Nonequilibrium noise in electrophoresis: the microion wind

TL;DR

This paper presents a theoretical analysis of how microion-induced noise affects colloidal particle dynamics in electric fields, revealing anisotropic, nonequilibrium fluctuations and complex relaxation behaviors.

Contribution

It introduces a novel theoretical framework for understanding nonequilibrium noise in electrophoresis, highlighting the role of microion fluctuations and frequency-dependent fluctuation-dissipation relations.

Findings

Microion motions cause anisotropic, nonequilibrium noise proportional to the electric field.

The fluctuation-dissipation ratio varies significantly with frequency.

Displacements from steady state relax with non-gradient velocity.

Abstract

We analyze theoretically the dynamics of a single colloidal particle in an externally applied electric field. The thermal motions of microions lead to an anisotropic, nonequilibrium source of noise, pro- portional to the field, in the effective Langevin equation for the colloid. The fluctuation-dissipation ratio depends strongly on frequency, and the colloid if displaced from its steady-state position relaxes with a velocity not proportional to the gradient of the logarithm of the steady-state probability.