Silica

large specific surface area, which provide desirable flow characteristics in dry powders used in tableting and capsule filling. The hydrophobic grades absorb less moistureand may offer an advantage in moisture-sensitive formulations.
Hydrophobic colloidal silica is also used to thixotropically control viscosity, to thicken and stabilize emulsions, or as a suspending agent in gels and semisolid preparations. Hydrophobic colloidal silica has a less pronounced effect on solution viscosity but can thicken and stabilize the oil phase of a water–oil emulsion. With other ingredients of similar refractive index, transparent gels may be formed. Generally, the uses and ranges of hydrophobic colloidal silica are similar to the concentrations used of the standard hydrophilic colloidal silicon dioxide.