Silicone defoamer Classification and Performance:
 
　　Oil (ointment)-type defoamer:
 
　　Oil-based defoamers use silicone oil directly as the defoaming agent. They are primarily employed in oil-phase systems where the presence of dispersants or emulsifiers is unacceptable. It is generally believed that silicone oils of different viscosities exhibit varying defoaming performance in the same foaming system: low-viscosity silicone oil defoamers deliver rapid defoaming but offer poorer lasting effectiveness, whereas high-viscosity silicone oil defoamers provide slower defoaming yet demonstrate superior persistence. Paste‑type defoamers are formulated by blending silicone oil with fine powders such as silica and alumina, resulting in a paste‑like product that is mainly used for defoaming in non‑aqueous systems.
 
　　The defoaming performance of dimethyl silicone oil depends on its degree of dispersion within the foaming system; the higher the dispersion, the more effective the defoaming. To enhance dispersion, mechanical agitation can be employed—such as high-speed stirring under heating—or a uniform emulsion of silicone oil in mineral oil can be prepared in advance using a colloid mill. Alternatively, the silicone oil may be formulated into an oily paste‑type defoamer by blending it with fine powders like precipitated silica, leveraging the dispersing action of these powders during application.
 
　　Solution-type defoamer:
 
　　Dimethyl silicone oil can be dissolved in an appropriate solvent to produce a silicone‑based, solution‑type defoamer. Silicone defoamers formulated with organic solvents such as chloroethane, toluene, and xylene are suitable for defoaming in oil‑soluble media, whereas those prepared with water‑miscible organic solvents like hexylene glycol and glycerin are ideal for aqueous solutions. The preparation of solution‑type silicone defoamers is straightforward and convenient; the silicone oil is dispersed in the foaming liquid by the organic solvent, thereby exerting its defoaming effect, while certain solvents may also contribute to defoaming during the diffusion process. However, this approach has not been widely adopted, primarily because extensive use would increase the cost of the defoamer and could potentially lead to environmental pollution.
 
　　Emulsion-type defoamer:
 
　　Silicone oil or silicone paste, when formulated into a silicone oil emulsion under vigorous stirring or in the presence of an emulsifier, can effectively enhance its dispersibility in aqueous media, making it widely used as a defoamer in water-based systems. Emulsion‑type defoamers are also the most commonly employed and highest‑volume‑consumed category of organosilicon defoamers.
 
　　Emulsion‑type silicone defoamers are typically formulated from dimethyl silicone oil, emulsifiers, emulsion stabilizers, and deionized water. The emulsifiers employed are predominantly low‑foaming nonionic types, such as Span, Tween, and polyethylene glycols; blended emulsifiers generally outperform single‑component formulations. Particle size is the most critical control parameter for emulsion‑type silicone defoamers. To achieve high defoaming efficiency and excellent storage stability, the particle size is usually required to be less than 10 μm.
 
　　Therefore, in addition to selecting an appropriate emulsifier and optimizing the milling conditions, thickening agents such as polyvinyl alcohol and methyl cellulose may also be added to increase the viscosity of the continuous phase.
 
　　When using emulsion‑type silicone antifoams, it is essential to first determine the temperature and pH of the foaming system, as these factors can affect emulsion stability and may even lead to demulsification.
 
　　Although emulsion‑type silicone defoamers suffer from drawbacks such as poor long-term storage stability, a tendency to separate into layers, and susceptibility to degradation, they remain popular with users thanks to their ease of use, broad applicability, pronounced defoaming performance, and moderate cost. Moreover, with advances in processing technologies, emulsion‑type silicone defoamers still have considerable room for further development.
 
　　Solid-type defoamer:
 
　　Solid‑type silicone antifoams exhibit excellent storage stability, are easy to transport, and are convenient to use. They can be employed not only in the production of non‑foaming or low‑foaming laundry detergents but also in other applications requiring defoaming.
 
　　There are three methods for preparing solid‑type organosilicone defoamers: (1) directly dispersing the organosilicone oil on the surface of a solid carrier; (2) melting the organosilicone oil together with low‑softening‑point fatty alcohols, fatty acids, fatty amides, fatty acid esters, or paraffin wax, and then applying the resulting melt to the surface of the solid carrier; (3) blending the organosilicone oil with a film‑forming agent, such that the film‑forming agent encapsulates the organosilicone defoaming component, thereby forming dispersed solid particles.
 
　　Modified silicone oil-based defoamer:
 
　　Modified silicone oils, which incorporate hydrophilic polyether segments into methyl silicone oils, can serve as self-emulsifying defoamers. They maintain excellent dispersibility in foaming systems over extended periods, thereby prolonging the service life of the defoamer. Currently, commonly used modified silicone oils for defoaming applications include polyether‑silicone oils, fluorinated‑hydrocarbon silicone oils, and long‑chain alkyl silicone oils, all of which have demonstrated remarkable performance and widespread adoption.
 
　　Terminal‑, pendant‑, and branched‑type polyether‑silicone oils can all serve as defoamers. Each exhibits a well‑defined cloud point: strong defoaming activity is observed only above this temperature, whereas below it the material tends to promote foaming. Moreover, leveraging the potent emulsifying properties of polyether‑silicone oils, when compounded with silicone pastes, they can self‑emulsify in aqueous systems to yield stable, highly effective defoamers. These formulations are widely employed for high‑temperature dyeing of polyester fibers, as well as for defoaming in various lubricants, cutting fluids, antifreeze solutions, and strongly acidic systems.
 
　　Long-chain alkyl silicone defoamers can be used in fermentation, food processing, healthcare, textiles, the petroleum industry, synthetic rubber and resins, coatings, and inks. Thanks to their excellent affinity for organic materials, these defoamers do not adversely affect the post‑processing properties of the final product. However, as the carbon chain length increases, their surface tension rises, leading to a corresponding decline in defoaming performance; therefore, selecting an appropriate carbon chain length is crucial. Long-chain alkyl silicones are effective both in non‑aqueous and aqueous systems.
 
　　Fluorinated silicone oils exhibit lower surface tension than other silicone oils; consequently, defoamers formulated with them are more effective at reducing the surface tension of various foaming systems, outperforming defoamers based on conventional silicone oils. They are primarily used as defoaming agents in non-aqueous systems that readily dissolve methyl silicone oils or methylphenyl silicone oils, such as aliphatic hydrocarbons, aromatic hydrocarbons, and naphtha.
 
　　Silicone defoamers not only exhibit excellent defoaming and foam‑suppressing performance but also offer the advantages of low dosage, good chemical inertness, and reliable operation under harsh conditions. In recent years, they have experienced rapid development, with new formulations and models tailored to diverse application environments continuously emerging, and their range of applications steadily expanding. Going forward, highly efficient, next‑generation silicone defoamers that are broadly applicable and capable of further enhancing product quality and equipment utilization will see continued advancement; in particular, polyether‑modified silicone defoamers and emulsion‑type defoamers with superior performance are expected to assume a dominant position in the market.