Electrophoresis of electrically neutral porous spheres induced by selective affinity of ions

TL;DR

This paper explores how electrically neutral porous spheres can undergo electrophoresis in electrolyte solutions due to asymmetric ion affinity, using electrohydrodynamics and theoretical models to derive analytical expressions.

Contribution

It introduces a theoretical framework for electrophoresis of neutral porous spheres driven by ion affinity differences, expanding understanding beyond charged particle electrophoresis.

Findings

Electrophoretic mobility depends on ion affinity asymmetry.

Mobility increases with salinity for large spheres.

Galvani potential influences sphere mobility.

Abstract

We investigate the possibility that electrically neutral porous spheres electrophorese in electrolyte solutions with asymmetric affinity of ions to spheres on the basis of electrohydrodynamics and the Poisson-Boltzmann and Debye-Bueche-Brinkman theories. Assuming a weak electric field and ignoring the double-layer polarization, we obtain analytical expressions for electrostatic potential, electrophoretic mobility, and flow field. In the equilibrium state, the Galvani potential forms across the interface of the spheres. Under a weak electric field, the spheres show finite mobility with the same sign as the Galvani potential. When the radius of the spheres is significantly larger than the Debye and hydrodynamic screening length, the mobility monotonically increases with increasing salinity.