1. Basic Knowledge of Hydrophilic and Hydrophobic Silica
Silica is inherently hydrophilic, while hydrophobic silica is modified with hydrophobic groups. Hydrophilic silica is generally added to aqueous systems. In organic systems, hydrophilic silica does not disperse well, while hydrophobic silica can disperse well.
Hydrophilic Fumed Silica
Hydrophilic fumed silica is produced by the hydrolysis of volatile chlorosilanes in an oxyhydrogen flame. Chemically, these loose white powders consist of high-purity amorphous silica. Hydrophilic silica is wettable and dispersible in water. In addition to its use in traditional industrial applications such as polyesters, silicones, paints, and coatings, hydrophilic fumed silica products are increasingly finding successful applications in high-tech fields. Fumed silica's nanoparticle properties and high purity have led to its use in the electronics and optical fiber industries. X-ray analysis reveals that hydrophilic fumed silica products have an amorphous structure. Depending on the market and application, we offer products with varying particle sizes and specific surface areas. Some fumed silica products are available in compressed form, and some are pharmaceutical grade.
Hydrophilic fumed silica's functions include: ease of processing and adjustment to optimal rheological properties; reinforcement of silicone elastomers; thickening of non-polar liquids; flow aid for food and industrial powders; high chemical purity; excellent insulating properties even at high temperatures; and conversion of liquids into powders, such as in pharmaceuticals and cosmetics.
Hydrophobic fumed silica
Hydrophobic silica is produced by the chemical reaction of hydrophilic fumed silica with reactive silanes (such as chlorosilane or hexamethyldisilazane). It exhibits hydrophobic properties (repelling water) and is non-dispersible in water. Various hydrophobic fumed silica grades have been developed to address specific technical challenges in industry. For example, hydrophobic fumed silica can be produced by treating hydrophilic grades with silanes or siloxanes to modify them. In the final product, the chemical treatment agent chemically bonds to the original hydrophilic oxide. In addition to the aforementioned advantages of hydrophilic grades, hydrophobic fumed silica products feature low hygroscopicity, excellent dispersibility, and rheological control capabilities, even in polar systems. Some products, through structural modification based on the hydrophobic treatment, can further assist customers in developing new products and improving product performance. For example, in liquid systems, hydrophobic fumed silica can be added at high dosages with minimal impact on the viscosity of the system. Functions of hydrophobic fumed silica: Optimal rheological properties for processing and use; thickening polar liquids such as epoxy resins; reinforcing silicone elastomers; high addition levels, such as in molded products; excellent hydrophobicity, improving corrosion resistance; improving dielectric properties, such as in cable composites; powder flow aid, such as in powder coatings and fire extinguishing agents; improving scratch resistance in coatings and plastics.
2. How to determine the hydrophilicity and hydrophobicity of silica?
Hydrophilicity, in simple terms, refers to untreated silica, which readily absorbs moisture from the air. Silica comes in powder and granules and is relatively inexpensive. Hydrophobicity refers to silica with a surface treatment that makes it less susceptible to moisture absorption. It is used in coatings and paints and is therefore more expensive.