What is a silicone defoamer?

A silicone defoamer, also called a silicone antifoam agent, is made mainly from polydimethylsiloxane (PDMS, silicone oil) mixed with hydrophobic particles such as treated silica. Strictly, defoamers remove existing foam and antifoams prevent new foam, but the terms are used interchangeably. Silicone defoamers work at very low concentrations (typically 10–100 ppm), are chemically inert and thermally stable, and perform across a broad pH and temperature range.

Silicone Defoamer Composition

• Silicone oil (PDMS) – about 5–30% in emulsions; surface tension ~20–21 mN/m vs 72 mN/m for water.
• Hydrophobic particles such as fumed silica (~10–30 nm) that puncture bubble films.
• Emulsifiers, carriers (water or oil) and sometimes modified silicones (polyether-, hydroxy- or amino-modified).

Forms: water-based emulsions, 100% active compounds/oils, powders and solutions.

How it works

1. Low-surface-tension silicone oil spreads over the bubble surface.
2. Hydrophobic particles break the film structure and speed drainage.
3. Bubbles destabilise, merge and collapse; residual silicone prevents new foam.

Pure silicone oil alone is less effective – combining it with silica and emulsifiers gives fast spreading and action.

Key Advantages

• Much smaller dose than mineral oil or organic defoamers
• Heat resistance often above 130–150 °C
• Works under high shear, extreme pH or high heat
• Quick knockdown plus persistence
• Generally low toxicity, with food-grade options available

Common Applications

• Pulp and paper
• Paints, coatings, inks and adhesives
• Wastewater treatment and chemical processing
• Textiles, detergents and fermentation
• Oil and gas
• Construction chemicals and agrochemicals

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