Local response in nanopores

Abstract

In this work the transient time correlation function (TTCF) algorithm is applied to study highly confined molecular fluids. We focus on linear polymer chains of various lengths trapped in a slab pore which is a few nanometres thick and made of atomistic walls, and the behaviour and response of the polymer melt subject to shear flow are considered. The shearing is produced by shifting the walls in opposite directions, and the temperature inside the channel is controlled by a thermostat applied to the wall atoms alone, so as to mimic the dissipation of heat as it occurs in real devices. It is shown how the TTCF algorithm can be applied to extract the fluid's dynamical and structural properties as they evolve from equilibrium and until a steady state has been established. We note that this procedure is applicable to fluids of any complexity and down to extremely low fields, comparable to those present in experimental devices. It is also shown that this technique can be used to probe local properties at specific locations across the channel. This feature is of particular significance because liquid properties inside nanoconfined geometries are mostly determined by the interactions at the interface and specifically by the structural reordering which affects the first few atomic/molecular layers close to the wall surface, e.g. slip.