Characteristics of methyl silicone oil
Methyl silicone oil has many special properties:
■ Good heat resistance
Due to the main chain of the silicone oil molecule being composed of -Si-O-Si- bonds, it has a structure similar to inorganic polymers, with high bond energy, and therefore excellent heat resistance.
■ Excellent oxidation resistance and weather resistance
■ Excellent electrical insulation
Silicone oil has good dielectric properties, and its electrical characteristics change very little with changes in temperature and cycle number. The dielectric constant decreases with increasing temperature, but the change is very small. The power factor of silicone oil is low and increases with increasing temperature, but there is no regular change with frequency. The volume resistivity decreases with increasing temperature.
■ Good water repellency
Although the main chain of silicone oil is composed of polar bonds Si-O, the non-polar alkyl groups on the side chains are oriented outward to prevent water molecules from entering the interior, thus playing a hydrophobic role. The interfacial tension of silicone oil to water is about 42 dyne/cm. When diffusing on glass, due to the water repellent property of silicone oil, a contact angle of about 103° is formed, which is comparable to that of paraffin wax.
■ Small viscosity-temperature coefficient
Silicone oil has low viscosity and little change with temperature, which is related to the helical structure of silicone oil molecules. Silicone oil is the best viscosity-temperature characteristic oil among various liquid lubricants, and this characteristic of silicone oil is very meaningful for damping equipment.
■ High resistance to compression
Due to the helical structure characteristics and large intermolecular distance of silicone oil molecules, it has high compressibility resistance. Using this characteristic of silicone oil, it can be used as a liquid spring, which can greatly reduce the volume compared to mechanical springs.
■ Low surface tension
Silicone oil is characterized by its low surface tension, which indicates high surface activity. Therefore, silicone oil has excellent defoaming and anti-foaming properties, as well as isolation and lubrication properties with other substances.
■ Non-toxic, odorless, and physiologically inert
From a physiological perspective, siloxane polymers are among the least reactive compounds known. Dimethyl silicone oil is inert to living organisms and does not cause rejection reactions in animal bodies. Therefore, they have been widely used in surgical and medical departments, pharmaceuticals, food, and cosmetics.
■ Good lubricity
Silicone oil has many excellent properties as a lubricant, such as high flash point, low freezing point, thermal stability, small viscosity change with temperature, non-corrosive to metals, no adverse effects on rubber, plastic, paint, organic paint film, low surface tension, and easy spreading on metal surfaces. In order to improve the steel-to-steel lubricity of silicone oil, lubricity additives that can be miscible in silicone oil can be added. Introducing chlorophenyl groups or substituting dimethyl groups with trifluoropropyl methyl groups on the siloxane chain can greatly improve the lubricity of silicone oil.