Silicone oil emulsion defoamers are generally oil-in-water (O/W) emulsions, that is, water is the continuous phase and silicone oil is the discontinuous phase. It pre-mixes silicone oil, emulsifier and thickener, then gradually adds water and mixes well, and finally grinds repeatedly in a colloid mill until a satisfactory emulsion is obtained.

Silicone oil emulsion type defoamer is the most widely used and the largest amount of defoamer among silicone defoamers. It is characterized by being easily dispersed in water systems and can be widely used as a defoamer for water phase systems. When in use, add the emulsion directly into the foaming system to obtain a good defoaming effect. In order to improve the defoaming effect of the emulsion and the accuracy of measurement, it is generally not used directly to use more than 10% thick silicone oil emulsion: instead, it should be diluted to less than 10% with cold water or directly with foaming liquid before use. It is taboo to dilute with hot or cold liquid, otherwise it will cause the emulsion to break. The stability of the emulsion will deteriorate after dilution, and stratification (oil floating) may also occur during storage, that is, demulsification. Therefore, the diluted lotion should be used up as soon as possible. Thickeners can be added to increase the stability of the emulsion, if desired. For the batch operation process, the silicone oil emulsion can be added once before the system is running, or it can be added in batches; for the continuous operation process, the silicone oil emulsion should be added continuously or intermittently at the appropriate part of the system.

When using emulsion-type defoamers, special consideration should be given to the temperature of the foaming system and the conditions of acidity and alkalinity, because the silicone oil emulsion is relatively delicate, and if it exceeds its application range, the emulsion will break prematurely and become inefficient or ineffective. (The amount of silicone oil emulsion is generally 10-100 ppm of the weight of the foaming liquid (according to silicone oil). Of course, in special cases, there are also less than 10 ppm and more than 100 ppm. The optimum amount is mainly determined through experiments.

Most of the general silicone oil emulsion defoamers are oil-in-water type. According to the different types of silicone oil, there are several types of silicone oil emulsion defoamers as follows:
1. Silicone oil emulsion based on dimethyl silicone oil
This kind of defoamer is prepared from simethicone plus emulsifier and water, and can be widely used in fermentation, food, papermaking, fiber, pharmaceuticals, synthetic resin, etc.

2. Silicone oil emulsion based on methyl ethoxy silicone oil
This kind of defoamer is made of methyl ethoxy silicone oil and compounding agent.

3. Silicone oil emulsion based on ethyl silicone oil
In recent years, silicone defoamers are developing in the direction of silicone-polyether block copolymerization (or graft copolymerization). This kind of defoamer has the characteristics of both silicone and polyether, so the defoaming power is greatly improved; silicone-polyether copolymerized defoamer can also be called self-emulsifying silicone defoamer, it is Block (or graft) hydrophilic ethylene oxide chain or oxyethylene oxide propylene chain in the silicone molecular chain, so that the hydrophobic siloxane part is combined with the hydrophilic polyether. Such molecules have larger Polarity, as a defoamer, it has a large spreading coefficient, can be uniformly dispersed in the foaming medium, and has high defoaming effect. It is a new type of high-efficiency defoamer. This kind of self-emulsifying silicone oil without the use of emulsifiers, the defoaming effect is quite satisfactory for some systems, and it is especially suitable for those occasions where the general silicone oil emulsion is not suitable and the general silicone oil emulsion is difficult to do.

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