Length-dependent thermal conductivity of single extended polymer chains

The low thermal conductivity of polymers will be one of the major roadblocks for the polymer-based microelectronics and macroelectronics due to the limited heat spreading capability. Despite that the thermal conductivity of bulk polymers is usually low, a single extended polymer chain could have very high thermal conductivity. In this paper we present atomistic simulation studies on the phonon transport in single extended polymer chains of various polymers as a function of polymer chain length. The thermal conductivity of single extended polymer chains can be 1--2 orders of magnitude higher than their bulk counterparts. The thermal conductivity of single extended polymer chains is a strong function of monomer type. For example, the thermal conductivity of the extended polymer chains with aromatic backbone can be up to 5 times as that of a polyethylene chain, while the thermal conductivity of the extended polymer chains with bond-strength or mass disorder can be only 1/25 as that of a polyethylene chain. We analyze the phonon transport mechanisms in single extended polymer chains of various polymers and find that the competition between ballistic phonon transport and diffusive phonon transport in a polymer chain leads to a diverging length-dependent thermal conductivity.