Influence of hydrodynamic interactions on lane formation in oppositely charged driven colloids

TL;DR

This study uses Brownian dynamics simulations to explore how hydrodynamic interactions affect lane formation in oppositely charged colloids under sedimentation and electrophoresis, revealing that hydrodynamics can suppress lane formation and induce phase separation.

Contribution

It provides the first detailed comparison of hydrodynamic effects versus neglect in lane formation of charged colloids under different driving conditions.

Findings

Hydrodynamics disfavor lane formation during sedimentation.

Lane phase separation occurs with hydrodynamics, unlike in simple Brownian models.

Electrophoretic lane behavior aligns with models neglecting hydrodynamics.

Abstract

The influence of hydrodynamic interactions on lane formation of oppositely charged driven colloidal suspensions is investigated using Brownian dynamics computer simulations performed on the Rotne-Prager level of the mobility tensor. Two cases are considered, namely sedimentation and electrophoresis. In the latter case the Oseen contribution to the mobility tensor is screened due to the opposite motion of counterions. The simulation results are compared to that resulting from simple Brownian dynamics where hydrodynamic interactions are neglected. For sedimentation, we find that hydrodynamic interactions strongly disfavor laning. In the steady-state of lanes, a macroscopic phase separation of lanes is observed. This is in marked contrast to the simple Brownian case where a finite size of lanes was obtained in the steady-state. For strong Coulomb interactions between the colloidal particles a lateral square lattice of oppositely driven lanes is stable similar to the simple Brownian dynamics. In an electric field, on the other hand, the behavior is found in qualitative and quantitative accordance with the case of neglected hydrodynamics.