Analysis of the basic characteristics of silicone oil
Source:iotachem.com
PostTime:2024-07-18 09:31:06
1. Surface tension of silicone oil
General properties of surface tension:
The surface tension of silicone oil is relatively low. For example, the surface tension of dimethyl silicone oil with a viscosity of 0.65 mm²/s is 15.9 mN/m at 25°C.
Relationship between surface tension and viscosity:
As the viscosity of silicone oil increases, its surface tension also increases. When the viscosity of dimethyl silicone oil exceeds 50mm²/s, the surface tension reaches a constant value of about 21.5mN/m.
Surface tension of methylphenyl silicone oil:
The surface tension of methylphenyl silicone oil is slightly higher than that of dimethyl silicone oil, and as the phenyl content increases, the surface tension also increases accordingly.
Since silicone oil has low surface tension, it spreads easily on metal surfaces.
The low surface tension of silicone oil also causes it to "crawl" on vertical surfaces, which means that the silicone oil can move down the surface without external forces.
2. Surface activity of silicone oil
Foaming properties:
Dimethicone fluids: have very low foaming properties, which makes them useful as defoamers in many applications.
Methylphenyl silicone fluids: exhibit varying degrees of foaming properties, depending on their chemical structure and phenyl content.
Surface activity:
Silicone oils can significantly reduce the surface tension of solutions in organic solvents, indicating that they are surface active. This property allows silicone oils to accumulate on the surface of the liquid phase.
Emulsification and defoaming effect in water:
Silicone oils are able to emulsify in water, causing the surface tension of the water to decrease, which is another reason why they are used as defoamers.
Defoaming mechanism:
Selection of defoaming agent: According to defoaming theory, an effective defoaming agent should be as insoluble as possible in the defoamed medium so as to achieve a high surface concentration in a smaller liquid volume.
Spreading pressure:
The defoamer should have a positive spreading pressure, which helps to quickly form a closed film on the surface of the foam layer.
Incompatibilities:
The defoaming agent should not form a mixture with the foaming agent in the surface film to maintain its defoaming effect.
Defoaming properties of dimethyl silicone oil:
In aqueous systems, dimethicone fluids meet all the requirements of defoamers because of their minimal volume solubility in water. They are spreadable and have very low miscibility with many organics and most inorganics, which makes them very effective in defoaming applications.
3. Lubricity of silicone oil
Due to the small intermolecular force of dimethyl silicone oil, the load capacity of its oil film is relatively low.
Boundary lubrication properties:
Under boundary lubrication conditions, dimethyl silicone oil does not have good lubricity for steel-steel contact combinations.
Lubrication of lightly loaded rolling bearings:
Dimethyl silicone oil is suitable for the lubrication of lightly loaded rolling bearings and exhibits good performance.
Lubrication of plastic bearings:
For bearings made of non-metallic materials such as nylon (dynamamide), polytetrafluoroethylene or phenolic resin, dimethyl silicone oil provides excellent lubrication properties.
Lubrication of metal materials:
In terms of metal materials, dimethyl silicone oil is also suitable for the combination of steel and bronze, aluminum, zinc or cadmium, as well as the combination of aluminum and bronze, and can achieve good lubrication effects.
The introduction of phenyl improves lubricity:
By introducing phenyl groups (forming methylphenyl silicone oil), the lubricity of silicone oil can be improved, making it more suitable for use as a bearing lubricant where pressure is not high.
Halogenation modification:
A method to further improve the lubricity of silicone oil is to halogenate the phenyl or aliphatic groups.
Use of additives:
The lubrication properties of dimethicone can be improved by adding various additives. For example, adding methyl ricinoleate can significantly enhance its lubricity.
