Beyond the Dynamic Density Functional theory for steady currents. Application to driven colloidal particles in a channel

TL;DR

This paper extends the dynamic density functional theory to include inertia effects for driven colloidal particles, analyzing steady states and revealing phenomena like wakes and temperature inhomogeneities beyond traditional DDFT.

Contribution

It introduces an approach considering particle inertia in steady-state analysis, deriving solutions via Hermite polynomial expansion, and highlights effects not captured by standard DDFT.

Findings

Rapid convergence of the expansion at high friction and low drift velocities

Confirmation of DDFT results in high friction regimes

Identification of wakes and temperature inhomogeneities behind potential barriers

Abstract

Motivated by recent studies on the dynamics of colloidal solutions in narrow channels, we consider the steady state properties of an assembly of non interacting particles subject to the action of a traveling potential moving at a constant speed while the solvent is modeled by a heat bath at rest in the laboratory frame. Since the description, we propose here, takes into account the inertia of the colloidal particles it is necessary to consider the evolution of both positions and momenta and study the governing equation for the one-particle phase-space distribution. We first derive the asymptotic form of its solutions as an expansion in Hermite polynomials and their generic properties, such as the force and energy balance and then we particularize our study to the case of an inverted parabolic potential barrier. We obtain numerically the steady state density and temperature profile and show that the expansion is rapidly convergent for large values of the friction constant and small drifting velocities. The present results on the one hand confirm the previous studies based on the dynamic density functional theory (DDFT) when the friction constant is large, on the other hand display effects such as the presence of a wake behind the barrier and a strong inhomogeneity in the temperature field which are beyond the DDFT description.