Silica sol having long-term stability and method for preparing the same

Abstract

The application discloses a kind of silicasol with long-term stability and preparation method thereof, belong to non-metallic element and its compound field, raw material includes: sodium silicate 5-10 parts, for preparation sodium silicate solution;0.2 parts-0.8 parts of polyacrylic acid are used to prepare polyacrylic acid solution.Step: polyacrylic acid solution and part of sodium silicate solution are added dropwise in the bottom liquid containing silica sol seed simultaneously, until polyacrylic acid solution is used up;Hydrochloric acid and part of sodium silicate solution are added dropwise in the bottom liquid simultaneously, until sodium silicate solution is used up;During the above two steps, keep stirring, maintain the pH of bottom liquid at 3-4.The application makes silica sol seed continuously adsorb newly generated silicic acid oligomer increase, inhibit Ostwald ripening during long-term storage, polyacrylic acid prevents silica sol particle from agglomerating by electrostatic repulsion and steric hindrance effect, and the feeding sequence is conducive to ensuring the amount relationship of sodium silicate and polyacrylic acid and the stability of bottom liquid pH.

Description

Technical Field

[0001] This invention relates to a silica sol with long-term stability and its preparation method, belonging to the field of non-metallic elements and their compounds. Background Technology

[0002] Silica sol, as an important nanomaterial, is widely used in coatings, catalyst supports, electronic packaging, precision polishing, and other fields. Its stability directly affects its application performance. Traditional silica sol preparation methods, such as sodium silicate ion exchange and tetraethyl orthosilicate hydrolysis, easily lead to uneven particle size distribution, resulting in a large number of small particles and agglomerates. Small particles are easily dissolved, leading to the growth of large particles (Ostwald ripening), accelerating agglomeration and precipitation. The presence of agglomerates reduces the dispersibility and transparency of the silica sol, affecting its application performance. Furthermore, silica sol exhibits even worse stability under harsh conditions such as high temperature and high salt content, easily undergoing gelation.

[0003] To improve the stability of silica sol, researchers have proposed various methods, such as adjusting pH and adding stabilizers. However, traditional stabilizers, such as inorganic salts and small-molecule organic acids, suffer from problems such as large dosage and limited effectiveness. Therefore, developing a method that can effectively control particle size distribution and improve the stability of silica sol under harsh conditions remains a hot research topic. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the present invention provides a silica sol with long-term stability and its preparation method, wherein the prepared silica sol is not prone to agglomeration and precipitation when left for a long time.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] In one aspect, this application provides a method for preparing a silica sol with long-term stability, wherein the raw materials, by weight, include: 5-10 parts of sodium silicate for preparing a sodium silicate solution; and 0.2-0.8 parts of polyacrylic acid for preparing a polyacrylic acid solution.

[0007] The preparation steps, in sequence, include:

[0008] The polyacrylic acid solution and part of the sodium silicate solution are simultaneously added dropwise to the base solution containing silica sol seeds until the polyacrylic acid solution is used up.

[0009] Hydrochloric acid and a portion of the sodium silicate solution are added dropwise to the base solution until the sodium silicate solution is used up.

[0010] During the above two steps, keep stirring to maintain the pH of the base solution at 3-4.

[0011] The silica sol prepared by the method provided in this application has a narrower particle size distribution and better long-term stability compared with silica sol in the prior art. The PAA / PAA-Na system effectively improves the stability of silica sol under harsh conditions such as high temperature and high salt.

[0012] Furthermore, the silica sol seeds have a particle size of 5-10 nm and are used in an amount of 0.5-1 part.

[0013] Furthermore, the weight-average molecular weight of the polyacrylic acid is 1500-2200.

[0014] Furthermore, the preparation steps of the substrate containing silica sol seeds include:

[0015] At the first dispersion speed, hydrochloric acid is added dropwise to a portion of the sodium silicate solution at the first drop rate until 0.4-0.8 parts by weight of hydrochloric acid is completely added, resulting in a bottom solution containing silica sol seeds;

[0016] In the step of simultaneously adding the polyacrylic acid solution and part of the sodium silicate solution to the base liquid containing silica sol seeds, the stirring speed used is less than the first dispersion speed, and the dropping rate of the polyacrylic acid solution is less than half of the first dropping rate.

[0017] In the step of simultaneously adding hydrochloric acid and a portion of the sodium silicate solution to the base liquid, the stirring speed used is no greater than the first dispersion speed, and the dropping rate of the hydrochloric acid is less than half of the first dropping rate.

[0018] Furthermore, the first dispersion rotation speed is 500-1000 rpm, and the first drip rate is 5-30 drops per minute;

[0019] In the step of simultaneously adding the polyacrylic acid solution and part of the sodium silicate solution to the base liquid containing silica sol seeds, the stirring speed is 200-300 rpm, and the dropping rate of the polyacrylic acid solution is 1-2 drops per minute.

[0020] In the step of simultaneously adding hydrochloric acid and part of the sodium silicate solution to the base liquid, the stirring speed is 300-500 rpm, and the dropping rate of the hydrochloric acid is 1-2 drops per minute.

[0021] Furthermore, prior to the step of simultaneously adding the polyacrylic acid solution and a portion of the sodium silicate solution to the substrate containing silica sol seeds, the method further includes the step of:

[0022] While stirring, 0.1-0.5 parts of methacrylethyl sulfobetaine are added dropwise to the base solution in the form of a methacrylethyl sulfobetaine solution.

[0023] Furthermore, in the step of adding 0.1-0.5 parts of methacryloylethyl sulfobetaine to the base liquid, the stirring speed is 200-300 rpm and the dropping rate is 1-2 drops per minute.

[0024] Furthermore, after the step of simultaneously adding hydrochloric acid and a portion of the sodium silicate solution to the base solution, the method further includes the step of:

[0025] Let it stand and age for 12-24 hours.

[0026] Furthermore, the solvent for the sodium silicate solution is 90-110 parts of deionized water.

[0027] Secondly, this application provides a silica sol with long-term stability, which is prepared by the method for preparing the silica sol with long-term stability described in the first aspect.

[0028] The beneficial effects of this invention are as follows: By simultaneously adding sodium silicate solution and acidic solution to the substrate, the silica sol seeds continuously adsorb newly generated silica oligomers, increasing the particle size through epitaxial growth. This achieves uniform growth of silica sol particles with a narrow particle size distribution, inhibiting Ostwald ripening during long-term storage. In the acidic solution, polyacrylic acid prevents the aggregation of silica sol particles through electrostatic repulsion and steric hindrance. Adding the polyacrylic acid solution first, followed by the sodium silicate solution, helps ensure the proper ratio of sodium silicate to polyacrylic acid dosage and helps stabilize the pH of the substrate within a predetermined range. Detailed Implementation

[0029] To make the objectives, technical solutions, and advantages of the embodiments of this disclosure clearer, the technical solutions of the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. All other embodiments obtained by those skilled in the art based on the described embodiments of this disclosure without creative effort are within the scope of protection of this invention.

[0030] It should be understood that, without conflict, any and all embodiments of the present invention can be combined with technical features of any other embodiment or multiple other embodiments to obtain other embodiments. The present invention includes such combinations to obtain other embodiments.

[0031] Unless otherwise specified, all technical and scientific terms used herein have the standard meaning in the field to which the claimed subject matter pertains. Where multiple definitions exist for a term, the definition herein shall prevail.

[0032] This application provides a method for preparing silica sol with long-term stability, including the following raw material composition and dosage range:

[0033] Sodium silicate (Na2SiO3·9H2O): 5-10 parts by weight.

[0034] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.2-0.8 parts by weight.

[0035] Deionized water: 90-110 parts by weight for preparing sodium silicate solution; and take 100 times the mass of polyacrylic acid to prepare 1 wt% polyacrylic acid solution.

[0036] Hydrochloric acid (37 wt%): Add until all sodium silicate solution is completely dissolved.

[0037] Silica sol seeds (particle size 5-10 nm): 0.5-1 parts by weight (as SiO2).

[0038] The silica sol seeds can be prepared by the Stöber method, or commercially available silica sol with uniform particle size can be purchased directly. The best option is to make your own silica sol with a particle size of 5-10 nm.

[0039] Preparation steps:

[0040] Simultaneously add polyacrylic acid solution and part of sodium silicate solution to the substrate containing silica sol seeds until the polyacrylic acid solution is used up.

[0041] Add hydrochloric acid and a portion of sodium silicate solution dropwise to the base solution until the sodium silicate solution is used up.

[0042] During the above two steps, keep stirring and maintain the pH of the base solution at 3-4.

[0043] It also includes step S3: let it stand and age for 12-24 hours.

[0044] Sodium silicate is the silicon source for silica sol. Under acidic conditions, it undergoes condensation to form silica sol particles.

[0045] Hydrochloric acid acts as an acidic catalyst, promoting the condensation reaction of sodium silicate while simultaneously adjusting the pH value.

[0046] Silica sol seeds, acting as crystal nuclei, can control the nucleation and growth process of silica sol, resulting in silica sols with narrow particle size distribution.

[0047] Polyacrylic acid (PAA), acting as a polymer stabilizer and partially acidic catalyst, prevents the aggregation of silica sol particles through electrostatic repulsion and steric hindrance. The carboxyl groups on the PAA molecular chain can carry a negative charge, which interacts with the positive charge on the surface of the silica sol particles, forming an electrostatic repulsion.

[0048] In this preparation method, silica sol seeds are used to control the particle size distribution, PAA provides electrostatic repulsion and steric hindrance, and the order of feeding ensures the material dosage relationship and pH stability during the preparation process, which together improve the stability of silica sol.

[0049] PAA with a molecular weight of approximately 2000 is preferred, as PAA in this molecular weight range has good dispersibility and stability, and can effectively stabilize silica sol.

[0050] Silica sol seeds are key components for controlling particle size distribution. Although they can be prepared in-house using the Stöber method, this method has stringent requirements for reaction conditions (such as temperature, stirring rate, and reactant concentration), making it difficult to control particle size uniformity. Furthermore, the Stöber method typically requires organic solvents, posing environmental pollution and safety risks. Currently available commercially available silica sols also suffer from wide particle size distributions and high prices. Therefore, simplifying the preparation process of silica sol seeds and achieving industrial-scale production is a problem that needs to be addressed.

[0051] In a preferred embodiment, silica sol seeds are generated in situ, simplifying the preparation process. Specifically, during the hydrolysis and condensation of sodium silicate, in-situ generation of silica sol seeds is achieved by controlling the reaction conditions. The specific method is as follows: a small amount of acid is first rapidly added to the sodium silicate solution to induce rapid nucleation and the formation of numerous tiny silica sol particles (i.e., seeds). Then, the remaining acid is slowly added dropwise to control the growth rate of the silica sol particles and prevent aggregation. By adjusting parameters such as the type, concentration, and dropping rate of the acid, the particle size and distribution of the silica sol seeds can be controlled.

[0052] Raw material composition and dosage range:

[0053] Sodium silicate (Na2SiO3·9H2O): 5-10 parts by weight.

[0054] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.2-0.8 parts by weight.

[0055] Deionized water: 90-110 parts by weight for preparing sodium silicate solution; and take 100 times the mass of polyacrylic acid to prepare 1 wt% polyacrylic acid solution.

[0056] Hydrochloric acid (37 wt%): Initially add 0.4-0.8 parts by weight rapidly; then add slowly until all sodium silicate solution is completely added.

[0057] Preparation steps:

[0058] Dissolve 5-10 parts by weight of sodium silicate (Na₂SiO₃·9H₂O) in 90-110 parts by weight of deionized water. Stir at 300 rpm for 30 minutes at room temperature (25±2℃) using a magnetic stirrer to ensure complete dissolution of the sodium silicate, yielding a clear and transparent sodium silicate solution. Dissolve 0.2-0.8 parts by weight of polyacrylic acid (PAA, molecular weight approximately 2,000) in deionized water to prepare a 1 wt% PAA solution.

[0059] Take one-seventh to one-tenth of the volume of sodium silicate solution as the base liquid (first part of sodium silicate solution), and rapidly add 0.4-0.8 parts by weight of hydrochloric acid while stirring vigorously at the first dispersion speed (500-1000 rpm), with the dropping speed controlled at 5-30 drops per minute.

[0060] Use a pH meter to monitor the pH value in real time. While stirring at a speed of 200-300 rpm, slowly add the PAA solution dropwise to the above mixture (the bottom liquid containing silica sol seeds), controlling the dropwise addition rate at 1-2 drops per minute. At the same time, add sodium silicate solution (second part sodium silicate solution) dropwise to maintain the pH value at 3-4.

[0061] Then, using a pH meter to monitor the pH value in real time, hydrochloric acid is slowly added dropwise while stirring at 300-500 rpm, with the addition rate controlled at 1 drop per minute. At the same time, sodium silicate solution (the third part of the sodium silicate solution) is also added dropwise to maintain the pH value at 3-4. The entire addition process lasts 30-60 minutes.

[0062] Aging: Transfer the reaction mixture to a clean container and allow it to stand at room temperature (25±2℃) for 24 hours to obtain a stable silica sol.

[0063] The sodium silicate solution consists of: the first part sodium silicate solution + the second part sodium silicate solution + the third part sodium silicate solution = the total sodium silicate solution (a sodium silicate solution prepared with 5-10 parts by weight of sodium silicate and 90-110 parts by weight of deionized water).

[0064] This embodiment achieves in-situ generation of silica sol seeds by controlling the dropwise addition of hydrochloric acid. First, a small amount of hydrochloric acid is rapidly added to induce nucleation and the formation of numerous tiny silica sol particles. Then, the remaining hydrochloric acid is slowly added to control the growth rate of the silica sol particles and prevent aggregation.

[0065] During the rapid addition of hydrochloric acid, sodium silicate undergoes rapid hydrolysis and polymerization to form nanoscale silica sol particles. These particles serve as seeds, providing nuclei for the subsequent growth of silica sol particles.

[0066] During the slow addition of hydrochloric acid, sodium silicate continues to hydrolyze and polymerize, and silica sol particles gradually grow from the seed to form silica sol with larger particle size.

[0067] This implementation method simplifies the preparation process of silica sol seeds and reduces production costs. The in-situ generated silica sol seeds have fewer impurities and better compatibility with subsequently grown silica sol particles, which is beneficial for improving the stability of the silica sol.

[0068] Polyacrylic acid (PAA), as a polymer stabilizer, primarily stabilizes silica sols through electrostatic repulsion and steric hindrance. In high-salt environments, salt ions shield the charges on the PAA molecular chains, reducing electrostatic repulsion and thus decreasing the PAA's stabilizing effect. Furthermore, high-salt environments also tend to cause PAA to curl, reducing the steric hindrance effect. Therefore, improving the stability of PAA in high-salt environments is an important research direction.

[0069] In the preferred embodiment, the raw material composition and dosage range are as follows:

[0070] Sodium silicate (Na2SiO3·9H2O): 5-10 parts by weight;

[0071] Deionized water: 90-110 parts by weight

[0072] Sodium silicate (Na2SiO3·9H2O): 5-10 parts by weight.

[0073] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.2-0.4 parts by weight.

[0074] Deionized water: 90-110 parts by weight for preparing sodium silicate solution; and take 100 times the mass of polyacrylic acid to prepare 1 wt% polyacrylic acid solution.

[0075] Hydrochloric acid (37 wt%): Add until all sodium silicate solution is completely dissolved.

[0076] Methacrylethyl sulfobetaine (SBMA): 0.1-0.5 parts by weight.

[0077] Silica sol seeds (particle size 5-10 nm): 0.5-1 parts by weight (as SiO2).

[0078] Preparation steps:

[0079] Dissolve 5-10 parts by weight of sodium silicate (Na₂SiO₃·9H₂O) in 90-110 parts by weight of deionized water. Stir at 300 rpm for 30 minutes at room temperature (25±2℃) using a magnetic stirrer to ensure complete dissolution of the sodium silicate, yielding a clear and transparent sodium silicate solution. Dissolve 0.2-0.4 parts by weight of polyacrylic acid (PAA, molecular weight approximately 2,000) in deionized water to prepare a 1 wt% PAA solution. Dissolve 0.1-0.5 parts by weight of SBMA in deionized water to prepare a 1 wt% SBMA solution.

[0080] While stirring at 200-300 rpm, add the SBMA solution dropwise to the substrate containing silica sol seeds, with the dropping rate controlled at 1-2 drops per minute.

[0081] Use a pH meter to monitor the pH value in real time. While stirring at a speed of 200-300 rpm, slowly add the PAA solution dropwise to the above mixture at a rate of 1-2 drops per minute. At the same time, add sodium silicate solution dropwise to maintain the pH value at 3-4.

[0082] Then, the pH value was monitored in real time using a pH meter. Hydrochloric acid was slowly added dropwise while stirring at a speed of 300-500 rpm, with the addition rate controlled at 1 drop per minute. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4.

[0083] Aging: Transfer the reaction mixture to a clean container and allow it to stand at room temperature (25±2℃) for 24 hours to obtain a stable silica sol.

[0084] SBMA has good water solubility and dispersibility, and carries both positive and negative charges. In high-salt environments, it can better maintain charge balance, enhance electrostatic repulsion, and improve the stability of silica sol.

[0085] SBMA and polyacrylic acid work together to improve the stability of silica sol in high-salt environments. SBMA molecules contain both quaternary ammonium salt groups and sulfonic acid groups, which help maintain charge balance and enhance electrostatic repulsion in high-salt conditions. SBMA and PAA are co-adsorbed on the surface of silica sol particles, inhibiting PAA curling in high-salt environments and improving steric hindrance, thus effectively preventing the aggregation of silica sol particles in high-salt conditions.

[0086] This implementation method improves the stability of silica sol in high-salt environments. The introduction of SBMA enhances electrostatic repulsion and improves steric hindrance, effectively preventing the aggregation of silica sol particles in high-salt environments. The order of addition of SBMA and PAA has a certain impact on the stability of the silica sol. Adding the SBMA solution first, followed by the PAA solution, yields better stabilization. The principle is that the sulfonic acid groups in the SBMA molecule preferentially form hydrogen bonds with the silanol groups on the silica sol surface, enhancing its adsorption. Then, PAA interacts with SBMA to form a more stable protective layer. If PAA is added first, it tends to occupy the active sites on the silica sol surface, hindering the adsorption of SBMA and reducing the stabilization effect.

[0087] Example 1: The product formula is as follows:

[0088] Sodium silicate (Na2SiO3·9H2O): 7.5 parts by weight (AR, Tianjin Damao Chemical Reagent Factory);

[0089] Deionized water: 100 parts by weight for preparing sodium silicate solution, 50 parts for preparing polyacrylic acid solution;

[0090] Hydrochloric acid (37 wt%): Continue adding until all sodium silicate solution is completely dissolved;

[0091] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.5 parts by weight (PAA-2000, Shanghai Maclean Biochemical Technology Co., Ltd.);

[0092] Silica sol seed solution (particle size 5-10 nm): 0.75 parts by weight (as SiO2).

[0093] The preparation method of the product is as follows:

[0094] Dissolve 7.5 parts by weight of sodium silicate (Na₂SiO₃·9H₂O) in 100 parts by weight of deionized water. Stir at 300 rpm for 30 minutes at room temperature (25±2℃) using a magnetic stirrer to ensure complete dissolution of the sodium silicate, yielding a clear and transparent sodium silicate solution. Dissolve 0.5 parts by weight of polyacrylic acid (PAA, molecular weight approximately 2000) in deionized water to prepare a 1 wt% PAA solution.

[0095] The pH value was monitored in real time using a pH meter. The PAA solution was slowly added dropwise to the bottom solution containing silica sol seeds while stirring at 300 rpm. The dropping rate was controlled at 1-2 drops per minute. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4.

[0096] Then, the pH value was monitored in real time using a pH meter. Hydrochloric acid was slowly added dropwise at a rate of 1 drop per minute while stirring at 500 rpm. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4. The entire addition process lasted about 45 minutes.

[0097] The reaction mixture was transferred to a clean container and allowed to stand at room temperature (25±2℃) for 24 hours to obtain a stable silica sol.

[0098] Perform performance testing on the product:

[0099] Particle size and distribution: The particle size and distribution of the silica sol were tested using a dynamic light scattering (DLS) instrument (model: Malvern Zetasizer Nano ZS). Before testing, the silica sol samples were diluted to an appropriate concentration. The testing temperature was 25℃, and the scattering angle was 173°. Test results: The average particle size was 20 nm, and the particle size distribution index (PDI) was 0.15. Test standard: ISO 22412:2017.

[0100] Stability: The silica sol samples were sealed and placed in a 60℃ oven for accelerated aging. Samples were taken every 24 hours, and particle size changes were tested using DLS. After 7 days of testing, the average particle size was 25nm, and the PDI was 0.20.

[0101] High salt stability: The silica sol sample was mixed with a 1M NaCl solution at a 1:1 volume ratio, and the presence of precipitate was observed. After 24 hours, no precipitate was formed.

[0102] Example 2: The product formula is as follows:

[0103] Sodium silicate (Na2SiO3·9H2O): 6 parts by weight (AR, Tianjin Damao Chemical Reagent Factory);

[0104] Deionized water: 95 parts by weight for preparing sodium silicate solution, 40 parts for preparing polyacrylic acid solution;

[0105] Hydrochloric acid (37 wt%): Continue adding until all the sodium silicate solution is completely dissolved;

[0106] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.4 parts by weight (PAA-2000, Shanghai Maclean Biochemical Technology Co., Ltd.);

[0107] Silica sol seed solution (particle size 5-10 nm): 0.6 parts by weight (as SiO2).

[0108] The preparation method of the product is as follows:

[0109] Dissolve 6 parts by weight of sodium silicate (Na₂SiO₃·9H₂O) in 95 parts by weight of deionized water. Stir at 300 rpm for 30 minutes at room temperature (25±2℃) using a magnetic stirrer to ensure complete dissolution of the sodium silicate, yielding a clear and transparent sodium silicate solution. Dissolve 0.4 parts by weight of polyacrylic acid (PAA, molecular weight approximately 2000) in deionized water to prepare a 1 wt% PAA solution.

[0110] The pH value was monitored in real time using a pH meter. The PAA solution was slowly added dropwise to the bottom solution containing silica sol seeds while stirring at 200 rpm. The addition rate was controlled at 1-2 drops per minute. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4.

[0111] Then, using a pH meter to monitor the pH value in real time, hydrochloric acid was slowly added dropwise at a rate of 1 drop per minute while stirring at 400 rpm. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4. The entire addition process lasted approximately 40 minutes.

[0112] The reaction mixture was transferred to a clean container and allowed to stand at room temperature (25±2℃) for 24 hours to obtain a stable silica sol.

[0113] Perform performance testing on the product:

[0114] Particle size and distribution: The particle size and distribution of the silica sol were tested using a dynamic light scattering (DLS) instrument (model: Malvern Zetasizer Nano ZS). Before testing, the silica sol samples were diluted to an appropriate concentration. The testing temperature was 25℃, and the scattering angle was 173°. Test results: The average particle size was 18 nm, and the particle size distribution index (PDI) was 0.13. Test standard: ISO 22412:2017.

[0115] Stability: The silica sol samples were sealed and placed in a 60℃ oven for accelerated aging. Samples were taken every 24 hours, and particle size changes were tested using DLS. After 7 days of testing, the average particle size was 23 nm, and the PDI was 0.18.

[0116] High salt stability: The silica sol sample was mixed with a 1M NaCl solution at a 1:1 volume ratio, and the presence of precipitation was observed. After 24 hours, no precipitation was formed. The silica sol sample was then mixed with a 2M NaCl solution at a 1:1 volume ratio, and the presence of precipitation was observed. After 24 hours, a small amount of precipitation was formed.

[0117] Example 3: The product formula is as follows:

[0118] Sodium silicate (Na2SiO3·9H2O): 7.5 parts by weight (AR, Tianjin Damao Chemical Reagent Factory);

[0119] Deionized water: 100 parts by weight for preparing sodium silicate solution, 50 parts for preparing polyacrylic acid solution;

[0120] Hydrochloric acid (37 wt%): Initially add 0.6 parts by weight rapidly; then add slowly until all sodium silicate solution is completely added;

[0121] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.5 parts by weight (PAA-2000, Shanghai Maclean Biochemical Technology Co., Ltd.).

[0122] The preparation method of the product is as follows:

[0123] Dissolve 7.5 parts by weight of sodium silicate (Na₂SiO₃·9H₂O) in 100 parts by weight of deionized water. Stir at 300 rpm for 30 minutes at room temperature (25±2℃) using a magnetic stirrer to ensure complete dissolution of the sodium silicate, yielding a clear and transparent sodium silicate solution. Dissolve 0.5 parts by weight of polyacrylic acid (PAA, molecular weight approximately 2000) in deionized water to prepare a 1 wt% PAA solution.

[0124] Take one-eighth of the sodium silicate solution by volume as the base liquid, and rapidly add 0.6 parts by weight of hydrochloric acid while stirring vigorously at the first dispersion speed (500 rpm), with the addition rate controlled at 5 drops per minute.

[0125] The pH value was monitored in real time using a pH meter. The PAA solution was slowly added dropwise to the mixture while stirring at 300 rpm, with the addition rate controlled at 1-2 drops per minute. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4.

[0126] Then, using a pH meter to monitor the pH value in real time, hydrochloric acid was slowly added dropwise at a rate of 1 drop per minute while stirring at 500 rpm. Simultaneously, sodium silicate solution was added dropwise to maintain the pH value at 3-4. This process continued for approximately 45 minutes until all the sodium silicate solution was added.

[0127] Aging: Transfer the reaction mixture to a clean container and allow it to stand at room temperature (25±2℃) for 24 hours to obtain a stable silica sol.

[0128] Perform performance testing on the product:

[0129] Particle size and distribution: The particle size and distribution of the silica sol were tested using a dynamic light scattering (DLS) instrument (model: Malvern Zetasizer Nano ZS). Before testing, the silica sol samples were diluted to an appropriate concentration. The testing temperature was 25℃, and the scattering angle was 173°. Test results: The average particle size was 17 nm, and the particle size distribution index (PDI) was 0.12. Test standard: ISO 22412:2017.

[0130] Stability: The silica sol samples were sealed and placed in a 60℃ oven for accelerated aging. Samples were taken every 24 hours, and particle size changes were tested using DLS. After 7 days of testing, the average particle size was 21 nm, and the PDI was 0.16.

[0131] High salt stability: The silica sol sample was mixed with a 1M NaCl solution at a 1:1 volume ratio, and the presence of precipitate was observed. After 24 hours, no precipitate was formed.

[0132] Example 4: The product formula is as follows:

[0133] Sodium silicate (Na2SiO3·9H2O): 7.5 parts by weight (AR, Tianjin Damao Chemical Reagent Factory);

[0134] Deionized water: 100 parts by weight for preparing sodium silicate solution, 30 parts for preparing polyacrylic acid solution, and 15 parts for preparing SMBA solution;

[0135] Hydrochloric acid (37 wt%): Continue adding until all sodium silicate solution is completely dissolved;

[0136] Methacrylethyl sulfobetaine (SBMA): 0.15 parts by weight (Shanghai Bid Pharmaceutical Technology Co., Ltd.);

[0137] Polyacrylic acid (PAA, molecular weight approximately 2000): 0.3 parts by weight (PAA-2000, Shanghai Maclean Biochemical Technology Co., Ltd.).

[0138] Silica sol seed solution (particle size 5-10 nm): 0.75 parts by weight (as SiO2).

[0139] The preparation method of the product is as follows:

[0140] Dissolve 7.5 parts by weight of sodium silicate (Na₂SiO₃·9H₂O) in 100 parts by weight of deionized water. Stir at 300 rpm for 30 minutes at room temperature (25±2℃) using a magnetic stirrer to ensure complete dissolution of the sodium silicate, yielding a clear and transparent sodium silicate solution. Dissolve 0.15 parts by weight of methacryloylethyl sulfobetaine (SBMA) in deionized water to prepare a 1 wt% SBMA solution. Dissolve 0.3 parts by weight of polyacrylic acid (PAA, molecular weight approximately 2000) in deionized water to prepare a 1 wt% PAA solution.

[0141] While stirring at 200 rpm, the SBMA solution was added dropwise to the substrate containing silica sol seeds at a rate of 1-2 drops per minute.

[0142] The pH value was monitored in real time using a pH meter. The PAA solution was slowly added dropwise to the mixture while stirring at 300 rpm, with the addition rate controlled at 1-2 drops per minute. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4.

[0143] Then, the pH value was monitored in real time using a pH meter. Hydrochloric acid was slowly added dropwise while stirring at a speed of 300-500 rpm, with the addition rate controlled at 1 drop per minute. Sodium silicate solution was also added dropwise to maintain the pH value at 3-4.

[0144] Aging: Transfer the reaction mixture to a clean container and allow it to stand at room temperature (25±2℃) for 24 hours to obtain a stable silica sol.

[0145] Perform performance testing on the product:

[0146] Particle size and distribution: The particle size and distribution of the silica sol were tested using a dynamic light scattering (DLS) instrument (model: Malvern Zetasizer Nano ZS). Before testing, the silica sol samples were diluted to an appropriate concentration. The testing temperature was 25℃, and the scattering angle was 173°. Test results: The average particle size was 21 nm, and the particle size distribution index (PDI) was 0.14. Test standard: ISO 22412:2017.

[0147] Stability: The silica sol samples were sealed and placed in a 60℃ oven for accelerated aging. Samples were taken every 24 hours, and particle size changes were tested using DLS. After 7 days of testing, the average particle size was 24nm, and the PDI was 0.17.

[0148] High salt stability: The silica sol sample was mixed with a 1M NaCl solution at a 1:1 volume ratio, and the presence of precipitation was observed. After 24 hours, no precipitation was formed. The silica sol sample was then mixed with a 2M NaCl solution at a 1:1 volume ratio, and the presence of precipitation was observed. After 24 hours, no precipitation was formed.

[0149] Comparison Example

[0150] The selected silica sol (model: Ludox HS-40, Sigma-Aldrich) has a SiO2 content of 40wt% and an average particle size of 12nm.

[0151] Performance testing of commercially available silica sol:

[0152] Particle size and distribution: The particle size and distribution of the silica sol were tested using a dynamic light scattering (DLS) instrument (model: Malvern Zetasizer Nano ZS). Before testing, the silica sol samples were diluted to an appropriate concentration. The testing temperature was 25℃, and the scattering angle was 173°. Test results: The average particle size was 12 nm, and the particle size distribution index (PDI) was 0.25. Test standard: ISO 22412:2017.

[0153] Stability: The silica sol samples were sealed and placed in a 60℃ oven for accelerated aging. Samples were taken every 24 hours, and particle size changes were tested using DLS. After 7 days of testing, the average particle size was 20nm, and the PDI was 0.35.

[0154] High salt stability: The silica sol sample was mixed with a 1M NaCl solution at a 1:1 volume ratio, and the presence of precipitation was observed. After 24 hours, a small amount of precipitate was formed.

[0155] The test results from the above examples and control group show that:

[0156] The silica sols prepared in Examples 1 and 2 have a narrow particle size distribution (PDI < 0.2) and good long-term stability (small particle size increase after 7 days of accelerated aging at 60°C).

[0157] The silica sol prepared in Example 3 further reduced the particle size and particle size distribution index, and improved the uniformity of the silica sol.

[0158] The silica sol prepared in Example 4 showed significantly improved stability in high-salt environments, remaining stable even in 2M NaCl solution.

[0159] Compared with commercially available silica sols, the silica sol prepared by this invention has better stability and high salt stability.

[0160] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "illustrative embodiment," "example," "specific example," or "some examples," etc., indicate that a specific feature, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0161] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. A method for preparing a silica sol with long-term stability, characterized in that, By weight, the raw materials include: 5-10 parts sodium silicate, used to prepare sodium silicate solution; and 0.2-0.8 parts polyacrylic acid, used to prepare polyacrylic acid solution. The preparation steps, in sequence, include: The polyacrylic acid solution and part of the sodium silicate solution are simultaneously added dropwise to the base solution containing silica sol seeds until the polyacrylic acid solution is used up. Hydrochloric acid and a portion of the sodium silicate solution are added dropwise to the base solution until the sodium silicate solution is used up. During the above two steps, keep stirring to maintain the pH of the base solution at 3-4; The preparation steps of the substrate containing silica sol seeds include: At the first dispersion speed, hydrochloric acid is added dropwise to a portion of the sodium silicate solution at the first drop rate until 0.4-0.8 parts by weight of hydrochloric acid is completely added, resulting in a bottom solution containing silica sol seeds; In the step of simultaneously adding the polyacrylic acid solution and part of the sodium silicate solution to the base liquid containing silica sol seeds, the stirring speed used is less than the first dispersion speed, and the dropping rate of the polyacrylic acid solution is less than half of the first dropping rate. In the step of simultaneously adding hydrochloric acid and a portion of the sodium silicate solution to the base liquid, the stirring speed used is no greater than the first dispersion speed, and the dropping rate of the hydrochloric acid is less than half of the first dropping rate.

2. The method for preparing a silica sol with long-term stability according to claim 1, characterized in that, The silica sol seeds have a particle size of 5-10 nm and are used in amounts of 0.5-1 part.

3. The method for preparing a silica sol with long-term stability according to claim 1, characterized in that, The weight-average molecular weight of the polyacrylic acid is 1500-2200.

4. The method for preparing a silica sol with long-term stability according to claim 1, characterized in that, The first dispersion rotation speed is 500-1000 rpm, and the first drip rate is 5-30 drops per minute; In the step of simultaneously adding the polyacrylic acid solution and part of the sodium silicate solution to the base liquid containing silica sol seeds, the stirring speed is 200-300 rpm, and the dropping rate of the polyacrylic acid solution is 1-2 drops per minute. In the step of simultaneously adding hydrochloric acid and part of the sodium silicate solution to the base liquid, the stirring speed is 300-500 rpm, and the dropping rate of the hydrochloric acid is 1-2 drops per minute.

5. The method for preparing a silica sol with long-term stability according to claim 1, characterized in that, Before the step of simultaneously adding the polyacrylic acid solution and a portion of the sodium silicate solution to the substrate containing silica sol seeds, the method further includes the following step: While stirring, 0.1-0.5 parts of methacrylethyl sulfobetaine are added dropwise to the base solution in the form of a methacrylethyl sulfobetaine solution.

6. The method for preparing a silica sol with long-term stability according to claim 5, characterized in that, In the step of adding 0.1-0.5 parts of methacryloylethyl sulfobetaine to the base liquid, the stirring speed is 200-300 rpm and the dropping rate is 1-2 drops per minute.

7. The method for preparing a silica sol with long-term stability according to claim 1, characterized in that, Following the step of simultaneously adding hydrochloric acid and a portion of the sodium silicate solution to the substrate, the method further includes the following step: Let it stand and age for 12-24 hours.

8. The method for preparing a silica sol with long-term stability according to claim 1, characterized in that, The solvent for the sodium silicate solution is 90-110 parts of deionized water.

9. A silica sol with long-term stability, characterized in that, It is prepared by the method for preparing silica sol with long-term stability according to any one of claims 1 to 8.