Effects of interfacial molecular mobility on thermal boundary conductance at solid-liquid interface

The effects of interfacial molecular mobility on the thermal boundary conductance (TBC) across graphene-water and graphene-perfluorohexane interfaces were investigated using non-equilibrium molecular dynamics simulations. The molecular mobility was varied by equilibrating nanoconfined water and perfluorohexane at different temperatures. The long-chain molecules of perfluorohexane exhibited a prominent layered structure, indicating a low molecular mobility, over a wide temperature range between 200 and 450 K. Alternatively, water increased its mobility at high temperatures, resulting in an enhanced molecular diffusion that significantly contributed to the interfacial thermal transport, in addition to the increasing vibrational carrier population at high temperatures. Furthermore, the TBC across the graphene-water interface exhibited a quadratic relationship with the rise in temperature, whereas for the graphene-perfluorohexane interface, a linear relationship was observed. The high rate of diffusion in interfacial water facilitated additional low-frequency modes, and a spectral decomposition of the TBC also indicated an enhancement in the same frequency range. Thus, the enhanced spectral transmission and higher molecular mobility of water with respect to perfluorohexane explained the difference in the thermal transport across the interfaces considered herein.