Defoamers are used to prevent the formation of foam or reduce or eliminate generated foam by reducing the surface tension of water, solution, suspension liquid, etc. At present, defoamers have been widely used in textile production, papermaking, the petroleum, food, pharmaceutical industries and other fields. Dispersibility is an important indicator for measuring the quality of defoamers as only substances with low solubility and high dispersibility can be used as the active ingredients for defoamers.
Silicone defoamers are mainly made of dimethyl silicone oils which have low solubility and dispersibility, so it's required to add fumed silica, emulsifier or other dispersion agents to help them achieve better dispersion effect.
Fumed silica ( also known as pyrogenic silica, colloidal silicon dioxide) can be divided into two types, hydrophilic and hydrophobic fumed silica, the former contains silicon hydroxyl that can form hydrogen bonds with water molecules, and can be used in water systems to promote the dispersion and stability of defoamers. Hydrophobic silica soot is obtained through surface chemical treatment of hydrophilic silica soot. By reducing the Si-OH amount to an appropriate level, hydrophobic silica soot used in water systems will have reduced association degree, which helps achieve the best defoaming effect. To use silica soot in defoamers, it's required to first mix it with dimethyl silicone oil to make a silicone paste, which helps improve its wettability with dimethyl silicone oil and its dispersibility in silicone oil. How the silicon paste is mixed will impact its stability and defoaming performance to a certain degree. When using hydrophilic fumed silica, as inorganic silica soot and silicone oil are less compatible, to achieve uniform mixing it’s required to mix the silicone oil with the fumed silica in a kneader to improve the wettability of the fumed silica in the silicone oil. As for the hydrophobic silica soot, its affinity with silicone oil is greatly improved because its surface has been treated with organic matter. The silicon paste made by fumed silica should be transparent or translucent. As an active ingredient in silicone oil defoamer, silicon paste can be used directly or after diluting with solvent or self-emulsifying through modification with emulsifier or polyether. Due to the presence of SiO2 particles, the silicone oil can quickly spread in the foaming liquid and such higher dispersion efficiency will lead to better defoaming effect.
Therefore, fumed silica is deemed as a very important dispersant for silicone defoamers.
HUBEI HUIFU NANOMATERIAL CO.,LTD. （former company name : Yichang Huifu Silicon Material Co., Ltd.） is a domestic company specializing in the research, development, production and sales of hydrophilic and hydrophobic fumed silica products. The company has led the formulation of domestic industry standards for fumed silica products and the international standard ISO18473-3:2018 "Fumed Silica in Silicone Rubber". By manufacturing series products such as HL-150\200\300\380 series hydrophilic fumed silica and HB-132\135\612\151 series hydrophobic fumed silica, the company is able to provide comprehensive solutions for customers in various industries.