What is Thermal Conductivity?

• In metals, valence electrons conduct heat energy + electric current
• Phonons – lattice vibrations – transport heat through non-metals
• κ= ραCp
• ρ = density
• α = thermal diffusivity
• Cp = heat capacity
• Transport is intrinsically important for thermal conductivity
• Phonon scattering → insulation

Thermal Conductivity, Electrical Insulation

Graphite:

• Full delocalization of π electrons → full aromaticity
• Electrical delocalization in graphite leads to high electrical conductivity and high thermal conductivity

hexagonal-Boron Nitride:

• Electrons are mainly distributed on N atoms → partial aromaticity
• Thermal conductivity arises from phonon vibrations

In-Plane vs Through-Plane Thermal Conductivity

For many applications, high through-plane thermal conductivity is desired to transport heat away from motors and sensitive electronics.

Anisotropic fillers (glass fiber, plate-like BN) will orient in the flow direction during injection molding.  Different degrees of orientation will be achieved depending on part geometry, part thickness, injection gate design, and injection molding process parameters such as temperature and pressure.

Particle Packing & Percolation

Percolation pathways through the more thermally conducting fillers will enhance the overall thermal conductivity of the formulation.  Factors such as particle size, shape, dispersion, and orientation will be affected by processing conditions and part design.

Thermal Conductivity of Common Polymer Resins

Taken from Chen, Du, Ginzburg, Progress in Polymer Science, 2006