1. Chemical Backbone of Thermal Silicone
Thermally conductive silicone is based on polysiloxane (–Si–O–Si–).
- Each Si atom alternates with O atoms, forming the “Si–O backbone.”
- The Si atoms are typically bonded to methyl groups (–CH₃) or other functional groups.
Basic structure:
–Si(CH₃)₂–O–Si(CH₃)₂–O–
2. Bond Angles (Bond Foot) in Si–O–Si
In this structure:
- Si atoms adopt sp³ hybridization → with an ideal 109.5° bond angle.
- The Si–O–Si bond angle is highly flexible, ranging from 120° to 150°.
- This “bendability” explains why silicone is soft, flexible, and resistant to breakage.
Analogy: The Si–O backbone behaves like a spring, because the bond angle can adjust freely.
3. Relationship Between Bond Angles and Thermal Conductivity
Why are bond angles relevant to thermal silicone?
- Backbone Flexibility (Variable Si–O–Si Angles)
- Provides excellent thermal stability (the chain does not collapse at high temperature).
- Allows thermal fillers (Al₂O₃, BN, AlN, graphite, etc.) to disperse evenly in the matrix.
- Strength of Si–O Bonds
- Si–O bonds have high bond energy (~452 kJ/mol, stronger than C–C bonds).
- This ensures long-term reliability of silicone under thermal conduction applications.
- Filler Interface Adaptability
- The flexible silicone chain (due to variable bond angles) can wrap around filler particles.
- This reduces interfacial voids → enhances thermal conductivity.
