A composite stabilizer for preparing silica microspheres and a method for preparing silica microspheres

Abstract

The present invention discloses a composite stabilizer for preparing silica microspheres and a method for preparing silica microspheres by using the composite stabilizer. This method is used for the large-scale preparation of uniform micron-sized silica microspheres. After finely adjusting the pH of the silica sol, the silica sol is dispersed into the composite stabilizer by using a microfluidic chip technology to form uniform silica sol droplets, which are then pre-cured by static polymerization and aged, thereby obtaining uniform silica microspheres with good dispersion of the dispersed phase. By using the method of the present invention, the large-scale controllable preparation of uniform silica microspheres can be realized.

Description

Technical Field

[0001] The present invention relates to a composite stabilizer for preparing silica microspheres, specifically to the composition of the composite stabilizer, and a method for preparing uniform silica microspheres by using the composite stabilizer and a microfluidic chip, belonging to the field of microsphere material preparation. Background Art

[0002] Silica microspheres are widely used in many industries and fields. For example, they are used as catalyst carriers for various catalytic reactions in the chemical industry, as stationary phase matrices for chromatographic analysis in the analytical field, and as separation matrix materials for the separation of high-value materials in the pharmaceutical industry.

[0003] The classical Stober method uses the hydrolysis and condensation reaction of organosilicon and is commonly used to prepare silica microspheres. This method is generally suitable for preparing nanoscale microspheres, but it is inadequate for preparing larger-sized microspheres, such as micron-sized silica microspheres. The spray drying method is also a common method for preparing silica microspheres. In this method, silica sol droplets are formed by spraying, and strong hot air is used to quickly solidify the silica sol droplets and disperse the particles into the oil phase, so silica microspheres can be prepared on a large scale. However, since the formation of silica sol droplets is basically uncontrollable, the diameter controllability of the microspheres prepared by this method is poor. The oil column forming method is also a common method for preparing silica microsphere materials. US Patent US2647875 uses a dropper to form silica sol droplets in an oil column forming device and heat them quickly at 95°C to form silica microspheres. In order to make the solidified silica microspheres pass through the oil layer and enter the lower water layer for collection, this method is generally suitable for preparing larger-sized microspheres with a size of more than 200 microns.

[0004] CN102190307A prepares silica microspheres by passing a mixture of water glass and a silanizing reagent through an oil column forming device to increase the specific surface area and pore volume.

[0005] JP62278113 uses a stirring method to disperse a mixture of sodium hydroxide and acidic silica sol into an unsaturated hydrocarbon and a chlorinated hydrocarbon to form an emulsion, and solidify the droplets under stirring to form silica microspheres. Silica sol droplets can be prepared by physical stirring, and at the same time, the fusion during the droplet solidification process is avoided. However, stirring is difficult to control the droplet size, so the controllability and uniformity of the prepared microspheres need to be improved.

[0006] US3782075 uses the polymerization-induced colloidal aggregation method to adsorb colloids and condense them through the polymerization reaction of urea and formaldehyde to form urea / formaldehyde-silica composite resin microspheres. This method has complex control conditions, is not easy to control the microsphere size, and the microspheres are prone to adhesion. A large amount of resin components in the composite microspheres need to be calcined to remove, so the microsphere structural strength is not high.

[0007] CN102936015A disperses aqueous silica sol into the stirred oil phase through the nozzle of the aqueous storage tank to form an emulsion, and then cures the droplets by heating to form silica microspheres. The controllability of the droplets formed by this spraying is not high, and during the heating and curing process, as the surface properties of the droplets change, the silica sol droplets are prone to demulsification and fusion. Avoiding droplet fusion by stirring will change the droplet size. Therefore, the uniformity of the microspheres prepared by this method is limited.

[0008] In summary, although there are many methods for preparing silica microspheres, in order to cure silica sol in the above-mentioned methods, silica sol with a high pH is generally used to quickly cure silica sol, and the controllability and uniformity of the size of the prepared silica microspheres are not good. This is related to the non-uniform preparation of silica sol droplets and the easy rupture or fusion of silica sol droplets during the subsequent curing process.

[0009] The microfluidic method is a new technology for preparing droplets. It uses fluid cutting and dispersion to form uniform droplets, so it is possible to obtain uniform microspheres. There is a literature report that uses TEOS and ammonia water as the dispersed phase to prepare TEOS droplets using a chip. In this method, hydrolysis reaction occurs in the chip, which easily clogs the microchannels and cannot be used for a long time. In addition, since the curing of these droplets is difficult and they are prone to fusion, it can only be applied to laboratory research and is not suitable for large-scale preparation.

[0010] CN106348252A introduces silica sol and oil phase into a microfluidic chip, uses fluid cutting to form silica sol droplets, and then introduces an alkaline precipitant into the emulsion in the chip. The precipitant enters the silica sol droplets through the oil-water interface to achieve curing. However, this method only describes the curing of droplets by introducing the precipitant into the silica sol droplets through the oil-water interface in the chip, and does not describe the post-treatment that is very crucial for the uniformity of the microspheres later. Moreover, introducing the precipitant into the microchannels of the microfluidic chip to form solids through the curing reaction easily clogs the microchannels, resulting in its inability to produce for a long time and is not suitable for the preparation of uniformly sized silica microspheres.

[0011] There is a report that after preparing silica sol droplets using microfluidic technology, the precipitant is then introduced into the emulsion fluid. Due to the uneven contact between the precipitant and the droplets, the curing is uneven, and it is easy to form hollow or deformed microspheres. Moreover, when the precipitant enters the droplets through the surface of the droplets, it changes the surface properties of the droplets, making the droplets prone to fusion and the microspheres prone to agglomeration. Therefore, this scheme is not suitable for large-scale preparation of microspheres.

[0012] There are also reports of introducing a polymerization precursor into silica sol, preparing droplets using microfluidic technology and then introducing them into an oil phase containing an initiator, and curing the droplets with the initiator. In this method, the particles are prone to adhesion, and a large amount of polymer needs to be removed, which not only results in low strength of the microspheres but also is not environmentally friendly. There are also reports of using a microfluidic chip to form silica sol droplets containing a photocurable material and then curing the silica gel microspheres by ultraviolet light curing. This method requires the use of photosensitive materials, which are expensive and not suitable for large-scale preparation. Due to the special nature of the microchannels, in order to form droplets and avoid clogging the microchannels, silica sol with a low pH is generally used. However, the change in surface properties during the droplet curing process makes them prone to fusion, seriously affecting the controllability and uniformity of microsphere preparation. Therefore, some special means are needed to cure the microspheres, resulting in a complex process and high cost, and it is not suitable for large-scale preparation of silica gel microspheres. In summary, the existing methods for preparing silica gel microspheres based on microfluidics are not applicable and are still in the laboratory stage, generally with a preparation scale of only a few milliliters per hour, and there is no feasible technology suitable for large-scale preparation. Summary of the Invention

[0013] The object of the present invention is to overcome the problems in the prior art that the controllability of preparing uniform micron-sized silica gel microspheres is poor and it is difficult to prepare on a large scale, and to provide a method for preparing monodisperse silica gel microspheres using microfluidic chip technology. The silica gel microspheres produced by this method have the advantages of controllable size and good uniformity.

[0014] To achieve the above object, in the first aspect of the present invention, a composite stabilizer is provided.

[0015] A composite stabilizer, which comprises a solvent, a first surfactant, and a second surfactant;

[0016] The first surfactant is sorbitan fatty acid ester;

[0017] The second surfactant is cetyl PEG / PPG-10 / 1 polydimethylsiloxane.

[0018] Optionally, the mass ratio of the first surfactant to the oil phase solvent is any value or a range value between any two values among 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10 wt%; the mass ratio of the second surfactant to the oil phase solvent is any value or a range value between any two values among 0.01%, 0.03%, 0.05%, 0.07%, 0.09%, 0.11%, 0.13%, 0.15%, 0.17%, 0.18%, 0.2 wt%.

[0019] Optionally, the first surfactant is selected from at least one of span 40, span 60, span 80, and span 85.

[0020] Optionally, the solvent is selected from at least one of alkanes with a boiling point > 60°C, kerosene with a boiling point > 60°C, mineral oil with a boiling point > 60°C, and liquid paraffin with a boiling point > 60°C;

[0021] Preferably, the solvent is selected from at least one of cyclohexane, kerosene, mineral oil, and liquid paraffin;

[0022] Preferably, the solvent is a mixture of kerosene and liquid paraffin.

[0023] The applicant of this application has found that by using SP and EM90, an organic-inorganic hybrid shell can be contained in the oil-water interface layer of silica sol droplets, and a solid shell will be formed during the droplet curing process, making the uniform droplets less likely to fuse and improving the stability during the droplet curing process.

[0024] In the second aspect of the present invention, a method for preparing silica microspheres is provided.

[0025] A method for preparing silica microspheres comprises the following steps:

[0026] (1) Adjust the pH of the silica sol to any value or a range value between any two values among 4, 4.5, 5, 5.5, 6, 6.5, 6.7, and 7 using an acid or a base;

[0027] (2) Introduce the silica sol obtained in step (1) and a composite stabilizer into a microfluidic chip to form uniform droplets;

[0028] (3) Pre-cure the obtained uniform droplets to obtain a solid hydrogel;

[0029] (4) Age the obtained solid hydrogel to obtain silica microspheres;

[0030] Among them, the composite stabilizer in step (2) is selected from at least one of the composite stabilizers described in any one of claims 1-4.

[0031] Optionally, in step (1), the acid is selected from at least one of inorganic acids and organic acids, and the base is an inorganic base;

[0032] Preferably, the acid is selected from at least one of nitric acid, sulfuric acid, acetic acid, and citric acid;

[0033] Preferably, the base is selected from at least one of NaOH, KOH, and ammonia water.

[0034] Optionally, in step (3), the pre-curing method is static curing;

[0035] Preferably, the pre-curing temperature is any value among 10°C, 15°C, 20°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or a value within the range composed of any two of these values, and the pre-curing residence time is any value among 0 h, 4 h, 8 h, 12 h, 16 h, 20 h, 24 h, 28 h, 32 h, 36 h, 40 h, 44 h, 48 h or a value within the range composed of any two of these values.

[0036] Optionally, in step (4), the aging method is organic base or inorganic base aging, the aging temperature is any value among 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or a value within the range composed of any two of these values, and the aging time is any value among 6 h, 8 h, 10 h, 12 h, 14 h, 16 h, 18 h, 20 h, 22 h, 24 h, 26 h, 28 h, 30 h, 36 h, 39 h, 42 h, 45 h, 48 h or a value within the range composed of any two of these values;

[0037] Preferably, the aging is carried out using triethylamine.

[0038] The applicant of the present application has found that by adopting the preferred aging scheme, that is, using triethylamine as the aging agent, it is possible to avoid the adhesion and caking of silica microspheres during drying, thereby improving the uniformity of the particles.

[0039] The applicant of the present application has found that by adopting the above treatment method, it is possible to transform the silica droplets previously formed by the microfluidic chip technology into micron-sized SiO2 microspheres, and the diameter deviation coefficient of the SiO2 microspheres is not greater than 7%. When the size of the generated SiO2 microspheres is between 30 - 100 μm, the single-chip sixteen-channel microfluidic chip used in the present application can achieve a silica sol treatment capacity of 0.2 - 1.2 L / h, which is more than a hundred times that of the existing microfluidic chip technology for preparing SiO2 microspheres, and can realize the batch preparation of uniform SiO2 micron microspheres.

[0040] Optionally, the silica microspheres obtained in step (4) also need to be washed, dried, and calcined;

[0041] Preferably, the drying temperature is any value among 60°C, 70°C, 80°C, 90°C, 100°C or a value within the range composed of any two of these values, and the drying time is any value among 6 h, 7 h, 8 h, 9 h, 10 h or a value within the range composed of any two of these values;

[0042] Preferably, the temperature of the roasting is any value among 400°C, 450°C, 500°C, 550°C, 600°C or a value within the range composed of any two of these values, and the time of the roasting is any value among 2 h, 2.5 h, 3 h, 3.5 h, 4 h, 4.5 h, 5 h, 5.5 h, 6 h or a value within the range composed of any two of these values.

[0043] With the preferred scheme, the aim is to obtain dry SiO2 microspheres with less impurities. However, even without performing steps such as filtration, washing, drying, and roasting, the silica gel microspheres with a diameter deviation coefficient ≤ 7% as described in the present invention can still be obtained. It's just that these silica gel microspheres still contain residues such as water, sorbitan fatty acid esters, EM90, and oil phase, and their strength is not high. After conventional steps such as filtration, washing, drying, and roasting, the surface of the silica gel microspheres has no impurities, has a higher strength, and is in a monodisperse state.

[0044] Through the above technical solutions, the beneficial effects that the present invention can produce include:

[0045] 1) For the method for preparing silica gel microspheres provided by the present invention, the silica gel microspheres prepared by the method described in the present invention have good size controllability and uniformity, and it is easy to solidify uniform droplets under the condition of not easily blocking the microchannels of the microfluidic chip, which is conducive to the large-scale preparation of uniform micron-sized SiO2 microspheres;

[0046] 2) The present invention provides a composite stabilizer, which will form an organic-inorganic hybrid outer shell layer during the solidification process of the silica sol droplets, reducing the particle adhesion, making the droplets less likely to fuse, improving the stability of the droplet solidification process, and being conducive to obtaining uniform microspheres;

[0047] 3) The present invention uses static pre-cured droplets to form uniform microspheres. Compared with the traditional stirring method, it avoids droplet rupture and fusion, and is more conducive to the formation of monodisperse and uniform SiO2 micron microspheres from uniform silica sol droplets. Description of the Drawings

[0048] Figure 1 is a microfluidic chip with 16 parallel stepped droplet generation channels used in Example 1, where (1) is the aqueous phase inlet; (2) is the stable phase inlet; (3) is the droplet outlet.

[0049] Figure 2 is a photo of the silica gel microspheres roasted at 500°C described in Example 1.

[0050] Figure 3 is the nitrogen adsorption isotherm of the silica gel microspheres described in Example 1.

[0051] Figure 4 is the pore size distribution of the silica gel microspheres described in Example 1.

[0052] Figure 5It is a photograph of microspheres prepared by the stirring method and calcined at 500 °C as described in Example 2.

[0053] Figure 6 It is a photograph of the silica microspheres as described in Comparative Example 1.

[0054] Figure 7 It is the nitrogen adsorption isotherm of the silica microspheres as described in Comparative Example 1.

[0055] Figure 8 It is the pore size distribution of the silica microspheres as described in Comparative Example 1. Detailed Description of the Invention

[0056] In the ranges disclosed herein, the endpoints and any values are not limited to the exact ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, between the endpoint values of each range, between the endpoint values of each range and individual point values, and between individual point values can be combined with each other to obtain one or more new numerical ranges, and these numerical ranges should be regarded as specifically disclosed herein.

[0057] The present invention will be described in detail below through examples. In the following examples, the specific surface area is the BET specific surface area, and the instrument used is ASAP2020 of Micromeritics.

[0058] In the following examples, the average pore size is calculated using the BJH calculation model.

[0059] In the following examples, the pictures of the obtained silica microspheres are obtained by the optical imaging method, and the instrument used is a Leica stereomicroscope, and the instrument model is S8APO.

[0060] In the following examples, the measurement method of the obtained diameter deviation coefficient is microscopic image measurement and statistics.

[0061] In the following examples, span is a product of Guoyao Chemical Company. Cetyl PEG / PPG-10 / 1 polydimethylsiloxane is a product of Degussa. Kerosene, mineral oil, and liquid paraffin are purchased from Damao Company. Triethylamine is a product of Xihua Company.

[0062] Example 1

[0063] (1) Preparation of the composite stabilizer: Kerosene and liquid paraffin (oil phase A), span 80 (additive B), and EM90 (additive C) were rapidly mixed at a mass ratio of 50:50:4:0.025 to obtain a composite stabilizer.

[0064] (2) Preparation of the silica sol: 1M nitric acid solution and alkaline silica sol with pH = 10 were mixed and rapidly mixed under stirring at a mass ratio of 3.0 / 40.0 to obtain a silica sol with pH = 6.5.

[0065] (3) Obtaining silica sol droplets: The silica sol and composite stabilizer were introduced into the attached Figure 1 As shown, in the homemade PMMA step microfluidic chip with a 16-channel parallel droplet generation structure (the average size of the water phase orifice at the droplet generation site is 28μm×28μm), the droplets generated in the chip are discharged into a collection container, the average droplet diameter is 146μm, and the diameter deviation coefficient is 7%.

[0066] (4) Precuring: The liquid droplets in the container are precured at room temperature for 16 h to form a hydrogel solid.

[0067] (5) Aging: After filtering out the oil phase from the hydrogel solid, the solid was washed with cyclohexane and ethanol, and then treated in 1 M ammonia water at 80°C for 8 h.

[0068] (6) Preparation of silica gel microspheres: The microspheres were filtered after washing with hot deionized water, and further dried at 80°C for 8 h, and then calcined in a muffle furnace at 500°C for 4 h to obtain silica gel microspheres.

[0069] The obtained silica microspheres are shown in the following figure. Figure 2 As shown in Figure 1, the average diameter is 81 μm and the diameter deviation coefficient is 7%. Its isothermal adsorption curve is shown in Figure 1. Figure 3 The BET surface area is 214 m 2 / g, pore volume 0.64cm 2 / g. Pore size distribution Figure 4 The average pore diameter is 12nm.

[0070] Example 2

[0071] (1) Preparation of composite stabilizer: kerosene and liquid paraffin (oil phase A), stabilizer Span 80 (additive B) and EM90 (additive C) were mixed and stirred in a mass ratio of 50:50:6:0.03 to obtain a composite stabilizer.

[0072] (2) Preparation of silica sol: 1 M nitric acid solution and alkaline silica sol were mixed and rapidly mixed under stirring at a mass ratio of 2.8 / 40.0 to prepare silica sol with a pH value of 6.7.

[0073] (3) Obtaining silica sol droplets: The silica sol and oil phase were introduced into the solution at flow rates of 0.8 L / h and 1.4 L / h, respectively, by gas driven pumps. Figure 1 In the homemade PMMA step microfluidic chip with 16 parallel droplet generation structures shown in the figure (the average orifice size at the droplet generation site is 16 μm×28 μm), the droplets generated by the chip are directed into a collection container.

[0074] (4) Pre-curing: Let it cure at room temperature for 6 h to form a hydrogel solid.

[0075] (5) Aging: Add 5% triethylamine to the above product and mix. Age at 80 °C for 8 h.

[0076] (6) Preparation of silica microspheres: Then wash with cyclohexane and ethanol, then wash with hot water and filter. Dry at 80 °C for 8 h, then program the temperature increase in a muffle furnace and calcine at 500 °C for 4 h to obtain silica microspheres.

[0077] The photograph of the obtained microspheres is as Figure 5 shown, with an average diameter of 63 μm and a diameter deviation coefficient of 7%.

[0078] Example 3

[0079] (1) Preparation of composite stabilizer: Mix kerosene and liquid paraffin (oil phase A), stabilizer Span 80 (stabilizer B) and EM90 (additive C) at a mass ratio of 50:50:6:0.03 and stir to prepare a composite stabilizer.

[0080] (2) Preparation of silica sol: Mix 1M nitric acid solution and alkaline silica sol, and quickly mix under stirring at a mass ratio of 2.8 / 40 to prepare a silica sol with pH = 6.7.

[0081] (3) Obtaining silica sol droplets: Introduce silica sol and oil phase into the microfluidic chip in Example 1 through a gas-driven pump at flow rates of 0.6 L / h and 1.8 L / h.

[0082] (4) Pre-curing: Introduce the outflow droplets in the microfluidic chip into an 80 °C composite stabilizer oil column with a length of 80 cm and cure for 5 min.

[0083] (5) Aging: Add 2% triethylamine and mix evenly. Treat at 80 °C for 8 h, wash with cyclohexane and ethanol, and then wash with hot deionized water and filter.

[0084] (6) Preparation of silica microspheres: Wash with cyclohexane and ethanol, then wash with hot deionized water and filter. Dry at 80 °C for 8 h, then program the temperature increase in a muffle furnace and calcine at 500 °C for 4 h to obtain silica microspheres.

[0085] Example 4

[0086] (1) Preparation of composite stabilizer: Mix liquid paraffin (oil phase A), stabilizer Span 85 (stabilizer B) and EM90 (additive C) at a mass ratio of 100:4:0.03 and stir to prepare a composite stabilizer.

[0087] (2) Preparation of silica sol: Mix 1M nitric acid solution and alkaline silica sol, and quickly mix them under stirring at a mass ratio of 3 / 40 to obtain silica sol with a pH value of 6.5.

[0088] (3) Obtaining silica sol droplets: Introduce silica sol and oil phase into the microfluidic chip in Example 1 through an injection pump at flow rates of 0.6 L / h and 1.8 L / h.

[0089] (4) Pre-curing: The outflow droplets in the microfluidic chip are introduced into an 80-cm-long oil column of oil phase at 50 °C for curing for 30 min.

[0090] (5) Aging: Add 2% triethylamine and mix evenly, treat at 80 °C for 8 h, wash with cyclohexane and ethanol, and then wash and filter with hot deionized water.

[0091] (6) Preparation of silica microspheres: Take out the pre-cured microspheres, add 5% triethylamine and mix evenly, treat at 80 °C for 8 h, wash with cyclohexane and ethanol, then wash and filter with hot water, dry at 80 °C for 8 h, and then program the temperature rise in a muffle furnace and calcine at 500 °C for 4 h to obtain silica microspheres.

[0092] Comparative Example 1

[0093] The preparation process is the same as that in Example 3, except that the preparation of silica sol droplets uses the traditional stirring method instead of the chip method. Specifically, 0.36 L of silica sol and 0.72 L of oil phase are introduced into a container and stirred to obtain them.

[0094] The photo of the microspheres obtained by the traditional mechanical stirring method is as Figure 6 shown, with an average diameter of 68 μm and a diameter deviation coefficient of 29%. Its isothermal adsorption curve is as Figure 7 shown, its BET surface area is 208 m 2 / g, and the pore volume is 0.58 cm 2 / g. The pore size distribution is as Figure 8 shown, with an average pore size of 11 nm.

[0095] Comparative Example 2

[0096] (1) Mix kerosene, liquid paraffin, stabilizer Span 80 and EM90 at a mass ratio of 50:50:6:0.03 and stir to obtain the oil phase.

[0097] (2) Mix 1M nitric acid solution and alkaline silica sol (commercially purchased), and quickly mix them under stirring at a mass ratio of 3.8 / 40 to obtain silica sol with a pH value of 2.8.

[0098] (3) Introduce silica sol and oil phase into the one as Figure 1In the self-made PMMA stepped microfluidic chip with 16 parallel droplet generation structures as shown, the droplets generated by the chip are exported into a collection container.

[0099] (4) Gelation does not occur at room temperature for 48 h to form solid microspheres.

[0100] Comparative Example 3

[0101] Using a single channel in the microfluidic chip described in this application, the aqueous phase is a silica sol solution with pH = 2.5, the continuous phase is a mineral oil containing 1% EM90, and the precipitation phase is a mineral oil containing 2 wt% TEA. An injection pump is used to drive a syringe, which enters the chip inlet through a connecting pipeline. The aqueous phase fluid enters the dispersion unit from the middle thick channel, and the oil phase fluid enters the dispersion unit from the thick channels on both sides of the thin channel. The precipitation phase is introduced into the formed emulsion from the chip outlet. The obtained silica microspheres have an average diameter of 45 μm and a diameter deviation coefficient of 10%.

[0102] Comparative Example 4

[0103] Using the microfluidic chip described in this application, the aqueous phase is a silica sol solution with pH = 2.5, the continuous phase is a mineral oil containing 1% EM90, and the precipitation phase is a mineral oil containing 2 wt% TEA. An injection pump is used to drive a syringe, which enters the chip inlet through a connecting pipeline. The aqueous phase fluid enters the dispersion unit from the middle thick channel at a flow rate of 0.12 L / h; the oil phase fluid enters the dispersion unit from the thick channels on both sides of the thin channel, and the precipitation phase is introduced into the formed emulsion from the chip outlet. The obtained silica microspheres have an average diameter of 45 μm and a diameter deviation coefficient of 12%.

[0104] By adopting the method described in this application, through comparison between Example 1 and Comparative Example 1, for the silica microspheres prepared by the chip method, the diameter deviation coefficient is increased from nearly 30% to 7%. By comparing Example 1 and Comparative Example 2, it can be considered that when the pH value is 2.8, coagulated silica cannot be obtained, and thus micron-sized silica microspheres cannot be prepared. By comparing Example 1, Comparative Example 3, and Comparative Example 4, when using the SP80 + EM90 composite stabilizer described in this application, silica microspheres with a diameter deviation coefficient of 7% can be obtained. Compared with the single-channel microfluidic chip without using the SP80 + EM90 composite stabilizer, the multi-channel microfluidic chip has a lower diameter deviation coefficient, and this diameter deviation coefficient is increased by at least 30%. Compared with the silica microspheres with a deviation coefficient of 12% obtained by using multi-channel EM90 mineral oil, the diameter deviation of the silica microspheres obtained by using the SP80 + EM90 composite stabilizer in this application is increased by at least 42%.

[0105] As described above, these are only several embodiments of the present invention and do not impose any form of limitation on the present invention. Although the present invention is disclosed above in preferred embodiments, it is not intended to limit the present invention. Any person skilled in the relevant art can make some changes or modifications within the scope of the technical solution of the present invention by using the disclosed technical content, which are equivalent to equivalent implementation cases and all fall within the scope of the technical solution.

Claims

1. A method for preparing silica microspheres, characterized in that, The steps are as follows: (1) Adjust the pH of the silica sol to 4 - 7 with an acid or a base; (2) Introduce the silica sol obtained in step (1) and the composite stabilizer into a microfluidic chip to form uniform droplets; (3) Pre-cure the obtained uniform droplets to obtain solid hydrogel microspheres; (4) Age the obtained solid hydrogel to obtain silica microspheres; Among them, the composite stabilizer described in step (2) includes an oil-phase solvent, a first surfactant, and a second surfactant; The first surfactant is sorbitan fatty acid ester; The second surfactant is cetyl PEG / PPG - 10 / 1 polydimethylsiloxane; The microfluidic chip described in step (2) has a functional unit that can disperse the silica sol into the composite stabilizer to form uniform droplets; In step (3), the pre-curing method is static curing.

2. The method according to claim 1, characterized in that, The mass ratio of the first surfactant to the oil-phase solvent is 1wt% - 10wt%, and the mass ratio of the second surfactant to the oil-phase solvent is 0.01wt% - 0.2wt%.

3. The method according to claim 1, characterized in that, The first surfactant is selected from at least one of Span 40, Span 60, Span 80, and Span 85.

4. The method according to claim 1, characterized in that, The oil-phase solvent is selected from at least one of alkanes with a boiling point > 60°C, kerosene with a boiling point > 60°C, mineral oil with a boiling point > 60°C, and liquid paraffin with a boiling point > 60°C.

5. The method according to claim 1, characterized in that, The oil-phase solvent is selected from at least one of cyclohexane, kerosene, mineral oil, and liquid paraffin.

6. The method according to claim 1, characterized in that, The oil-phase solvent is a mixture of kerosene and liquid paraffin.

7. The method according to claim 1, characterized in that, The acid described in step (1) is selected from at least one of inorganic acids and organic acids, and the base is an inorganic base.

8. The method according to claim 7, characterized in that, The acid is selected from at least one of nitric acid, sulfuric acid, acetic acid, and citric acid; The base is selected from at least one of NaOH, KOH, and ammonia water.

9. The method according to claim 1, characterized in that, The pre-curing temperature is 10 - 80°C, and the pre-curing residence time is 0 - 48h.

10. The method according to claim 1, characterized in that, In step (4), the aging method is aging with an organic base or an inorganic base, the aging temperature is 60 - 90°C, and the aging time is 2 - 48h.

11. The method according to claim 10, characterized in that, The aging is carried out with triethylamine.

12. The method according to claim 1, characterized in that, The silica microspheres obtained in step (4) also need to be washed, dried, and calcined.

13. The method according to claim 12, characterized in that, The drying temperature is 60 - 100°C, and the drying time is 2 - 24h; The calcination temperature is 400 - 600°C, and the calcination time is 2 - 6h.

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