Diffusiophoretic Behavior of Polyelectrolyte Coated Particles*

Diffusiophoresis is the movement of particles under a solute concentration gradient. This occurs due to the generation of fluid flow at the solid-liquid interface: diffusio-osmosis (counter diffusiophoresis). In electrolyte diffusiophoresis, the particle velocity is described by the relative electrolyte gradient and the diffusiophoretic mobility, which depends on both the zeta potential of the particle and the diffusivity contrast between electrolyte cations and anions. Spatial and temporal variations in electrolyte concentration in experimental systems can lead to variations in the zeta potential of particles, which can have a large influence on diffusiophoretic behavior. Here, we show that adsorption of a single bilayer of the polyelectrolyte pair (PDADMAC/PSS) on the particle surface results in effectively constant zeta potential values with respect to electrolyte concentration, allowing a constant potential assumption to describe the experimental observations. Moreover, we show that the concentration of background salt during the coating process of the polyelectrolyte pairs plays a critical role in the final near-constant value of particle zeta potential obtained. This work highlights the utility of using simple polyelectrolyte pairs to tune the zeta potential and maintain constant values for precise control of diffusiophoretic transport during experimental observations.