There are two types of fumed silica: non-treated and treated, the former is hydrophilic and the latter is hydrophobic.

The fumed silica produced by the gas phase method is directly accumulated, purified, collected, compressed, and packaged without any other chemical reagent treatment, and its surface retains hydroxyl groups, so it is hydrophilic. When fumed silica is treated with chemical reagents, the surface hydroxyl groups are replaced by corresponding groups (generally hydrophobic groups), so it is hydrophobic. These products are further divided into two subcategories: fully processed and incompletely processed. Hydrophobic silicas cannot be wetted by water, cannot be dispersed in water, and have a density greater than that of water, but they can float on the surface of water.

Regardless of whether it is hydrophilic or hydrophobic gas-silicon, the principle of action is generally based on the formation of hydrogen bonds between the hydroxyl groups on the surface of gas-silicon and resins, monomers and gas-silicon to form a three-dimensional network structure to achieve related effects.

In addition to the hydroxyl groups on the surface of the silicon, the hydrophobic fumed silicon can also rely on the entanglement between the modified alkyl groups on the surface of the silicon to form a three-dimensional network structure. Therefore, hydrophilic fumed silicon can only be used in systems with low polarity (hydrogen bonds cannot be formed under high polarity), while hydrophobic fumed silicon is mainly used in systems with high polarity (you can rely on modified Alkyl winding plays a role). In the adhesive and composite materials industry, product application requirements are required to select particle size (generally speaking, the smaller the gas silicon particle size, the better the effect, but the difficulty of dispersion also increases), the type of surface modification (dimethyldichlorosilane , hexamethyldisilazane, etc.).

In the field of material application, gas silicon is mainly divided into liquid system, dry system, and solid system. Under different systems, their application mechanisms are somewhat different. Let’s understand them separately below:

Liquid system: There are a large number of hydroxyl groups on the surface of fumed silica, which can form hydrogen bonds between aggregates. When it is fully dispersed in the liquid system, it will form a network structure of silica. This network can increase the viscosity of the liquid and produce thixotropy. The main functions are thickening, thixotropy, anti-settling, anti- Hanging etc. This feature can be widely used in mechanical spraying liquid phase materials to obtain better and thicker spraying effects.

In order to obtain a good rheological effect in the system, the appropriate dispersion of silica particles in the liquid system is a decisive factor. Excessive dispersion will cause the network structure between silica particles to be completely destroyed, even for a long time Its network structure is also difficult to restore when the shear force is stopped.