Effect of polymer-particle interactions on diffusiophoresis of latex particles

In this study, we experimentally investigate the impacts of polymer-particle interactions on the diffusiophoresis of polystyrene microspheres. Using a microfluidic setup, we reveal how the background polymers surrounding a charged particle dictate the diffusiophoretic motion of the particle. For non-adsorbing polymers, the depletion of polymer chains near the particle surface via steric exclusion alters the local viscosity of the Debye layer, which is distinct from the bulk, thereby directly affecting the diffusiophoretic flow. On the other hand, adsorbing polymers affect particle diffusiophoresis by reducing the effective thickness of the Debye layer. While the polymer adsorption or depletion leads to a monotonic change in the particle mobility with respect to the varying degree of each effect, we observe non-monotonic mobility when the migrating particles are under the simultaneous influence of both the polymer depletion and adsorption. Our findings reveal significant roles played by the relative difference between the polymer size and the effective Debye screening length in determining the observed particle motion, thus providing valuable insights into particle phoretic transport in complex environments.