A method for preparing in-situ grafted dispersed nano-silica

Abstract

This invention discloses a method for preparing in-situ grafted and dispersed nano-silica, relating to the field of nanomaterial preparation technology, comprising the following steps: Step ①, mixing sodium-free silica sol solution, water, and polyol in a high-pressure reactor; Step ②, gradually raising the reactor temperature from room temperature to 150-180℃, initially introducing acid anhydride gas or liquid at a certain flow rate, and maintaining temperature, constant pressure, and rotation speed until the pH value reaches 4.0-5.0±0.5, obtaining a primary mixture of hydrated nano-silica; Step ③, pumping an organosilicon coupling agent into the high-pressure reactor using a high-pressure metering pump, maintaining temperature and pressure, stirring the reaction for 30-90 minutes, then cooling, depressurizing, purging with nitrogen, and separating the reaction liquid to obtain grafted and dispersed nano-silica. This application aims to achieve readily available and inexpensive raw materials, reduce the difficulty of preparing nano-silica; solve the problems of dispersibility and compatibility with organic matter in nano-silica; simplify the procedure and improve preparation efficiency.

Description

Technical Field

[0001] This invention belongs to the field of nanomaterial preparation technology, and specifically relates to a method for preparing in-situ grafted dispersed nano-silica. Background Technology

[0002] Solid particles with a size smaller than 100 nm are generally referred to as nanoparticles. The special properties of nanomaterials are mainly reflected in their surface effects, small size effects, quantum effects, and macroscopic quantum tunneling effects, as well as their special photoelectric properties, high magnetoresistivity, nonlinear resistance, and high strength, high toughness, and excellent stability even at high temperatures. Therefore, nanomaterials have a very wide range of applications. Nano-silica (Nano-SiO2) is an amorphous, non-toxic, odorless, and pollution-free white powdery non-metallic material. It has high toughness, high temperature resistance, corrosion resistance, wear resistance, and infrared absorption properties. It is currently the world's largest-scale industrially produced nanomaterial.

[0003] Nano-SiO2 has a three-dimensional network structure, and its surface contains hydroxyl groups (silanol groups) in different bonding states. One type is isolated silanol groups with a molecular structure of 7326 cm⁻¹. -1 The typical wavelength of silanol groups has a strong adsorption force on polar substances; secondly, there are coupled hydroxyl groups; and thirdly, there are doubled hydroxyl groups. Silanol groups have high surface energy, strong hydrophilicity, and are in a thermodynamically unstable state, making them prone to aggregation. In applications, they are difficult to disperse uniformly in organic media, resulting in poor bonding with organic matter, causing interfacial defects, and thus reducing the performance of the materials used.

[0004] Methods for preparing nano-silica (Nano-SiO2) mainly include: gas-phase method, precipitation method, Sol-Gel method, hydrothermal synthesis method, microemulsion reaction method, azeotropic distillation method, and centrifugal reaction method. The obtained products exhibit good physicochemical properties, but their surfaces contain three types of hydroxyl groups, exhibiting significant hydrophilicity. Among these, the linked associative silanol groups and twinned silanol groups are formed after the aggregation of nano-silica (Nano-SiO2) and are secondary structures (500-900 nm). How to perform in-situ grafting and dispersion of primary structure (20-50 nm) nascent nano-silica (Nano-SiO2) particles is a challenge in the industry.

[0005] Grafting hydrophobic groups onto the surface of nano-silica (Nano-SiO2) reduces the number of hydroxyl groups, changing it from hydrophilic-oleophobic to hydrophobic-oleophobic. Simultaneously, it increases the steric hindrance between nano-silica (Nano-SiO2) particles, reduces particle aggregation, and enhances the compatibility of nano-silica (Nano-SiO2) with organic media. This significantly improves the application effect and expands the application range of nano-silica (Nano-SiO2). Therefore, in-situ grafting and dispersion modification treatment on the surface of nano-silica (Nano-SiO2) particles has significant practical implications.

[0006] How to establish the optimal timing for in-situ modification so that nano-silica (Nano-SiO2) retains its primary structure (20-50nm) in its initial formation state, reduces secondary aggregation of nanoparticles (500-900nm secondary structure), and prevents the formation of agglomerates (above 1000nm) is a technical problem that urgently needs to be solved in this field.

[0007] The mechanism of surface modification of nano-silica (Nano-SiO2) is based on the presence of hydroxyl groups on the surface of nano-silica (Nano-SiO2). The challenge lies in how to prevent adjacent hydroxyl groups from bonding together via hydrogen bonds (aggregates), how to isolate the positively charged hydrogen atoms, and how to eliminate or reduce the number of silanol groups on the surface through certain modification processes, so that nano-silica (Nano-SiO2) is both hydrophilic and oleophilic or completely hydrophobic. These remain technical challenges for those skilled in the art.

[0008] Solving these problems involves methods such as dehydration condensation reactions with hydroxyl-containing compounds, reactions with silane coupling agents, and esterification reactions with epoxy compounds. These methods demonstrate the advanced level of nano-silica (Nano-SiO2) synthesis and modification technology and represent a trend of innovation in the industry. Summary of the Invention

[0009] In view of this, the purpose of this application is to provide: a method for preparing in-situ grafted and dispersed nano-silica (Nano-SiO2). This aims to reduce the difficulty of preparing nano-silica (Nano-SiO2); solve the problems of dispersibility and compatibility of nano-silica (Nano-SiO2) with organic matter; simplify the procedure; and improve preparation efficiency.

[0010] The specific plan is as follows:

[0011] A method for preparing in-situ grafted dispersed nano-silica includes the following steps:

[0012] Step ①: Mix sodium-free silica sol solution, water, and polyol in a high-pressure reactor;

[0013] Step ②: Gradually raise the temperature of the reactor from room temperature to 150-180℃. At the beginning of the temperature rise, maintain a certain flow rate to introduce acid anhydride gas or liquid, and maintain constant temperature, constant pressure, and constant rotation speed until the pH value reaches 4.0-5.0±0.5 to obtain a primary mixture of hydrated nano-silica (Nano-SiO2).

[0014] Step ③: Pump the organosilicon coupling agent into the high-pressure reactor using a high-pressure metering pump, maintain the temperature and pressure, and stir the reaction for 30-90 minutes. Then cool down, depressurize, and purge with nitrogen to separate the reaction liquid to obtain grafted and dispersed nano-silica (Nano-SiO2) and polyol aqueous solution.

[0015] Furthermore, in step ①, the sodium-free silica sol solution is sodium silicate and sodium metasilicate with different moduli. A 5%-30% aqueous solution is passed through a cation exchange resin to obtain a sodium-free silica sol solution of a certain concentration.

[0016] Furthermore, in step ①, the polyol is one or a mixture of two or more of the following: ethylene glycol (EG), 1,3'-propanediol (1,3-PDO), 1,4-butanediol (1,4-BDO), 1,5-pentanediol (1,5-PDO), diethylene glycol (DPG), glycerol (VG), and pentaerythritol (PETP).

[0017] Polyol solutions are used in the precipitation process. The hydroxyl groups (silanol groups) on the surface of nano-silica (Nano-SiO2) are partially blocked, thereby reducing the hydrophilicity of silica and preventing the formation of silica agglomerates. This results in highly dispersed products in a nano-state with a narrow particle size distribution.

[0018] Furthermore, the acid anhydride gas or liquid mentioned in step ② is one or a mixture of two or more of the following: carbonic anhydride (carbon dioxide CO2), sulfite anhydride (sulfur dioxide SO2), acetic anhydride (C4H6O3), sulfuric anhydride (SO3), nitric anhydride (N2O5), nitrite anhydride (NO2), and phosphoric anhydride (P2O5).

[0019] The acid anhydride is reacted in a polyol medium to precipitate the corresponding acid anhydride (SiO2) in the orthosilicic acid solution, resulting in highly dispersed primary particles of nano-silica (20-50 nm).

[0020] Furthermore, the temperature of 150-180℃ mentioned in step ② is the reaction temperature, and the constant pressure reflects the saturated vapor pressure of the reaction liquid in the reaction system. This is beneficial for: the liquid-phase reaction of gaseous acid anhydrides, increasing the solubility of polyols, increasing the number of alcohol hydroxyl groups in the reaction liquid, enhancing the interaction between silanol groups on the surface of silica through hydrogen bonds, significantly reducing the formation of aggregates, and only producing primary particles (20-50nm) of nano-silica (Nano-SiO2).

[0021] Furthermore, the organosilane coupling agent in step ③ is: vinyltrichlorosilane (H2C=CHSiCl3), vinyltriethoxysilane H2C=CHSi(OEt)3, vinyltris(2-methoxyethoxy)silane H2C=CHSi(OC2H4OMe)3, vinyltriacetyloxysilane H2C=CHSi(OCOMe)3, vinylmethyldichlorosilane H2C=CHSiMeCl2, γ-mercaptopropyltrimethoxysilane HSC3H6Si(OMe)3,

[0022] γ-Methacryloxypropyltrichlorosilane H2C=C(Me)-CO-OC3H6SiCl3, α-decenoyloxypropyltrimethoxysilane One or more of the following: After modification with organosilanes, the tendency to break down aggregated structures is significantly reduced, thus decreasing the immersion heat in water (reducing the affinity of alcohol hydroxyl groups on the SiO2 surface for hydrogen bonds with water).

[0023] The present invention is further configured such that: in step ③, a certain amount of organosilane coupling agent is used for in-situ grafting onto the surface of nascent nano-silica (Nano-SiO2) primary particles (30-50 nm), resulting in more pronounced hydrophobicity. The increase in hydrophobicity is maximized when a modification ratio of 1:0.1-0.3 (silica:silane coupling agent) mol is used, and the hydrophobicity-induced effect causes the nano-silica (Nano-SiO2) to precipitate. For this reason, a method for preparing in-situ grafted dispersed nano-silica (Nano-SiO2) is needed, and it is important to evaluate the grafting equivalent formed by the silanol groups generated on the surface of nano-silica (Nano-SiO2). Specifically, silanol group measurements are performed at 7326 cm⁻¹ using spectrophotometry. -1 The typical NIR wavelength is used to calculate the degree of grafting of the functional groups.

[0024] The present invention is further configured such that the polyol aqueous solution obtained from the separation reaction solution in step ③ can be reused after passing the component content test.

[0025] As can be seen from the above scheme, this application provides a method for preparing in-situ grafted and dispersed nano-silica (Nano-SiO2), which has the following beneficial effects:

[0026] By using an aqueous solution of polyol as an organic medium, the surface properties of silica are altered from hydrophilic to partially hydrophobic. This is because the polyol blocks the surface centers (silicic acid groups) of newly formed primary silica particles (30-50 nm), causing the silicic acid groups to bind to the polyol hydroxyl groups via hydrogen bonds. This process of agglomeration formation is blocked, resulting in optimal dispersion and suitable siliceous conditions for the outer surface development, facilitating in-situ grafting of nano-silica (Nano-SiO2).

[0027] During the precipitation of primary structure nano-silica (30-50 nm) in an aqueous solution of acid anhydride (hydrophobic inducer), organosilanes are in situ grafted onto the nano-silica to modify silanol groups, resulting in nano-silica of 7326 cm⁻¹. -1 The typical wavelength is reduced; the absolute value of the zeta potential of the modified nano-silica is reduced. Both indicate that: the in-situ grafted and dispersed nano-silica has increased surface hydrophobicity and is easily soluble in organic matter; the silica particles have a primary structure (30-50 nm) and the aggregate structure (secondary structure) disappears.

[0028] Its application in polymeric organisms improves the interfacial interaction between nano-silica (Nano-SiO2) and polymers, thereby achieving higher bonding efficiency.

[0029] By using wet modification, i.e., in-situ grafting during precipitation, the advantages of this method include controlling the particle size and distribution of nano-silica (Nano-SiO2), reducing the surface silanol hydroxyl groups, improving hydrophobicity, reducing agglomeration, better dispersion of nanoparticles in polymer organic matter, improving material mechanical properties, and even transparency. Simultaneously, it achieves the goals of reducing the difficulty of preparing nano-silica, simplifying the process, and improving preparation efficiency. Attached Figure Description

[0030] Figure 1 This is a transmission electron microscope image of the in-situ grafted dispersed nano-silica prepared in Example 1.

[0031] Figure 2 This is a transmission electron microscope image of the in-situ grafted dispersed nano-silica prepared in Example 2.

[0032] Figure 3 The image shows a transmission electron microscope (TEM) image of nano-silica prepared for Comparative Example 1.

[0033] Figure 4 The image shown is a transmission electron microscope (TEM) image of the nano-silica prepared in Comparative Example 2. Detailed Implementation

[0034] The technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0035] It should be mentioned that the following is a detailed description of a method for preparing in-situ grafted dispersed nano-silica according to this application.

[0036] The silicon source used is obtained by removing sodium ions from commercially available sodium-free silica sol or sodium metasilicate (Na2O·m-SiO2·H2O) aqueous solution through cation exchange resin adsorption. Unless otherwise specified, all other equipment and commercially available products are standard and readily available.

[0037] Example 1

[0038] A method for preparing in-situ grafted dispersed nano-silica. The method includes the following steps:

[0039] (1) Weigh 500g of sodium-free silica sol with a 10% orthosilicic acid content and a pH of 7 (neutral). Add 30g of ethylene glycol to a 2L high-pressure reactor and stir evenly at room temperature until the weight ratio of ethylene glycol to water in the silica sol is 1:15. Ethylene glycol (EG) solution is a hydrophobic inducing factor (agent) in the precipitation system. Under the premise of ensuring good airtightness of the reactor, replace the air in the reactor with carbon dioxide (CO2) 3-5 times.

[0040] (2) Turn on the heating and temperature control system, and gradually raise the temperature of the reactor from room temperature to 150-160℃. Initially, maintain carbon dioxide (carbonic anhydride CO2) charge at a flow rate of 10 cm³ / min and a stirring speed of n = 500-600 r / min. As CO2 continues to be added, the pressure reaches 0.7-0.8 MPa. The pH of the reaction system is 5.0. Stop the carbon dioxide charge, maintain the pressure and temperature, and stir the reaction for 0.5-1 h. Primary nano-silica (Nano-SiO2) particles are obtained.

[0041] (3) Use a miniature high-pressure metering pump to dispense 2.0 g of vinyltriethoxysilane Pump the solution into the reactor, maintaining a molar ratio of orthosilicic acid to grafted organosilane of 1:0.1-0.1. Keep the reaction temperature at 150-160℃ and the pressure at 0.7-0.8 MPa. Stir at a speed of n = 500-600 r / min for 30 min. Allow the reactor to cool to room temperature, depressurize, and purge with nitrogen. Filter the reaction solution through a membrane; the filtrate is an aqueous ethylene glycol solution that can be reused. Vacuum dry the filter cake at 105℃ for 10 h to obtain 50 g of nano-silica. Take a sample and perform particle size analysis using a transmission electron microscope (TEM), as shown in the attached image. Figure 1 .

[0042] Example 2

[0043] (1) Weigh 500g of sodium-free silica sol with a 15% orthosilicic acid content and a pH of 7 (neutral). Reuse the recycled ethylene glycol solution from Example 1 by adding it to a 2L high-pressure reactor. Stir until homogeneous at room temperature, and calculate the ratio to ensure the weight ratio of ethylene glycol to water in the silica sol is 1:15. Ethylene glycol (EG) solution is a hydrophobic inducing factor (agent) in the precipitation system. Under the premise of ensuring good airtightness of the reactor, replace the air in the reactor with carbon dioxide (CO2) 3-5 times.

[0044] (2) Turn on the heating and temperature control system to gradually raise the temperature of the reactor from room temperature to 150-160℃. Initially, maintain a carbon dioxide (carbonic anhydride CO2) purging flow rate of 10 cm³. 3 The stirring speed was 500-600 r / min, and the pressure reached 0.7-0.8 MPa as CO2 was continuously introduced. The pH of the reaction system was 5.0. Carbon dioxide introduction was stopped, and the pressure and temperature were maintained while stirring for 0.5-1 h. Primary nano-silica (Nano-SiO2) particles were obtained.

[0045] (3) Use a miniature high-pressure metering pump to dispense 4.8 g of vinyltriethoxysilane Pump the solution into the reactor. The molar ratio of orthosilicic acid to grafted organosilane is 1:0.1-0.1. Maintain the reaction temperature at 150-160℃ and the pressure at 0.7-0.8MPa. Stir at a speed of n = 500-600 r / min for 30 min. After the reaction, allow the reactor to cool to room temperature, depressurize, and purge with nitrogen. Filter the reaction solution through a membrane; the filtrate is an aqueous ethylene glycol solution, which can be reused. Dry the filter cake under vacuum at 105℃ for 10 h to obtain 76.3 g of nano-silica. Take a sample and perform particle size analysis using transmission electron microscopy (TEM), as shown in the attached image. Figure 2 .

[0046] After the ethylene glycol aqueous solution was reused 6 times, the concentration decreased with the number of uses and the moisture in the sodium-free silica sol. The concentrated ethylene glycol could be reused by evaporating the water.

[0047] Using an aqueous ethylene glycol solution as the organic medium, ethylene glycol addition blocks the surface centers (silanol groups) of newly formed primary silica nanoparticles. The silanol groups on the silica surface bind to the ethylene glycol hydroxyl groups through hydrogen bonds, and the reaction mechanism is as follows:

[0048]

[0049] In the nascent nano-silica surface, a large number of adjacent silanol groups are prevented from interacting with silanol groups through hydrogen bonds.

[0050] In ethylene glycol media, the formation of aggregates is significantly reduced, establishing conditions for obtaining optimal dispersion and proper development of the outer surface.

[0051] After in-situ grafting with vinylsilane, a tendency to break down aggregated structures was observed, resulting in the displacement of ethylene glycol. Therefore, the examples verified that the quality of ethylene glycol remained unchanged and it could be reused. The terminal vinyl groups of the graft coupling agent are electrostatically inert and do not introduce interactions.

[0052]

[0053] For the samples of Example 1 and Example 2, after the hydroxyl groups were modified during the in-situ grafting precipitation process and ethylene glycol was replaced, no tendency to form aggregate structures was detected.

[0054] Example 3

[0055] (1) Weigh 500g of sodium-free silica sol with a 10% orthosilicic acid content and a pH of 7 (neutral). Add 30g of glycerol (glycerol) to a 2L high-pressure reactor and stir until homogeneous at room temperature, ensuring the weight ratio of glycerol to water in the silica sol is 1:15. Glycerol (VG) solution is a hydrophobic inducing factor (agent) in the precipitation system. Under the premise of ensuring good airtightness of the reactor, replace the air in the reactor with sulfur dioxide (sulfurous anhydride SO2) 1-2 times.

[0056] (2) Turn on the heating and temperature control system, and gradually raise the temperature of the reactor from room temperature to 150-160℃. Initially, maintain the flow of sulfur dioxide (sulfurous anhydride SO2) at a flow rate of 6 cm³ / min. 3 The stirring speed was 500-600 r / min. With continuous SO2 charging and increasing temperature, the pressure reached 0.7-0.8 MPa. The pH of the reaction system was 5.0. The sulfur dioxide charging was stopped, and the pressure and temperature were maintained while stirring for 0.5-1 h. Primary nano-silica (Nano-SiO2) particles were obtained.

[0057] (3) Use a miniature high-pressure metering pump to deliver 3g of vinyltriacetyloxysilane Pump the mixture into the reactor. The molar ratio of orthosilicic acid to grafted organosilane is 1:0.1-0.1. Maintain the reaction temperature at 150-160℃ and the pressure at 0.7-0.8MPa. Stir at a speed of n = 500-600 r / min for 30 min. Allow the reactor to cool to room temperature, depressurize, and purge with nitrogen. Filter the reaction solution through a membrane. The filtrate is an aqueous glycerol solution. Evaporate the filtrate, adjust the pH to neutral, and reuse the solution. Dry the filter cake under vacuum at 105℃ for 10 h to obtain 51.2 g of nano-silica. Take a sample and perform particle size analysis using a transmission electron microscope (TEM) in the same manner as in Example 1.

[0058] Example 4

[0059] (1) Weigh 500g of sodium-free silica sol with a 10% orthosilicic acid content and a pH of 7 (neutral). Add 30g of glycerol (glycerol) to a 2L high-pressure reactor and stir until homogeneous at room temperature, ensuring the weight ratio of glycerol to water in the silica sol is 1:15. Glycerol (VG) solution is a hydrophobic inducing factor (agent) in the precipitation system. Under the premise of ensuring good airtightness of the reactor, replace the air in the reactor with sulfur dioxide (sulfurous anhydride SO2) 1-2 times.

[0060] (2) Turn on the heating and temperature control system, and gradually raise the temperature of the reactor from room temperature to 150-160℃. Initially, maintain the flow of sulfur dioxide (sulfurous anhydride SO2) at a flow rate of 6 cm³ / min. 3 The stirring speed was 500-600 r / min. With continuous SO2 charging and increasing temperature, the pressure reached 0.7-0.8 MPa. The pH of the reaction system was 5.0. The sulfur dioxide charging was stopped, and the pressure and temperature were maintained while stirring for 0.5-1 h. Primary nano-silica (Nano-SiO2) particles were obtained.

[0061] (3) Use a miniature high-pressure metering pump to deliver 2.7g of γ-methacryloyloxypropyltrichlorosilane

[0062] Pump the solution into the reactor. The molar ratio of orthosilicic acid to grafted organosilane is 1:0.1-0.1. Maintain the reaction temperature at 150-160℃ and the pressure at 0.7-0.8MPa. Stir at a speed of n = 500-600 r / min for 30 min. Allow the reactor to cool to room temperature, depressurize, and purge with nitrogen. Filter the reaction solution through a membrane. The filtrate is an aqueous glycerol solution. Evaporate the filtrate, adjust the pH to neutral, and reuse the solution. Dry the filter cake under vacuum at 105℃ for 10 h to obtain 51.2 g of nano-silica. Take a sample and perform particle size analysis using a transmission electron microscope (TEM), as in Example 2.

[0063] Comparative Example 1

[0064] (1) Weigh 500g of sodium-free silica sol with a 10% orthosilicic acid content and a pH of 7 (neutral). Add 30g of ethylene glycol to a 2L high-pressure reactor and stir evenly at room temperature until the weight ratio of ethylene glycol to water in the silica sol is 1:15. Ethylene glycol (EG) solution is a hydrophobic inducing factor (agent) in the precipitation system. Under the premise of ensuring good airtightness of the reactor, replace the air in the reactor with carbon dioxide (CO2) 3-5 times.

[0065] (2) Turn on the heating and temperature control system, and gradually raise the temperature of the reactor from room temperature to 150-160℃. Initially, maintain carbon dioxide (carbonic anhydride CO2) charge at a flow rate of 10 cm³ / min and a stirring speed of n = 500-600 r / min. As CO2 continues to be added, the pressure reaches 0.7-0.8 MPa. The pH of the reaction system is 5.0. Stop the carbon dioxide charge, maintain the pressure and temperature, and stir the reaction for 0.5-1 h. Primary nano-silica (Nano-SiO2) particles are obtained.

[0066] (3) Use a micro high-pressure metering pump to dispense 2g of 3-aminopropyltriethoxysilane Pump the solution into the reactor, maintaining a molar ratio of orthosilicic acid to grafted organosilane of 1:0.1-0.1. Keep the reaction temperature at 150-160℃ and the pressure at 0.7-0.8 MPa. Stir at a speed of n = 500-600 r / min for 30 min. Allow the reactor to cool to room temperature, depressurize, and purge with nitrogen. Filter the reaction solution through a membrane; the filtrate is an aqueous ethylene glycol solution that can be reused. Vacuum dry the filter cake at 105℃ for 10 h to obtain 50 g of nano-silica. Take a sample and perform particle size analysis using a transmission electron microscope (TEM), as shown in the attached image. Figure 3 .

[0067] Comparative Example 2

[0068] (1) Weigh 500g of sodium-free silica sol with a 10% orthosilicic acid content and a pH of 7 (neutral). Add 30g of ethylene glycol to a 2L high-pressure reactor and stir evenly at room temperature until the weight ratio of ethylene glycol to water in the silica sol is 1:15. Ethylene glycol (EG) solution is a hydrophobic inducing factor (agent) in the precipitation system. Under the premise of ensuring good airtightness of the reactor, replace the air in the reactor with carbon dioxide (CO2) 3-5 times.

[0069] (2) Turn on the heating and temperature control system, and gradually raise the temperature of the reactor from room temperature to 150-160℃. Initially, maintain carbon dioxide (carbonic anhydride CO2) charge at a flow rate of 10 cm³ / min and a stirring speed of n = 500-600 r / min. As CO2 is continuously added, the pressure reaches 0.7-0.8 MPa. The pH of the reaction system is 5.0. Stop the carbon dioxide charge, maintain the pressure and temperature, and stir the reaction for 0.5-1 h. Obtain primary nano-silica (Nano-SiO2) particles, filter through a membrane, and wash with 500 ml × 2 ml of distilled water. Dry the filter cake under vacuum at 105℃ for 12 h. Take samples and perform particle size analysis using a transmission electron microscope (TEM). See Appendix. Figure 4 .

[0070] The difference between Comparative Example 1 and Example 1 is that in step (3) of Comparative Example 1, 3-aminopropyltriethoxysilane was added to prepare nano-silica through in-situ grafting. Scanning electron microscopy observation provides the potential to evaluate the aggregation tendency of nanoparticles.

[0071] Examples 1, 2, 3, and 4 demonstrate that in-situ grafting of silanes, during the precipitation process, displaces polyols, significantly limiting or even eliminating the secondary structure (500-900 nm) and the tendency to form aggregates (above 1900 nm) in nano-silica. Comparative Example 1 illustrates that not all grafted silanes exhibit a tendency to reduce aggregation.

[0072] The in-situ grafting of modified silicon cations onto the surface of aminosilanes forms hydrogen bonds between adjacent modified nano-silica particles, increasing the tendency for primary nano-silica (30-50nm) particles to aggregate.

[0073]

[0074] The difference between Comparative Example 2 and Example 1 is that primary particles (30-50 nm) of nano-silica were prepared in an aqueous ethylene glycol medium. After drying and dehydration, the primary particles (30-50 nm) lost the hydroxyl complexation protection of ethylene glycol and repolymerized to form secondary structures (500-900 nm), and agglomerates also appeared.

[0075] The specific embodiments and comparative examples used in this application, which describe the principle and implementation of a method for preparing in-situ grafted dispersed nano-silica, are intended to help understand the method and core ideas of this application and should not be construed as limiting this application.

Claims

1. A method for preparing in-situ grafting dispersed nanosilica, characterized in that, Includes the following steps: Step ①: Mix sodium-free silica sol solution, water, and polyol in a high-pressure reactor; Step ②: Gradually raise the temperature of the reactor from room temperature to 150-180℃. At the beginning of the temperature rise, maintain a certain flow rate to introduce acid anhydride gas or liquid, and maintain constant temperature, constant pressure, and constant rotation speed until the pH value reaches 4.0-5.0±0.5 to obtain a primary mixture of hydrated nano silica. Step ③: Pump the organosilicon coupling agent into the high-pressure reactor using a high-pressure metering pump, keep it warm and pressurized, and stir the reaction for 30-90 minutes. Then cool down, depressurize, purge with nitrogen, and separate the reaction liquid to obtain grafted and dispersed nano-silica and polyol aqueous solution. In step ①, the sodium-free silica sol solution is a commercially available sodium-free silica sol or sodium metasilicate aqueous solution obtained by adsorption of sodium ions by cation exchange resin. The acid anhydride gas or liquid mentioned in step ② is: carbon dioxide (CO2) or sulfur dioxide (SO2); The polyols mentioned are: one or a mixture of two or more of the following: ethylene glycol, 1,3'-propanediol, 1,4-butanediol, 1,5-pentanediol, diethylene glycol, glycerol, and pentaerythritol; The organosilane coupling agent in step ③ is one or a mixture of two or more of the following: vinyltrichlorosilane, vinyltriethoxysilane, vinyltri(2-methoxyethoxy)silane, vinyltriacetoxysilane, vinylmethyldichlorosilane, γ-mercaptopropyltrimethoxysilane, and γ-methacryloyloxypropyltrichlorosilane.

2. The method for preparing in-situ grafted dispersed nano-silica according to claim 1, characterized in that, The polyol mentioned is ethylene glycol or glycerol.

3. The method for preparing in-situ grafted dispersed nano-silica according to claim 1, characterized in that, The organosilane coupling agent in step ③ is one of vinyltrichlorosilane (H2C=CHSiCl3), vinyltriethoxysilane, vinyltriacetoxysilane, and γ-methacryloyloxypropyltrichlorosilane.

4. The method for preparing in-situ grafted dispersed nano-silica according to claim 1, characterized in that, In step ③, the organosilicon coupling agent is grafted in situ onto the surface of hydrated nano-silica primary particles, with a ratio of hydrated nano-silica to organosilicon coupling agent of 1 mol to 0.1-0.3 mol; the particle size of the hydrated nano-silica primary particles is 30-50 nm.

5. The method for preparing in-situ grafted dispersed nano-silica according to claim 1, characterized in that, Polyols, as hydrophobic inducers, can be recovered and reused in aqueous solutions.

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