Fumed silica (K-200) is used as a thickener and thixotropic agent in liquid systems; typical dosage is 0.5-3% by weight of the total formulation, giving a rheology that flows under shear and rebuilds structure at rest.

What is K-200 fumed silica?

K-200 is a high-purity hydrophilic amorphous fumed silica with a specific surface area of about 200 m²/g. Surface silanol (Si-OH) groups form a temporary three-dimensional network through hydrogen bonding. This network raises viscosity at rest and breaks down temporarily under shear (mixing, pumping), increasing flow. When shear stops, the structure rebuilds. This reversible behaviour is called thixotropy.

SİLİKON KİMYASALLARIHydrophilic Amorphous Fumed Silica (K-200)Hydrophilic amorphous fumed silica for rheology and thixotropy control.

What is it used for?

  • Sag control and anti-drip in unsaturated polyester and epoxy resins.
  • Anti-settling, pigment suspension and brush/roll flow control in paints, varnishes and coatings.
  • Consistency and application-profile control in adhesives and sealants.
  • Building structural viscosity in gels and pastes.
  • Powder flow and anti-caking applications.

Dosage: how much should you use?

Dosage always depends on the target rheology, the polarity of the liquid system and the quality of dispersion. Treat the ranges below as a starting point and confirm them in small trial batches.

ApplicationTypical dosage (wt%)Target effect
Light viscosity adjustment0.5 - 1.0Mild thickening, anti-settling
Sag / drip control1.0 - 2.0Pronounced thixotropy
High structure / paste2.0 - 3.0Strong gel structure
In polar systems (water, glycols) the thickening efficiency of hydrophilic silica can drop; consider a higher dosage or a hydrophobic grade. In apolar resins, hydrophilic K-200 is highly efficient.

How to disperse it

Performance depends directly on dispersion quality. Poor dispersion lowers thickening efficiency and causes seeds and clarity problems.

  1. Add the silica slowly without raising a dust cloud; wet the powder first.
  2. Break up aggregates with a high-shear mixer (dissolver / high-speed disc).
  3. Apply enough shear time and energy to fully develop the thixotropic structure.
  4. If needed, mix under vacuum to remove entrapped air.
Fumed silica is a very fine powder; use a suitable dust mask and local exhaust ventilation when weighing and adding to prevent inhalation. Refer to the safety data sheet (SDS).

Hydrophilic or hydrophobic: which to choose?

K-200 is a hydrophilic grade with untreated surface silanol groups. It thickens apolar and moderately polar organic systems (resins, solvent-borne coatings) strongly. Where water repellency, moisture resistance or stability in highly polar systems is needed, a surface-modified hydrophobic grade is preferred. Confirm with samples based on system polarity.

How much fumed silica is needed to thicken a resin?

For most unsaturated polyester and epoxy resins, 1-2 wt% K-200 is enough for sag control. Use 0.5-1% for mild thickening and 2-3% for a strong gel structure. Confirm the exact ratio in a small trial batch.

How does K-200 create thixotropy?

The three-dimensional network formed by hydrogen bonding of silanol groups raises viscosity at rest and breaks down temporarily under shear to ease flow; the structure returns when shear stops. This reversible behaviour is thixotropy.

Does fumed silica work in water-based systems?

Hydrophilic K-200 can show lower thickening efficiency in polar/water-based systems. You may need a higher dosage or a hydrophobic grade there; in apolar resins it is highly efficient.

What does good dispersion require?

Adding the powder without a dust cloud, breaking up aggregates with a high-shear mixer, and enough shear energy to fully develop the thixotropic structure. Poor dispersion lowers efficiency and causes seeds.