Different materials have different thermal conductivity mechanisms. For metallic crystals, the free electrons in their lattices play an important role in the thermal conductivity function, while the phonons in metallic crystals can be ignored for their electrical conductivity function. However, the thermal conductivity mechanism of non-metallic mainly rely on the irregular movement of molecules and atoms to complete, due to the non-crystalline can also be viewed as a fine crystal, so it can also be analyzed through the phonon movement to the thermal conductivity mechanism, in addition to some of the projection is very good for the glass or a single crystal, which the photons of the conductivity of the photons also plays a very important role, so it can be summarized in the material inside the thermal conductivity carriers a total of There are three kinds of carriers of thermal conductivity within the material, namely, phonons, electrons and photons.
The heat conduction inside the polymer material is mainly transmitted by phonons. There are crystal structure and amorphous structure in polymer materials, and the molecular chain in the crystal structure is well arranged, which can realize the rapid transmission of phonons. However, the thermal conductivity of polymer materials is not high, which is mainly due to the existence of amorphous structures in polymer materials as well. The molecular chains in the amorphous structure are entangled with each other in an irregular arrangement, and the atoms in the molecular chains have a variety of vibration modes, which leads to the scattering of phonons in the transmission process and reduces the thermal conductivity of polymer materials.
At present, its thermal conductivity is generally improved by two methods: (1) improving the crystallinity and utilizing the propagation of phonons in the lattice to conduct heat. However, the method is complex, high cost, and difficult to achieve large-scale industrialized production. (2) Add thermal conductive fillers with high thermal conductivity such as aluminum nitride, boron nitride and carbon nanotubes to prepare filled thermal conductive composites. This method is widely used because of easy processing and molding and low cost.