Effects of Newtonian and shear thinning fluid mixing on electrokinetic instability in microchannel flows with conductivity gradients
Phys. Rev. Fluids 11, 023702 – Published 10 February, 2026
DOI: https://doi.org/10.1103/v4rm-zsg2
Abstract
Electrokinetic instability (EKI) emerges when fluids with differing electrical conductivities interact with an applied electric field, resulting in interfacial waves that can either disrupt or enhance microfluidic processes. Previous studies on EKI have primarily focused on Newtonian fluids, though many practical applications involve the mixing of different rheological fluids. This work investigates the effects of Newtonian and shear thinning rheology mixing on EKI using a T-shaped microchannel. We find that adding xanthan gum (XG) polymer to the high-conductivity buffer results in lower threshold electric fields and higher wave speeds/amplitudes than the configuration with XG in the low-conductivity buffer. In contrast, the threshold electric fields for the configuration with XG in both buffers are in between the two rheology mixing configurations. These findings suggest the gradient of rheology interacts with that of conductivity and may itself be able to induce instability in electrokinetic flows. We also perform a scaling analysis to account for the fluid shear thinning effect on the electric Rayleigh number in terms of a power-law model. The critical values of this dimensionless number for the onset of EKI exhibit similar variations to the threshold electric field across fluid configurations and XG concentrations.
