What Is a Silicon Defoamer?
Silicon defoamers are defoamers with excellent defoam curing properties due to their extremely low surface tension and insolubility in other substances.
The main component is polysiloxane, which is insoluble or insoluble in all substances and solvents, and has low interfacial tension with water, so it functions as a good defoaming agent in very small amounts in both aqueous and non-aqueous systems.
Uses of Silicon Defoamers
Silicon defoamers are used in a variety of fields. Specifically, it de-foams foam generated in all industrial fields, including chemical, petroleum, fermentation, printing, paper manufacturing, textile, and wastewater treatment. It is also used as a food additive because it is tasteless, odorless, and extremely low in toxicity.
In addition to being highly effective in defoaming in small quantities, it maintains its liquid state over a wide range of temperatures, and its physical properties do not change significantly except for viscosity. As a result, it has excellent heat and weather resistance and can be used under harsh conditions. It is also chemically and physiologically inert, tasteless, and odorless.
Principle of Silicon Defoamers
Bubbles in a liquid exist when the gas mixed in the liquid is covered by a thin liquid film. This film is formed by the surfactant in the liquid. In other words, the gas is wrapped in a film of surfactant. In other words, on the surface of the foam (the liquid layer called lamella), the hydrophobic groups of the surfactant are on the air side and the hydrophilic groups of the surfactant are on the water side, surrounding the gas in a stable structure.
Silicon defoamers disrupt the molecular order of the surfactant to achieve their anti-foam curing properties. The viscosity of the foam surface is due to the pseudo-bridging structure between surfactant adsorbents. The surface tension of the silicon defoamer is so small that when it adheres to the foam surface, it draws in the interfacial adsorbent substances on the foam surface, breaking the pseudo-bridging structure on the foam surface and separating the foam, thereby significantly lowering the surface tension of the foam and demonstrating its defoaming effect.
Surfactants also have a phenomenon called the Marangoni effect, which occurs when a bias in surface adsorption density creates a gradient in surface tension, causing surfactants to move back into thin areas. This phenomenon maintains the elasticity of the surfactant layer and allows the foam to exist stably. However, in the presence of silicon defoamer, the surfactant layer is replaced by silicon with low intermolecular forces, and the foam surface loses its elasticity, leading to defoaming.
The phenomenon in which small bubbles with high internal pressure in a foam are continuously absorbed by larger bubbles with low internal pressure is called gas diffusion. When surfactant is present, the gas diffusion rate in the lamella layer decreases and the foam is in a stable state. However, if a portion of the surfactant layer on the foam surface is replaced by silicon defoamer, silicon can promote gas diffusion and defoaming due to its high gas permeability.
Types of Silicon Defoamers
Silicon defoamers include “oil type,” “oil compound type,” “self-emulsifying type,” “emulsion type,” “solution type,” “solid type,” and “powder type,” and are used according to the target to be de-foamed.
1. Oil-Based Silicon Defoamer
Oil-based silicon defoamer is a solvent- and additive-free defoamer. Because it is non-silica, it can be used in oil-based foaming fluids that are not suitable for mixing with water or solvents.
They are inexpensive, fast-acting, and heat resistant. However, the oily component is strong enough to cause oil to float. Therefore, it may cause problems when used for drainage into rivers, etc., and must be handled with care.
2. Oil-Compound Silicon Defoamer
Oil-compound silicon defoamer is made of silicone oil with powdered silica powder, and is made of silicone resin only, so it exhibits the inherent properties of silicone. It is effective for both oil-based and water-based foaming solutions. Since no emulsifier is added, it cannot be used as-is in water-based foaming solutions.
3. Self-Emulsifying Silicon Defoamer
Self-emulsifying silicon defoamers are effective in both acidic and alkaline applications. They are also highly persistent and can be used in a wide range of applications. The disadvantage is that they are more expensive than other defoamers.
4. Emulsion-Type Silicon Defoamer
Emulsion-type silicon defoamers are general-purpose defoamers for water-based foaming solutions. They are easy to handle, safe, and available in many varieties. Therefore, they are used for food additives and wastewater treatment.
Disadvantages include limited storage conditions. Weaknesses include low resistance to high-temperature foaming solution, alkali resistance, and acid resistance.
5. Solution-Type Silicon Defoamer
Solution-type silicon defoamers are made by dissolving silicone fluid in a solvent, which allows the addition of various functionalities depending on the solvent. They are mainly used for defoaming oil-based foaming solutions. Although they are highly effective for oil-based foams, they are less effective for water-based foams.
6. Solid and Powdered Silicon Defoamers
Solid and powder silicon defoamers are manufactured by adsorbing silicone fluid onto a highly oil-absorbent powder or solid. They have good storage stability, easy handling, and workability. They are also effective in dispersing well in aqueous foam solutions, but are difficult to use in non-aqueous foam solutions.