Molecular simulations of thermal transport across interfaces: solid–vapour and solid–solid

Using molecular simulations, we have investigated heat transfer across the solid–fluid interface between water and silicon and silica wafers, and solid–solid interfaces in superlattices and thin solid films. The system set-up has allowed us to focus on the resistance associated with both the fluid and solid interfaces. For instance, by maintaining the solid phase at a constant temperature we can focus solely on the fluid-side resistance. Our results show that the thermal or Kapitza resistance at fluid side of the solid–fluid decreases significantly as the surface is made more hydrophilic. This is primarily due to increases in fluid adsorption and absorption at the surface, which enhance the intermolecular collision frequency at the interface. Increasing this frequency also reduces the dependence of thermal transport on variations in the interfacial temperature and pressure. Hence, decreasing the density diminishes the intermolecular collision frequency, which increases the thermal resistance. By maintaining the fluid at a constant temperature we have also examined the interface resistance on the solid side. Our results show that these interfacial resistances can diminish the wall heat flux by an order of magnitude in comparison with a hypothetical system for which the overall fluid–solid contact resistances are negligible. Finally, we consider the solid phase as a superlattice in which case the interfacial resistances produced between different solid layers can significantly lower the heat transfer. Our simulations show significant resistance to thermal transport between thin films of the solid phase which constitute the superlattice, providing insight into how a superinsulator can be designed.