The difference and application of hydrophilic silica and hydrophobic silica
1. Basic knowledge of hydrophilic and hydrophobic silica
Silica generally is hydrophilic, hydrophobic silica is modified by hydrophobic groups. Hydrophilicity is usually added to the aqueous system. In the organic system, the hydrophilic silica can not be well dispersed after being added, and the hydrophobic silica can be well dispersed.
Hydrophilic silica
Hydrophilic silica was prepared by hydrolysis of volatile chlorosilane in oxyhydrogen flame. From a chemical point of view, these loose white powders are composed of high-purity amorphous silica. Hydrophilic silica can be wetted with water and dispersed in water. In addition to the traditional industrial fields, such as polyester, silicone, paint and coating, hydrophilic fumed silica products are more and more successfully applied in high-tech fields. The nano particle characteristics and high purity of fumed silica play a leading role in the application of electronic and optical fiber industry. The product of hydrophilic fumed silica has amorphous structure by X-ray analysis. According to different market and application fields, we can provide products with different particle sizes and specific surface areas. Some fumed silica products can be compressed and supplied. Some products are medical grade.
Functions of hydrophilic fumed silica: suitable for processing and adjusting to good rheological property; reinforcing of silicone elastomer; thickening of non-polar liquid; flow aid of food and industrial powder; high chemical purity; excellent insulation performance even at high temperature; liquid into powder, such as medicine and cosmetics.
Hydrophobic silica
Hydrophobic silica is prepared by the chemical reaction of hydrophilic fumed silica with active silane (such as chlorosilane or hexamethyldisilazane). It is hydrophobic (hydrophobic) and cannot be dispersed in water. In order to solve some special technical problems in industry, various types of hydrophobic fumed silica have been developed. For example, the hydrophobic fumed silica is produced by treating the modified hydrophilic fumed silica with silane or siloxane. In the final product, the chemical treatment agent is bound to the original hydrophilic oxide by chemical bond. In addition to the above advantages of hydrophilic products, hydrophobic fumed silica products are characterized by low moisture absorption, good dispersion, and rheological adjustment ability even for polar systems. Some products, after structural modification on the basis of hydrophobic treatment, can provide further help for customers to develop new products and improve product performance. For example, in the liquid system, hydrophobic fumed silica can reach a high content, but has little effect on the viscosity of the system.
Functions of hydrophobic fumed silica: suitable rheological property in processing and use; thickening of polar liquid, such as epoxy resin; reinforcement of silicone elastomer; high addition amount, such as in molded products; good hydrophobicity, improving corrosion resistance; improving dielectric properties, such as in cable composite; powder flow aid, such as in powder coating and fire extinguishing agent; coating and plastic High scratch resistance.
2. How to judge the hydrophilicity and hydrophobicity of silica?
Hydrophilicity simply speaking, white carbon black has not been treated, it is easy to absorb water in the air, white carbon black is divided into powder and particles, the price is low. Hydrophobicity refers to that white carbon black has been treated on the surface, it is not easy to absorb water in the air, it is used for coating and paint, the price is high
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