Alternating Current Electroosmotic Flow of Viscoelastic Jeffreys Fluids in a pH-Regulated Slit Nanochannel

This study investigates the electroosmotic flow (EOF) of viscoelastic Jeffreys fluids in a pH-regulated parallel-plate nanochannel, with a focus on analyzing the effects of solution pH, background salt concentration, and alternating current (AC) electric field frequency on flow characteristics. In micro- and nanoscale fluidic systems, surface charge characteristics critically govern electrokinetic flow. The surface charges in this study originate from the protonation and deprotonation reactions of silanol (SiOH) groups on the channel walls. Different from the constant surface electric potential assumed in existing studies, the surface electric potential here varies with solution pH and background salt concentration. By modulating solution pH and thereby tuning surface charge density, active and reversible control of EOF can be realized. By solving the coupled Poisson–Boltzmann equation, momentum equation, and Jeffreys constitutive equation, we obtain an analytical solution for the electric potential distribution and semi-analytical solution for the velocity field. The results show that under the chosen parameter conditions, the relaxation time λ1 enhances the velocity amplitude, while the retardation time λ2 weakens it. The EOF velocity amplitude of Jeffreys fluids is enhanced by greater pH deviation from the isoelectric point, lower ionic concentration, and higher electric field frequency. In nanochannel flows, the effect of the oscillating Reynolds number on the velocity amplitude is negligible.