Silicone defoamers are highly effective and widely used defoaming products in various industrial fields. Their unique chemical composition gives them excellent defoaming and antifoaming properties. The following will analyze in detail the main components of silicone defoamers and their mechanism of action.
One. Core ingredients of silicone defoamer
1. Silicone oil (polysiloxane)
Silicone oil is the main active ingredient of silicone defoamers, usually accounting for 5%-20% of the formula. Mainly includes:
Dimethyl silicone oil (polydimethylsiloxane, PDMS): molecular weight between 1000-100000, wide viscosity range (10-100000cSt)
Modified silicone oil: such as hydroxy silicone oil, amino silicone oil, polyether modified silicone oil, etc., used to improve compatibility with specific systems
Silicone oil molecules have a unique -Si-O- main chain and -CH₃ side chain, forming low surface tension (about 21mN/m, much lower than 72mN/m of water) and low polarity, which is the basis of its defoaming ability.
2. Hydrophobic particles
Accounting for about 5%-15% of the formula, the main types include:
Silicon dioxide (fumed silica): particle size 10-30nm, specific surface area 150-300m²/g
Hydrophobic calcium carbonate
Polytetrafluoroethylene (PTFE) powder
Metal soaps (such as aluminum stearate, calcium stearate)
These particles are surface treated with silicone oil or organosilane (such as hexamethyldisilazane) and are highly hydrophobic with a contact angle of >90°.
3. Emulsifier/dispersant
Accounting for about 3%-10% of the formula, used to stabilize emulsion defoamers:
Non-ionic surfactants: Span/Tween series, polyoxyethylene ethers
Anionic surfactants: sodium dodecylbenzene sulfonate (SDBS)
Special silicone surfactants: such as polyether-modified silicone
4. Carrier medium
Accounts for about 50%-80% of the formula:
Water (emulsion type)
Mineral oil, white oil (oil-based type)
Alcohols (such as propylene glycol)
Ester (such as isopropyl palmitate)
Two. Auxiliary ingredients
Thickener (0.1%-2%): carboxymethyl cellulose (CMC), polyacrylic acid
Preservative (0.05%-0.3%): isothiazolinone, sodium benzoate
pH adjuster: citric acid, triethanolamine
Synergist: higher fatty alcohol (such as octanol), polyether
Three. Detailed explanation of the mechanism of action
1. Three-stage theory of defoaming process
Phase 1: Foam recognition and approach
The low surface tension of silicone oil enables it to spread spontaneously on the surface of the foam liquid film
Hydrophobic particles approach the bubble interface through gravity or Brownian motion
Phase 2: Liquid film penetration
Silicone oil-particle complex forms a "bridge" structure on the liquid film
According to the Marangoni effect, the surface tension gradient causes local liquid flow
Particles produce a "contact angle asymmetry" effect, destroying the mechanical balance of the liquid film
Phase 3: Foam rupture
Forming local weak points (micropores <100nm)
Gas in the bubble diffuses rapidly through the Plateau boundary
Eventually leading to bubble merging or rupture
2. Molecular mechanism of foam suppression
Surface competitive adsorption: silicone oil molecules preferentially occupy the gas-liquid interface, hindering the arrangement of foaming agent molecules
Reduced surface elasticity: silicone oil film reduces Gibbs elastic modulus (can be reduced to <1mN/m)
Marangoni effect suppression: eliminates the "self-healing" ability caused by surface tension gradient
Four. Special formula types
Self-emulsifying type: contains polyether modified silicone oil (such as PEOS), which can be dispersed spontaneously in water
Powder type: adsorbs silicone oil on porous carriers (such as SiO₂, oil loading can reach 80%)
Food grade: uses USP grade silicone oil (viscosity 100-1000cSt) and GRAS certified excipients
High temperature type: uses phenyl silicone oil (temperature resistance > 300℃) and special fillers
Five. Factors affecting performance
Silicone oil viscosity: Medium viscosity (1000-10000 cSt) is usually the best
Particle size: The best is 1/10-1/5 of the foam film thickness (usually 0.1-10 μm)
HLB value: Adjust according to different systems (the water phase usually requires HLB 4-7)
Zeta potential: Emulsion type needs to maintain stability of > ±30 mV
Modern silicone defoamers can achieve rapid defoaming (<10 seconds) and long-term antifoaming (>24 hours) at ppm-level addition levels by precisely controlling these parameters.
