There are two methods for modifying silica sol: chemical modification and physical blending. Chemical modification can obtain better performance, while the latter has poor stability due to the lack of chemical bond formation. Common chemical modification methods include metal ion modification and silane coupling agent modification.
Metal ion modification
This method uses metal ions to modify the surface of silica sol, which can effectively improve the stability of the sol and produce highly stable silica sol. The modification principle is: adding multivalent metal hydroxides or metal oxides to the sol, the silanol groups on the surface of the colloid particles are replaced by metal ions, and the metal ions act as stabilizers.
Among them, aluminum-modified and boron-modified silica sols are more studied.
The purpose of the modification is to allow negatively charged inorganic particles to be added to increase the electronegativity of the silica sol, thereby greatly improving the stability of the silica sol. In addition, after the silica sol is modified by metal, the metal ions enter the fixed layer, which reduces the potential and thins the hydration layer of the micelle, thereby effectively reducing the gel concentration of the silica sol and increasing the drying rate. Therefore, this property can be used to prepare quick-drying coatings.
After metal ion modification, the degree of gelation of silica sol in different PH systems is reduced, the stability is greatly improved, the particle size is small and uniform, and the specific surface area is larger. It can be used in particle retention and filtration systems in various industries, and for adding certain hydrophobicity, antistatic and flame retardancy to some materials to improve the overall performance.
Silane coupling agent modification
This method combines the characteristics of inorganic and organic materials to modify the material. Inorganic materials have the advantages of high strength, high hardness and good aging resistance, but have the disadvantages of brittleness, poor toughness and relatively single surface functional groups; organic materials usually have the advantages of good elasticity, toughness and processability, but have the disadvantages of not being resistant to high temperatures, poor aging resistance and poor solvent resistance and stability.
Silica sol is modified by silane coupling agent (linking inorganic Si and organic components), which effectively prevents the agglomeration of silica sol particles. The obtained organic-inorganic hybrid material has the advantages of both organic and inorganic materials, and even produces new properties that a single material does not have (which can meet certain special use requirements).
Silica sol modified by silane coupling agent has better dispersibility in the organic phase, and its surface flexibility, strength and hydrophobicity are enhanced. It has been widely used in coatings, separation membranes and nanocomposites, and has broad application prospects in optoelectronic materials, coatings, ceramic materials and biomedicine. Adding modified silica sol to the coating can significantly improve the physical and chemical properties of the coating, such as processing performance, flexibility and strength.
https://www.silicasol.net/product.html