Diffusiophoresis in the presence of a pH gradient

TL;DR

This paper investigates how pH gradients affect diffusiophoresis of polystyrene particles, highlighting the role of zeta potential variations and the isoelectric point in particle motion within pore geometries.

Contribution

It provides experimental and theoretical insights into pH-dependent diffusiophoresis and diffusioosmosis, emphasizing the impact of the isoelectric point on particle behavior.

Findings

pH influences diffusiophoretic mobility via zeta potential changes

sign reversal of particle motion near the isoelectric point

wall diffusioosmosis affects particle trajectories

Abstract

Diffusiophoresis is the spontaneous motion of particles under gradients of solutes. In electrolyte-driven diffusiophoresis, the zeta potential of the particles is an important surface property that characterizes diffusiophoretic mobility. However, the zeta potential is not a fixed material property and colloidal surfaces often show varying potentials depending on the physical chemistry of the surrounding fluid, e.g., solute type, ionic strength, and pH. In this article, we study experimentally and theoretically pH-dependent diffusiophoresis of polystyrene particles using a dead-end pore geometry. In particular, the influence of the isoelectric point (pI) on diffusiophoresis is demonstrated in the absence and presence of wall diffusioosmosis. Throughout the paper, we show with experiments and model calculations how the pH-dependent diffusiophoresis and diffusioosmosis influence the particle motion in dead-end pore configurations, including changes that occur when there is a sign change in the zeta potential near the pI.