Methyl silicone oil is a linear polyorganosiloxane with Si-O-Si as the main chain and two methyl groups and trimethylsiloxy groups terminated on Si. It is liquid at normal temperature and its structural formula is as follows:

Methyl silicone oil is generally colorless, odorless, non-toxic, non-volatile liquid, insoluble in water, methanol, ethylene glycol, miscible with benzene, dimethyl ether, carbon tetrachloride or kerosene, slightly soluble in acetone, Dioxane, ethanol and butanol. Since the molecular interaction between the methyl silicone oil is small, the molecular chain is spiral, and the organic group can rotate freely, so it has excellent spreading properties, lubricity, high and low temperature resistance, weather resistance, radiation resistance, high flash point, Low surface tension and physiological inertness, widely used in daily chemical, machinery, electrical, textile, coating, pharmaceutical and food industries.

Methyl silicone oil properties
Methyl silicone oil has many special properties:
■ Good heat resistance
In the silicone oil molecule, since the main chain is composed of a -Si-O-Si- bond, it has a structure similar to that of an inorganic polymer, and has a high bond energy, so that it has excellent heat resistance.

■ Good oxidation resistance and weather resistance

■ Good electrical insulation
Silicone oil has good dielectric properties, and its electrical characteristics change little with changes in temperature and cycle number. The dielectric constant decreases with increasing temperature, but with little change. Silicone oil has a low power factor and increases with temperature, but there is no rule with frequency. The volume resistivity decreases as the temperature rises.

■ Good hydrophobicity
Although the main chain of the silicone oil consists of the polar bond Si-O, the non-polar alkyl groups on the side chains are oriented outward, preventing water molecules from entering the interior and acting as a hydrophobic agent. The interfacial tension of silicone oil to water is about 42 dynes/cm. When diffused on the glass, due to the water repellency of the silicone oil, a contact angle of about 103° is formed, which is comparable to paraffin.

■ Small viscosity coefficient
Silicone oils have low viscosity and small changes with temperature, which is related to the helical structure of silicone oil molecules. Silicone oil is a type of oil with the best viscosity-temperature characteristics of various liquid lubricants. This property of silicone oil makes sense for damping equipment.

■ High compression resistance
Since the silicone oil molecules have a large helical structure characteristic and a large inter-molecular distance, they have high compression resistance. By utilizing this property of silicone oil, it can be used as a liquid spring, and the volume can be greatly reduced compared with a mechanical spring.

■ Low surface tension
Low surface tension is a characteristic of silicone oil. Low surface tension means high surface activity, therefore, silicone oil has excellent defoaming and antifoaming properties, isolation property with other substances, and lubricating properties.

■ Non-toxic, odorless and physiologically inert
From a physiological point of view, siloxane polymers are one of the most inactive compounds known. Dimethicone is inert to organisms and has no rejection reaction with animal organisms. Therefore, they have been widely used in the departments of surgery and medicine, medicine, 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, no corrosion of metal, and no adverse effect on rubber, plastic, paint, organic paint film and low surface tension. Easy to spread on metal surfaces and other characteristics. In order to improve the lubricity of the steel of the silicone oil to the steel, a lubricity additive which is miscible with the silicone oil may be added. The introduction of a chlorophenyl group on the siloxane chain or the substitution of a dimethyl group with a trifluoropropyl group greatly improves the lubricating properties of the silicone oil.