CN1308233C - Process for preparing amphiphilic nano silicon dioxide - Google Patents

Abstract

A preparation method of nano- _SiO2 , which is to remove impurities by sodium silicate, in the presence of amphiphilic block polyether silanol compound, perform cation exchange through polystyrene cation exchange resin, and then pass polystyrene anion After the anion exchange of the exchange resin, add NaOH solution to adjust the pH value, after standing still, heat, then cool to room temperature, and concentrate through ultrafiltration membrane ultrafiltration to obtain an amphiphilic nano- _SiO2 dispersion with an average particle size of 10-50nm . The surface of nano silicon dioxide particles in the dispersion is modified with amphiphilic block polyether, which is stable under acidic and alkaline conditions, does not agglomerate, and can be dispersed in water-based and oil-based systems at a nanometer scale.

Description

A kind of preparation method of amphiphilic nano silicon dioxide

Technical field

The invention relates to a method for preparing amphiphilic nano- _SiO2 .

Background technique

Nano-SiO ₂ is widely used, involving almost all industries that use SiO ₂ powder.

At present, there are two methods of preparing nano-SiO ₂ : dry method and wet method. Dry methods include gas phase method and arc method, wet method precipitation method and gel method.

The gas phase method mostly uses silicon tetrachloride as the raw material, and uses silicon tetrachloride gas to hydrolyze under high temperature of hydrogen and oxygen flow to obtain smoky silicon dioxide. The method has expensive raw materials, high energy consumption, complex technology and high equipment requirements, which limit the use of products.

The gel method is to add acid to reduce the alkalinity to induce the polymerization reaction of silicate, so that the particle size of the highly polymerized silicate ion in the form of colloidal particles in the system is continuously increased, forming a silica sol with opalescent characteristics. After the sol is formed, as the pH value of the system further decreases, the zeta potential of the negatively charged SiO ₂ particles adsorbed by ^OH- also decreases correspondingly, and the stability of the particles decreases, and the SiO ₂ particles pass through the hydrated Na ⁺ adsorbed on the surface. The bridging effect will condense to form silica gel, and the nano powder will be obtained after dehydration. The raw material of this method is the same as that of the precipitation method, except that the precipitation is not directly formed, but a gel is formed, and then dried and dehydrated. The product characteristics are similar to the dry method product, and the price is cheaper than the dry method product, but the process is more complicated than the precipitation method, and the cost is also high. . This method is rarely used.

The precipitation method is that the silicate is acidified to obtain loose, finely dispersed SiO ₂ crystals that are precipitated in a flocculent structure. The raw materials of this method are easy to get, the production process is simple, the energy consumption is low, and the investment is small, but the product quality is not as good as the products using the gas phase method and the gel method. This method is currently the main production method.

Due to the high cost of dry preparation of nano-SiO ₂ , it is difficult to popularize, and the flocculation and drying process of wet preparation of nano-SiO ₂ makes nano-silica particles with a large specific surface area agglomerate and difficult to redisperse. Therefore, the preparation of highly dispersed nano-SiO ₂ is still a difficult problem to solve.

The main component of silica sol is also silica, and the particle size of its dispersed colloid in water is also in the nanoscale range. Silica sol can be prepared by ion exchange method: ion exchange method is also called particle growth method, this kind of silica sol production method uses water glass as raw material, through ion exchange reaction, preparation of seed crystal, particle growth reaction, concentration step, purification Steps and other processes to prepare silica sol products.

However, the silica particles of silica sol exist in the state of hydrosol, and a large amount of water is bound to the surface and charged. The stability is greatly affected by pH, and it is easy to agglomerate. Therefore, it is difficult for silica in silica sol to be applied in lipophilic materials such as polymers at the nanometer dispersion scale.

Representative nano-silica preparation and modification methods are: CN94104007 introduces a preparation method of ultrafine monodisperse hydrophobic silica particles, which utilizes and controls the hydrolysis of ethyl silicate to obtain hydrophobic nano-silica Silicon particle; CN97125800 has introduced the method for preparing nano silicon dioxide by the silicate of alkali metal, obtains porous silicon dioxide particle; EP0987219 has introduced the preparation of superfine silicon dioxide; AT391122B has introduced the preparation of silicon dioxide hydrosol . The nano-silica products prepared by the above methods have hydrophobic or hydrophilic properties, and the production cost is relatively high, while the preparation methods of amphiphilic nano-silica are rare.

Contents of Invention

The purpose of the present invention is to provide a kind of new nano-silica preparation approach for the existing technology in the preparation and application of nano- _SiO2 , which is easy to agglomerate, and the nano- _SiO2 prepared by the method can be used in aqueous phase (very Uniform dispersion can be achieved in the polar solvent phase), and can also be uniformly dispersed in the oil phase (non-polar solvent phase) and polymer matrix.

In the present invention, in the in-situ system for preparing nano _-SiO2 by ion exchange method, block polyether silanols capable of reacting with _SiO2 surface hydroxyl groups are added, and the block polyether silanols react with the surface hydroxyl groups of _SiO2 to make The surface of nano-SiO ₂ has amphiphilic polyether groups, and the particle size distribution of nano-SiO ₂ is between 10 and 50 nm. Depending on the effect of the hydrophilic groups on its surface, nano-SiO ₂ can be uniformly distributed in the water phase. Relying on the effect of lipophilic groups on its surface, nano- _SiO2 can be evenly distributed in the oil phase.

The detailed technical scheme of the present invention is:

After filtering out impurities with sodium silicate (water glass) with a modulus of 3.4 and a content of 3 to 10%, in the presence of amphiphilic block polyether silanol compounds, ion-exchange to liquid through polystyrene cation exchange resin The pH value of the solution reaches 2-3, and then undergoes ion exchange with polystyrene anion exchange resin until the pH value of the liquid reaches 4-6. Add NaOH solution to adjust the pH value to the range of 8.5-10.5, and let it stand for 12-24 hours. , heated at 60-80°C for 2-6 hours, cooled to room temperature, concentrated by ultrafiltration through an ultrafiltration membrane with a molecular weight of 20,000 to 50,000 to a solid content of 20-35%, to obtain a surface-modified amphiphilic block polyether Silanol and particle monodisperse nano-silica dispersion. The particle size of nano _SiO2 particles in the nano liquid is 10-50 nm, and the performance is stable under acidic and alkaline conditions, and no precipitation phenomenon occurs.

Wherein, the consumption of amphiphilic block polyether silanol compound is 0.5～5% (mass ratio) of sodium silicate, molecular formula is:

Wherein, the value of x is in the range of 12-120, and the value of y is in the range of 10-100. The hydrophilic segment is a polyethylene oxide segment, the lipophilic segment is a polypropylene oxide segment, and the hydrophilic and lipophilic segments are connected by methyl silanol.

The silanol group in the block polyether silanol compound reacts with the -OH group on the silica in situ at the same time as the silica is formed, and simultaneously generates a stable Si-O-Si covalent bond, directly in one step The nano-silicon dioxide modified with block polyether on the surface is prepared, which effectively prevents the agglomeration of the nano-silicon dioxide. The block polyether chain in the block polyether silanol compound is an amphiphilic polymer chain. After it is bound to the surface of nano- _SiO2 particles through silanol groups, the surface of silica nanoparticles is also hydrophilic. Group and lipophilic group, this amphiphilicity enables nano-silica particles to be dispersed in water and extracted by oily organic monomers, which greatly expands its application field.

The beneficial effect of the invention is that the nano-SiO ₂ with a particle size distribution of 10-50nm and uniform distribution in the water phase and the oil phase can be prepared, the reaction condition is mild, and the cost is low. Compared with the preparation methods of various nano-silica powders, its advantages are: it avoids the drying process of powder preparation by wet method, and it is directly applied in the form of liquid medium dispersion, which greatly reduces the agglomeration of nanoparticles, and the cost is relatively low. Low.

Specific implementation plan

Below in conjunction with embodiment the present invention is further described.

Example 1: After filtering out impurities with sodium silicate (water glass) with a modulus of 3.4 and a content of 3%, in the presence of amphiphilic block polyether silanol compounds, wherein the amphiphilic block polyether silanol The dosage of the compound is 0.5% of sodium silicate, the x value of the block polyether silanol is 12, and the y value is 10. Perform ion exchange through polystyrene cation exchange resin until the pH value of the liquid reaches 2, then perform ion exchange through polystyrene anion exchange resin until the pH value of the body reaches 4, add NaOH solution, adjust the pH value to 8.5, and let it stand for 12 Hours later, heat at 60° C. for 6 hours, cool to room temperature, and be concentrated to a solid content of 20% by ultrafiltration through an ultrafiltration membrane with a molecular weight of 50,000 to obtain an average particle diameter of 50 nm _amphiphilic nano-SiO dispersion. It is stable under acidic and alkaline conditions, and can be dispersed in ethanol, acetone and methyl methacrylate at the nanometer scale.

Example 2: After filtering out impurities with sodium silicate (water glass) with a modulus of 3.4 and a content of 10%, in the presence of amphiphilic block polyether silanol compounds, wherein the amphiphilic block polyether silanol The dosage of the compound is 5% of the sodium silicate, the x value of the block polyether silanol is 120, and the y value is 100. Perform ion exchange through polystyrene cation exchange resin until the pH value of the liquid reaches 3, then perform ion exchange through polystyrene anion exchange resin until the pH value of the body reaches 6, add NaOH solution, adjust the pH value to 10.5, and let it stand for 24 Hours later, heat at 80° C. for 2 hours, cool to room temperature, and be concentrated to a solid content of 35% by ultrafiltration through an ultrafiltration membrane with a molecular weight of 40,000 to obtain an average particle diameter of 30 nm amphiphilic nano- _SiO dispersion. It is stable under acidic and alkaline conditions, and can be dispersed in water, toluene and styrene at the nanometer scale.

Example 3: After filtering out impurities with sodium silicate (water glass) with a modulus of 3.4 and a content of 5%, in the presence of amphiphilic block polyether silanol compounds, wherein the amphiphilic block polyether silanol The dosage of the compound is 2% of the sodium silicate, the x value of the block polyether silanol is 60, and the y value is 50. Perform ion exchange through polystyrene cation exchange resin until the pH value of the liquid reaches 3, then conduct ion exchange through polystyrene anion exchange resin until the pH value of the body reaches 5, add NaOH solution, adjust the pH value to the range of 9, and statically After placing for 24 hours, heat at 80° C. for 2 hours, cool to room temperature, and be concentrated to a solid content of 30% by ultrafiltration through an ultrafiltration membrane with a molecular weight of 20,000 to obtain an average particle diameter of 10 nm amphiphilic nano- _SiO . The dispersion is stable under acidic and alkaline conditions, and can be dispersed in ethanol, acetone, ethyl acetate, toluene, styrene and methyl methacrylate at a nanoscale.

Claims (3)

1, a kind of nano _{- SiO} The preparation method is characterized in that after sodium silicate filters out impurities, in the presence of amphiphilic block polyether silanol compound, do cation exchange through polystyrene cation exchange resin, and then After anion exchange with polystyrene anion exchange resin, NaOH solution is added to adjust the pH value. After standing still, it is heated, then cooled to room temperature, and concentrated by ultrafiltration membrane ultrafiltration to obtain a surface-modified amphiphilic block polyether Silanol and particle monodisperse nano silicon dioxide dispersion liquid with an average particle diameter of 10-50nm. 2. The preparation method according to claim 1, characterized in that the sodium silicate has a modulus of 3.4 and a content of 3 to 10%, and in the presence of amphiphilic block polyether silanol compound, it undergoes polystyrene cation exchange The resin is ion-exchanged until the pH value of the liquid reaches 2-3, and then the polystyrene anion-exchange resin is used for ion-exchange until the pH value of the liquid reaches 4-6, and NaOH solution is added to adjust the pH value to the range of 8.5-10.5. After standing for 12 to 24 hours, heat at 60 to 80°C for 2 to 6 hours, cool to room temperature, and concentrate through an ultrafiltration membrane with a molecular weight of 20,000 to 50,000 to a solid content of 20 to 35%. The amount of ether silanol added is 0.5-5% of sodium silicate in mass ratio. 3. The preparation method according to claim 1, characterized in that the amphiphilic block polyether silanol used is a two-stage block polyether, and its molecular formula is:

The value of x is in the range of 12 to 120, the value of y is in the range of 10 to 100, the hydrophilic segment is polyethylene oxide segment, the lipophilic segment is polypropylene oxide segment, and the hydrophilic and lipophilic segment Linked with methylsilanol.