01 Oil-based defoamer 
The Characteristics and Effects of Silicone Oil
Oil-type defoamers, as the name suggests, are defoamers with silicone oil as the main component. They are particularly suitable for oil-phase foaming systems that do not allow the presence of additives such as dispersants and emulsifiers. The viscosity of silicone oil has a significant impact on its defoaming effect in foaming systems. Low-viscosity silicone oil defoams quickly but lacks persistence; while high-viscosity silicone oil defoams more slowly, it can provide a longer-lasting anti-foaming effect. 
The function of ointment-type defoamers
In addition, ointment-type defoamers, which are made by adding silica, alumina and other micro-powders to silicone oil, can enhance their defoaming ability in non-aqueous systems. The addition of micro-powders can enhance the defoaming ability in non-aqueous systems, and mechanical stirring can improve the dispersion effect. 
02 Solution-type Defoamer 
By dissolving dimethyl silicone oil in organic solvents such as perchloroethane, toluene and xylene, silicone oil-based defoaming agents suitable for oil-soluble media can be made. Similarly, if water-soluble organic solvents such as hexanediol and glycerol are selected, defoaming agents suitable for aqueous solutions can be prepared. This type of solution defoaming agent is easy to prepare. During use, the silicone oil disperses in the foaming liquid with the help of the solvent to achieve the defoaming purpose. However, it should be noted that excessive use may increase costs and cause environmental pollution. 
03 Emulsion-type defoamer 
By vigorous stirring or the action of emulsifiers, silicone oil or silicone grease can be made into silicone oil emulsion, which can effectively improve the dispersibility of silicone oil in the aqueous phase and thus become an ideal choice for defoaming in water systems. Emulsion-type silicone defoamers are based on dimethyl silicone oil and incorporate emulsifiers, emulsion stabilizers, and deionized water, among other components. Among them, nonionic emulsifiers with low foaming properties such as Span, Tween, and polyethylene glycol are widely used. To obtain efficient and stable silicone oil emulsions, it is usually required that the particle size be controlled below 10 μm. Silicone oil emulsions are prepared through emulsifiers, have good dispersibility, but are prone to stratification and have poor storage stability. 
▲ Stability and Modified Silicone Oil
It should be noted that different types of polyether silicone oil (such as end-capped, side-capped, and branched types) exhibit strong defoaming properties above the cloud point but may promote foaming below it. However, by leveraging their strong emulsifying ability and compounding with silicone grease, they can self-emulsify into stable and highly efficient defoamers in water systems, finding wide application in defoaming processes for high-temperature polyester fiber dyeing, lubricating oils, cutting oils, antifreeze, and strong acid systems. By introducing hydrophilic groups, the storage stability and service life can be enhanced. Commonly used modified silicone oils include polyether silicone oil, fluorocarbon-based silicone oil, and long-chain alkyl silicone oil, all of which perform well in various applications. 
04 Solid and Modified Silicone Oil 
On the other hand, solid and hydrophilic silicone defoamers play a significant role in the production of low-foaming and non-foaming laundry detergents and other applications where defoaming is required, due to their excellent storage stability and ease of transportation and use. Their preparation methods include direct dispersion, melt attachment, and encapsulation with film-forming substances. Solid defoamers are convenient for storage and use and are suitable as standard industrial defoamers. 
Long-chain alkyl silicone oil defoamers have demonstrated their effectiveness in multiple fields such as fermentation, food processing, medical care, textiles, petroleum, synthetic rubber and resins, coatings and inks. Due to their excellent affinity for organic materials, they do not interfere with the subsequent processing of products. However, it is worth noting that their surface tension increases with the length of the carbon chain, which in turn leads to a decrease in defoaming efficiency. Therefore, when choosing, determining the appropriate carbon chain length is particularly crucial. Fluorocarbon-based silicone oils, with their extremely low surface tension, are especially suitable for non-aqueous systems and have outstanding defoaming performance. These defoamers are particularly applicable to non-aqueous systems such as aliphatic hydrocarbons, aromatic hydrocarbons, and naphtha, among which methyl silicone oil or methyl phenyl silicone oil have high solubility.