Hydrophobic silica is a kind of silica material whose surface properties change from hydrophilic to hydrophobic after special treatment.
On the basis of fumed silica or precipitated silica, the surface is connected with hydrophobic groups by chemical modification methods, such as through silane coupling agent treatment, the hydrophobic part of silane reacts with the hydroxyl group on the surface of silicon dioxide, so that the surface of silicon dioxide is covered by hydrophobic groups.
Physical property
- The appearance is generally white powder, similar to ordinary silica.
- Has a nanoscale particle size, which gives it a large specific surface area. However, due to the hydrophobic surface, it exhibits unique properties when in contact with water, such as not being as easily soaked by water as hydrophilic silica, and there will be a hydrophobic phenomenon similar to the "lotus leaf effect".
Chemical property
- High chemical stability, can be stable in a certain degree of acid, alkali environment.
- Hydrophobic groups on the surface give it a good affinity for organic compounds, can be well dispersed in many organic solvents, and has a repellent to water.
Application field
- Paint industry: can significantly improve the waterproof, moisture-proof performance of paint. When coatings are used on surfaces such as outdoor buildings and ships, hydrophobic silica can prevent moisture from penetrating into the coating, thereby extending the service life of the coating, while also improving the rheology of the coating and making the coating easier to apply.
- Cosmetics industry: In some waterproof cosmetics, such as waterproof mascara, waterproof lipstick and other products, hydrophobic silica as an important additive, can prevent the cosmetics from being dissolved or washed away by water, to help the product maintain a good makeup effect.
- Electronic materials: Used in packaging materials for electronic products to prevent moisture from causing damage to electronic components, while its good dispersion helps to improve the performance of packaging materials
In the hydrophobic modification of silica, the commonly used auxiliaries are mainly the following:
General modification agent
1. Silane coupling agent
- Type and characteristics: This is the most commonly used class of additives. Such as methyl trimethoxy-silane, vinyl trimethoxy-silane, etc. Its molecular structure generally contains active groups that can react with the hydroxyl group on the surface of silicon dioxide (such as methoxy group) and organic groups with hydrophobicity (such as methyl group and vinyl group).
- Principle of action: The active group in the silane coupling agent will chemically react with the hydroxyl group on the surface of silicon dioxide to form a chemical bond, while the hydrophobic group on the other end will extend outwards, thus changing the properties of the surface of silicon dioxide from hydrophilic to hydrophobic.
2. Silicone oil
- Type and characteristics: like dimethyl silicone oil, etc. Silicone oil has good chemical stability, low surface tension and excellent hydrophobicity.
- Principle of action: Silicone oil can be covered on the surface of silicon dioxide by physical adsorption or partial chemical bonding. In the physical adsorption process, due to the hydrophobicity of silicone oil itself, a hydrophobic layer will be formed on the surface of silicon dioxide, thereby reducing the possibility of contact between silicon dioxide and water.
