Heat transfer in soft nanoscale interfaces: the influence of interface curvature

We investigate, using transient non-equilibrium molecular-dynamics simulations, heat-transfer through nanometer-scale interfaces consisting of n-decane (2-12 nm diameter) droplets in water. Using computer simulation results of the temperature relaxation of the nanodroplet as a function of time we have computed the thermal conductivity and the interfacial conductance of the droplet and the droplet/water interface respectively. We find that the thermal conductivity of the n-decane droplets is insensitive to droplet size, whereas the interfacial conductance shows a strong dependence on the droplet radius. We rationalize this behavior in terms of a modification of the n-decane/water surface-tension with droplet curvature. This enhancement in interfacial conductance would contribute, in the case of a suspension, to an increase in the thermal conductivity with decreasing particle radius. This notion is consistent with recent experimental studies of nanofluids. We also investigate the accuracy of different diffusion equations to model the temperature relaxation in non stationary non equilibrium processes. We show that the modeling of heat transfer across a nanodroplet/fluid interface requires the consideration of the thermal conductivity of the nanodroplet as well as the temperature discontinuity across the interface. The relevance of this result in diffusion models that neglect thermal conductivity effects in the modeling of the temperature relaxation is discussed.