Generic theory of colloidal transport

TL;DR

This paper presents a comprehensive theoretical framework for understanding colloidal particle motion in fluid mixtures, emphasizing the roles of external forces, surface slip, and dissipative phenomena in various transport scenarios.

Contribution

It introduces a generic linear response theory for surface fluxes and clarifies force balances in colloidal transport, including active self-propulsion mechanisms.

Findings

Differentiates flow perturbations caused by net forces and slip velocities.

Shows concentration and pressure gradients can induce particle motion without net forces.

Provides a unified description of passive and active colloidal transport phenomena.

Abstract

We discuss the motion of colloidal particles relative to a two component fluid consisting of solvent and solute. Particle motion can result from (i) net body forces on the particle due to external fields such as gravity; (ii) slip velocities on the particle surface due to surface dissipative phenomena. The perturbations of the hydrodynamic flow field exhibits characteristic differences in cases (i) and (ii) which reflect different patterns of momentum flux corresponding to the existence of net forces, force dipoles or force quadrupoles. In the absence of external fields, gradients of concentration or pressure do not generate net forces on a colloidal particle. Such gradients can nevertheless induce relative motion between particle and fluid. We present a generic description of surface dissipative phenomena based on the linear response of surface fluxes driven by conjugate surface forces. In this framework we discuss different transport scenarios including self-propulsion via surface slip that is induced by active processes on the particle surface. We clarify the nature of force balances in such situations.