Hollow silicon dioxide microsphere as well as preparation method and application thereof

Abstract

The invention relates to a hollow silicon dioxide microsphere and a preparation method and application thereof, the hollow silicon dioxide microsphere has a dielectric constant less than or equal to 2.5, a dielectric loss tangent angle less than or equal to 0.001, a purity greater than 95%, a sphericity rate greater than or equal to 99%, a wall thickness greater than 0 and less than or equal to 0.42 [mu] m, and an average diameter of 0.1 [mu] m-5 [mu] m, and the hollow rate, the wall thickness and the average particle size satisfy a relational expression, eta is the hollow rate, t is the wall thickness, and R is 1 / 2 of the average particle size. The hollow silicon dioxide microspheres provided by the invention are high in spherical rate, firm in wall thickness, uniform in particle size distribution, high in purity, relatively excellent in dielectric property and extremely low in content of metal impurities, and can meet the application requirements of high-speed and high-frequency substrates, in addition, the preparation method provided by the invention is few in adopted raw materials, simple in preparation process, low in cost and high in efficiency.

Description

Technical Field

[0001] The present invention relates to the technical field of hollow spherical silicon micropowder, in particular to hollow silicon dioxide microspheres and a preparation method and application thereof. Background Art

[0002] Hollow silica microspheres are nano- or micron-sized materials with a unique structure, consisting of a silicon dioxide (SiO2) exterior and a hollow interior. Compared to solid materials, they offer lower density, larger surface area, lower thermal conductivity, and unique optical properties. This makes them a versatile material, not only finding applications in traditional industrial applications but also showing great potential in emerging technologies such as nanotechnology, biomedical engineering, and energy storage.

[0003] Hollow silica microspheres are a special type of filler. Due to their hollow interior and lack of impurities, they contain more air or vacuum (the dielectric constant of air is close to 1) when filled with the same volume compared to solid particles (dielectric constant of approximately 3.8). Therefore, the introduction of hollow silica microspheres into high-speed, high-frequency substrate materials can significantly reduce the dielectric constant (Dk) of the composite material, reduce energy loss during signal transmission, and enhance the overall thermal stability and mechanical strength of the substrate.

[0004] At present, the main preparation methods of hollow silica microspheres include template method, self-assembly method, sol-gel method, microemulsion method or hydrothermal synthesis method, among which the most widely used is the template method. The template method mainly uses polymer microspheres (such as polystyrene microspheres) as hard templates, deposits a layer of silica on their surface, and then removes the internal template material through methods such as calcination, leaving a hollow structure; or uses soft templates, such as vesicles or self-assembled micelles, to form a shell layer through a sol-gel process, and then removes the template by heating or other means, and utilizes the self-assembly behavior of surfactants or polymers in solution to form microspheres with a cavity structure. However, in the process of removing the template using the soft template combined with the sol-gel method, due to the template material and other reasons, the template removal process is complicated and time-consuming. Some template materials are difficult to completely remove, and the residual will affect the performance of the prepared product.

[0005] CN113816388A discloses a method for preparing low-dielectric hollow silica microspheres. The preparation scheme comprises mixing polyvinyl pyrrolidone, styrene, azobisisobutyronitrile, a cationic comonomer acryloyloxyethyltrimethylammonium chloride, water, and ethanol to prepare a template ball dispersion, then adjusting the pH, adding an organosilicon source hydrolysis solution, drying, and calcining to prepare silica microspheres. Although the hollow silica microspheres prepared by the method have controllable wall thickness and a dense surface, the ball formation rate and the purity of the prepared hollow silica are not high due to the silicon source used and the regulation of the sintering temperature.

[0006] CN102167336A discloses a method for preparing hollow mesoporous silica spheres. The method involves synthesizing a precursor in the presence of a cationic surfactant, then etching with sodium carbonate or sodium hydroxide. The mesoporous silica spheres are then obtained by controlling the etching temperature and time. Because alkali metals are used as catalysts, metallic impurities (such as sodium, iron, potassium, magnesium, and calcium) are inevitably introduced, significantly affecting the chemical properties.

[0007] CN107827118A discloses a method for preparing hollow mesoporous silica spheres with adjustable shell thickness. Hexadecyltrimethylammonium bromide is dissolved in ammonia water, ethyl orthosilicate is added, and white powder is obtained after alcohol washing. The white powder is then placed in an ethanol solution containing hydrochloric acid to obtain mesoporous hollow silica spheres. The above method can prepare hollow silica with a mesoporous structure.

[0008] In summary, the hollow silica microspheres provided by the existing preparation process generally have problems such as the shell surface is not sealed and dense, the shell thickness is too thin, the surface is easily broken, and it is impossible to take into account high purity, high sphericity and excellent dielectric properties. As a result, the existing hollow silica microspheres cannot meet the application requirements of high-speed and high-frequency substrate materials.

[0009] Therefore, in view of the shortcomings of hollow silica microspheres prepared by the existing technology, there is an urgent need to provide a hollow silica microsphere with better overall performance and its preparation process, which can take into account the advantages of high purity, high sphericity and strong shell of hollow silica microspheres to meet the application requirements of high-speed and high-frequency substrate materials. Summary of the Invention

[0010] To address the above technical problems, the present invention provides hollow silica microspheres, their preparation method, and applications. The hollow silica microspheres provided by the present invention have high sphericity, thick and strong walls, uniform particle size distribution, high purity, excellent dielectric properties, and extremely low levels of various metal impurities, meeting the application requirements of high-speed and high-frequency substrates.

[0011] To achieve this object, the present invention adopts the following technical solutions:

[0012] In a first aspect, the present invention provides hollow silica microspheres, wherein the dielectric constant of the hollow silica microspheres is ≤2.5, such as 2.5, 2.4, 2.3, 2.2, 2.1 or 2; the dielectric loss tangent is ≤0.001, such as 0.001, 0.0009, 0.0008, 0.0007, 0.0006, 0.0005, 0.0004, 0.0003, 0.0002 or 0.0001; the purity is greater than 95%, such as 95.1%, 95.5%, 96%, 96.5%, 97%, 97.5%, 98%, 98.5%, 99%, 99.5% or 99.9%; the sphericity is ≥99%, such as 99%, 99.1%, 99.2%, 99.3%, 99.4%, 99.6%, 99.7%, 99.8%, 99.9%, 99.10%, 99.11%, 99.12%, 99.13%, 99.14%, 99.15%, 99.16%, 99.17%, 99.18%, 99.19%, 99.20%, 99.21%, 99.22%, 99.23%, 99.24%, 99.25%, 99.26%, 99.27%, 99.28%, 99.29%, 99.29%, 99.2 .5%, 99.6%, 99.7%, 99.8% or 99.9%, etc.; 0<wall thickness≤0.42μm, for example, the wall thickness can be 0.01μm, 0.05μm, 0.1μm, 0.12μm, 0.15μm, 0.18μm, 0.2μm, 0.22μm, 0.25μm, 0.28μm, 0.3μm, 0.32μm, 0.3 5μm, 0.38μm, 0.4μm or 0.42μm, etc.; the average diameter is 0.1μm-5μm, for example, 0.1μm, 0.2μm, 0.5μm, 0.8μm, 1μm, 1.5μm, 2μm, 2.5m, 3μm, 3.5μm, 4μm, 4.5μm or 5μm, etc., and the hollow ratio, the wall thickness and the average particle size satisfy the relationship: Here, η is the hollow ratio, t is the wall thickness, and R is 1 / 2 of the average particle size.

[0013] As a preferred technical solution of the present invention, the hollow silica microspheres have a hollow ratio of 30%-80%, for example, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%.

[0014] In a second aspect, the present invention further provides a method for preparing hollow silica microspheres, the preparation method comprising the following steps:

[0015] The silicon source mixture is added to the monodisperse polystyrene sphere gel to react with each other to obtain silica microspheres, which are then heat-treated to obtain hollow silica microspheres.

[0016] The raw materials of the silicon source mixture include a first silicon source, a second silicon source, a catalyst and an alcohol-water mixture; the monodisperse polystyrene sphere glue is obtained by polymerization reaction of a cationic initiator and a styrene-containing stabilizer solution, and the styrene-containing stabilizer solution includes pretreated styrene after alkali washing and a stabilizer solution.

[0017] In the present invention, a hard template method is adopted to prepare hollow silica microspheres. The polystyrene sphere template has a certain hardness and deformation resistance. If the polystyrene sphere template has uniform size and high sphericity, the subsequent silicon source nucleation on the surface of the template can ensure that the silica microspheres also have a better morphology with uniform size and high sphericity. In addition, during the subsequent heat treatment removal process, combined with a relatively suitable temperature, the template can be completely removed without causing the occurrence of wall breakage.

[0018] In addition, the preparation method of the present invention also has the following advantages: ① After the pretreated styrene is first added to the stabilizer solution for the first mixing, the system containing the pretreated styrene is first completely dispersed and fully stabilized, and then the cationic initiator is added thereto for polymerization reaction. First, the polymerization reaction can be carried out more thoroughly, and the size and morphology of the polystyrene sphere template obtained after polymerization are more uniform, avoiding the disorder of the template, which in turn affects the subsequent preparation of silica microspheres. Second, the selective control of the polymerization reaction path can be achieved, and the polymerization degree and particle size distribution can be more finely regulated. At the same time, cationic polymerization exhibits a very fast polymerization rate, which is beneficial to improve Production efficiency; ② In the present invention, styrene is first pretreated, and the internal polymerization inhibitor is removed by alkali washing to improve the activity of styrene polymerization. After being combined with the subsequent stabilizer solution, the morphology of the polymerized polystyrene spheres is uniform, and the spheres are dispersed and uniform in size; ③ In the present invention, a cationic initiator is directly used, which can, on the one hand, play a role in initiating polymerization, and on the other hand, after its hydrolysis, can make the surface of the polystyrene sphere template have a positive charge, without the need to add other raw materials such as cationic comonomers or cationic surfactants, thereby avoiding the addition of more raw materials and introducing more metal impurities, which in turn affects the preparation of the template, while also reducing costs and simplifying the process.

[0019] As a preferred technical solution of the present invention, the method for preparing the silicon source mixed solution includes: mixing the first silicon source, the second silicon source, the catalyst and the alcohol-water mixed solution under stirring or ultrasonic dispersion conditions to obtain the silicon source mixed solution.

[0020] In the present invention, the first silicon source belongs to the outer layer silicon source, which mainly forms the outer shell and preliminarily controls the size of the silica microspheres obtained after nucleation on the surface of the template polystyrene sphere, while having a certain mechanical strength to maintain the hollow structure of the sphere after heat treatment; in addition, during the nucleation process on the surface of the template polystyrene sphere, the first silicon source has a large spatial steric hindrance, which makes it impossible to densely nucleate on the template surface, while the second silicon source belongs to the inner layer silicon source, and its addition can effectively fill the space between the polystyrene sphere template and the outer shell formed by the first silicon source, stabilize the internal structure of the silica layer, and thus form a dense silica layer. Through the synergistic effect of the two, the prepared hollow silica microspheres have appropriate wall thickness, high density and a certain hollow ratio (the proportion of the area that is completely hollow inside).

[0021] As a preferred technical solution of the present invention, the method of mixing the first silicon source, the second silicon source, the catalyst and the alcohol-water mixture for reaction includes: first mixing the first silicon source and the alcohol-water mixture evenly, then adding the catalyst for mixed reaction, and then adding the second silicon source and mixing evenly to obtain a silicon source mixture.

[0022] Preferably, the first silicon source includes any one of methoxysilane, methylsilane, ethoxysilane, ethylsilane, propoxysilane, propylsilane, butoxysilane, vinylsilane or trimethoxysilane, or a combination of at least two thereof.

[0023] Preferably, the methoxysilane includes any one of tetramethoxysilane, n-octyltrimethoxysilane, dodecyltrimethoxysilane, hexadecyltrimethoxysilane or phenyltrimethoxysilane, or a combination of at least two thereof.

[0024] Preferably, the methylsilane includes dimethoxydimethylsilane and / or triethoxymethylsilane.

[0025] Preferably, the ethoxysilane includes tetraethoxysilane and / or n-octyltriethoxysilane.

[0026] Preferably, the ethylsilane includes any one of dimethoxydiethylsilane, trimethoxyethylsilane or triethoxyethylsilane, or a combination of at least two thereof.

[0027] Preferably, the propoxysilane includes tetrapropoxysilane and / or tetraisopropoxysilane.

[0028] Preferably, the propylsilane includes dimethoxydiisopropylsilane.

[0029] Preferably, the vinylsilane includes trimethoxyvinylsilane and / or triethoxyvinylsilane.

[0030] Preferably, the butoxysilane includes tetrabutoxysilane.

[0031] Preferably, the catalyst comprises hydrochloric acid and / or oxalic acid.

[0032] Preferably, the second silicon source includes any one of ethyl orthosilicate, methyl orthosilicate or butyl orthosilicate, or a combination of at least two of them.

[0033] Preferably, during the preparation of the silicon source mixture, the first silicon source is added in parts by mass, such as 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, and the alcohol-water mixture is added in parts by mass, such as 1 part, 10 parts, 20 parts, 30 parts, 40 parts, 50 parts, 60 parts, 70 parts, 80 parts, 90 parts, 100 parts, 110 parts, 120 parts, 100 parts, 200 parts, 300 parts, 400 parts, 50 ... 0 parts or 120 parts, etc., 0.01 parts to 5 parts of catalyst are added, for example, 0.01 parts, 0.05 parts, 0.1 parts, 0.5 parts, 0.8 parts, 1 parts, 1.5 parts, 2 parts, 2.5 parts, 3 parts, 3.5 parts, 4 parts, 4.5 parts or 5 parts, etc., and 1 part to 10 parts of the second silicon source are added, for example, 1 part, 2 parts, 3 parts, 4 parts, 5 parts, 6 parts, 7 parts, 8 parts, 9 parts or 10 parts, etc.

[0034] In the present invention, the raw materials of the silicon source mixture are regulated to contain 1-10 parts of the first silicon source and 1-10 parts of the second silicon source, so that the reaction is uniform and the internal structure is stable. If the first silicon source is too much, the silica shell formed will be too thick, the silica layer will be too thick, and the internal space of the hollow structure will be reduced. At the same time, too high a concentration will cause heterogeneous nucleation or abnormal growth. If the second silicon source content is too much, it will affect the stability of the internal structure. Under high temperature treatment conditions, the cavity shape will be irregular and not completely hollow (part of the second silicon source will exist in the hollow part), making it difficult to form an ideal cavity. Secondly, in the process of removing the template, it will hinder the smooth escape of gas, causing internal pressure accumulation, thereby affecting the integrity of the hollow structure. Thirdly, it will participate in unnecessary side reactions, generate other impurities or by-products, and thus affect the purity and performance of the product.

[0035] Preferably, the alcohol-water mixture comprises, by mass: 0.1-2 parts of deionized water, for example, 0.1 part, 0.5 part, 0.8 part, 1 part, 1.2 parts, 1.5 parts, 1.8 parts or 2 parts, and 1-50 parts of alcohol solution, for example, 1 part, 5 parts, 10 parts, 15 parts, 20 parts, 25 parts, 30 parts, 35 parts, 40 parts, 45 parts or 50 parts, etc.

[0036] In the present invention, by regulating the mass relationship between deionized water and alcohol solution, the reaction rate can be controlled within a range that is beneficial to the reaction. Excessive deionized water will lead to excessive hydrolysis, thereby affecting the balance of the condensation reaction. Alcohol, as a solvent, helps to stabilize the formed siloxane intermediate and can slow down the hydrolysis rate to a certain extent, making the reaction more controlled.

[0037] Preferably, the alcohol solution includes any one of methanol, ethanol or isopropanol, or a combination of at least two of them.

[0038] Preferably, the mass ratio of the monodisperse polystyrene sphere glue to the silicon source mixed solution is 1:(1.2-2.0), such as 1:1.2, 1:1.4, 1:1.6, 1:1.8 or 1:2.0.

[0039] As a preferred technical solution of the present invention, the mixing reaction includes a process of stirring and standing.

[0040] Preferably, the stirring speed is 200 rpm-250 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm.

[0041] Preferably, the stirring time is 20 min-60 min, for example, 20 min, 30 min, 40 min, 50 min, or 60 min.

[0042] Preferably, the stirring temperature is 50°C-100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0043] Preferably, the standing time is 40 min-80 min, for example, 40 min, 50 min, 60 min, 70 min or 80 min.

[0044] Preferably, the mixing reaction further includes drying.

[0045] Preferably, the drying temperature is 80°C-150°C, such as 80°C, 100°C, 120°C or 150°C.

[0046] Preferably, the drying time is 8 h to 12 h, for example, 8 h, 9 h, 10 h, 11 h or 12 h.

[0047] Preferably, the temperature of the heat treatment is 500°C-1100°C, for example, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, 850°C, 900°C, 950°C, 1000°C, 1050°C or 1100°C, etc.

[0048] Preferably, the heating rate of the heat treatment is 0.3°C / min-10°C / min, for example, 0.3°C / min, 0.5°C / min, 1°C / min, 3°C / min, 5°C / min, 8°C / min or 10°C / min.

[0049] Preferably, the heat treatment time is 2 h to 8 h, for example, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h or 8 h.

[0050] As a preferred technical solution of the present invention, the preparation method of the monodisperse polystyrene sphere glue includes: alkali washing styrene to obtain pretreated styrene, adding the pretreated styrene to a stabilizer solution and mixing evenly, adding a cationic initiator to carry out polymerization reaction to obtain a monodisperse polystyrene sphere glue.

[0051] Preferably, the cationic initiator includes any one or a combination of at least two of 2,2-azobisisobutylamidine dihydrochloride, an onium salt organic compound, a Lewis acid, or an alkyl halide.

[0052] It should be noted that the present invention does not make any specific requirements or special limitations on the Lewis acid. As long as it is a type commonly used by those skilled in the art, it is applicable to the present invention. For example, it can be any one of anhydrous aluminum trichloride, boron trifluoride or ferric chloride, or a combination of at least two of them.

[0053] It should be noted that the present invention does not impose any specific requirements or special limitations on the alkyl halide. As long as it is a type commonly used by those skilled in the art, it is applicable to the present invention, for example, it can be chloromethylbenzene.

[0054] It should be noted that the present invention does not impose any specific requirements or special limitations on the onium salt organic compound. Any organic compound commonly used by those skilled in the art is applicable to the present invention, for example, it may be a triarylsulfonium salt.

[0055] Preferably, the amount of the cationic initiator added is 0.05 mol%-4.0 mol% of the molar amount of the pretreated styrene, for example, 0.05 mol%, 0.1 mol%, 0.5 mol%, 1 mol%, 1.5 mol%, 2 mol%, 2.5 mol%, 3 mol%, 3.5 mol% or 4 mol%, etc.

[0056] In the present invention, by regulating the addition amount of the cationic initiator to be 0.05mol%-4.0mol% of the molar amount of the pretreated styrene, the particle size of the template polystyrene spheres can be better controlled to avoid the problem of template sphere agglomeration caused by excessive surface energy due to its too small size. If the amount of cationic initiator added is too much, the rate of the polymerization reaction will be destroyed, making the particle size of the polystyrene spheres uncontrolled, not only resulting in spheres with too small particle size, but also making the spheres disorderly and uneven in size, thereby affecting the subsequent preparation of silica microspheres; if the amount of cationic initiator added is too little, the number of sites in the solution that can trigger nucleation is reduced, resulting in a decrease in the nucleation rate, a decrease in the number of polystyrene spheres generated or a prolongation of the nucleation time, and at the same time causing the silica microspheres formed to have a larger particle size and a wider particle size distribution.

[0057] Preferably, the process of adding the cationic initiator also includes stirring.

[0058] Preferably, the stirring speed is 200 rpm-250 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm.

[0059] Preferably, the polymerization reaction temperature is 50°C-100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0060] Preferably, the polymerization reaction time is ≥20 h, for example, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 40 h, 50 h or 80 h.

[0061] In the present invention, by matching the polymerization reaction temperature and time and regulating each within a reasonable range, the polymerization reaction can be carried out more completely and thoroughly, avoiding the problems of reduced yield of template polystyrene spheres and uneven sphere size. If the reaction temperature is low or the feed is increased, the reaction time should be appropriately extended to ensure a more complete polymerization reaction; if the reaction temperature is high or the feed is reduced, the reaction time should be appropriately shortened as long as the polymerization reaction is more complete.

[0062] Preferably, the stirring speed of the polymerization reaction is 200 rpm-250 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm.

[0063] As a preferred technical solution of the present invention, the alkali solution used in the alkali washing includes an ammonia solution and / or a urea solution.

[0064] Preferably, the concentration of the alkali solution is 8wt%-15wt%, for example, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt% or 15wt%.

[0065] Preferably, the volume ratio of the alkali solution to the styrene is 1:(3-5), such as 1:3, 1:4 or 1:5.

[0066] Preferably, the stabilizer solution comprises any one of a polyvinyl pyrrolidone aqueous solution, a polyvinyl alcohol aqueous solution or a sodium lauryl sulfate aqueous solution, or a combination of at least two thereof.

[0067] Preferably, the concentration of the stabilizer solution is 0.2 wt%-0.8 wt%, such as 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt% or 0.8 wt%.

[0068] Preferably, the uniform mixing includes the steps of defoaming and stirring.

[0069] Preferably, the defoaming method includes nitrogen blowing.

[0070] Preferably, the defoaming time is 3 min-15 min, for example, 3 min, 5 min, 8 min, 10 min, 12 min or 15 min.

[0071] Preferably, the stirring speed is 200 rpm-250 rpm, for example, 200 rpm, 210 rpm, 220 rpm, 230 rpm, 240 rpm or 250 rpm.

[0072] Preferably, the stirring temperature is 50°C-100°C, for example, 50°C, 60°C, 70°C, 80°C, 90°C or 100°C.

[0073] Preferably, the stirring time is 0.5h-2h, such as 0.5h, 1h, 1.5h or 2h.

[0074] As a preferred technical solution of the present invention, the preparation method comprises the following steps:

[0075] The silicon source mixture is added to the monodisperse polystyrene sphere glue, wherein the mass ratio of the monodisperse polystyrene sphere glue to the silicon source mixture is 1:(1.2-2.0), the mixture is stirred at 50°C-100°C at a speed of 200rpm-250rpm for 20min-60min for mixing reaction, the mixture is allowed to stand for 40min-80min, and the mixture is dried at 80°C-150°C for 8h-12h to obtain silica microspheres, and the silica microspheres are heated to 500°C-1100°C at a heating rate of 0.3°C / min-10°C / min and heat-treated for 2h-8h to obtain hollow silica microspheres;

[0076] The raw materials of the silicon source mixed solution include a first silicon source, a second silicon source, a catalyst and an alcohol-water mixed solution;

[0077] The method for preparing the silicon source mixed solution comprises: firstly mixing 1-10 parts of a first silicon source with 1-120 parts of an alcohol-water mixed solution, then adding 0.01-5 parts of a catalyst for mixed reaction, and then adding 1-10 parts of a second silicon source and mixing them evenly to obtain a silicon source mixed solution; wherein the alcohol-water mixed solution comprises, by weight, 0.1-2 parts of deionized water and 1-50 parts of an alcohol solution;

[0078] The monodisperse polystyrene sphere glue is obtained by polymerization reaction of a cationic initiator and a styrene-containing stabilizer solution, wherein the styrene-containing stabilizer solution comprises pretreated styrene after alkali washing and a stabilizer solution;

[0079] The preparation method of the monodisperse polystyrene sphere glue comprises: alkali washing styrene to obtain pretreated styrene, adding the pretreated styrene to a stabilizer solution with a concentration of 0.2wt%-0.8wt%, removing bubbles for 3-15 minutes, stirring at 50°C-100°C and a speed of 200rpm-250rpm for 0.5h-2h, mixing evenly, adding a cationic initiator under the stirring condition of 200rpm-250rpm, stirring at 50°C-100°C and a speed of 200rpm-250rpm for ≥20h, and performing a polymerization reaction to obtain the monodisperse polystyrene sphere glue;

[0080] The volume ratio of the alkali solution used in the alkali washing to the styrene is 1:(3-5), and the concentration of the alkali solution used in the alkali washing is 8wt%-15wt%; the added amount of the cationic initiator is 0.05mol%-4.0mol% of the molar amount of the pretreated styrene.

[0081] In a third aspect, the present invention further provides an application of hollow silica microspheres, wherein the hollow silica microspheres described in the first aspect, or the hollow silica microspheres prepared by the preparation method described in the second aspect, are applied to high-speed and high-frequency substrates.

[0082] Compared with the prior art, the present invention has at least the following beneficial effects:

[0083] 1) The hollow silica microspheres provided by the present invention have a dielectric constant ≤ 2.5, a dielectric loss tangent ≤ 0.001, a purity > 95%, a sphericity ≥ 99%, a wall thickness 0 < ≤ 0.42 μm, an average diameter of 0.1 μm-5 μm, a high sphericity and purity, a uniform particle size distribution, and all metal impurities can be controlled below 0.5 ppm, which can meet the application requirements of high-speed and high-frequency substrates.

[0084] 2) The preparation method provided by the present invention uses less raw materials, has a simple preparation process, is low in cost and high in efficiency, and the prepared template polystyrene spheres have uniform size and high sphericity. The subsequent silicon source nucleation on the surface can ensure that the silica microspheres also have a better morphology with uniform size and high sphericity. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 This is a TEM image of the hollow silica microspheres prepared in Example 1 of the present invention at 1 μm.

[0086] Figure 2 This is a TEM image of the hollow silica microspheres prepared in Example 1 of the present invention at a measurement of 200 nm.

[0087] Figure 3This is a TEM image of the hollow silica microspheres prepared in Example 6 of the present invention at 1 μm.

[0088] Figure 4 3 is a SEM image of the hollow silica microspheres prepared in Comparative Example 1 of the present invention.

[0089] Figure 5 3 is a SEM image of the hollow silica microspheres prepared in Comparative Example 2 of the present invention.

[0090] Figure 6 3 is a SEM image of the hollow silica microspheres prepared in Comparative Example 3 of the present invention. DETAILED DESCRIPTION

[0091] The technical solution of the present invention will be further described below with reference to the accompanying drawings and through specific embodiments. However, the following examples are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention shall be subject to the claims.

[0092] Unless otherwise stated, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0093] Example 1

[0094] This embodiment provides hollow silica microspheres and a preparation method thereof, the preparation method comprising the following steps:

[0095] (1) thoroughly washing 80 mL of styrene with 20 mL of a 10 wt% ammonia solution and deionized water in sequence to obtain pretreated styrene;

[0096] (2) adding the pretreated styrene prepared in step (1) to a 0.5 wt% aqueous solution of polyvinylpyrrolidone, blowing nitrogen for 10 min, and stirring at 75° C. and 200 rpm for 0.5 h to perform a first mixing to obtain a mixed solution;

[0097] (3) adding 2.0 mol% of the pretreated styrene in 2,2-azobisisobutylamidine dihydrochloride to the mixed solution of step (2) under stirring at 250 rpm, stirring at 75° C. and 250 rpm for 24 h to carry out polymerization reaction, and cooling to room temperature to obtain a monodisperse polystyrene sphere gel;

[0098] (4) Under ultrasonic dispersion conditions, 10 g of n-octyltrimethoxysilane was dissolved in 42 g of an alcohol-water mixture (40 g of ethanol and 2 g of deionized water), and the mixture was stirred at 25 r / min for 1 h to mix evenly. 0.2 g of hydrochloric acid was added and the stirring was continued for 1 h to mix and react, and then 10 g of methyl orthosilicate was slowly added and the stirring was continued for 1 h to mix evenly to obtain a silicon source mixture. The silicon source mixture was added to the monodisperse polystyrene sphere colloid described in step (3), and the mass ratio of the monodisperse polystyrene sphere colloid to the silicon source mixture was 1:1.5. The mixture was stirred at a speed of 200 rpm for 30 min at a temperature of 60 ° C. for a second mixing, and the mixture was allowed to stand for 60 min. After drying at 120 ° C for 10 h, silica microspheres were obtained.

[0099] (5) The silica microspheres prepared in step (4) were heated to 600°C at a heating rate of 4°C / min, kept at this temperature for 5 hours, and subjected to heat treatment. After natural cooling, hollow silica microspheres were obtained.

[0100] The hollow silica microspheres prepared in this example have uniform size, uniform wall thickness, uniform morphology, and high sphericity.

[0101] Figure 1 The TEM image of the hollow silica microspheres prepared in Example 1 of the present invention at 1 μm is shown. Figure 2 The TEM image of the hollow silica microspheres prepared in Example 1 of the present invention at 200 nm is shown. As can be seen from the figure, the hollow silica microspheres prepared in the present invention have a high sphericity and uniform particle size, a clear boundary between the wall and the hollow part, a good morphology, and a uniform wall thickness, which is an ideal hollow silica microsphere structure.

[0102] Example 2

[0103] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (3), n-octyltrimethoxysilane is replaced by an equal amount of phenyltrimethoxysilane, and methyl orthosilicate is replaced by hexyl orthosilicate. The remaining preparation methods and parameters remain the same as those of Example 1.

[0104] The hollow silica microspheres prepared in this example have uniform size, uniform wall thickness, uniform morphology, and high sphericity.

[0105] Example 3

[0106] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (3), n-octyltrimethoxysilane is replaced by an equal amount of phenyltrimethoxysilane, the hydroalcoholic solution is 45 g of methanol and 2 g of deionized water, the catalyst is replaced by an equal amount of oxalic acid, and methyl orthosilicate is replaced by hexyl orthosilicate. The remaining preparation methods and parameters are consistent with those of Example 1.

[0107] The hollow silica microspheres prepared in this example have uniform size, uniform wall thickness, uniform morphology, and high sphericity.

[0108] Example 4

[0109] This embodiment provides hollow silica microspheres and a preparation method thereof, the preparation method comprising the following steps:

[0110] (1) thoroughly washing 60 mL of styrene with 20 mL of a 15 wt% ammonia solution and deionized water in sequence to obtain pretreated styrene;

[0111] (2) adding the pretreated styrene prepared in step (1) to a 0.8 wt% aqueous solution of polyvinylpyrrolidone, blowing nitrogen for 3 minutes, and stirring at 50° C. and 200 rpm for 0.5 hours to perform a first mixing to obtain a mixed solution;

[0112] (3) adding 0.05 mol% of the pretreated styrene in the amount of 2,2-azobisisobutylamidine dihydrochloride to the mixed solution of step (2) under stirring at 200 rpm, stirring at 250 rpm for 20 h at 50° C. to carry out polymerization reaction, and cooling to room temperature to obtain a monodisperse polystyrene sphere gel;

[0113] (4) Under ultrasonic dispersion conditions, 1 g of n-octyltriethoxysilane was dissolved in 22 g of an alcohol-water mixture (20 g of ethanol and 1 g of deionized water), and the mixture was stirred at 25 r / min for 1 h to mix evenly. 2 g of hydrochloric acid was added and the stirring was continued for 1 h to mix and react, and then 1 g of butyl orthosilicate was slowly added and the stirring was continued for 1 h to mix evenly to obtain a silicon source mixture. The silicon source mixture was added to the monodisperse polystyrene sphere colloid described in step (3), and the mass ratio of the monodisperse polystyrene sphere colloid to the silicon source mixture was 1:1.2. The mixture was stirred at a speed of 250 rpm at a temperature of 50 ° C for 20 min, and a second mixing was performed. The mixture was allowed to stand for 40 min and dried at 80 ° C for 12 h to obtain silica microspheres.

[0114] (5) The silica microspheres prepared in step (4) were heated to 500°C at a heating rate of 0.5°C / min, kept at this temperature for 2 hours, and subjected to heat treatment. After natural cooling, hollow silica microspheres were obtained.

[0115] The hollow silica microspheres prepared in this example have uniform size, uniform wall thickness, uniform morphology, and high sphericity.

[0116] Example 5

[0117] This embodiment provides hollow silica microspheres and a preparation method thereof, the preparation method comprising the following steps:

[0118] (1) thoroughly washing 100 mL of styrene with 20 mL of a 10 wt% ammonia solution and deionized water in sequence to obtain pretreated styrene;

[0119] (2) adding the pretreated styrene prepared in step (1) to a 0.2 wt% aqueous solution of polyvinylpyrrolidone, blowing nitrogen for 15 minutes, and stirring at 100° C. and 250 rpm for 2 hours to perform a first mixing to obtain a mixed solution;

[0120] (3) adding 4 mol% of the pretreated styrene in 2,2-azobisisobutylamidine dihydrochloride to the mixed solution of step (2) under stirring at 250 rpm, stirring at 100° C. and 250 rpm for 80 h to carry out polymerization reaction, and cooling to room temperature to obtain a monodisperse polystyrene sphere gel;

[0121] (4) Under stirring conditions, 10 g of triethoxymethylsilane was dissolved in 52 g of an alcohol-water mixture (50 g of ethanol and 2 g of deionized water), and stirred at 25 r / min for 1 h to mix evenly. Then, 1 g of hydrochloric acid was added and the stirring was continued for 1 h to mix and react. Then, 10 g of butyl orthosilicate was slowly added and the stirring was continued for 1 h to mix evenly to obtain a silicon source mixture. The silicon source mixture was added to the monodisperse polystyrene sphere glue described in step (3). The mass ratio of the monodisperse polystyrene sphere glue to the silicon source mixture was 1:2.0. The mixture was stirred at a temperature of 100 ° C and a speed of 200 rpm for 60 min, and a second mixing was performed. The mixture was allowed to stand for 80 min and dried at 150 ° C for 8 h to obtain silica microspheres.

[0122] (5) The silica microspheres prepared in step (4) were heated to 1100° C. at a heating rate of 5° C. / min, kept at this temperature for 8 h, and subjected to heat treatment. After natural cooling, hollow silica microspheres were obtained.

[0123] The hollow silica microspheres prepared in this example have uniform size, uniform wall thickness, uniform morphology, and high sphericity.

[0124] Example 6

[0125] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (4), the total mass of the silicon source is kept unchanged, n-octyltrimethoxysilane is replaced with 5 g, and methyl orthosilicate is replaced with 15 g. The remaining preparation methods and parameters remain the same as those of Example 1.

[0126] The hollow silica microspheres prepared in this example were uneven in size, not completely hollow inside, and their wall thickness could not be measured.

[0127] Figure 3 The TEM image of the hollow silica microspheres prepared in Example 6 of the present invention at 1 μm is shown. As can be seen from the figure, the hollow silica microspheres prepared in the present invention are uneven in size, the interior is not completely hollow, and the boundary between the wall and the hollow part is blurred.

[0128] Example 7

[0129] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (4), the total mass of the silicon source is kept unchanged, n-octyltrimethoxysilane is replaced with 15 g, and methyl orthosilicate is replaced with 5 g. The remaining preparation methods and parameters remain the same as those of Example 1.

[0130] The hollow silica microspheres prepared in this example are uneven in size, exhibit heterogeneous nucleation and abnormal growth, have uneven wall thickness, and have a large difference in wall thickness between individual hollow silica microspheres.

[0131] Example 8

[0132] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (3), the content of 2,2-azobisisobutylamidine dihydrochloride is 4.2 mol %. The remaining preparation methods and parameters are consistent with those of Example 1.

[0133] The hollow silica microspheres prepared in this example have uniform wall thickness, but uneven size, low purity and low sphericity.

[0134] Example 9

[0135] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (4), the amount of ethanol used is 60 g, and the remaining preparation methods and parameters remain the same as those of Example 1.

[0136] The hollow silica microspheres prepared in this example have uniform wall thickness, but uneven size, low purity and low sphericity.

[0137] Example 10

[0138] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (3), the polymerization reaction time is 18 h, and the remaining preparation methods and parameters remain the same as those of Example 1.

[0139] The hollow silica microspheres prepared in this example have uniform wall thickness, but uneven size, low purity and low sphericity.

[0140] Example 11

[0141] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (3), the polymerization reaction temperature is 30° C., and the remaining preparation methods and parameters remain the same as those of Example 1.

[0142] The hollow silica microspheres prepared in this example have uniform wall thickness, but uneven size, low purity and low sphericity.

[0143] Example 12

[0144] This embodiment provides hollow silica microspheres and a preparation method thereof. The preparation method differs from that of Example 1 in that, in step (3), the polymerization reaction temperature is 120° C., and the remaining preparation methods and parameters remain consistent with those of Example 1.

[0145] The hollow silica microspheres prepared in this example have uniform wall thickness, but uneven size, low purity and low sphericity.

[0146] Comparative Example 1

[0147] This comparative example provides a method for preparing hollow silica microspheres. The difference between the preparation method and Example 1 is that step (1) is omitted and styrene is directly added to the stabilizer solution. The remaining preparation methods and parameters are consistent with Example 1.

[0148] The hollow silica microspheres prepared in this comparative example were uneven in size and contained a large number of agglomerated particles. The dispersion was extremely poor and the wall thickness could not be measured.

[0149] Figure 4 The SEM image of the hollow silica microspheres prepared in Comparative Example 1 of the present invention is shown. As can be seen from the figure, the hollow silica microspheres are agglomerated, have different sizes, and have a poor sphericity.

[0150] Comparative Example 2

[0151] This comparative example provides a method for preparing hollow silica microspheres. The difference between the preparation method and Example 1 is that the process of adding the pretreated styrene described in step (1) to the stabilizer solution in step (2) is omitted, and the cationic initiator is directly added to the pretreated styrene. The rest of the preparation method and parameters are consistent with Example 1.

[0152] The hollow silica microspheres prepared in this comparative example were uneven in size and contained a large number of agglomerated particles. The dispersion was extremely poor and the wall thickness could not be measured.

[0153] Figure 5 The SEM image of the hollow silica microspheres prepared in Comparative Example 2 of the present invention is shown. As can be seen from the figure, the hollow silica microspheres are agglomerated, have different sizes, and have a poor sphericity.

[0154] Comparative Example 3

[0155] This comparative example provides a method for preparing hollow silica microspheres. The difference between the preparation method and Example 1 is that the addition of ethyl orthosilicate in step (4) is omitted, and a silicon source is used, that is, 20g of n-octyltrimethoxysilane is dissolved in an alcohol-water mixture (40g of ethanol and 2g of deionized water), and the mixture is stirred at 25r / min for 1h to mix evenly, and then 0.2g of hydrochloric acid is added and the stirring is continued for 1h to obtain a silicon source mixture. The rest of the preparation method and parameters are consistent with Example 1.

[0156] The hollow silica microspheres prepared in this comparative example are uneven in size, have extremely poor dispersion, and exhibit heterogeneous nucleation and abnormal growth. The wall thickness is uneven, and the wall thickness of individual hollow silica microspheres varies greatly. The silica wall is not dense and has a large number of pores.

[0157] Figure 6 The SEM image of the hollow silica microspheres prepared in Comparative Example 3 of the present invention is shown. As can be seen from the figure, the hollow silica microspheres are agglomerated, have different sizes, and have poor purity and sphericity.

[0158] Comparative Example 4

[0159] This comparative example provides a method for preparing hollow silica microspheres. The difference between the preparation method and Example 1 is that the addition of n-octyltrimethoxysilane in step (4) is omitted, and a silicon source is used, that is, 20g of methyl orthosilicate is dissolved in an alcohol-water mixture (40g of ethanol and 2g of deionized water), and the mixture is stirred at 25r / min for 1h to mix uniformly, and then 0.2g of hydrochloric acid is added and the stirring is continued for 1h to obtain a silicon source mixture. The rest of the preparation method and parameters are consistent with Example 1.

[0160] The hollow silica microspheres prepared in this comparative example were uneven in size, and had poor purity and sphericity.

[0161] Comparative Example 5

[0162] This comparative example provides a method for preparing hollow silica microspheres. The difference between the preparation method and Example 1 is that step (2) and step (3) are combined, and the pretreated styrene, polyvinylpyrrolidone aqueous solution and 2,2-azobisisobutylamidine dihydrochloride are directly mixed. The rest of the preparation method and parameters are consistent with Example 1.

[0163] The hollow silica microspheres prepared in this comparative example had poor morphology, purity and sphericity.

[0164] Comparative Example 6

[0165] This comparative example provides a method for preparing hollow silica microspheres. The difference between the preparation method and Example 1 is that the cationic initiator is replaced by peroxydicarbonate in step (3), and the rest of the preparation method and parameters are consistent with Example 1.

[0166] The hollow silica microspheres prepared in this comparative example had poor morphology, and self-nucleation in the solution was common, resulting in a large number of solid silica microspheres with poor purity and sphericity.

[0167] The hollow silica microspheres provided in Examples 1-12 and Comparative Examples 3-6 were tested for average diameter, wall thickness, purity, hollowness, sphericity, and dielectric properties. The specific test parameters are shown in Table 1.

[0168] The dielectric properties test method is as follows: hollow silica microspheres are mixed with a mixed adhesive (such as PTFE powder, paraffin, etc., with a proportion of less than 5%) and pressed into a dense shape with a diameter matching the resonant cavity. The resonant cavity is calibrated using a standard sample with a known Dk (such as quartz, Dk = 3.8) or no sample (air, Dk = 1). The test sample is placed in the center of the resonant cavity (avoiding air gaps). The sample position is changed or re-pressed for testing. The test is performed three times and the average value is taken.

[0169] Table 1

[0170]

[0171]

[0172] Note: “ / ” indicates that the corresponding test was not performed due to poor morphology, poor purity, sphericity and other properties, which did not meet expectations. In Example 6, the hollowness and wall thickness could not be obtained because the interior of the prepared product was not completely hollow.

[0173] The test results show that:

[0174] (1) It can be seen from Examples 1 to 5 that the present invention pre-treats the template raw material styrene, and after mixing it with a stabilizer solution to stabilize the pre-treated styrene system, performs a polymerization process to make the size of the prepared polystyrene sphere template uniform and avoid disorder. Subsequently, the hollow silica microspheres prepared by combining a silicon source mixture containing two silicon sources have high sphericity, high purity, strong wall thickness and uniform particle size distribution. Specifically, the sphericity can reach 99% or above, the purity can reach 98%, the particle size distribution is narrow and uniform, the average particle size is concentrated between 0.1μm and 5μm, and the dielectric properties are excellent.

[0175] (2) It can be seen from Examples 1 and 6-7 that the present invention can make the reaction uniform and the internal structure stable by regulating 1 part to 10 parts of the first silicon source and 1 part to 10 parts of the second silicon source. If the first silicon source is too much, that is, in Example 7, the silica shell formed will be too thick and the silica layer will be too thick, thereby reducing the internal space of the hollow structure. At the same time, too high a concentration will cause heterogeneous nucleation or abnormal growth, resulting in a decrease in purity and sphericity. In addition, the wall thickness of the hollow silica microspheres is uneven, and the wall thickness of individual hollow silica microspheres is different. If the second silicon source content is too much, that is, in Example 6, firstly, it will affect the stability of the internal structure. Under high temperature treatment conditions, the cavity shape will be irregular and not completely hollow (part of the second silicon source will exist in the hollow part), making it difficult to form an ideal cavity. Secondly, in the process of removing the template, it will hinder the smooth escape of gas, causing internal pressure accumulation, thereby affecting the integrity of the hollow structure. Thirdly, it will participate in unnecessary side reactions, generate other impurities or by-products, thereby causing a decrease in purity and sphericity.

[0176] (3) It can be seen from Examples 1 and 8 to 12 that the present invention can better control the particle size and yield of the template polystyrene spheres by further regulating the amount of cationic initiator added, the amount of ethanol used, and the time and temperature of the polymerization reaction, and thus regulate the size, purity and sphericity of the hollow silica microspheres using them as templates.

[0177] (4) It can be seen from Example 1 and Comparative Example 1 that the present invention pre-treats styrene and removes the internal polymerization inhibitor by alkali washing to improve the activity of styrene polymerization. After combining with the subsequent stabilizer solution, the morphology of the polymerized polystyrene spheres is uniform, the spheres are dispersed and the size is uniform. When the pre-treatment is omitted, the hollow silica microspheres prepared are uneven in size, and there are a large number of agglomerated particles, and the dispersibility is extremely poor.

[0178] (5) It can be seen from Example 1 and Comparative Example 2 that when the cationic initiator is directly added to the pretreated styrene and the process of adding the pretreated styrene to the stabilizer solution is omitted, the process stability of the polymerization reaction is low, and the size and morphology of the polystyrene sphere template obtained after polymerization cannot achieve a uniform effect.

[0179] (6) It can be seen from Example 1 and Comparative Examples 3-4 that the use of a single silicon source cannot achieve uniform size of the prepared hollow silica microspheres, nor can it achieve uniform wall thickness and dense wall effects. At the same time, the purity and sphericity will also be significantly reduced.

[0180] (7) It can be seen from Example 1 and Comparative Example 5 that directly mixing the pretreated styrene, the polyvinylpyrrolidone aqueous solution and 2,2-azobisisobutylamidine dihydrochloride, that is, the process of dispersing and stabilizing the styrene and the process of the polymerization reaction are carried out simultaneously, still cannot ensure that the size and morphology of the polystyrene sphere template obtained after polymerization are uniform, nor can the polymerization reaction path be selectively controlled, and the polymerization degree and particle size distribution cannot be more finely regulated.

[0181] (8) It can be seen from Example 1 and Comparative Example 6 that if a cationic initiator is not used, it is impossible to ensure that silica nucleates uniformly on the surface of the polystyrene sphere template, and a large amount of solid silica will exist after silica nucleates in the solution, resulting in a significant reduction in the purity of the hollow silica microspheres.

[0182] In summary, the hollow silica microspheres provided by the present invention have a high sphericity, a solid wall thickness, a uniform particle size distribution, high purity, relatively good dielectric properties, and extremely low content of various metal impurities, which can meet the application requirements of high-speed and high-frequency substrates, and the preparation method provided by the present invention uses less raw materials, a simple preparation process, low cost, and high efficiency. In terms of the preparation method, the present invention pre-treats the template raw material styrene first, and after mixing it with a stabilizer solution to stabilize the pre-treated styrene system, a polymerization process is performed to make the prepared polystyrene sphere template uniform in size, avoiding confusion, and subsequently combining it with a silicon source mixture containing two silicon sources to prepare hollow silica microspheres with high sphericity, high purity, a solid wall thickness, and a uniform particle size distribution, and extremely low content of various metal impurities.

[0183] The applicant declares that the above is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the scope of protection and disclosure of the present invention.

Claims

1. A hollow silica microsphere, characterized in that: The hollow silica microspheres have a dielectric constant of ≤2.5, a dielectric loss tangent of ≤0.001, a purity of >95%, a sphericity of ≥99%, a wall thickness of 0<≤0.42 μm, an average diameter of 0.1 μm-5 μm, and a relationship between the hollowness, the wall thickness, and the average particle size: Here, η is the hollow ratio, t is the wall thickness, and R is 1 / 2 of the average particle size.

2. The hollow silica microspheres according to claim 1, characterized in that The hollow silica microspheres have a hollow ratio of 30% to 80%.

3. A method for preparing hollow silica microspheres according to claim 1 or 2, characterized in that: The preparation method comprises the following steps: The silicon source mixture is added to the monodisperse polystyrene sphere gel to react with each other to obtain silica microspheres, which are then heat-treated to obtain hollow silica microspheres. The raw materials of the silicon source mixture include a first silicon source, a second silicon source, a catalyst and an alcohol-water mixture; the monodisperse polystyrene sphere glue is obtained by polymerization reaction of a cationic initiator and a styrene-containing stabilizer solution, and the styrene-containing stabilizer solution includes pretreated styrene after alkali washing and a stabilizer solution.

4. The preparation method according to claim 3, characterized in that The method for preparing the silicon source mixed solution comprises: mixing a first silicon source, a second silicon source, a catalyst and an alcohol-water mixed solution for reaction under stirring or ultrasonic dispersion conditions to obtain the silicon source mixed solution.

5. The preparation method according to claim 4, characterized in that The method of mixing the first silicon source, the second silicon source, the catalyst and the alcohol-water mixture for reaction comprises: firstly mixing the first silicon source and the alcohol-water mixture evenly, then adding the catalyst and mixing and reacting, and then adding the second silicon source and mixing evenly to obtain a silicon source mixture; Preferably, the first silicon source comprises any one or a combination of at least two of methoxysilane, methylsilane, ethoxysilane, ethylsilane, propoxysilane, propylsilane, butoxysilane, vinylsilane or trimethoxysilane; Preferably, the second silicon source comprises any one of ethyl orthosilicate, methyl orthosilicate or butyl orthosilicate, or a combination of at least two thereof; Preferably, during the preparation of the silicon source mixture, the first silicon source is added in an amount of 1-10 parts, the alcohol-water mixture is added in an amount of 1-120 parts, the catalyst is added in an amount of 0.01-5 parts, and the second silicon source is added in an amount of 1-10 parts by mass; Preferably, the alcohol-water mixture comprises, by mass: 0.1-2 parts of deionized water and 1-50 parts of alcohol solution; Preferably, the mass ratio of the monodisperse polystyrene sphere glue to the silicon source mixed solution is 1:(1.2-2.0).

6. The preparation method according to any one of claims 3 to 5, characterized in that The mixing reaction includes a process of stirring and standing; Preferably, the temperature of the heat treatment is 500°C-1100°C; Preferably, the heating rate of the heat treatment is 0.3°C / min-10°C / min; Preferably, the heat treatment time is 2h-8h.

7. The preparation method according to any one of claims 3 to 6, characterized in that The preparation method of the monodisperse polystyrene sphere glue comprises: alkali washing styrene to obtain pretreated styrene, adding the pretreated styrene to a stabilizer solution and mixing evenly, and then adding a cationic initiator to carry out polymerization reaction to obtain the monodisperse polystyrene sphere glue; Preferably, the cationic initiator includes any one or a combination of at least two of 2,2-azobisisobutylamidine dihydrochloride, an onium salt organic compound, a Lewis acid or an alkyl halide; Preferably, the amount of the cationic initiator added is 0.05 mol% to 4.0 mol% of the molar amount of the pretreated styrene; Preferably, the polymerization reaction temperature is 50°C-100°C; Preferably, the polymerization reaction time is ≥20 h.

8. The preparation method according to claim 7, characterized in that The alkali solution used in the alkali washing includes an ammonia solution and / or a urea solution; Preferably, the volume ratio of the alkali solution to the styrene is 1:(3-5); Preferably, the stabilizer solution comprises any one of a polyvinyl pyrrolidone aqueous solution, a polyvinyl alcohol aqueous solution or a sodium lauryl sulfate aqueous solution, or a combination of at least two thereof.

9. The preparation method according to claim 3, characterized in that The preparation method comprises the following steps: The silicon source mixture is added to the monodisperse polystyrene sphere glue, wherein the mass ratio of the monodisperse polystyrene sphere glue to the silicon source mixture is 1:(1.2-2.0), the mixture is stirred at 50°C-100°C at a speed of 200rpm-250rpm for 20min-60min for mixing reaction, the mixture is allowed to stand for 40min-80min, and the mixture is dried at 80°C-150°C for 8h-12h to obtain silica microspheres, and the silica microspheres are heated to 500°C-1100°C at a heating rate of 0.3°C / min-10°C / min and heat-treated for 2h-8h to obtain hollow silica microspheres; The raw materials of the silicon source mixed solution include a first silicon source, a second silicon source, a catalyst and an alcohol-water mixed solution; The method for preparing the silicon source mixed solution comprises: firstly mixing 1-10 parts of a first silicon source with 1-120 parts of an alcohol-water mixed solution, then adding 0.01-5 parts of a catalyst for mixed reaction, and then adding 1-10 parts of a second silicon source and mixing them evenly to obtain a silicon source mixed solution; wherein the alcohol-water mixed solution comprises, by weight, 0.1-2 parts of deionized water and 1-50 parts of an alcohol solution; The monodisperse polystyrene sphere glue is obtained by polymerization reaction of a cationic initiator and a styrene-containing stabilizer solution, wherein the styrene-containing stabilizer solution comprises pretreated styrene after alkali washing and a stabilizer solution; The preparation method of the monodisperse polystyrene sphere glue comprises: alkali washing styrene to obtain pretreated styrene, adding the pretreated styrene to a stabilizer solution with a concentration of 0.2wt%-0.8wt%, removing bubbles for 3-15 minutes, stirring at 50°C-100°C and a speed of 200rpm-250rpm for 0.5h-2h, mixing evenly, adding a cationic initiator under the stirring condition of 200rpm-250rpm, stirring at 50°C-100°C and a speed of 200rpm-250rpm for ≥20h, and performing a polymerization reaction to obtain the monodisperse polystyrene sphere glue; The volume ratio of the alkali solution used in the alkali washing to the styrene is 1:(3-5), and the concentration of the alkali solution used in the alkali washing is 8wt%-15wt%; the added amount of the cationic initiator is 0.05mol%-4.0mol% of the molar amount of the pretreated styrene.

10. An application of hollow silica microspheres, characterized in that: The hollow silica microspheres according to claim 1 or 2, or the hollow silica microspheres prepared by the preparation method according to any one of claims 3 to 9, are applied to high-speed and high-frequency substrates.

Images