Preparation method and application of silica sol with reversible freezing properties

Abstract

This invention proposes a method for preparing and applying a silica sol with reversible freezing properties. The silica sol is obtained by hydrolyzing bissilane coupling agents KH560 and KH570 under acidic conditions, followed by synergistic modification by dropwise addition to the original silica sol. The surface of the nano-silica particles is simultaneously covalently grafted with silane coupling agents KH560 and KH570, forming an organic-inorganic hybrid interface layer. Through the synergistic effect of the bissilane coupling agents, the silica sol is endowed with reversible freezing properties: after complete freezing below -40°C, it does not produce irreversible gelation after thawing at room temperature. The changes in particle size, viscosity, and pH value are small, and it remains stable after at least 15 freeze-thaw cycles. At the same time, it can recover quickly after thawing at room temperature. This breaks through the technical bottleneck of traditional silica sols that permanently fail after low-temperature freezing, significantly improving its stability in low-temperature storage, transportation, and use. It can be widely used in antifreeze coatings, low-temperature adhesives, cryopreservation media, and other fields.

Description

Technical Field

[0001] This invention relates to the field of silica sol modification technology, specifically to a method for preparing and applying a silica sol with reversible freezing properties. Background Technology

[0002] Silica sol is a colloidal dispersion system of nano-silica (SiO2) particles in water or organic solvents. Due to its high specific surface area, excellent adhesion, and film-forming properties, it is widely used in precision casting, coatings, catalyst supports, chemical mechanical polishing, and building protection materials. However, traditional silica sol suffers from serious stability defects at low temperatures: when the temperature drops below the freezing point (e.g., -18°C), the dispersion medium freezes, and ice crystal growth leads to extreme concentration of nanoparticles in the unfrozen areas. The silanol groups (Si-OH) on the particle surface undergo irreversible dehydration condensation reactions at localized high concentrations, forming Si-O-Si covalent bonds, resulting in permanent gels or precipitation. Even after thawing, these chemical cross-links cannot be broken, causing the silica sol to completely fail. This characteristic of "permanent failure upon freezing at low temperatures" greatly limits the storage, transportation, and use of silica sol in cold regions (such as winter outdoor construction, cold chain transportation, polar or high-altitude environments).

[0003] To address the aforementioned issues, existing technologies attempt to improve the low-temperature stability of silica sols by adding antifreeze agents (such as ethylene glycol and glycerol), increasing the pH value, or using surfactant adsorption. However, the extensive use of antifreeze agents alters the intrinsic properties of silica sols (such as viscosity, solid content, and surface reactivity) and cannot fundamentally prevent direct contact and condensation of particles under freeze-thaw conditions; surfactant adsorption, on the other hand, exhibits poor stability and is prone to desorption during freeze-thaw cycles. Therefore, developing a "reversible" silica sol system that can protect particles during low-temperature freezing and fully restore its original properties after thawing has become a pressing technical challenge in this field.

[0004] In recent years, surface modification of silane coupling agents has attracted attention due to the stability of covalent bonds and the designability of organic functional layers. KH560 (γ-glycidoxypropyltrimethoxysilane) and KH570 (γ-methacryloyloxypropyltrimethoxysilane) are two common silanes. The former contains epoxy groups, which can form flexible hydrophilic chains through ring-opening reactions; the latter contains methacryloyloxy groups, which provide hydrophobicity and steric hindrance. Existing literature reports that using KH560 to modify silica sol can restore it to a colloidal state after 5 freeze-thaw cycles, with no significant difference in particle morphology, size and distribution. However, this technology still has the following shortcomings: (1) the extreme freeze-thaw cycles are limited, and performance deterioration and gelation occur after about 8-10 cycles; (2) the low temperature application range is limited, and the freeze-thaw resistance effect decreases significantly below -25℃; (3) the recovery time after thawing is long, and there is a transition turbidity period, which affects the actual use efficiency.

[0005] Therefore, it is necessary to propose a method for preparing silica sol with freeze reversibility to solve the problems of insufficient extreme freeze-thaw cycles, ultra-low temperature adaptability and recovery rate in the existing technology, and to meet the needs of silica sol for a wider range of applications. Summary of the Invention

[0006] This invention proposes a method for preparing and applying silica sol with reversible freezing properties, which solves the problems of insufficient maximum freeze-thaw cycles, low-temperature adaptability, and recovery rate of existing silica sol technologies.

[0007] The technical solution of this invention is implemented as follows: The first aspect of the present invention is to provide a method for preparing a silica sol with reversible freezing properties, comprising the steps of: S1. Take silane coupling agents KH560 and KH570 in a mass ratio of 1:(0.5~2) and then hydrolyze them under acidic conditions to obtain a hydrolysate; S2. While stirring, add the hydrolysate dropwise into the silica sol. After the dropwise addition is complete, heat the solution to 50~90℃ to allow it to react fully, and then cool it. S3. Adjust the pH of the reaction product obtained in step S2 to 7-9, filter or centrifuge to remove unreacted residues, and obtain a silica sol with reversible freezing properties.

[0008] Further, in step S1, the mass ratio of the silane coupling agents KH560 and KH570 is 1:(0.8~1.5).

[0009] Furthermore, in step S1, the acidic conditions have a pH value of 3 to 5, and the hydrolysis time is 0.5 to 1.5 hours.

[0010] Further, in step S2: the droplet acceleration of the hydrolysate is 1~10 mL / min; And / or, the reaction time is 2 to 8 hours.

[0011] Furthermore, in step S2, the solid content of the silica sol is 15~45wt%.

[0012] Furthermore, in step S2, the average particle size of the nano-silica in the silica sol is 5~100 nm; And / or, the dispersion solvent of the silica sol is one or more of water, alcohol, ketone, and ester solvents.

[0013] Further, in step S1, the sum of the masses of the silane coupling agents KH560 and KH570 is a, and the mass of silicon dioxide in the silica sol in step S2 is b, where a:b = (1~20):100.

[0014] A second aspect of the present invention is to provide a silica sol with reversible freezing properties, which is prepared by the preparation method described in the first aspect.

[0015] A third aspect of the invention is to provide the application of the silica sol with freeze-reversible properties described in the second aspect in a low-temperature environment, said application comprising at least one of the following: a) Use antifreeze coatings or exterior wall coatings in cold regions; b) Precision casting binders for low-temperature environments; c) Cryopreservation media for biological or pharmaceutical products; d) Building admixtures for winter construction; e) Adhesives or sealants for polar or high-altitude environments.

[0016] Furthermore, the low-temperature environment is -30°C to 0°C.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention imparts excellent freeze-reversibility to silica sol through the synergistic modification of bissilane coupling agents KH560 and KH570. Compared with the single KH560 modification technology reported in the existing literature, the silica sol synergistically modified by this invention has a more than 50% increase in the ultimate freeze-thaw cycle, good recovery after thawing, no excessive turbidity, and significantly improved ease of use. The modified silica sol maintains good stability within a wide pH range (2-11) and can still recover and remain stable at ultra-low temperatures of -40℃, breaking through the temperature range limitations of the prior art and broadening the application range of silica sol under low-temperature conditions.

[0018] The modified silica sol of this invention can be directly stored, transported and used in low-temperature environments ranging from -40℃ to 0℃ without the need for insulation measures, which significantly reduces the logistics and usage costs in cold regions. It can be widely used in antifreeze coatings, low-temperature adhesives, biological cryopreservation media, winter construction admixtures, polar equipment materials and other fields, and has broad market prospects. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a method for preparing a silica sol with reversible freezing properties, comprising the following steps: S1. Mix silane coupling agents KH560 and KH570 at a mass ratio of 1:(0.5~2), add deionized water, adjust the pH value to acidic by an acid regulator, and hydrolyze to obtain hydrolysate; S2. While stirring, add the hydrolysate dropwise into the silica sol. After the dropwise addition is complete, heat the solution to 50~90℃ to allow it to react fully, and then cool it. S3. Adjust the pH of the reaction product obtained in step S2 to 7-9, filter or centrifuge to remove unreacted residues, and obtain a silica sol with reversible freezing properties.

[0021] In this invention, the silane coupling agent KH560 is γ-glycidoxypropyltrimethoxysilane, whose molecular structure contains epoxy groups, which can open the ring to form a flexible hydrophilic chain; the silane coupling agent KH570 is γ-methacryloyloxypropyltrimethoxysilane, whose molecular structure contains methacryloyloxy groups, providing hydrophobicity and steric hindrance effects; the two work synergistically to form an organic-inorganic hybrid interface layer on the surface of nano-silica particles. In the liquid state, the chain segments of the interface layer extend to form a stable steric hindrance and solvation layer; during freezing, the chain segments compress and deform to absorb the stress of ice crystal growth, preventing irreversible condensation between particles; after thawing, the chain segments re-extend, restoring the original dispersed state. Specifically, after the silica sol is completely frozen below -18°C, upon thawing at room temperature, no irreversible gel is produced, and the change rate of its particle size, viscosity, and pH value does not exceed 10% of the pre-freezing values.

[0022] In this invention, the preparation method does not simply involve mixing two silanes. Instead, it involves "synergistic pre-hydrolysis" of the two silanes under specific weakly acidic conditions to precisely control the final co-grafting ratio on the silica surface. This ensures that the two functional groups can work synergistically in the optimal ratio, achieving a significant performance boost. In a preferred embodiment, the mass ratio of the silane coupling agents KH560 and KH570 is 1:(0.8~1.5).

[0023] In a preferred embodiment, the acidic conditions have a pH of 3-5, the hydrolysis temperature is 25-45℃, and the time is 0.5-1.5 h. Hydrolysis is preferably performed under ultrasonic conditions for 40-60 min. Silane coupling agents KH560 and KH570 are hydrolyzed to obtain epoxy groups and long-chain hydrophobic methacryloxy groups, respectively. The epoxy groups bond to the silicon surface, and the methacryloxy groups provide steric hindrance, achieving a synergistic "anchoring + stretching" effect: KH560 strongly anchors to the silica surface, while the organic long chains of KH570 provide physical entanglement and steric stability. These two factors synergistically enhance stress transfer and interfacial bonding strength. This results in the modified silica sol maintaining excellent stability over a wide pH range (2-11) and achieving a breakthrough improvement in "freeze-reversibility" far exceeding that of single silane modification or simple mixed modification.

[0024] In a preferred embodiment, the acidic conditions have a pH of 3.5 to 4.5. The acid regulator is one or more of glacial acetic acid, citric acid, hydrochloric acid, or dilute sulfuric acid. The hydrolysis of the two silanes is mildly promoted, while a controlled and limited condensation reaction occurs between their silanol intermediates, forming a relatively stable "synergistic hydrolytic oligomer" or "quasi-copolymer oligosilanol mixture".

[0025] In a preferred embodiment, the hydrolysate is added at a rate of 1-10 mL / min, preferably 2-5 mL / min. After addition, the reaction is carried out at 50-90°C for 2-8 hours, more preferably at 60-80°C for 3-5 hours, with a stirring speed of 200-800 rpm maintained during the reaction. This ensures that the hydrolysate reacts fully with the active sites on the silica surface. The sum of the masses of the silane coupling agents KH560 and KH570 is a, and the mass of silica in the silica sol in step S2 is b, where a:b = (1-20):100, preferably a:b = (2-10):100. The two functionally complementary silane coupling agents, KH560 (containing epoxy groups) and KH570 (containing methacryloyloxy groups), are pre-hydrolyzed together in a weakly acidic aqueous system, "assembling" two independent silane monomers with significantly different activities into a "composite precursor" with homogenized reactivity and a fixed ratio of the two components. Then, this composite precursor is dropwise added to a silica dispersion. They compete for active sites on the silica surface with more similar kinetics, allowing the ratio of the two functional groups in the final silane-grafted layer on the particle surface to be adjusted by changing the ratio of the two silane coupling agents. This strategy overcomes the bottleneck of uncontrollable surface composition due to differences in silane activity in traditional stepwise grafting or simple mixing methods.

[0026] In a preferred embodiment, the solid content of the silica sol is 15-45 wt%, and the average particle size of the nano-silica in the silica sol is 5-100 nm, preferably 10-50 nm. Because the two functional groups coexist on the surface in an optimized ratio, the epoxy groups of KH560 and the methacryloyloxy groups of KH570 (providing hydrophobicity and steric hindrance) work synergistically, the prepared silica sol solves the problem of low-temperature stability of small-particle-size, high-concentration products: unmodified small-particle-size (10-30 nm) silica sol is extremely prone to agglomeration and gelation at low temperatures, typically only reaching a content of 15%, and forms an irreversible hard gel after a single freeze-thaw cycle. Through the synergistic modification with dual silanes of this invention, the flexible buffer layer formed by grafting KH560 and KH570 onto the surface effectively buffers ice crystal growth stress and prevents irreversible condensation between particles. Ultimately, the modified silica sol product with a particle size of 10-50 nm remains stable after at least 15 freeze-thaw cycles at -18°C within a solid content range of 15-40%, and can recover even at ultra-low temperatures of -40°C. Furthermore, no antifreeze agent needs to be added.

[0027] In some embodiments, silica sol with a solid content of 15-45 wt% and a particle size of 10-50 nm is completely frozen at -18°C to -20°C for more than 24 hours, and then thawed at room temperature (20-25°C). The recovery time is short, and there is no obvious turbidity period during the thawing process. No gelation, precipitation, or stratification occurs, and the average particle size change rate is ≤5%, the viscosity change rate is ≤5%, and the pH change rate is ≤3%.

[0028] In some embodiments, silica sol with a solid content of 15-45 wt% and a particle size of 10-50 nm can be restored to a sol state after being completely frozen at -40°C and then thawed, with a particle size change rate of ≤12% and a viscosity change rate of ≤15%.

[0029] In a preferred embodiment, the dispersion solvent of the silica sol is a common solvent, including but not limited to one or more of water, alcohol, ketone, and ester solvents.

[0030] This invention also proposes applications of the freeze-reversible silica sol prepared by the above method in low-temperature environments, including but not limited to one or more of the following fields: a) Use antifreeze coatings or exterior wall coatings in cold regions; b) Precision casting binders for low-temperature environments; c) Cryopreservation media for biological or pharmaceutical products; d) Building admixtures for winter construction; e) Adhesives or sealants for polar or high-altitude environments.

[0031] In the above applications, the low-temperature environment refers to storage, transportation, or use conditions ranging from -30°C to 0°C.

[0032] Taking the application of silica sol in coatings as an example, it typically plays a reinforcing role in water-based silicone rubber coatings. The silane coupling agent modification of this invention introduces active functional groups into the system, enhancing the interfacial bonding between the silica sol and the silicone rubber matrix. This invention uses KH560 and KH570 dual-silane synergistic modification of silica sol. Compared to single KH560 modification, it exhibits superior reinforcing effect and wider environmental adaptability in the coating. The mechanical properties of the modified silica sol as a reinforcing filler coating are significantly better than those of the unmodified silica sol-reinforced coating. The dual-silane synergistic modification of silica sol in this invention further improves all mechanical properties. This improvement is mainly attributed to the following mechanism: 1) "Anchoring + Extension" Dual-Function Interface Design: After the epoxy groups of KH560 open their rings, they chemically bond with the active groups (such as hydroxyl and amino groups) in the silicone rubber matrix, forming strong anchoring points; the long methacryloyloxy chain of KH570 physically entangles with the silicone rubber molecular chain, forming a secondary cross-linking network. The synergistic effect of these two elements significantly enhances the interfacial bonding strength between the silica sol and the silicone rubber matrix, thereby improving the tensile strength and shear strength of the coating. 2) Crosslinking density optimization: Single KH560 modification only introduces epoxy groups into the system, resulting in relatively limited crosslinking points. This invention, through the introduction of KH570, increases the number of hydrophobic long-chain physical crosslinking points in the system, forming a dual network structure of "chemical crosslinking + physical entanglement." This structure increases the network density of the coating, leading to a gradual increase in strength. However, under the constraint of the network, the deformation capacity is somewhat suppressed, resulting in a lower elongation at break compared to the unmodified coating, but a significant improvement in overall mechanical properties. 3) Improved particle dispersion: The synergistic modification with bissilanes effectively inhibits the agglomeration of nano-silica particles, resulting in a more uniform distribution within the silicone rubber matrix. Uniformly dispersed nanoparticles can more effectively transfer and disperse stress, reducing localized stress concentration and thus improving the overall mechanical properties of the coating.

[0033] The following are preferred embodiments of the present invention. Unless otherwise specified, the reagents used are standard commercially available reagents in the art, and the experimental methods used are means that are well mastered by those skilled in the art.

[0034] Example 1

[0035] 100 g of acidic silica sol with a solid content of 30% (average particle size 11.5 nm) was heated to 40 °C with stirring. 2 g of KH560 and 2 g of KH570 (mass ratio 1:1) were weighed out, mixed, and 20 g of deionized water was added. The pH was adjusted to 4.0 with glacial acetic acid, and hydrolyzed at 35 °C for 40 minutes. The hydrolysate was added dropwise to the silica sol at a rate of 3 mL / min. After the addition was complete, the temperature was raised to 70 °C, and the reaction was allowed to proceed for 4 hours. After cooling, the pH was adjusted to 8.0 with ammonia to obtain the target modified silica sol.

[0036] Example 2

[0037] 100 g of silica sol with a solid content of 20% (average particle size 11.5 nm) was heated to 40 °C with stirring. 1.5 g of KH560 and 1.5 g of KH570 (mass ratio 1:1) were weighed out, mixed, and 20 g of deionized water was added. The pH was adjusted to 4.0 with glacial acetic acid, and hydrolyzed at 35 °C for 40 minutes. The hydrolysate was added dropwise to the silica sol at a rate of 3 mL / min. After the addition was complete, the temperature was raised to 70 °C, and the reaction was allowed to proceed for 4 hours. After cooling, the pH was adjusted to 8.0 with ammonia to obtain the target modified silica sol.

[0038] Example 3

[0039] 100 g of silica sol with a solid content of 20% (average particle size 20.4 nm) was heated to 40 °C with stirring. 1.5 g of KH560 and 1.2 g of KH570 (mass ratio 1:0.8) were weighed out, mixed, and 25 g of deionized water was added. The pH was adjusted to 3.5 with glacial acetic acid, and hydrolyzed at 30 °C for 45 minutes. The hydrolysate was added dropwise to the silica sol at a rate of 5 mL / min. After the addition was complete, the temperature was raised to 60 °C, and the reaction was allowed to proceed for 5 hours. After cooling, the pH was adjusted to 8.5 with ammonia to obtain the target modified silica sol.

[0040] Example 4

[0041] 100g of silica sol with a solid content of 40% (average particle size 31.2nm) was heated to 40℃ with stirring. 2g of KH560 and 2.4g of KH570 (mass ratio 1:1.2) were weighed separately, mixed, and 20g of deionized water was added. The pH was adjusted to 4.5 with glacial acetic acid, and hydrolyzed at 40℃ for 40 minutes. The hydrolysate was added dropwise to the silica sol at a rate of 2mL / min. After the addition was complete, the temperature was raised to 80℃, and the reaction was allowed to proceed for 3 hours. After cooling, the pH was adjusted to 9 with ammonia to obtain the target modified silica sol.

[0042] Comparative Example 1

[0043] Take 100g of acidic silica sol with a solid content of 30% (average particle size 11.5nm). Weigh 3.08g of KH560 and 0.92g of KH570 (mass ratio approximately 1:0.3), and follow the same steps as in Example 1.

[0044] Comparative Example 2

[0045] Take 100g of acidic silica sol with a solid content of 30% (average particle size 22.6 nm). Weigh 1.0g of KH560 and 3.0g of KH570 (mass ratio 1:3), and follow the same steps as in Example 1.

[0046] Comparative Example 3 (KH560 single modification)

[0047] 100 g of acidic silica sol with a solid content of 30% (average particle size 11.8 nm) was heated to 40 °C with stirring. 4 g of KH560 was added, followed by 20 g of deionized water. The pH was adjusted to 4.0 with glacial acetic acid, and hydrolyzed at 35 °C for 40 minutes. The hydrolysate was added dropwise to the silica sol at a rate of 3 mL / min. After the addition was complete, the temperature was raised to 70 °C, and the reaction was allowed to proceed for 4 hours. After cooling, the pH was adjusted to 8.0 with ammonia to obtain a monosilane coupling agent modified silica sol.

[0048] Experimental Example

[0049] 1. Gel properties after thawing at different freeze-thaw temperatures

[0050] The modified silica sols prepared in Examples 1-4 were frozen at -18°C for 24 hours and then thawed at room temperature. The particle size change rate and viscosity change rate before freezing and after thawing were measured, and whether gelation or precipitation occurred during or after thawing was observed. The results are shown in Table 1.

[0051] Table 1:

[0052] 2. Limiting freeze-thaw cycle test

[0053] The modified silica sols prepared in Examples 1-4 and Comparative Examples 1-3 were simultaneously subjected to repeated freeze-thaw cycles at -18°C. After each freeze-thaw cycle, the sols were thawed at room temperature for 24 hours. Particle size, viscosity, and Zeta potential were measured after 5, 8, 10, and 15 freeze-thaw cycles, until gelation or significant precipitation (particle size change rate >20% or visible gelation) occurred. The maximum number of freeze-thaw cycles was recorded. Examples 1-3 showed slight turbidity after 10 freeze-thaw cycles but no gelation. After 15 freeze-thaw cycles, the particle size change was within 16%, and the sols were recoverable after thawing. Comparative Examples 1-3 showed significant precipitation and gelation after 15 freeze-thaw cycles, which were irreversible, as shown in Table 2. Specifically, when testing every 2-3 freeze-thaw cycles, Comparative Example 3 showed turbidity after 8 cycles, significant precipitation after 10 cycles, and significant gelation after 12 cycles. Comparing Example 1 and Comparative Example 3, the changes in particle size, precipitation, and gelation with increasing freeze-thaw cycles are shown in Table 3.

[0054] Table 2:

[0055] Table 3:

[0056] As can be seen from Tables 2-3 above, the synergistically modified silica sol of this invention can still recover after 15 freeze-thaw cycles, and the maximum number of freeze-thaw cycles is increased by more than 50% compared with the comparative example. This is because the long-chain hydrophobic groups of KH570 provide additional steric hindrance protection during repeated freeze-thaw cycles, forming a "double buffer layer" synergistic effect, which significantly improves durability.

[0057] 3. Comparison of freeze-thaw recovery rates

[0058] The modified silica sols prepared in Examples 1-4 and Comparative Example 3 were frozen at -18°C for 24 hours and then allowed to thaw at room temperature (25°C) (to return to a flowable state). The viscosity was measured every 30 minutes, and the time required to recover to within 90% of the initial viscosity was recorded. The results are shown in Table 3.

[0059] Table 3:

[0060] As can be seen from the results in Table 3, the chain rearrangement in Comparative Example 3 required a relatively long time after thawing. In contrast, the long chain of KH570 in the synergistically modified "double buffer layer" of Examples 1-3 was able to recover its extended conformation more quickly after thawing, forming steric hindrance and thus accelerating the stability of the system.

[0061] 4. Stability Comparison

[0062] The modified silica sols prepared in Examples 1-4 and Comparative Examples 1-3 were simultaneously placed in an oven at 60°C for accelerated aging experiments. The particle size changes and the time to gelation / precipitation after different time periods were tested, and the results are shown in Table 4.

[0063] Table 4:

[0064] As shown in Table 4, the silane-modified silica sols prepared in Examples 1-4 of this invention maintained a stable sol state after 12 months of storage at 60°C, exhibiting no gelation or precipitation, and a particle size change rate of less than 7%, demonstrating excellent long-term storage stability. In contrast, Comparative Examples 1-3 showed varying degrees of precipitation or gelation within 6-10 months, with a significantly increased particle size change rate. This is because the synergistic modification of KH560 and KH570 in this invention forms a dense "double buffer layer" on the silica surface, effectively inhibiting long-term aggregation and sedimentation between particles.

[0065] 5. Impact on coating performance

[0066] Silica sol typically plays a reinforcing role in waterborne silicone rubber coatings. Modification with silane coupling agents can introduce active functional groups into the system, enhancing the interfacial bonding between the silica sol and the silicone rubber matrix. This invention employs a synergistic modification of silica sol with KH560 and KH570 bissilanes, exhibiting superior reinforcing effects and wider environmental adaptability in the coating compared to modification with KH560 alone.

[0067] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a silica sol with reversible freezing properties, characterized in that the steps include... include: S1. Take silane coupling agents KH560 and KH570 in a mass ratio of 1:(0.5~2) and then hydrolyze them under acidic conditions to obtain a hydrolysate; S2. While stirring, add the hydrolysate dropwise into the silica sol. After the dropwise addition is complete, heat the solution to 50~90℃ to allow it to react fully, and then cool it. S3. Adjust the pH of the reaction product obtained in step S2 to 7-9, filter or centrifuge to remove unreacted residues, and obtain a silica sol with reversible freezing properties.

2. The preparation method according to claim 1, characterized in that, In step S1, the mass ratio of the silane coupling agents KH560 and KH570 is 1:(0.8~1..5).

3. The preparation method according to claim 1, characterized in that, In step S1, the acidic conditions have a pH value of 3 to 5, and the hydrolysis time is 0.5 to 1.5 h.

4. The preparation method according to claim 1, characterized in that, In step S2: the droplet loading rate of the hydrolysate is 1~10 mL / min; And / or, the reaction time is 2 to 8 hours.

5. The preparation method according to claim 1, characterized in that, In step S2, the solid content of the silica sol is 15~45wt%.

6. The preparation method according to claim 1, characterized in that, In step S2, the average particle size of the nano-silica in the silica sol is 5~100 nm; And / or, the dispersion solvent of the silica sol is one or more of water, alcohol, ketone, and ester solvents.

7. The preparation method according to claim 1, characterized in that, In step S1, the sum of the masses of the silane coupling agents KH560 and KH570 is a, and the mass of silicon dioxide in the silica sol in step S2 is b, where a:b = (1~20):

100.

8. A silica sol with reversible freezing properties, characterized in that, It is prepared by the preparation method described in any one of claims 1-7.

9. The application of the silica sol with freeze-reversible properties as described in claim 8 in a low-temperature environment, characterized in that, The application includes at least one of the following: a) Use antifreeze coatings or exterior wall coatings in cold regions; b) Precision casting binders for low-temperature environments; c) Cryopreservation media for biological or pharmaceutical products; d) Building admixtures for winter construction; e) Adhesives or sealants for polar or high-altitude environments.

10. The application as described in claim 9, characterized in that, The low-temperature environment is from -30°C to 0°C.

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