Most industrial methyl silicone oils are polydimethylsiloxane (PDMS), with the structure [–Si(CH₃)₂–O–]ₙ. Longer molecular chains create higher molecular weight and viscosity. Low-viscosity oils flow quickly and spread easily, while high-viscosity oils form thicker, more persistent films.
Kinematic viscosity is normally expressed in cSt or mm²/s:
1 cSt = 1 mm²/s
Dynamic viscosity is expressed in cP and must be converted using density:
cP = cSt × density
Because PDMS has a density of approximately 0.96–0.97 g/cm³, 1 cSt is roughly equivalent to 0.96–0.97 cP.
| Viscosity | Main characteristics | Typical applications |
|---|---|---|
| 1–20 cSt | Fast spreading, thin film, higher volatility | Defoamer base oils, precision instruments, impregnation and selected personal-care formulations |
| 50–350 cSt | Balanced flow and film thickness | Plastic release agents, general lubrication, textile finishing and light damping |
| 500–10,000 cSt | Thick film, strong adhesion, low volatility | Damping fluids, grease base oils, sealing and high-temperature defoaming |
| 10,000–1,000,000 cSt | Very slow flow and strong viscoelasticity | High damping, cushioning, silicone grease and vacuum sealing |
For high-speed, light-load equipment, select a lower viscosity. For low-speed, heavy-load applications, a higher viscosity usually provides a stronger lubricating film. However, excessive viscosity increases starting resistance and may prevent the oil from entering small clearances.
Low-viscosity silicone oils can show significant evaporation at elevated temperatures. Semiconductor, optical and enclosed electronic applications should therefore evaluate volatile content and residual cyclic siloxanes, not viscosity alone.
The IOTA-201 PDMS series covers viscosities from 1 to 1,000,000 cSt:
5–50 cSt: rapid spreading and precision lubrication
100–500 cSt: release, general lubrication and damping
1,000–10,000 cSt: grease base oils and sealing
Above 100,000 cSt: high damping and specialty cushioning
For applications sensitive to outgassing, the IOTA-M-X low-volatility series is available in 100, 350, 500, 1,000 and 10,000 mm²/s grades. Its published specifications include volatility below 0.2% at 150°C for three hours and total D3–D10 cyclic siloxanes below 300 ppm.
Products from IOTA-201, Dow Corning 200 Fluid and Wacker AK are all PDMS-based, but finished-product performance can still differ because of volatile content, molecular-weight distribution, viscosity tolerance, impurity control and batch consistency.
Selection principle: first define the viscosity range from the application, then compare volatility, batch tolerance, compatibility and total cost. For precision damping or torque control, specify the test temperature and a narrow acceptable viscosity range.
For complete specifications or sample testing, visit www.siliconeoil.net or contact Iota Silicone Oil Anhui Co., Ltd. Test the product under actual operating conditions before full-scale production.
