# Deconstructing temperature gradients across fluid interfaces: the structural origin of the thermal resistance of liquid-vapor interfaces

## TL;DR

This paper reveals that the thermal resistance at liquid-vapor interfaces originates from a low density fluid layer adsorbed on the liquid surface, which acts as a boundary between gas-like and liquid-like thermal transport mechanisms.

## Contribution

It identifies the structural origin of interfacial thermal resistance as an adsorbed low density fluid layer, linking atomic structure to thermal transport properties.

## Key findings

- Thermal resistance is linked to a low density adsorbed fluid layer.
- Thermal conductance is proportional to the number of atoms in the TRL.
- The TRL marks the transition from ballistic to collision-dominated transport.

## Abstract

The interfacial thermal resistance determines condensation-evaporation processes and thermal transport across material-fluid interfaces. Despite its importance in transport processes, the interfacial structure responsible for the thermal resistance is still unknown. By combining non-equilibrium molecular dynamics simulations and interfacial analyses that remove the interfacial thermal fluctuations we show that the thermal resistance of liquid-vapor interfaces is connected to a low density fluid layer that is adsorbed at the liquid surface. This thermal resistance layer (TRL) defines the boundary where the thermal transport mechanism changes from that of gases (ballistic) to that characteristic of dense liquids, dominated by frequent particle collisions involving very short mean free paths. We show that the thermal conductance is proportional to the number of atoms adsorbed in the TRL, and hence we explain the structural origin of the thermal resistance in liquid-vapor interfaces.