The basic structural unit of organic silica gel is composed of silicon-oxygen chain links, and the side chain is connected to various other organic groups through silicon atoms. Therefore, the structure of the organic silicon coating material contains both "organic groups" and "inorganic structures". This special composition and molecular structure make it integrate the characteristics of organic substances and the functions of inorganic substances. The outstanding properties of organic silica gel products are:
1 High temperature resistance
Because the molecular structure of organic silicon has structural characteristics similar to inorganic polymers, its bond energy is very high, so it has excellent heat resistance. The operating temperature of rubber-type silicone is about 250°C, and resin-type silicone can be used for a long time at 350°C.
2 Low temperature resistance
The rubber-type silicone has a long bond, a large bond angle, and is very soft. The glass transition temperature is generally around -123℃, and it can be used for a long time in the range of -50 to 250℃. Special products can be used in the range of -100 to 300℃, such as silicone rubber containing 7.5 (molar content) phenyl groups. It still maintains elasticity at -112°C.
3 Weather resistance
There are no double bonds in the main chain of organic silica gel, so it is not easily decomposed by ultraviolet light and ozone. Long-term exposure to outdoor or high ozone concentration environment will not cause cracking and viscous creep, and the physical and electrical properties are basically unchanged. Resin-type organic silica gel will not turn yellow even under strong ultraviolet radiation, and its color can remain unchanged for many years.
In organic silica gel, the methyl group is connected to the silicon atom by a bond, thereby increasing the space for free rotation, and the hydrogen atom on the methyl group arranged outwards repels the hydrogen atom of the water, making the water molecule difficult to be hydrophilic. The oxygen is close to, so it has strong hydrophobicity. The methyl hydrogen polysiloxane or polyethyl hydrogen siloxane containing Si-H bond has reactivity and strong orientation, and can be cross-linked into a hydrophobic film under the action of a catalyst at low temperature.
5 Air permeability
Because the polysiloxane molecule has a spiral structure and large free space, the silicone rubber coating film has good gas and vapor permeability, such as nitrogen, oxygen, carbon dioxide and other gases in the air at room temperature. The rate is 30 to 50 times higher than that of natural rubber, and it is selective. Therefore, it has been widely used in gas and water vapor separation membranes, artificial heart-lung machines, oxygen enrichment devices, etc.
6 Low surface tension and low surface energy
The main chain of organosilicon is very flexible, and its intermolecular force is much weaker than that of hydrocarbons. Therefore, it has lower viscosity than hydrocarbons of the same molecular weight, weak surface tension, low surface energy, and strong film-forming ability. This low surface tension and low surface energy are the main reasons for its various applications: hydrophobicity, defoaming, foam stability, anti-sticking, lubrication, glazing and other excellent properties.
7 Electrical insulation performance
Silicone products have good electrical insulation properties. Their dielectric loss, voltage withstand, arc resistance, corona resistance, volume resistivity and surface resistivity are among the best insulating materials, and their electrical properties are affected by temperature and frequency. The impact is very small. Therefore, they are a kind of stable electrical insulating materials, which are widely used in the electronics and electrical industries. In addition to excellent heat resistance, silicone also has excellent water repellency, which is a guarantee for high reliability of electrical equipment used in wet conditions.
8 Physiologically inert (non-toxic)
Silicone elastomers are correctly selected with reliable cross-linking and catalytic systems. The fully cross-linked products are non-toxic and harmless, and can be used in the food and medical industries.