1. Viscosity change law
Temperature dependence
Viscosity decreases with increasing temperature: phenyl silicone oil is a non-Newtonian fluid, and its viscosity is negatively correlated with temperature. At high temperature, the molecular chain movement intensifies, the intermolecular force weakens, and the viscosity decreases significantly.
Viscosity-temperature coefficient characteristics: The viscosity-temperature coefficient (sensitivity of viscosity change with temperature) of phenyl silicone oil is lower than that of ordinary silicone oil, indicating that its viscosity stability is better at high temperature and is suitable as a high-temperature lubricant or heat transfer medium.
Effect of phenyl content on viscosity
Phenyl substitution effect: The introduction of phenyl will improve the thermal stability of silicone oil, but may increase the rigidity of the molecular chain, resulting in a slower rate of viscosity decrease at high temperature. The higher the phenyl content, the lower the sensitivity of viscosity to temperature, but too high a phenyl content may lead to poor low-temperature fluidity.
Critical phenyl content: Studies have shown that when the phenyl content is 10%-20%, silicone oil can take into account both fluidity and thermal stability at high temperatures, and the viscosity changes more smoothly.
Thermal oxidation and viscosity change
High temperature thermal oxidation: Above 200°C, phenyl silicone oil may undergo thermal oxidation reaction to generate cross-linked structures or small molecular volatiles, resulting in increased viscosity or gelation. The introduction of phenyl can improve antioxidant properties, but the oxidation products may still affect viscosity stability.
Oxidation induction period: The oxidation induction period of phenyl silicone oil (the time from the beginning of oxidation to a significant change in viscosity) is longer than that of ordinary silicone oil, which is suitable for short-term high temperature applications, but long-term high temperature still requires the assistance of antioxidants.
Shear rate and viscosity
Shear thinning effect: At high temperatures, the viscosity of phenyl silicone oil further decreases under the action of shear force, showing shear thinning behavior. This is beneficial for lubrication applications, but excessive shear force should be avoided to cause viscosity instability.

2. Control strategy
Optimize phenyl content and molecular structure
Adjust the phenyl ratio: Select the appropriate phenyl content (10%-20%) according to the application temperature range to balance high temperature stability and low temperature fluidity.
Side chain modification: Introduce long-chain alkyl or functional groups (such as amino, epoxy) to enhance the flexibility of the molecular chain and reduce the rate of viscosity drop at high temperature.
Antioxidant addition
Choose high-efficiency antioxidants: such as phenolic and amine antioxidants (such as 2,6-di-tert-butyl-p-cresol, hindered amines), which can prolong the oxidation induction period of phenyl silicone oil at high temperature and stabilize viscosity.
Compound antioxidant system: Combine the main antioxidant with the auxiliary antioxidant (such as phosphorus system, sulfur system) to synergistically inhibit the oxidation reaction and reduce viscosity changes.
Viscosity regulator and additives
Thickener or viscosity reducer: Adjust the high temperature viscosity by adding nanoparticles (such as silica, alumina) or high molecular polymers. Nanoparticles can enhance viscosity stability, but the amount added needs to be controlled to avoid agglomeration.
Rheology modifier: Introduce non-ionic surfactants or polymers to improve shear stability at high temperatures and reduce viscosity fluctuations.
Process optimization and application design
Temperature control: In high temperature applications, the actual working temperature is reduced by cooling systems or insulation materials to reduce viscosity changes.
Shear rate control: Optimize the design of the lubrication system to avoid excessive viscosity drop due to excessive shear rate.
Regular maintenance and replacement: Regularly test the viscosity of phenyl silicone oil in high-temperature applications and replace oxidized or degraded silicone oil in time.
Development of new phenyl silicone oil
High molecular weight phenyl silicone oil: Increasing the molecular weight can enhance the high-temperature viscosity stability, but it is necessary to balance processability and cost.
Branched or cross-linked phenyl silicone oil: Through branching or lightly cross-linked structure, the molecular chain movement at high temperature is reduced and the viscosity is stabilized.