the fibers, ultimately causing fiber breakage or bending deformation and compromising the overall structural integrity. Conversely, excessively slow heating rates and prolonged sintering can cause microcracks inside the fibers, or even lead to fiber structural collapse and high fiber brittleness.

[0045] In another aspect, the present invention provides Janus-structured silicon nitride / silica nanofibers obtained by the preparation method described in any one of the above technical solutions. In some embodiments of the present invention, the diameter of the Janus-structured silicon nitride / silica nanofibers is 400-600 nm, that is, the diameter distribution of the obtained Janus-structured silicon nitride / silica nanofibers is in the range of 400-600 nm.

[0046] In another aspect, the present invention provides an application of the Janus structure silicon nitride / silica nanofibers described above as a wave-transparent material.

[0047] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings and embodiments. The embodiments of this application are only examples, and all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0048] Example 1 (1) Polysilazane, polycaprolactone, and ferric acetylacetone were dissolved in a mixed solvent of N,N-dimethylformamide and tetrahydrofuran (volume ratio 3:7) to obtain a silicon nitride precursor spinning solution, wherein the content of polysilazane was 10 wt%, the content of polycaprolactone was 5 wt%, and the content of ferric acetylacetone was 5 wt%. Tetraethyl orthosilicate, yttrium acetylacetonate, and polyvinylpyrrolidone were dissolved in ethanol to obtain a silica precursor spinning solution, wherein the content of tetraethyl orthosilicate was 12 wt%, the content of polyvinylpyrrolidone was 6 wt%, and the content of yttrium acetylacetonate was 7 wt%.

[0049] (2) The silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were respectively added to two push syringes connected to parallel electrospinning needles for parallel electrospinning. The spinning voltage was 20 kV, the push speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were both 0.02 mL / min, the distance from the spinneret to the receiving plate was 18 cm, the spinning time was 6 h, and the parallel electrospinning needles were composed of two 21G flat stainless steel needles to obtain Janus structure silicon nitride / silica precursor nanofibers. The Janus structure silicon nitride / silica precursor nanofibers were deposited on the receiving plate to form a thin film.

[0050] (3) The Janus structure silicon nitride / silica precursor nanofibers were vacuum dried at 60°C for 2 h, and then heated to 600°C at a rate of 10°C / min in a nitrogen atmosphere, and kept at the temperature for 2 h to cure crosslinking. After cooling to room temperature, the temperature was then raised to 1500°C at a rate of 15°C / min in a nitrogen atmosphere and kept at this temperature for 8 h to obtain flexible Janus structure silicon nitride / silica nanofibers in the form of a thin film, wherein the diameter of the flexible Janus structure silicon carbonitride / silica nanofibers is 400-600 nm.

[0051] The structure of the flexible Janus-structured silicon nitride / silica nanofibers in Example 1 was characterized using transmission electron microscopy, and the results are as follows: Figure 2 As shown, by Figure 2 It can be seen that the two sides of the same nanofiber have a large difference in depth under TEM, indicating that the nanofiber has a Janus structure.

[0052] Furthermore, the dielectric constant of the flexible Janus structure silicon nitride / silica nanofibers in Example 1 showed very little fluctuation in the four bands (S (2-4 GHz), C (4-8 GHz), X (8-12 GHz), and Ku (12-18 GHz)) when tested at frequencies of 2-18 GHz, and remained consistently between 2.0 and 2.2. Figure 3As shown, the maximum transmittance is 99.4% at 2.4 GHz.

[0053] Example 2 (1) Polyborosilazane, polyacrylonitrile, and titanium isopropoxide were dissolved in N,N-dimethylformamide to obtain a silicon nitride precursor spinning solution, wherein the content of polyborosilazane was 14 wt%, the content of polyacrylonitrile was 10 wt%, and the content of titanium isopropoxide was 6 wt%. Epoxysilane, copper acetate, and polyvinylpyrrolidone were dissolved in a mixed solvent of methanol and isopropanol (volume ratio 8:2) to obtain a silica precursor spinning solution, wherein the content of epoxysilane was 12 wt%, the content of polyvinylpyrrolidone was 9 wt%, and the content of copper acetate was 5 wt%.

[0054] (2) The silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were respectively added to two push syringes connected to parallel electrospinning needles for parallel electrospinning. The spinning voltage was 18 kV, the push speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were both 0.018 mL / min, the distance from the spinneret to the receiving plate was 16 cm, the spinning time was 6 h, and the parallel electrospinning needles were composed of two 21G flat stainless steel needles to obtain Janus structure silicon nitride / silica precursor nanofibers. The Janus structure silicon nitride / silica precursor nanofibers were deposited on the receiving plate to form a thin film.

[0055] (3) The Janus structure silicon nitride / silica precursor nanofibers were vacuum dried at 60°C for 2 h, and then heated to 500°C at a rate of 8°C / min in a nitrogen atmosphere, and kept at the temperature for 3 h to cure crosslinking. After cooling to room temperature, the temperature was then raised to 1700°C at a rate of 15°C / min in a nitrogen atmosphere and kept at this temperature for 6 h to obtain flexible Janus structure silicon nitride / silica nanofibers in the form of a film, wherein the diameter of the flexible Janus structure silicon carbonitride / silica nanofibers is 400-600 nm.

[0056] Example 3 (1) Polyborosilazane, polyethylene oxide, and nickel acetylacetone were dissolved in a mixed solvent of dichloroethane and toluene (volume ratio 2:8) to obtain a silicon nitride precursor spinning solution, wherein the content of polyborosilazane was 15 wt%, the content of polyethylene oxide was 6 wt%, and the content of nickel acetylacetone was 8 wt%. Tetrabutyl orthosilicate, aluminum isopropoxide, and polyethylene oxide were dissolved in a mixed solvent of ethanol and propanol (volume ratio 2:8) to obtain a silica precursor spinning solution, wherein the content of tetrabutyl orthosilicate was 15 wt%, the content of polyethylene oxide was 10 wt%, and the content of aluminum isopropoxide was 6 wt%.

[0057] (2) The silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were respectively added to two push syringes connected to parallel electrospinning needles for parallel electrospinning. The spinning voltage was 16 kV, the push speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were both 0.02 mL / min, the distance from the spinneret to the receiving plate was 14 cm, the spinning time was 6 h, and the parallel electrospinning needles were composed of two 21G flat stainless steel needles to obtain Janus structure silicon nitride / silica precursor nanofibers. The Janus structure silicon nitride / silica precursor nanofibers were deposited on the receiving plate to form a thin film.

[0058] (3) The Janus structure silicon nitride / silica precursor nanofibers were vacuum dried at 60°C for 2 h, and then heated to 400°C at a rate of 5°C / min in a nitrogen atmosphere, and kept at the temperature for 4 h to cure crosslinking. After cooling to room temperature, the temperature was then raised to 1600°C at a rate of 15°C / min in a nitrogen atmosphere and kept at this temperature for 7 h to obtain flexible Janus structure silicon nitride / silica nanofibers in the form of a thin film, wherein the diameter of the flexible Janus structure silicon carbonitride / silica nanofibers is 400-600 nm.

[0059] Example 4 (1) Polyborosilazane, polyvinyl alcohol, and aluminum acetylacetonate were dissolved in a mixed solvent of dichloroethane and toluene (volume ratio 2:8) to obtain a silicon nitride precursor spinning solution, wherein the content of polyborosilazane was 15 wt%, the content of polyvinyl alcohol was 8 wt%, and the content of aluminum acetylacetonate was 8 wt%. Tetrapropyl orthosilicate, zinc acetylacetone, and polyvinyl butyral were dissolved in butanol to obtain a silica precursor spinning solution, wherein the content of tetrapropyl orthosilicate was 13 wt%, the content of polyvinyl butyral was 5 wt%, and the content of zinc acetylacetone was 10 wt%.

[0060] (2) The silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were respectively added to two push syringes connected to parallel electrospinning needles for parallel electrospinning. The spinning voltage was 20 kV, the push speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution were both 0.025 mL / min, the distance from the spinneret to the receiving plate was 16 cm, the spinning time was 6 h, and the parallel electrospinning needles were composed of two 21G flat stainless steel needles to obtain Janus structure silicon nitride / silica precursor nanofibers. The Janus structure silicon nitride / silica precursor nanofibers were deposited on the receiving plate to form a thin film.

[0061] (3) The Janus structure silicon nitride / silica precursor nanofibers were vacuum dried at 60°C for 2 h, and then heated to 400°C at a rate of 5°C / min in a nitrogen atmosphere, and kept at the temperature for 4 h to cure crosslinking. After cooling to room temperature, the temperature was then raised to 1600°C at a rate of 15°C / min in a nitrogen atmosphere and kept at this temperature for 7 h to obtain Janus structure silicon nitride / silica nanofibers in thin film form, wherein the diameter of the Janus structure silicon carbonitride / silica nanofibers is 400-600 nm.

[0062] Comparative Example 1 Janus-structured silicon nitride / silica nanofibers were prepared using the method described in Example 1, with the only difference being that iron acetylacetone was not added to the silicon nitride precursor spinning solution, and yttrium acetylacetone was not added to the silica precursor spinning solution.

[0063] The flexibility of the two Janus-structured silicon nitride / silica nanofiber membranes obtained in Example 1 and Comparative Example 1 was tested. It was found that the nanofiber membrane obtained in Example 1, with the metal salt added to the spinning solution, exhibited excellent flexibility and did not break even when bent. Figure 4 As shown; however, the nanofiber membrane obtained in Comparative Example 1, which did not contain any metal salts in the spinning solution, is highly brittle and breaks when bent, as shown. Figure 5 As shown. This is mainly attributed to the lack of organometallic salts added to the spinning solution, resulting in a lack of metal carbide filling at the grain boundaries, thus forming defects.

[0064] Although preferred embodiments of the invention have been shown and described, it is conceivable that those skilled in the art can devise various modifications to the invention within the spirit and scope of the appended claims.

Claims

1. A method for preparing flexible Janus-structured silicon nitride / silica nanofibers, comprising the following steps: Prepare spinning solutions for silicon nitride precursors and silicon dioxide precursors, wherein, The silicon nitride precursor spinning solution comprises a silicon nitride precursor, a first spinning aid, a first organometallic salt, and a first organic solvent; the silica precursor spinning solution comprises a silica precursor, a second spinning aid, a second organometallic salt, and a second organic solvent. The silicon nitride precursor spinning solution and the silica precursor spinning solution were electrospun side by side to obtain Janus-structured silicon nitride / silica precursor nanofibers. The Janus-structured silicon nitride / silica precursor nanofibers were sequentially dried, cured, crosslinked, and pyrolyzed at high temperature to obtain flexible Janus-structured silicon nitride / silica nanofibers.

2. The preparation method according to claim 1, characterized in that, The silicon nitride precursor includes at least one of polycarbosilane, polysilazane, polyboronsilazane, and perhydropolysilazane, and the content of the silicon nitride precursor is 5-20 wt%.

3. The preparation method according to claim 1 or 2, characterized in that, The first spinning aid includes at least one of polyacrylonitrile, polyvinylpyrrolidone, polycaprolactone, polyvinyl alcohol, and polyethylene oxide, and the content of the first spinning aid is 2-15 wt%; the first organometallic salt is at least one of organoferric salt, organonickel salt, organoaluminum salt, organozirconium salt, organotitanium salt, organoyttrium salt, organocopper salt, organozinc salt, and organolithium salt, and the content of the first organometallic salt is 2-8 wt%; the first organic solvent includes at least one of dichloroethane, dichloromethane, xylene, chloroform, toluene, tetrahydrofuran, N,N-dimethylformamide, and N,N-dimethylacetamide.

4. The preparation method according to claim 1, characterized in that, The silica precursor includes one of silane coupling agent precursors and inorganic silicate precursors, wherein the silane coupling agent precursor includes at least one of epoxy silane, methyl silane and amino silane, and the inorganic silicate precursor includes one of tetraethyl orthosilicate, tetrapropyl orthosilicate and tetrabutyl orthosilicate, and the content of the silica precursor is 8-20 wt%.

5. The preparation method according to claim 1 or 4, characterized in that, The second spinning aid includes at least one of polyvinyl acetate, polyvinyl butyral, polyvinylpyrrolidone, polyacrylonitrile, and polyethylene oxide, and the content of the second spinning aid is 3-20 wt%; the second organometallic salt is at least one of organoiron salt, organonickel salt, organoaluminum salt, organozirconium salt, organotitanium salt, organoyttrium salt, organocopper salt, organozinc salt, and organolithium salt, and the content of the second organometallic salt is 2-10 wt%; the second organic solvent includes at least one of ethanol, methanol, isopropanol, acetone, butanol, tetrahydrofuran, dichloromethane, N,N-dimethylformamide, and chloroform.

6. The preparation method according to claim 1, characterized in that, The parameters for the parallel electrospinning include: a spinning voltage of 10-20 kV, a distance of 10-20 cm between the spinneret and the receiving plate, the same propulsion speed of the silicon nitride precursor spinning solution and the silicon dioxide precursor spinning solution, which is 0.01-0.03 mL / min, and the diameter of the two spinnerets of the parallel electrospinning needles is 0.7-0.9 mm.

7. The preparation method according to claim 1, characterized in that, The curing and crosslinking are carried out in a protective atmosphere, the curing and crosslinking temperature is 200-600℃, the heating rate from room temperature to curing temperature is 5-15℃ / min, and the holding time after heating to curing temperature is 1-5 h.

8. The preparation method according to claim 1, characterized in that, The high-temperature pyrolysis is carried out in a protective atmosphere, the temperature of the high-temperature pyrolysis is 1300-1700℃, the time is 3-8 h, and the rate of heating from room temperature to the temperature of the high-temperature pyrolysis is 10-25℃ / min.

9. Flexible Janus-structured silicon nitride / silica nanofibers obtained by the preparation method according to any one of claims 1-8.

10. The application of the flexible Janus structure silicon nitride / silica nanofibers of claim 9 as a wave-transparent material.

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