阅读说明：本技术 低介电空心二氧化硅微球的制备方法 (Preparation method of low-dielectric hollow silicon dioxide microspheres ) 是由 尹亚玲 郑海涛 沈晓燕 于 2020-06-18 设计创作，主要内容包括：本发明提供了一种低介电空心二氧化硅微球的制备方法,本方法采用聚苯乙烯作为空心微球的模板,并加入阳离子共聚单体丙烯酰氧乙基三甲基氯化铵(DAC),向聚合物链上引入正电荷基团,制备出带正电的聚苯乙烯球。本方法无需加入活化剂,使得球体表面自带正电就能够吸引硅源以均匀包覆于模板上。通过本发明提供的煅烧方法,能够得到致密的球体结构。本发明整体提供了一种模板法制备二氧化硅微球的方法,制备出来的微球成球率高,致密不易破球,且具有较低的低介电常数,提高基板模量和耐热性使得特别适用于覆铜板行业的需要。(The invention provides a preparation method of low dielectric hollow silica microspheres, which adopts polystyrene as a template of the hollow microspheres, adds a cationic comonomer acryloyloxyethyl trimethyl ammonium chloride (DAC), and introduces positive charge groups to a polymer chain to prepare positively charged polystyrene spheres. According to the method, an activating agent is not required to be added, so that the silicon source can be attracted to be uniformly coated on the template by the spherical surface with positive electricity. By the calcining method provided by the invention, a compact spherical structure can be obtained. The invention integrally provides a method for preparing silicon dioxide microspheres by a template method, the prepared microspheres have high balling rate, are compact and difficult to break, have lower low dielectric constant, and improve the modulus and heat resistance of a substrate, so that the method is particularly suitable for the requirement of the copper-clad plate industry.)

1. A preparation method of low dielectric hollow silicon dioxide microspheres is characterized in that,

preparing a template ball solution, wherein the template ball solution comprises 1-6% by mass of polyvinylpyrrolidone, 5-25% by mass of styrene, 0.2-1.2% by mass of azobisisobutyronitrile, 0.01-10% by mass of cationic comonomer acryloyloxyethyl trimethyl ammonium chloride, water and ethanol;

step two, preparing template sphere dispersion liquid, uniformly stirring the solution obtained in the step one, introducing nitrogen for 10-30min, heating the solution to 50-80 ℃, and continuously stirring for 10-30h to obtain the template sphere dispersion liquid;

step three, preparing an organic silicon source hydrolysis solution, adding an acid catalyst into the methyltrimethoxysilane solution at the temperature of 30-50 ℃, and stirring at the stirring speed of 200-400r/min for 2-5h to ensure that the pH value of the solution is 3-4;

step four, adding a certain amount of alkaline catalyst into the template sphere dispersion liquid obtained in the step two, and stirring for 3-10min to enable the pH value of the template sphere dispersion liquid to be 10-12;

step five, adding the organic silicon source hydrolysis solution prepared in the step three into the step four, stirring, and standing for 6-24 hours at room temperature;

and sixthly, washing the filtered solution, putting the filtered substance into an oven, baking and drying at 40-70 ℃, and calcining to prepare the silicon dioxide microspheres.

2. The method as claimed in claim 1, wherein the temperature of the filtrate in step six is first raised to 400-600 ℃ at 0.3 ℃/min and then maintained for 2-4h, and then raised to 800-1000 ℃ at 3 ℃/min.

3. The preparation method of the low dielectric hollow silica microspheres according to claim 1 or 2, wherein the prepared silica microspheres have a wall thickness of 50-200nm and a particle size of 0.3-3 um.

4. The method for preparing hollow silica microspheres with low dielectric constant according to claim 1 or 2, wherein the acidic catalyst in the third step is hydrochloric acid.

5. The method for preparing hollow silica microspheres with low dielectric constant according to claim 1 or 2, wherein the basic catalyst in the fourth step is ammonia water.

6. The preparation method of the hollow silica microspheres with low dielectric constant according to claim 1 or 2, wherein the mass ratio of water to ethanol in the first step is 1: 9.

7. The method for preparing hollow silica microspheres with low dielectric constant according to claim 1 or 2, wherein the solid content of the template sphere dispersion liquid in the second step is 10-30%.

8. The method for preparing hollow silica microspheres with low dielectric constant according to claim 1 or 2, wherein the mass ratio of methyltrimethoxysilane to water in the trimethyltrimethoxysilane solution in the step is 1: 5-25.

9. The preparation method of the low dielectric hollow silica microspheres according to claim 1 or 2, wherein the mass ratio of the basic catalyst to the methyltrimethylsilane is 1: 1 to 10.

10. The method for preparing hollow silica microspheres with low dielectric constant of claim 2, wherein the filtrate of the sixth step is first heated to 550 ℃ at a rate of 0.3 ℃/min and then kept at the temperature for 3 hours, and then heated to 950 ℃ at a rate of 3 ℃/min.

11. A copper-clad plate, characterized in that, the hollow silica microspheres prepared by the method of claims 1 to 9 are used as filler.

Technical Field

The invention relates to the technical field of non-metallic materials, in particular to a method for preparing hollow silicon dioxide microspheres by using polystyrene microspheres prepared by styrene polymerization as a template body.

Background

The hollow silica microsphere is a multi-scale multi-layer nano structure which is composed of nano particles, has the size ranging from nano to micron and is provided with a hollow cavity. Compared with the corresponding block material, the material has larger specific surface area, smaller density, special mechanical, optical, electrical and other physical properties and application values.

The silica microspheres as the nanoscale inorganic material have the excellent characteristics of low density, low thermal expansion coefficient, high insulativity, low dielectric constant, stable chemical performance and the like in the filler used for the copper-clad plate, and have very wide application fields. Particularly in the integrated circuit packaging and copper-clad plate industry, the hollow silicon dioxide is used as a key core raw material, and particularly, the silicon dioxide filler with the hollow structure is applied to the copper-clad plate, so that the cost can be reduced, the thermal expansion coefficient can be reduced, the modulus of the substrate can be improved, the heat resistance can be improved, and the like.

The prior art methods for preparing hollow silica microspheres include template method, gel method, microemulsion method, etc.

The Chinese patent with the publication number of CN110775981A and the name of silica microspheres and the manufacturing method thereof discloses a method for preparing silica microspheres by adopting a template method. Specifically, the present inventors have made extensive studies to produce micro-nano silica microspheres by a method using a template, and as a result, have found that silica microspheres having a particle size of a micro-nanometer order and a uniform particle size distribution can be obtained by using a graft copolymer of branched polyethyleneimine (hereinafter, also referred to as bPEI) and polyalkylmethacrylate as a template, and that the particle size of the obtained silica microspheres can be controlled by changing the concentration of the graft copolymer in the production of silica microspheres, thereby completing the present invention. Therefore, in the invention, the tool compound is used as the template sphere to prepare the silica microsphere so as to achieve the purposes of uniform particle size distribution and particle size control. But the disadvantage is that the surface of the silicon dioxide prepared by the method has more mesopores, so the dielectric constant is higher.

The preparation method of the nano silica microspheres with the particle size of 10-20nm under the name of CN110683552A discloses the preparation of the silica microspheres by a gel method. Referring to the 'preparation method of nano silica microspheres with particle size of 10-20 nm' described in paragraph 006 of the specification, tetraethoxysilane is dissolved in ethanol to prepare a solution A, ammonia water is dissolved in ethanol to prepare a solution B, and a dispersant is dissolved in ethanol to prepare a solution C; dripping the solution A and the solution C into the solution B at the same time, and reacting to obtain wet gel; and drying and foaming the wet gel at constant temperature in the air atmosphere to obtain dry gel, and heating and calcining the dry gel in stages in the air atmosphere to obtain the nano silicon dioxide microspheres. However, the particle size and wall thickness of the hollow silica microspheres prepared by the method are difficult to control, the surface of the template particles is functionalized by a sol-gel method, generally, a surfactant is added to self-assemble the surface of the template particles, then, a silica layer is formed on the surface of the template by utilizing silane hydrolysis/condensation reaction, and finally, the hollow microspheres also need to be calcined to remove the template to obtain the hollow silica microspheres. Because the surfactant is added and the amount of the surfactant is difficult to control the uniform nucleation of the silicon dioxide in the solution, the silicon dioxide is not polymerized into spheres on the surface of the template but is condensed into spheres in the solution.

The method for preparing the silica microspheres by adopting a microemulsion method is disclosed in a preparation method of the silica microspheres with the publication number of CN 110482558A. Specifically, the description in paragraph 0027 of the specification states that "the precursor solution is jetted to form uniform droplets by a jet flow method, and the droplets are dispersed in a seed suspension, the polymer seeds quickly absorb the droplets and grow, after reaction, silica composite microspheres are obtained, and the porous silica microspheres are calcined. The precursor solution provided by the invention has uniform droplet size, is easier to be completely absorbed by polymer seeds, reduces the time required by the whole preparation process, and improves the production efficiency. Said invention utilizes the polarity difference between silane and different solvents (including supercritical substance), under the action of surfactant the oil-in-water or water-in-oil emulsion can be obtained, and uses the 'water pool' in the liquid drop as microreaction container, and utilizes the interface chemical reaction to make silane undergo the process of hydrolysis-condensation on the surface of microdroplet, and after the thermal treatment the hollow structure silicon dioxide microsphere can be formed. The control of the thickness, the surface form and the particle size of the hollow microsphere shell is realized in the dynamic balance of surface tension and hydrostatic force, and the preparation of the hollow microsphere by the microemulsion method is easily restricted by the process conditions and the properties of the hollow microsphere because the surface tension and the hydrostatic force are related to the properties of the substance and the external environment. The structural control thereof is complicated because of too many influencing factors. Therefore, the method is difficult to obtain the hollow microspheres with uniform particle size and uniform wall thickness.

The applicant researches further, and the prepared hollow silica microspheres have the general requirements of ensuring uniform particle size distribution of the silica microspheres and no agglomeration. It must also be ensured that the wall thickness of the hollow microspheres is such that the spheres are not broken during calcination by the gas pressure generated by the gasification of the internal template body which would otherwise impact the walls of the spheres. Meanwhile, the applicant finds that the dielectric constant of the silica microsphere is influenced by two factors in the aspect of the sphere structure, namely the hollow structure of the silica and the compactness of the surface of the silica. The former requires control of the thickness of the walls of the silica microspheres to achieve a proper hollow structure, and the latter requires control of the calcination process to make the silica surface dense. Based on the applicant, a preparation method of hollow silica is provided to achieve the purpose of preparing silica with low dielectric constant.

What is the reason why the hollow silica microspheres prepared by the existing method have high dielectric constants needs technical solutions specifically directed to the above three patent documents.

Disclosure of Invention

In order to solve the technical problems, the invention provides a preparation method of low-dielectric hollow silica microspheres, and aims to provide a preparation method of hollow silica microspheres with good dispersibility, uniform particle size distribution, proper wall thickness and low dielectric constant.

A method for preparing low dielectric hollow silicon dioxide microspheres,

preparing a template ball solution, wherein the template ball solution comprises 1-6% by mass of polyvinylpyrrolidone, 5-25% by mass of styrene, 0.2-1.2% by mass of azobisisobutyronitrile, 0.01-10% by mass of cationic comonomer acryloyloxyethyl trimethyl ammonium chloride, water and ethanol;

step two, preparing template sphere dispersion liquid, uniformly stirring the solution obtained in the step one, introducing nitrogen for 10-30min, heating the solution to 50-80 ℃, and continuously stirring for 10-30h to obtain the template sphere dispersion liquid;

step three, preparing an organic silicon source hydrolysis solution, adding an acid catalyst into the methyltrimethoxysilane solution at the temperature of 30-50 ℃, and stirring at the stirring speed of 200-400r/min for 2-5h to ensure that the pH value of the solution is 3-4;

step four, adding a certain amount of alkaline catalyst into the template sphere dispersion liquid obtained in the step two, and stirring for 3-10min to enable the pH value of the template sphere dispersion liquid to be 10-12;

step five, adding the organic silicon source hydrolysis solution prepared in the step three into the step four, stirring, and standing at room temperature for 6-24 hours;

and sixthly, washing the filtered solution, putting the filtered substance into an oven, baking and drying at 40-70 ℃, and calcining to prepare the silicon dioxide microspheres.

Preferably, the filtrate in the sixth step is first heated to 400-600 ℃ at a speed of 0.3 ℃/min and then is kept at the temperature for 2-4h, and then is heated to 800-1000 ℃ at a speed of 3 ℃/min.

Preferably, the wall thickness of the prepared silicon dioxide microspheres is 50-200nm, and the particle size is 0.3-3 um. (where the wall thickness is 50-200nm, where the last time an engineer was communicated with the wall thickness is limited by the specified mass range of the compound added in the previous step, below a data value or above a data value, where the desired wall thickness was not obtained, and there was a positive correlation within a range

Preferably, the acidic catalyst in step three is hydrochloric acid.

Preferably, the alkaline catalyst in the fourth step is ammonia water.

Preferably, the mass ratio of the water to the ethanol in the first step is 1: 9.

Preferably, the solid content of the template sphere dispersion liquid in the second step is 10-30%.

Preferably, the mass ratio of methyltrimethoxysilane to water in the trimethyltrimethoxysilane solution in the step is 1: 5-25.

Preferably, in the fifth step, the mass ratio of the basic catalyst to the methyltrimethylsilane is 1: 5.

preferably, the filtrate in the sixth step is heated to 550 ℃ at a speed of 0.3 ℃/min and is kept at the temperature for 3h, and the temperature is continuously heated to 950 ℃ at a speed of 3 ℃/min.

The copper-clad plate is prepared by using the silica microspheres prepared by the method as a filler.

The preparation method of the low dielectric hollow silica microspheres has the advantages that,

1. the preparation method can obtain the low dielectric hollow silica microspheres with controllable wall thickness and smooth and compact surfaces. The invention adopts a hard template method to prepare the hollow silica microspheres, and the Polystyrene (PS) microspheres are used as template spheres and are not easy to deform and break. Positive charge groups are introduced to a polymer chain by one-time feeding and adding a cationic comonomer of acryloyloxyethyl trimethyl ammonium chloride (DAC), so as to prepare the polystyrene spheres with positive charges. Positively charged polystyrene spheres are obtained by using the cationic comonomer acryloyloxyethyltrimethyl ammonium chloride (DAC) as comonomer. The method ensures that the polystyrene spheres can quickly capture the generated silica sol through electrostatic interaction, does not need to add a cationic surfactant for surface modification in the later period, and avoids direct and uniform nucleation of the silicon dioxide in the solution

2. In the selection of the silicon source, methyltrimethoxysilane (MTMS) is selected as the silicon source, a methyl group is arranged on the molecular structure, and the existence of the methyl group can avoid the silane from generating agglomeration in the polycondensation process, thus being beneficial to obtaining the monodisperse hollow silicon dioxide microsphere, the hydrolytic polycondensation process can be carried out at a lower temperature, stirring is not needed, the standing is carried out, and the energy consumption in the reaction process can be effectively reduced.

3. The calcining process can ensure that the surface of the calcined hollow silica microsphere is compact, has no holes and has low dielectric constant. In the invention, the temperature is raised to 600 ℃ of 400-. Meanwhile, the wall thickness and the particle size are controlled by adjusting the proportion of the ammonia water and the organic silicon source.

Drawings

FIG. 1 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 1.

FIG. 2 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 2.

FIG. 3 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 3 in accordance with the present invention.

FIG. 4 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 4 in accordance with the present invention.

FIG. 5 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 4 in accordance with the present invention.

FIG. 6 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 6 in accordance with the present invention.

FIG. 7 is a scanning electron microscope image of hollow silica microspheres prepared under the process conditions of example 7 in accordance with the present invention.

Detailed Description

The present invention will be described in detail below with reference to specific embodiments shown in the drawings. These embodiments are not intended to limit the present invention, and structural, methodological, or functional changes made by those skilled in the art according to these embodiments are included in the scope of the present invention.

The first embodiment is as follows:

step 1.1, dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene and 0.29g of initiator azodiisobutyronitrile for 10min, then putting the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring the mixture at room temperature to form a homogeneous solution;

step 1.2, deoxidizing the homogeneous solution for 30min by blowing nitrogen at room temperature, then heating to 70 ℃, and continuing stirring for reaction for 24h to obtain polystyrene sphere dispersion liquid;

step 1.3, adding 10g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 1.4, adding 2g of Cetyl Trimethyl Ammonium Bromide (CTAB) and 3ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 1.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 1.3, stopping stirring, and standing at room temperature for 8 h;

and step 1.5, filtering the solution obtained in the step 1.4, washing the solution with distilled water and ethanol for one time respectively, then putting the solution into an oven for drying at 50 ℃ for 3h, heating the solution to 550 ℃ at the speed of 0.3 ℃/min in a muffle furnace, keeping the temperature for 3h to remove polystyrene spheres, and then continuing heating the solution to 950 ℃ at the speed of 3 ℃/min to obtain the low dielectric hollow silica microspheres with smooth and compact surfaces.

As shown in the attached figure 1, FIG. 1 is a scanning electron microscope image of a hollow silica microsphere prepared by introducing cations on the surface of a polystyrene sphere by adding CTAB at the later stage without adding acryloyloxyethyltrimethyl ammonium chloride in the synthesis process of the polystyrene sphere. The graph shows that the particle size of the spheres is not uniform, self-aggregation occurs on the surfaces of the spheres, and the measured dielectric constant is 3.0.

Example two

Step 2.1, ultrasonically dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene, 0.29g of initiator azodiisobutyronitrile and cationic comonomer acryloyloxyethyltrimethyl ammonium chloride for 10min, then placing the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring at room temperature to form a homogeneous solution;

step 2.2, deoxidizing the homogeneous phase solution for 30min by blowing nitrogen at room temperature, then heating to 70 ℃, and continuing stirring for reaction for 24h to obtain a polystyrene sphere dispersion liquid with positive charges;

step 2.3, adding 5g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 2.4, adding 3ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 2.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 2.3, stopping stirring, and standing at room temperature for 8 h;

and 2.5, filtering the solution obtained in the step 2.4, washing the solution by using distilled water and ethanol respectively for one time, then putting the solution into an oven for drying at 50 ℃ for 3h, heating the solution to 550 ℃ at the speed of 0.3 ℃/min in a muffle furnace, keeping the temperature for 3h to remove polystyrene spheres, and then continuously heating the solution to 950 ℃ at the speed of 3 ℃/min to obtain the low dielectric hollow silica microspheres with smooth and compact surfaces. As shown in the attached FIG. 2, FIG. 2 is a scanning electron microscope image of a hollow silica microsphere prepared by adding acryloyloxyethyltrimethyl ammonium chloride during the synthesis of polystyrene spheres.

Compared with example 1, in example 2, after 5g of methyltrimethoxysilane was added, the wall thickness of the spheres was 30nm, the particle size of the spheres was uniform, the surfaces of the spheres were smooth and free from self-aggregation, but the thickness of the walls was too thin, the spheres were broken, and the dielectric constant was 3.3.

EXAMPLE III

Step 3.1, ultrasonically dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene, 0.29g of initiator azodiisobutyronitrile and cationic comonomer acryloyloxyethyltrimethyl ammonium chloride for 10min, then placing the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring at room temperature to form a homogeneous solution;

step 3.2, deoxidizing the homogeneous phase solution for 30min by blowing nitrogen at room temperature, then heating to 70 ℃, and continuing stirring for reaction for 24h to obtain a polystyrene sphere dispersion liquid with positive charges;

step 3.3, adding 8g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 3.4, adding 3ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 3.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 3.3, stopping stirring, and standing at room temperature for 8 h;

and 3.5, filtering the solution obtained in the step 3.4, washing the solution by using distilled water and ethanol respectively for one time, then putting the solution into an oven for drying at 50 ℃ for 3h, heating the solution to 550 ℃ at the speed of 0.3 ℃/min in a muffle furnace, keeping the temperature for 3h to remove polystyrene spheres, and then continuously heating the solution to 950 ℃ at the speed of 3 ℃/min to obtain the low dielectric hollow silica microspheres with smooth and compact surfaces. As shown in the attached figure III, FIG. 3 is a scanning electron microscope image of the hollow silica microsphere prepared by adding acryloyloxyethyltrimethyl ammonium chloride during the synthesis of polystyrene spheres.

Compared with example 2, in example 3, after 8g of methyltrimethoxysilane was added, the wall thickness of the spheres was 50nm, the particle size of the spheres was uniform, the surfaces of the spheres were smooth and free from self-aggregation, and the dielectric constant was measured to be 2.5.

Example four

Step 4.1, ultrasonically dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene, 0.29g of initiator azobisisobutyronitrile and cationic comonomer acryloyloxyethyltrimethyl ammonium chloride for 10min, then placing the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring at room temperature to form a homogeneous solution;

step 4.2, deoxidizing the homogeneous phase solution for 30min by blowing nitrogen at room temperature, then heating to 70 ℃, and continuing stirring for reaction for 24h to obtain a polystyrene sphere dispersion liquid with positive charges;

step 4.3, adding 10g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 4.4, adding 3ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 4.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 4.3, stopping stirring, and standing at room temperature for 8 h;

and 4.5, filtering the obtained solution, washing the solution by using distilled water and ethanol for one time respectively, then putting the solution into an oven for drying at 50 ℃ for 3h, heating the solution to 550 ℃ at the speed of 0.3 ℃/min in a muffle furnace, preserving the temperature for 3h to remove polystyrene spheres, and then continuously heating the solution to 950 ℃ at the speed of 3 ℃/min to obtain the low dielectric hollow silica microspheres with smooth and compact surfaces. As shown in FIG. 4, FIG. 4 is a scanning electron microscope image of the hollow silica microspheres prepared with methyltrimethylsilane in an amount of 10 g.

Example 4 the addition ratio of methyltrimethoxysilane was increased, the wall thickness of the spheres was 80nm, the particle size of the spheres was uniform, the surface was smooth and no self-aggregation occurred, and the measured dielectric constant was 2.3.

EXAMPLE five

Step 5.1, ultrasonically dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene, 0.29g of initiator azobisisobutyronitrile and cationic comonomer acryloyloxyethyltrimethyl ammonium chloride for 10min, then loading the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring at room temperature to form a homogeneous solution;

step 5.2, deoxidizing the homogeneous phase solution for 30min by blowing nitrogen at room temperature, then heating to 70 ℃, and continuing stirring for reaction for 24h to obtain a polystyrene sphere dispersion liquid with positive charges;

step 5.3, adding 15g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 5.4, adding 3ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 5.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 5.3, stopping stirring, and standing at room temperature for 8 h;

and 5.5, filtering the obtained solution, washing the solution by using distilled water and ethanol for one time respectively, then putting the solution into an oven for drying at 50 ℃ for 3h, heating the solution to 550 ℃ at the speed of 0.3 ℃/min in a muffle furnace, preserving the temperature for 3h to remove polystyrene spheres, and then continuously heating the solution to 950 ℃ at the speed of 3 ℃/min to obtain the low dielectric hollow silica microspheres with smooth and compact surfaces. As shown in the attached FIG. 5, FIG. 5 is a scanning electron microscope image of the hollow silica microspheres prepared with methyl trimethylsilane added in an amount of 15 g.

Example 5 the addition of methyltrimethoxysilane was increased further, the wall thickness of the spheres was 100nm, the particle size of the spheres was uniform, the surfaces were smooth and no self-aggregation occurred, and the dielectric constant was 1.9.

EXAMPLE six

Step 6.1, ultrasonically dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene, 0.29g of initiator azobisisobutyronitrile and cationic comonomer acryloyloxyethyltrimethyl ammonium chloride for 10min, then placing the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring at room temperature to form a homogeneous solution;

6.2, deoxidizing the homogeneous solution for 30min by blowing nitrogen at room temperature, heating to 70 ℃, and continuously stirring for reacting for 24h to obtain a polystyrene sphere dispersion liquid with positive charges;

step 6.3, adding 15g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 6.4, adding 6ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 6.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 6.3, stopping stirring, and standing at room temperature for 8 h;

and 6.5, filtering the obtained solution, washing the solution by using distilled water and ethanol for one time respectively, then putting the solution into an oven for drying at 50 ℃ for 3h, heating the solution to 550 ℃ at a speed of 0.3 ℃/min in a muffle furnace, preserving the temperature for 3h to remove polystyrene spheres, and then continuously heating the solution to 950 ℃ at a speed of 3 ℃/min to obtain the low dielectric hollow silica microspheres with smooth and compact surfaces. As shown in FIG. 6, FIG. 6 is a scanning electron micrograph of the hollow silica microspheres obtained when the amount of ammonia added was increased to 6 ml.

The difference between the addition amounts of the ammonia water in example 6 and example 5 is mainly reflected, the addition ratio of the ammonia water is continuously increased, the surface of the sphere is rough, the shell particles are stacked and loose, many holes are formed, and the measured dielectric constant is 3.5.

EXAMPLE seven

Step 7.1, ultrasonically dissolving 1.5g of polyvinylpyrrolidone, 45g of ethanol, 5g of distilled water, 15g of styrene, 0.29g of initiator azobisisobutyronitrile and cationic comonomer acryloyloxyethyltrimethyl ammonium chloride for 10min, then loading the mixture into a 250mL three-neck flask (comprising a nitrogen inlet, a stirring paddle inlet and a condensation port), and stirring at room temperature to form a homogeneous solution;

step 7.2, deoxidizing the homogeneous phase solution for 30min by blowing nitrogen at room temperature, then heating to 70 ℃, and continuing stirring for reacting for 24h to obtain polystyrene sphere dispersion liquid with positive charges;

step 7.3, adding 15g of methyltrimethoxysilane into 50ml of water, uniformly mixing, heating to 35 ℃, adding hydrochloric acid, adjusting the pH to 3, and continuously stirring for 3 hours to obtain an organosilane precursor hydrolysate;

step 7.4, adding 3ml of ammonia water into the polystyrene sphere dispersion liquid obtained in the step 7.2, stirring for 6min, adding the organic silicon source precursor hydrolysate prepared in the step 7.3, stopping stirring, and standing at room temperature for 8 h;

and 7.5, filtering the obtained solution, washing the solution by using distilled water and ethanol respectively for one time, then putting the solution into an oven for drying at 50 ℃ for 3h, then heating the solution to 550 ℃ in a muffle furnace at the speed of 5 ℃/min, and preserving the temperature for 8h to remove the polystyrene spheres, thus obtaining the hollow silicon dioxide microspheres. As shown in fig. 7, fig. 7 is a scanning electron microscope image of the hollow silica microspheres obtained by changing the calcination process.

The difference between the calcination process in example 7 and that in example 5 is mainly reflected in that the temperature rise rate is increased, the shell layer is easily broken by the volatile gas too fast, and the dielectric constant is 3.1.

The detection method comprises the following steps:

1. dielectric constant

The dielectric constant at 1GHz was measured by the plate method according to IPC-TM-6502.5.5.9.

Finally, it should be noted that: the above embodiments are only for illustrating the technical solutions of the present invention, and not for limiting the same; although the present invention has been described in detail with reference to the foregoing embodiments, it will be understood by those skilled in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and such modifications or substitutions do not depart from the spirit and scope of the respective technical solutions of the embodiments of the present invention.