A study of influence factors to improve the heat transfer of pure-polydimethylsiloxane (PDMS): A molecular dynamics study

Molecular dynamics simulation were performed to study the influence factors on the heat transfer of polydimethylsiloxane (PDMS), a kind of thermal interface materials (TIMs). The results show that the amorphous PDMS has larger thermal conductivities compared with that of crystalline PDMS, and longer chains are beneficial to the thermal conductivity. Based on the conclusion above, the differences of the structure on the backbone were analyzed. It was found that the amorphous PDMS backbone have flatter torsional potential surface, thus have a certain rotational softness compared with the crystalline PDMS. More interestingly, through the distribution of dihedral angle, we also found that the distribution of the dihedral angle of the amorphous PDMS backbone keep constant with the increasing of the chain lengths, but for crystalline PDMS, the dihedral angle moves to smaller angles for longer chains, indicating that amorphous PDMS have relative stable backbone structure. By calculating the phonon density of state (PDOS), we found that more silicone (Si) and oxygen (O) atoms are beneficial to the vibration of the backbone, thus increasing the thermal conductivity. In all, through the simulation, we concluded that the six factors (amorphous state, langer chains, good rotational softness, stronger vibration, more Si and O atoms and higher density along the heat flux direction) have positive effect on the thermal conductivity, which can provide the reliable theoretical basis for the selection of the better configuration to improve the thermal conductivity.