Hollow silicon dioxide microsphere and preparation method thereof

Abstract

The invention relates to a hollow silicon dioxide microsphere and a preparation method thereof, the preparation method comprises the following steps: carrying out hydrolysis-polymerization reaction by adopting a trifunctional group organic alkoxy silane monomer containing double bonds at the end group to obtain polysilsesquioxane liquid drops with narrow particle size distribution, then adding a block copolymer surfactant, and carrying out polymerization reaction to obtain the hollow silicon dioxide microsphere. A polysilsesquioxane liquid drop emulsion is obtained; then adding a strong alkali solution to carry out a dissolution reaction to obtain a hollow polysilsesquioxane microsphere dispersion liquid; then adding a photoinitiator, and carrying out a cross-linking curing reaction on the shell of the hollow polysilsesquioxane microsphere under the irradiation of ultraviolet light to obtain a hollow polysilsesquioxane template microsphere; and finally carrying out heat treatment to obtain the hollow silicon dioxide microspheres. The hollow silicon dioxide microspheres which are regular in form, good in monodispersity and narrow in particle size distribution can be obtained, and the particle size and the wall thickness can be regulated and controlled.

Description

Technical Field

[0001] This invention relates to the field of silica materials technology, specifically to a hollow silica microsphere and its preparation method. Background Technology

[0002] Hollow silica microspheres play a crucial role in several high-tech fields due to their unique structure. They can be used as low-dielectric fillers in microelectronic chips to reduce signal delay, and their size-matched design allows for targeted drug delivery. Furthermore, they contribute to lightweighting and thermal insulation in advanced composite materials.

[0003] As the application of hollow silica in high-end fields deepens, its performance requirements are trending towards precision and high reliability, specifically including: precise shell thickness, adjustable particle size and distribution, high mechanical strength, good sphericity and surface smoothness, and controllable surface chemical properties. However, currently, the synthesis of high-purity hollow microspheres generally relies on technical routes such as hard templates and soft templates.

[0004] For example, CN116119674A discloses a method for preparing hollow silica microspheres using a hard template method. This method uses submicron-sized polystyrene spheres as templates, hexadecyltrimethylammonium bromide as a cationic surfactant, and tetraethyl orthosilicate as a silicon source to synthesize hollow silica microspheres. However, although the hard template method can effectively construct cavities, it often faces problems such as cumbersome steps, potential structural collapse or mesopore blockage due to template removal, and the inability to control particle size and wall thickness.

[0005] CN104787769A discloses a method for preparing silica hollow microspheres using a template. This method involves preparing polymer template spheres through nanoprecipitation of anionic sodium polyacrylate or sodium polymethacrylate in alcohol. A silicon source precursor is then added, and a silica shell is obtained via a sol-gel method. After the reaction, the template is washed away with water to obtain well-dispersed hollow particles. This method employs a soft template approach, relying on intermolecular forces to spontaneously form an ordered structure. While this may simplify the process, the assembly process is extremely sensitive to kinetic conditions, exhibiting poor reproducibility. Furthermore, the mechanical strength of the resulting materials is typically low, making it difficult to meet the high stability requirements of practical applications.

[0006] Therefore, it is crucial to develop a method for synthesizing hollow silica microspheres that can meet the urgent need for precise control of particle size and wall thickness, and that is simple to process and suitable for large-scale preparation. Summary of the Invention

[0007] To address the above problems, the present invention aims to provide a hollow silica microsphere and its preparation method. Compared with the prior art, the present invention can obtain hollow silica microspheres with regular morphology, good monodispersity, and narrow particle size distribution, and the particle size and wall thickness can be controlled.

[0008] To achieve this objective, the present invention adopts the following technical solution:

[0009] In a first aspect, the present invention provides a method for preparing hollow silica microspheres, the method comprising the following steps:

[0010] (1) Mixed trifunctional organoalkoxysilane monomers with double bonds at the end groups are dispersed with water to obtain an aqueous emulsion. An alkaline catalyst is added to the aqueous emulsion to carry out a hydrolysis-polymerization reaction to obtain polysilsesquioxane droplets. Then, a block copolymer surfactant is added to obtain a polysilsesquioxane droplet emulsion.

[0011] (2) The polysilsesquioxane droplet emulsion obtained in step (1) and the strong alkaline solution are mixed and dissolved for 3-10 minutes at a pH of 12-14 to obtain a hollow polysilsesquioxane microsphere dispersion.

[0012] (3) Add a photoinitiator to the hollow polysilsesquioxane microsphere dispersion obtained in step (2), and allow the shell of the hollow polysilsesquioxane microsphere to undergo a cross-linking and curing reaction under ultraviolet light irradiation. Then, perform solid-liquid separation, washing and drying in sequence to obtain hollow polysilsesquioxane template microspheres.

[0013] (4) The hollow polysilsesquioxane template microspheres obtained in step (3) are subjected to heat treatment to obtain hollow silica microspheres.

[0014] In the preparation method provided by this invention, oligomeric polysilsesquioxane droplets are first formed during a hydrolysis-polymerization reaction using an organoalkoxysilane monomer and an alkaline catalyst. The droplet size is controlled by adjusting the hydrolysis-polymerization reaction time. When the desired particle size is reached, a block copolymer surfactant is added to stabilize the droplet structure through physical adsorption and non-covalent interactions, resulting in a polysilsesquioxane droplet emulsion. Then, a strong alkaline solution is added to the polysilsesquioxane droplet emulsion, which dissolves the low-bond-energy oligomers within the droplets, generating fragments. During this process, an osmotic pressure difference is established inside and outside the droplet, which drives water molecules to migrate into the interior of the droplet, ultimately constructing a complete hollow structure. The wall thickness is controlled by controlling the dissolution reaction time. Subsequently, the shell of the hollow microsphere is further cross-linked and solidified by initiating a polymerization reaction of the end-group double bonds through ultraviolet light irradiation, ultimately forming a structurally stable hollow polysilsesquioxane template microsphere. Finally, the obtained microspheres are subjected to inorganic calcination to promote the sintering and densification of the shell, ultimately preparing hollow silica microspheres with a complete structure and a dense shell.

[0015] In this invention, the pH value of the dissolution reaction is 12-14, for example, it can be 12, 12.5, 13, 13.5 or 14, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0016] In this invention, controlling the pH value of the dissolution reaction can prevent the alkalinity from being insufficient to dissolve the oligomers inside the droplets when the pH value is too low, thus preventing the formation of a hollow structure. At the same time, it can also prevent the alkalinity from being too strong when the pH value is too high, which would completely disintegrate the droplet template and thus destroy the structure formation.

[0017] In this invention, the dissolution reaction time is 3-10 min, for example, it can be 3 min, 4 min, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0018] In this invention, the wall thickness of the hollow structure is controlled by adjusting the dissolution reaction time. If the dissolution time is too short, the oligomeric silsesquioxane inside the droplet will not dissolve completely, resulting in the formation of a hollow structure. This also hinders the penetration of external moisture, which not only inhibits the effective expansion of the hollow structure but also affects the wall thickness of the final product. If the dissolution time is too long, the template droplet will dissolve completely.

[0019] In this invention, the solid-liquid separation method can be a conventional method in the art, such as filtration or centrifugation.

[0020] In this invention, the washing method can be a conventional method in the art, such as washing with anhydrous ethanol and deionized water alternately until the filtrate is neutral.

[0021] Preferably, the trifunctional organoalkoxysilane monomer in step (1) includes any one or a combination of at least two of methacryloyloxymethyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, or 3-(methacryloyloxy)propyltrimethoxysilane.

[0022] In this invention, a trifunctional organoalkoxysilane monomer with double bonds at the end group is preferably used, which can undergo cross-linking and curing under the action of an initiator and ultraviolet light, thereby forming a structurally stable hollow polysilsesquioxane template microsphere.

[0023] Preferably, the volume ratio of the trifunctional organoalkoxysilane monomer to water is 1:(100-200), for example, it can be 1:100, 1:110, 1:120, 1:130, 1:140, 1:150, 1:160, 1:170, 1:180, 1:190 or 1:200, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0024] Preferably, stirring is performed during the dispersion process.

[0025] Preferably, the stirring rate during the dispersion process is 1000-2000 rpm, for example, it can be 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm or 2000 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0026] In this invention, it is preferable to stir and disperse the organoalkoxysilane monomer and water to promote the hydrolysis process.

[0027] Preferably, the alkaline catalyst in step (1) includes any one or a combination of at least two of ammonia, sodium hydroxide, potassium hydroxide, triethylamine or ethylenediamine.

[0028] Preferably, the pH value of the hydrolysis-polymerization reaction is 9-11, for example, it can be 9, 9.5, 10, 10.5 or 11, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] Preferably, the temperature of the hydrolysis-polymerization reaction in step (1) is 0-25℃, for example, it can be 0℃, 2℃, 4℃, 6℃, 8℃, 10℃, 12℃, 14℃, 16℃, 18℃, 20℃, 22℃, 24℃ or 25℃, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0030] Preferably, the hydrolysis-polymerization reaction time is 1-6 hours, for example, it can be 1 hour, 1.2 hours, 1.5 hours, 1.8 hours, 2 hours, 2.2 hours, 2.5 hours, 2.8 hours, 3 hours, 3.2 hours, 3.5 hours, 3.8 hours, 4 hours, 4.2 hours, 4.5 hours, 4.8 hours, 5 hours, 5.2 hours, 5.5 hours, 5.8 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0031] In this invention, by optimally controlling the time of the hydrolysis-polymerization reaction, the size of the initial droplets can be adjusted, thereby controlling the final size of the product to 1-4 μm.

[0032] Preferably, stirring is performed during the hydrolysis-polymerization reaction.

[0033] Preferably, the stirring rate in the hydrolysis-polymerization reaction is 5-50 rpm, for example, it can be 5 rpm, 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, 40 rpm, 45 rpm or 50 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] Preferably, the average droplet size in the polysilsesquioxane droplet emulsion is 0.5-2 μm, for example, it can be 0.5 μm, 0.6 μm, 0.8 μm, 1 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm or 2 μm, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0035] Preferably, the block copolymer surfactant comprises a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer.

[0036] Preferably, the block copolymer surfactant includes any one or a combination of at least two of Pluronic F108, Pluronic F127, or Pluronic F98.

[0037] In this invention, an amphiphilic block copolymer surfactant is used because the block copolymer surfactant has hydrophilic and hydrophobic blocks, which can spontaneously aggregate at the droplet interface and stabilize the droplet interface.

[0038] Preferably, the block copolymer surfactant is added in the form of a block copolymer surfactant solution.

[0039] Preferably, the mass concentration of the block copolymer surfactant solution is 4-6%, for example, it can be 4%, 4.2%, 4.4%, 4.5%, 4.6%, 4.8%, 5%, 5.2%, 5.4%, 5.5%, 5.6%, 5.8% or 6%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0040] Preferably, the volume of the block copolymer surfactant solution accounts for 1-2% of the volume of the aqueous emulsion, for example, it can be 1%, 1.2%, 1.4%, 1.6%, 1.8% or 2%, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0041] Preferably, acid is added after the hydrolysis-polymerization reaction to bring the pH value to neutral.

[0042] Preferably, the acid includes any one or a combination of at least two of hydrochloric acid, nitric acid, or sulfuric acid.

[0043] In this invention, by preferably adding acid for neutralization, the hydrolysis and condensation of monomers can be further terminated.

[0044] Preferably, the strong alkaline solution in step (2) contains sodium hydroxide and / or potassium hydroxide.

[0045] Preferably, the volume ratio of the strong alkaline solution to the polysilsesquioxane droplet emulsion is (3-6):1, for example, it can be 3:1, 3.5:1, 4:1, 4.5:1, 5:1, 5.5:1 or 6:1, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0046] Preferably, the concentration of the strong alkaline solution is 100-200 mmol / L, for example, it can be 100 mmol / L, 110 mmol / L, 120 mmol / L, 130 mmol / L, 140 mmol / L, 150 mmol / L, 160 mmol / L, 170 mmol / L, 180 mmol / L, 190 mmol / L or 200 mmol / L, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] Preferably, the temperature of the dissolution reaction is 0-25℃, for example, it can be 0℃, 2℃, 4℃, 6℃, 8℃, 10℃, 12℃, 14℃, 16℃, 18℃, 20℃, 22℃, 24℃ or 25℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0048] Preferably, stirring is performed during the dissolution reaction.

[0049] Preferably, the stirring rate during the dissolution reaction is 5-50 rpm, for example, it can be 5 rpm, 10 rpm, 15 rpm, 20 rpm, 25 rpm, 30 rpm, 35 rpm, 40 rpm, 45 rpm or 50 rpm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0050] Preferably, the average particle size of the microspheres in the hollow polysilsesquioxane microsphere dispersion is 1-4 μm, for example, it can be 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0051] Preferably, the photoinitiator in step (3) includes any one or a combination of at least two of 1-hydroxy-cyclohexyl-phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone or 2-hydroxy-2-methylphenylpropanone.

[0052] In this invention, the photoinitiator can be a photoinitiator with the above-mentioned components commonly used in the art, which can be commercially available. For example, 2-hydroxy-2-methylphenylacetone can be commercially available Darocur 1173.

[0053] Preferably, the percentage of the volume of the photoinitiator to the volume of the hollow polysilsesquioxane microsphere dispersion is 1-3‰, for example, it can be 1‰, 1.2‰, 1.4‰, 1.6‰, 1.8‰, 2‰, 2.2‰, 2.4‰, 2.6‰, 2.8‰ or 3‰, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0054] Preferably, the irradiation time of the ultraviolet light is 20-40 minutes, for example, it can be 20 minutes, 22 minutes, 24 minutes, 26 minutes, 28 minutes, 30 minutes, 32 minutes, 34 minutes, 36 minutes, 38 minutes or 40 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0055] Preferably, the drying temperature is 90-110℃, for example, 90℃, 92℃, 94℃, 96℃, 98℃, 100℃, 102℃, 104℃, 106℃, 108℃ or 110℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0056] Preferably, the average particle size of the hollow polysilsesquioxane template microspheres is 1-4 μm, for example, it can be 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] Preferably, the heat treatment in step (4) includes a first heat treatment and a second heat treatment performed sequentially.

[0058] Preferably, the first heat treatment includes: heating to a first endpoint temperature at a first heating rate and performing a first calcination at the first endpoint temperature.

[0059] Preferably, the first heat treatment is performed in an air atmosphere.

[0060] Preferably, the first heating rate is 3-5℃ / min, for example, it can be 3℃ / min, 3.2℃ / min, 3.4℃ / min, 3.6℃ / min, 3.8℃ / min, 4℃ / min, 4.2℃ / min, 4.4℃ / min, 4.6℃ / min, 4.8℃ / min or 5℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0061] Preferably, the first endpoint temperature is 300-600℃, for example, it can be 300℃, 320℃, 340℃, 360℃, 380℃, 400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃ or 600℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0062] Preferably, the first calcination time is 4-6 hours, for example, it can be 4 hours, 4.2 hours, 4.4 hours, 4.6 hours, 4.8 hours, 5 hours, 5.2 hours, 5.4 hours, 5.6 hours, 5.8 hours or 6 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0063] Preferably, the second heat treatment includes: heating to a second endpoint temperature at a second heating rate and performing a second calcination at the second endpoint temperature.

[0064] Preferably, the second heating rate is 8-10℃ / min, for example, it can be 8℃ / min, 8.2℃ / min, 8.4℃ / min, 8.6℃ / min, 8.8℃ / min, 9℃ / min, 9.2℃ / min, 9.4℃ / min, 9.6℃ / min, 9.8℃ / min or 10℃ / min, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0065] Preferably, the second endpoint temperature is 800-1000℃, for example, it can be 800℃, 820℃, 840℃, 860℃, 880℃, 900℃, 920℃, 940℃, 960℃, 980℃ or 1000℃, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0066] Preferably, the second calcination time is 5-8 hours, for example, it can be 5 hours, 5.5 hours, 6 hours, 6.5 hours, 7 hours, 7.5 hours or 8 hours, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0067] In this invention, by optimizing and controlling the process conditions of the second heat treatment, the densification of the microsphere structure can be further controlled, and the wall thickness can also be assisted in regulating it.

[0068] In this invention, to obtain hollow silica microspheres with a dense outer shell, a stepwise heat treatment is performed on the hollow polysilsesquioxane template microspheres. First, a first heat treatment is performed, in which the organic template agent inside the microspheres is completely removed through a slow oxidation process in an air atmosphere. Then, a second heat treatment is performed, in which the sintering and densification of the silica shell is promoted at a high temperature. Finally, hollow silica microspheres with a complete structure and a dense outer shell are successfully prepared.

[0069] As a preferred embodiment of the first aspect of the present invention, the preparation method includes the following steps:

[0070] (1) A trifunctional organoalkoxysilane monomer with double bonds at the mixed end groups is dispersed with water, wherein the volume ratio of the trifunctional organoalkoxysilane monomer to water is 1:(100-200). During the dispersion process, the mixture is stirred at a rate of 1000-2000 rpm to obtain an aqueous emulsion. An alkaline catalyst is added to the aqueous emulsion and a hydrolysis-polymerization reaction is carried out at a pH of 9-11, a stirring rate of 5-50 rpm, and a temperature of 0-25℃ for 1-6 h to obtain polysilsesquioxane droplets. Then, a block copolymer surfactant is added to stabilize the droplet interface, and acid is added to neutralize the pH to obtain a polysilsesquioxane droplet emulsion with an average droplet size of 0.5-2 μm.

[0071] The trifunctional organoalkoxysilane monomer includes any one or a combination of at least two of methacryloyloxymethyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, or 3-(methacryloyloxy)propyltrimethoxysilane; the alkaline catalyst includes any one or a combination of at least two of ammonia, sodium hydroxide, potassium hydroxide, triethylamine, or ethylenediamine; the block copolymer surfactant includes any one or a combination of at least two of Pluronic F108, Pluronic F127, or Pluronic F98; the block copolymer surfactant is added in the form of a block copolymer surfactant solution with a mass concentration of 4-6% and a volume of 1-2% of the aqueous emulsion volume; the acid includes any one or a combination of at least two of hydrochloric acid, nitric acid, or sulfuric acid.

[0072] (2) The polysilsesquioxane droplet emulsion obtained in step (1) is mixed with a strong alkaline solution with a concentration of 100-200 mmol / L, wherein the strong alkaline solution contains sodium hydroxide and / or potassium hydroxide. The mixture is subjected to a dissolution reaction for 3-10 min at a pH of 12-14, a temperature of 0-25℃, and a stirring rate of 5-50 rpm. The volume ratio of the strong alkaline solution to the polysilsesquioxane droplet emulsion is (3-6):1, thereby obtaining a hollow polysilsesquioxane microsphere dispersion. The average particle size of the microspheres in the hollow polysilsesquioxane microsphere dispersion is 1-4 μm.

[0073] (3) Add a photoinitiator to the hollow polysilsesquioxane microsphere dispersion obtained in step (2). The photoinitiator includes any one or a combination of at least two of 1-hydroxy-cyclohexyl-phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone or 2-hydroxy-2-methylphenylpropanone. The volume of the photoinitiator accounts for 1-3‰ of the volume of the hollow polysilsesquioxane microsphere dispersion. Irradiate with ultraviolet light for 20-40 min. Under ultraviolet light irradiation, the shell of the hollow polysilsesquioxane microsphere undergoes a cross-linking and curing reaction. Then, perform solid-liquid separation and washing in sequence. After drying at 90-110℃, hollow polysilsesquioxane template microspheres are obtained. The average particle size of the hollow polysilsesquioxane template microspheres is 1-4 μm.

[0074] (4) The hollow polysilsesquioxane template microspheres obtained in step (3) are subjected to heat treatment. The heat treatment includes a first heat treatment and a second heat treatment performed sequentially. The first heat treatment includes heating at 3-5℃ / min to a first endpoint temperature of 300-600℃ and performing a first calcination at the first endpoint temperature for 4-6 hours. The second heat treatment includes heating at 8-10℃ / min to a second endpoint temperature of 800-1000℃ and performing a second calcination at the second endpoint temperature for 5-8 hours to obtain hollow silica microspheres.

[0075] Secondly, the present invention provides a hollow silica microsphere, wherein the hollow silica microsphere is obtained by the preparation method of the hollow silica microsphere described in the first aspect of the present invention.

[0076] The hollow silica microspheres provided by this invention use hollow polysilsesquioxane microspheres as templates and obtain monodisperse hollow silica microspheres with narrow particle size distribution through subsequent heat treatment. The particle size and wall thickness are adjustable, the hollowness is excellent, and the morphology is regular.

[0077] Preferably, the average particle size of the hollow silica microspheres is 1-4 μm, for example, it can be 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, 3.2 μm, 3.5 μm, 3.8 μm or 4 μm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0078] Preferably, the wall thickness of the hollow silica microspheres is 200-400 nm, for example, it can be 200 nm, 220 nm, 240 nm, 260 nm, 280 nm, 300 nm, 320 nm, 340 nm, 360 nm, 380 nm or 400 nm, but is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0079] Preferably, the hollow silica microspheres have a hollowness of 30-80%, for example, 30%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75% or 80%, but are not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0080] Compared with the prior art, the present invention has the following beneficial effects:

[0081] (1) The preparation method provided by the present invention uses trifunctional organoalkoxysilane monomers with double bonds at the end groups. Hollow polysilsesquioxane template microspheres can be obtained through a combination of hydrolysis-polymerization reaction, dissolution reaction, cross-linking and curing reaction. After removing the template by heat treatment, hollow silica microspheres can be obtained directly. The process is not only simple, but also the reaction conditions are mild, green and pollution-free, and it has good application prospects.

[0082] (2) In the preparation method provided by the present invention, the size of the initial droplets can be controlled by controlling the time of the hydrolysis-polymerization reaction, thereby controlling the size of the product. By controlling the time of the dissolution reaction and the synergistic effect of the second heat treatment process, the wall thickness can be effectively controlled.

[0083] (3) The present invention can obtain hollow silica microspheres with regular shape, good monodispersity and narrow particle size distribution, and the particle size and wall thickness can be controlled. Under better conditions, the average particle size is 1-4 μm, the wall thickness is 200-400 nm, and the hollowness is 30-80%. Attached Figure Description

[0084] Figure 1 This is a TEM image of the hollow silica microspheres provided in Embodiment 1 of the present invention. Detailed Implementation

[0085] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0086] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0087] Example 1

[0088] This embodiment provides a method for preparing hollow silica microspheres, the method comprising the following steps:

[0089] (1) A trifunctional organoalkoxysilane monomer (3-(methacryloyloxy)propyltrimethoxysilane) with a double bond at the mixed end group is dispersed with water. The volume ratio of the trifunctional organoalkoxysilane monomer to water is 1:100. During the dispersion process, the mixture is stirred at a rate of 1000 rpm to obtain an aqueous emulsion. An alkaline catalyst, ammonia, is added to the aqueous emulsion. The mixture is subjected to a hydrolysis-polymerization reaction for 1 h at a pH of 10, a stirring rate of 20 rpm, and a temperature of 25 °C to obtain polysilsesquioxane droplets. Then, a Pluronic F127 solution (mass concentration of 5%) is added to stabilize the droplet interface. The volume of the Pluronic F127 solution is 1% of the volume of the aqueous emulsion. Hydrochloric acid is added until the pH value is neutral to obtain a polysilsesquioxane droplet emulsion.

[0090] (2) The polysilsesquioxane droplet emulsion obtained in step (1) and the NaOH aqueous solution with a concentration of 150 mmol / L were mixed and dissolved for 10 min under the conditions of pH 13, temperature 25℃ and stirring speed 20 rpm. The volume ratio of the NaOH aqueous solution to the polysilsesquioxane droplet emulsion was 4:1 to obtain a hollow polysilsesquioxane microsphere dispersion.

[0091] (3) Add photoinitiator 2-hydroxy-2-methylphenylacetone to the hollow polysilsesquioxane microsphere dispersion obtained in step (2). The volume of the photoinitiator accounts for 1‰ of the volume of the hollow polysilsesquioxane microsphere dispersion. Irradiate with ultraviolet light for 30 min. Under ultraviolet light irradiation, the shell of the hollow polysilsesquioxane microsphere undergoes a cross-linking and curing reaction. Then centrifuge, and then wash with anhydrous ethanol and deionized water alternately four times. Then dry at 90°C for 12 h to obtain hollow polysilsesquioxane template microspheres.

[0092] (4) The hollow polysilsesquioxane template microspheres obtained in step (3) are subjected to heat treatment. The heat treatment includes a first heat treatment and a second heat treatment performed sequentially. The first heat treatment includes heating at 3°C / min to a first endpoint temperature of 300°C and performing a first calcination at the first endpoint temperature for 6 hours. The second heat treatment includes heating at 10°C / min to a second endpoint temperature of 950°C and performing a second calcination at the second endpoint temperature for 8 hours to obtain hollow silica microspheres.

[0093] This embodiment also provides hollow silica microspheres obtained by the above preparation method, and the TEM image of the hollow silica microspheres is shown below. Figure 1 As shown.

[0094] Example 2

[0095] This embodiment provides a method for preparing hollow silica microspheres, the method comprising the following steps:

[0096] (1) A trifunctional organoalkoxysilane monomer (methacryloyloxymethyltrimethoxysilane) with double bonds at mixed end groups is dispersed with water. The volume ratio of the trifunctional organoalkoxysilane monomer to water is 1:150. During the dispersion process, the mixture is stirred at a rate of 1000 rpm to obtain an aqueous emulsion. An alkaline catalyst, sodium hydroxide, is added to the aqueous emulsion. The hydrolysis-polymerization reaction is carried out for 3 h at a pH of 9, a stirring rate of 5 rpm, and a temperature of 0 °C to obtain polysilsesquioxane droplets. Then, Pluronic F108 solution (mass concentration of 5%) is added to stabilize the droplet interface. The volume of Pluronic F127 solution accounts for 1.5% of the volume of the aqueous emulsion. Hydrochloric acid is added until the pH value is neutral to obtain a polysilsesquioxane droplet emulsion.

[0097] (2) The polysilsesquioxane droplet emulsion obtained in step (1) and the NaOH aqueous solution with a concentration of 200 mmol / L were mixed and dissolved for 10 min at a pH of 13.2, a temperature of 0℃ and a stirring rate of 5 rpm. The volume ratio of the NaOH aqueous solution to the polysilsesquioxane droplet emulsion was 3:1 to obtain a hollow polysilsesquioxane microsphere dispersion.

[0098] (3) Add photoinitiator 1-hydroxy-cyclohexyl-phenyl ketone to the hollow polysilsesquioxane microsphere dispersion obtained in step (2). The volume of the photoinitiator accounts for 1‰ of the volume of the hollow polysilsesquioxane microsphere dispersion. Irradiate with ultraviolet light for 30 min. Under ultraviolet light irradiation, the shell of the hollow polysilsesquioxane microsphere undergoes a cross-linking and curing reaction. Then centrifuge, and then wash with anhydrous ethanol and deionized water alternately four times. Then dry at 90°C for 12 h to obtain hollow polysilsesquioxane template microspheres.

[0099] (4) The hollow polysilsesquioxane template microspheres obtained in step (3) are subjected to heat treatment. The heat treatment includes a first heat treatment and a second heat treatment performed sequentially. The first heat treatment includes heating at 3°C / min to a first endpoint temperature of 600°C and performing a first calcination at the first endpoint temperature for 4 hours. The second heat treatment includes heating at 10°C / min to a second endpoint temperature of 1000°C and performing a second calcination at the second endpoint temperature for 5 hours to obtain hollow silica microspheres.

[0100] Example 3

[0101] This embodiment provides a method for preparing hollow silica microspheres, the method comprising the following steps:

[0102] (1) Mixed trifunctional organoalkoxysilane monomers (3-acryloyloxypropyltrimethoxysilane) with double bonds at the end groups and dispersion, wherein the volume ratio of the trifunctional organoalkoxysilane monomers to water is 1:200, and the hydrolysis reaction is stirred at a rate of 1000 rpm to obtain an aqueous emulsion. An alkaline catalyst sodium hydroxide is added to the aqueous emulsion, and the hydrolysis-polymerization reaction is carried out for 2 h at a pH of 11, a stirring rate of 50 rpm, and a temperature of 15 °C to obtain polysilsesquioxane droplets. Then, Pluronic F98 solution (mass concentration of 5%) is added to stabilize the droplet interface. The volume of Pluronic F127 solution accounts for 1.5% of the volume of the aqueous emulsion, and hydrochloric acid is added until the pH value is neutral to obtain a polysilsesquioxane droplet emulsion.

[0103] (2) The polysilsesquioxane droplet emulsion obtained in step (1) and the NaOH aqueous solution with a concentration of 100 mmol / L were mixed and dissolved for 3 min at a pH of 12.9, a temperature of 15℃ and a stirring rate of 50 rpm. The volume ratio of the NaOH aqueous solution to the polysilsesquioxane droplet emulsion was 6:1, and a hollow polysilsesquioxane microsphere dispersion was obtained.

[0104] (3) Add photoinitiator 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone to the hollow polysilsesquioxane microsphere dispersion obtained in step (2). The volume of the photoinitiator accounts for 1‰ of the volume of the hollow polysilsesquioxane microsphere dispersion. Irradiate with ultraviolet light for 30 min. Under ultraviolet light irradiation, the shell of the hollow polysilsesquioxane microsphere undergoes a cross-linking and curing reaction. Then centrifuge, and then wash with anhydrous ethanol and deionized water alternately four times. Then dry at 90°C for 12 h to obtain hollow polysilsesquioxane template microspheres.

[0105] (4) The hollow polysilsesquioxane template microspheres obtained in step (3) are subjected to heat treatment. The heat treatment includes a first heat treatment and a second heat treatment performed sequentially. The first heat treatment includes heating at 3°C / min to a first endpoint temperature of 500°C and performing a first calcination at the first endpoint temperature for 5 hours. The second heat treatment includes heating at 10°C / min to a second endpoint temperature of 800°C and performing a second calcination at the second endpoint temperature for 8 hours to obtain hollow silica microspheres.

[0106] Example 4

[0107] This embodiment provides a method for preparing hollow silica microspheres. The only difference between this method and Example 1 is that the hydrolysis-polymerization reaction time in step (1) is 3 hours.

[0108] Example 5

[0109] This embodiment provides a method for preparing hollow silica microspheres. The only difference between this method and Example 1 is that the hydrolysis-polymerization reaction time in step (1) is 6 hours.

[0110] Example 6

[0111] This embodiment provides a method for preparing hollow silica microspheres. The only difference between this method and Example 1 is that the hydrolysis-polymerization reaction time in step (1) is 0.5 h.

[0112] Example 7

[0113] This embodiment provides a method for preparing hollow silica microspheres. The only difference between this method and Example 1 is that the hydrolysis-polymerization reaction time in step (1) is 15 hours.

[0114] Example 8

[0115] This embodiment provides a method for preparing hollow silica microspheres. The only difference between this method and Example 4 is that the dissolution reaction time in step (2) is 5 min.

[0116] Comparative Example 1

[0117] This embodiment provides a method for preparing silica microspheres. The only difference between this method and Example 4 is that the dissolution reaction time in step (2) is 1 min.

[0118] Comparative Example 2

[0119] This embodiment provides a method for preparing silica microspheres. The only difference between this method and Example 4 is that the concentration of the NaOH aqueous solution is adjusted in step (2) so that the pH of the dissolution reaction is 10.

[0120] Comparative Example 3

[0121] This embodiment provides a method for preparing silica microspheres. The only difference between this method and Example 4 is that the concentration of the NaOH aqueous solution is adjusted in step (2) so that the pH of the dissolution reaction is greater than 14.

[0122] Comparative Example 4

[0123] This comparative example provides a method for preparing silica microspheres. The only difference between this method and Example 1 is that no surfactant is added in step (1).

[0124] The average particle size of the silica microspheres obtained in the above examples and comparative examples was detected using a laser particle size analyzer, and the results are shown in Table 1.

[0125] The wall thickness of the silica microspheres obtained in the above embodiments and comparative examples was detected using the TEM image method, and the results are shown in Table 1.

[0126] The inner and outer diameters of the silica microspheres were measured using TEM, and the ratio of hollow volume to total volume was calculated to obtain the hollowness ratio. The results are shown in Table 1.

[0127] Table 1

[0128]

[0129] In Table 1, " / " indicates that the data is not available.

[0130] The following points can be observed from Table 1:

[0131] (1) As can be seen from the data of Examples 1-3, the hollow silica microspheres provided by the present invention have an average particle size of 1.92-2.82 μm, a wall thickness of 200-400 nm, and a hollowness of 30-75% under preferred conditions.

[0132] (2) A comprehensive comparison of the data from Examples 1 and 4-7 shows that, by controlling the hydrolysis-polymerization reaction time under optimal conditions (1-6h), Examples 1 and 4-5 can achieve an average particle size of 1.92-3.76μm for hollow silica microspheres, with adjustable particle size, a wall thickness of 200-300nm, and a hollowness of 30-80%. In Example 6, the hydrolysis-polymerization reaction time was too short, resulting in a small average particle size and a reduced hollowness. In Example 7, the average particle size was larger, and the hollowness increased, but the product showed more breakage under an electron microscope. At the same time, the preparation time was extended, and the production efficiency was reduced.

[0133] (3) By comparing the data of Example 4, Example 8 and Comparative Example 1, it can be seen that Example 4 and Example 8, by controlling the dissolution reaction time under better conditions (3-10 min), can make the average particle size of hollow silica microspheres 2.74-2.67 μm, and the particle size is adjustable, the wall thickness is 200-400 nm, and the hollowness is 40-70%; while in Comparative Example 1, due to the short dissolution reaction time, a hollow structure could not be formed, and the interior was hollow.

[0134] (4) Comparing the data of Example 4 and Comparative Examples 2-3, it can be seen that in Comparative Example 2, the oligomers inside the droplets failed to dissolve due to the low pH value, thus forming a solid structure and retaining the size and shape of the initial template; in Comparative Example 3, the oligomers were completely dissolved due to the high pH value, which caused the structure with the droplets as template to be unable to be maintained and eventually collapsed.

[0135] (5) Comparing the data of Example 1 and Comparative Example 4, it can be seen that the lack of surfactant in Comparative Example 4 leads to the instability of polysilsesquioxane droplets, which in turn dissolves under alkaline conditions and cannot yield hollow silica microspheres.

[0136] In summary, the present invention can obtain hollow silica microspheres with regular morphology, good monodispersity, and narrow particle size distribution, and the particle size and wall thickness can be controlled.

[0137] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for preparing hollow silica microspheres, characterized in that, The preparation method includes the following steps: (1) Mixed trifunctional organoalkoxysilane monomers with double bonds at the end groups are dispersed with water to obtain an aqueous emulsion. An alkaline catalyst is added to the aqueous emulsion to carry out a hydrolysis-polymerization reaction to obtain polysilsesquioxane droplets. Then, a block copolymer surfactant is added to obtain a polysilsesquioxane droplet emulsion. (2) The polysilsesquioxane droplet emulsion obtained in step (1) and the strong alkaline solution are mixed and dissolved for 3-10 minutes at a pH of 12-14 to obtain a hollow polysilsesquioxane microsphere dispersion. (3) Add a photoinitiator to the hollow polysilsesquioxane microsphere dispersion obtained in step (2), and allow the shell of the hollow polysilsesquioxane microsphere to undergo a cross-linking and curing reaction under ultraviolet light irradiation. Then, perform solid-liquid separation, washing and drying in sequence to obtain hollow polysilsesquioxane template microspheres. (4) The hollow polysilsesquioxane template microspheres obtained in step (3) are subjected to heat treatment to obtain hollow silica microspheres.

2. The preparation method according to claim 1, characterized in that, The trifunctional organoalkoxysilane monomer in step (1) includes any one or a combination of at least two of methacryloyloxymethyltrimethoxysilane, 3-acryloyloxypropyltrimethoxysilane, or 3-(methacryloyloxy)propyltrimethoxysilane; Preferably, the volume ratio of the trifunctional organoalkoxysilane monomer to water is 1:(100-200); Preferably, stirring is performed during the dispersion process; Preferably, the stirring rate during the dispersion process is 1000-2000 rpm.

3. The preparation method according to claim 1 or 2, characterized in that, The alkaline catalyst in step (1) includes any one or a combination of at least two of ammonia, sodium hydroxide, potassium hydroxide, triethylamine or ethylenediamine; Preferably, the pH value of the hydrolysis-polymerization reaction is 9-11.

4. The preparation method according to any one of claims 1-3, characterized in that, The temperature of the hydrolysis-polymerization reaction in step (1) is 0-25℃; Preferably, the hydrolysis-polymerization reaction takes 1-6 hours; Preferably, stirring is performed during the hydrolysis-polymerization reaction; Preferably, the stirring rate in the hydrolysis-polymerization reaction is 5-50 rpm; Preferably, the average droplet size in the polysilsesquioxane droplet emulsion is 0.5-2 μm.

5. The preparation method according to any one of claims 1-4, characterized in that, The block copolymer surfactant in step (1) includes a polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; Preferably, the block copolymer surfactant includes any one or a combination of at least two of Pluronic F108, Pluronic F127, or Pluronic F98; Preferably, the block copolymer surfactant is added in the form of a block copolymer surfactant solution; Preferably, the mass concentration of the block copolymer surfactant solution is 4-6%; Preferably, the volume of the block copolymer surfactant solution accounts for 1-2% of the volume of the aqueous emulsion; Preferably, acid is added after the hydrolysis-polymerization reaction to bring the pH value to neutral; Preferably, the acid includes any one or a combination of at least two of hydrochloric acid, nitric acid, or sulfuric acid.

6. The preparation method according to any one of claims 1-5, characterized in that, The strong alkaline solution in step (2) contains sodium hydroxide and / or potassium hydroxide; Preferably, the volume ratio of the strong alkaline solution to the polysilsesquioxane droplet emulsion is (3-6):1; Preferably, the concentration of the strong alkali solution is 100-200 mmol / L; Preferably, the temperature of the dissolution reaction is 0-25°C; Preferably, stirring is performed during the dissolution reaction; Preferably, the stirring rate during the dissolution reaction is 5-50 rpm; Preferably, the average particle size of the microspheres in the hollow polysilsesquioxane microsphere dispersion is 1-4 μm.

7. The preparation method according to any one of claims 1-6, characterized in that, The photoinitiator in step (3) includes any one or a combination of at least two of 1-hydroxy-cyclohexyl-phenyl ketone, 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propanone or 2-hydroxy-2-methylphenylpropanone; Preferably, the volume percentage of the photoinitiator relative to the volume of the hollow polysilsesquioxane microsphere dispersion is 1-3‰; Preferably, the irradiation time of the ultraviolet light is 20-40 minutes; Preferably, the drying temperature is 90-110°C; Preferably, the hollow polysilsesquioxane template microspheres have an average particle size of 1-4 μm.

8. The preparation method according to any one of claims 1-7, characterized in that, The heat treatment in step (4) includes a first heat treatment and a second heat treatment performed sequentially. Preferably, the first heat treatment includes: heating to a first endpoint temperature at a first heating rate and performing a first calcination at the first endpoint temperature; Preferably, the first heat treatment is performed in an air atmosphere; Preferably, the first heating rate is 3-5℃ / min; Preferably, the first endpoint temperature is 300-600℃; Preferably, the first calcination time is 4-6 hours; Preferably, the second heat treatment includes: heating to a second endpoint temperature at a second heating rate and performing a second calcination at the second endpoint temperature; Preferably, the second heating rate is 8-10℃ / min; Preferably, the second endpoint temperature is 800-1000℃; Preferably, the second calcination time is 5-8 hours.

9. A hollow silica microsphere, characterized in that, The hollow silica microspheres are obtained by the preparation method of hollow silica microspheres according to any one of claims 1-8.

10. The hollow silica microspheres according to claim 9, characterized in that, The hollow silica microspheres have an average particle size of 1-4 μm. Preferably, the wall thickness of the hollow silica microspheres is 200-400 nm; Preferably, the hollow silica microspheres have a hollowness ratio of 30-80%.

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