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Fumed silicon dioxide is the earliest and the first to implement a nano inorganic powder material for industrial production, with its superior stability, reinforcement, thickening and thixotropic properties, is widely used in silicone rubber, viscose agents, paints, inks and copier toner, unsaturated polyester resins and composites, is a national high-tech fields and the defense industry needed, essential raw materials.

But fumed silicon dioxide surface modification contains a large amount of hydroxyl groups and polar groups, so easy to collide with each other together, to form a secondary between aggregates of primary particles, the impact of fumed silica in the organic polymer uniformly dispersed, can not meet the special needs of certain sectors thereof, and therefore there is a need for targeted chemical modification of fumed silica surface treatment, the fumed silica hydrophilic surface becomes hydrophobic, thereby improving fumed silica nano particles and organic molecules between wettability, dispersion, bonding strength, improve the overall performance of the composite material.

Modified fumed silicon dioxide principle:

Fumed silica before the modification, the surface generally three hydroxyl groups, first isolated the free hydroxyl groups with a certain pitch, "together" in the surface of the particles; the second is even born, the formation of hydrogen bond association hydroxy; Third, hydroxy twins, two hydroxyl groups attached to a silicon atom. Of fumed silica is modified through a certain process to select a suitable hydroxyl-reactive surface treatment agent with the silicon dioxide surface to reduce the amount of the surface silanols, so fumed silica surface hydrophobic. Generally volatile substances, can occur with white carbon surface hydroxyl chemical reactions can be used as a modifier.

Modifier used include organic chlorosilanes, silane coupling agents, alcohols, amines:

(1) as a modifier of organic chlorosilane, commonly used is dimethyldichlorosilane and trimethylchlorosilane.

(2) a silane coupling agent as a modifier, commonly used are bis (trimethylsilyl) amine, hexamethyl silazane vinyl, vinyl silane and the like.

(3) an alcohol compound as the modifier.

(4) an amine compound as the modifier.



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