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



Lattice Vibration Modes of h-BN

9 optical modes which decompose at the Brillouin zone center as E1u + A2u + 2 E2g + 2 B1g

In plane and out-of-plane vibrational modes in TC THz frequency range (B1g, E2g)

Nanophotonics 2020, 9 (11), 3483 – 3504



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


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