Does electrophoretic velocity depend on particle size in viscoelastic fluids?

In theory, electrophoretic velocity is independent of particle size in an unbounded Newtonian fluid under the thin electric double layer approximation. However, recent theoretical studies have challenged this notion, revealing that the electrophoretic velocity may exhibit a dependency on particle size in non-Newtonian fluids. We report a systematic experimental study of this phenomenon in viscoelastic polyethylene oxide (PEO) solutions through a rectangular microchannel. By manipulating the molecular weight as well as the concentration of PEO polymer, we aim to examine the individual and combined influences of fluid viscoelasticity and shear thinning at different levels on the electrophoretic velocity of spherical particles with (nearly) identical zeta potentials (in a Newtonian fluid) but of different diameters. Our findings indicate a significant amplification of the difference in electrophoretic velocity across various particle sizes with increasing polymer molecular weight and polymer concentration.