Particle diffusiophoresis in viscous polymer solutions*

We study the effect of polymer molecules on diffusiophoresis of polystyrene latex under salt gradients. For a given solution (macro)viscosity, we show that the particle diffusiophoresis is sensitive to the microviscosity of the solution within the Debye layer, which is determined by the polymer size and concentration. Steric exclusion of the polymer molecules from the Debye layer directly influences diffusioosmotic flow therein, and thus the particle diffusiophoresis, which we confirm experimentally by varying the polymer chain length and the thickness of the Debye layer. Our results offer useful insights into applications that involve controlling colloidal transport in viscous polymer solutions such as colloidal film deposition, painting, and drug delivery.