Silicone defoamers are a type of high-efficiency defoamers with polysiloxane as the main active ingredient, which are widely used in chemical, food, pharmaceutical, textile, sewage treatment and other industries. Its core ingredients and auxiliary materials work together to destroy the stability of foam by reducing surface tension.
Main active ingredients: polysiloxanes
Dimethyl silicone oil (polydimethylsiloxane, PDMS)
The most common silicone defoaming ingredient, with low surface tension (about 20-21 mN/m, much lower than 72 mN/m of water), can quickly spread on the foam surface and destroy the elasticity of the liquid film. The molecular weight is usually between 1000-100,000, and high molecular weight silicone oil has better durability.
Modified silicone oil
By introducing groups such as polyether (such as ethylene oxide/propylene oxide copolymer), alkyl or aryl groups, its hydrophilicity and compatibility are improved. For example:
Polyether modified silicone oil: suitable for water-based systems, with both defoaming and anti-foaming functions.
Fluorosilicone oil: fluorinated segments further enhance hydrophobicity and are used in extreme conditions (such as strong acids and high temperatures).
Hydrophobic particles (enhanced defoaming efficiency)
Fumed silica (white carbon black)
Nano-sized particles (particle size 10-30 nm), hydrophobically treated (such as hexamethyldisilazane modification). Its mechanism of action includes: puncturing the foam liquid film to accelerate drainage; synergizing with silicone oil to form a "point-surface" structure to increase the spreading speed.
Hydrophobic silicates (such as diatomaceous earth, talc)
Lower cost, but slightly less efficient than silica.
Carrier solvent (adjusts viscosity and dispersibility)
Water: used for emulsion defoamers, and needs to be combined with emulsifiers (such as Span/Tween series).
Mineral oil/white oil: reduces costs and improves the compatibility of the oil phase system.
Alcohols (such as propylene glycol): assist in dissolution and improve low temperature stability.
Emulsifiers and stabilizers (for emulsion products)
Nonionic surfactants (such as polyoxyethylene ethers)
Help silicone oil disperse into tiny droplets (particle size is usually 1-10 μm) to prevent storage stratification.
Thickeners (such as CMC, xanthan gum)
Maintain emulsion stability and prevent particle sedimentation.
Functional additives
Preservatives (such as sodium benzoate): extend shelf life.
pH adjusters (such as citric acid): adapt to different acid and alkaline environments.
Antioxidants (such as BHT): prevent silicone oil from oxidizing at high temperatures.
Formula example (emulsion defoamer)
| Ingredient | Content (wt%) | Function |
| Dimethyl silicone oil | 10-30 | Main defoaming ingredient |
| Fumed silica | 1-5 | Enhance defoaming durability |
| Emulsifier (Span-60) | 2-8 | Stabilize emulsion |
| Water | Balance | Carrier |
Mechanism of action
Rapid spreading: The low surface tension of silicone oil allows it to quickly cover the foam surface.
Liquid film drainage: Hydrophobic particles destroy the local structure of the liquid film and accelerate liquid loss.
Foam suppression: Silicone oil molecules adsorb at the gas-liquid interface, preventing the formation of stable foam.
Application Notes
Compatibility: Polyether modified silicone oil is suitable for the fermentation industry (such as antibiotic production) to avoid inhibiting the activity of bacterial strains.
Temperature limit: Conventional silicone oil has a temperature resistance of -40℃~150℃, and fluorosilicone oil is required if the temperature exceeds this limit.
Addition amount: Usually 0.01-0.1%, excessive amount may cause oil spots or affect product transparency.
