The correct approach is to identify the source of contamination first, and then determine whether to replace the material with a low-volatility silicone oil or optimize the entire formulation and manufacturing process.
The following potential sources should be investigated separately:
Base silicone oil or plasticizing components
Potting compounds, sealants, or coatings
Curing agents, catalysts, and other additives
Cleaning agents, release agents, and assembly adhesives
Plastics, foams, and wire-harness materials
Incomplete curing or insufficient post-baking and devolatilization
If the silicone oil is replaced without identifying the actual contamination source, the fogging problem may continue.
Conventional volatility is normally measured as the mass loss of a material under specified temperature and time conditions. Lens fogging, however, depends on whether volatile substances migrate and condense on a cooler surface.
These two indicators are related but are not equivalent. For optical and enclosed electronic equipment, fogging or condensable-material tests should be conducted under simulated operating conditions, taking into account the actual temperature, aging time, enclosure level, and condensation location.
Low-volatility methyl silicone oil is suitable for applications requiring electrical insulation, lubrication, damping, or a formulation base oil, while also requiring controlled low-molecular-weight content and evaporation loss.
The appropriate viscosity should be selected according to the required flow, penetration, dispensing, and processing performance.
Low-volatility vinyl silicone oil can be used in addition-cure silicone formulations. However, vinyl content, viscosity, volatility control, and the crosslinking system must be matched together. Selection should not be based solely on the description “vinyl silicone oil.”
If the contamination comes from the cured silicone compound, replacing only the base oil may not be sufficient. The base polymer, crosslinker, catalyst system, additives, and curing conditions may all need to be adjusted.
Commercial low-fogging silicone products are generally designed around fogging performance as an independent requirement rather than being defined by viscosity alone.
Before selecting a material, the following information should be provided:
Long-term operating temperature and peak thermal-aging temperature
Whether the equipment is fully enclosed or operates under vacuum
Actual temperature of the contaminated surface
Whether the material is used as a liquid or after curing
Whether it is located near lenses, cameras, sensors, or electrical contacts
Current material composition and curing conditions
Time and location of fogging, as well as the composition of the deposited film
A specific material grade should not be recommended when these conditions are unknown.
Considering silicone oil viscosity while ignoring low-molecular-weight components
Treating low volatility as equivalent to low fogging
Testing only individual raw materials instead of the complete cured system
Performing thermal-aging tests immediately after shortening the curing time
Failing to establish blank samples and single-material control groups
Assuming that the contamination must come from a silicone material
First, inspect the appearance of the deposited film and conduct composition analysis when necessary. Next, test the base oil, silicone compound, and other assembly materials separately.
Candidate systems should then undergo thermal-aging and condensation testing under specified or simulated operating conditions. Finally, verify electrical insulation, adhesion, hardness, stress behavior, and long-term stability.
As a full-chain silicone solutions provider, IOTA SILICONE OIL (Anhui) CO., LTD. can help screen suitable low-volatility methyl silicone oils, vinyl silicone oils, and other silicone materials according to the operating temperature, enclosure conditions, optical sensitivity, and curing system.
The final solution should be validated using the complete component or a representative simulation of the actual operating environment.
No. Sealants, potting compounds, plastics, cleaning agents, and assembly additives may also release condensable substances.
No such guarantee should be made without testing. Low-volatility and low-fogging tests evaluate different properties under different conditions. Validation under simulated operating conditions is still required.
Viscosity can be used as a reference, but it cannot replace testing for low-molecular-weight components and volatility under specified conditions.
A qualified base oil does not prove that the crosslinker, additives, residual solvents, and curing by-products also meet low-fogging requirements.
Selection based only on the product name is not recommended. Vacuum applications must also consider outgassing, condensable volatile materials, and the equipment’s acceptable contamination level.
At minimum, provide the material list, thermal-aging conditions, enclosure status, curing process, fogging location, and the time at which the fogging appears.
