Time-periodic electroosmotic flow and solute dispersion in a slip-regulated microchannel conveying Maxwell viscoelastic fluid

Abstract

Electrokinetic transport and solute dispersion have key roles in microfluidic mixing and detection analysis. Dispersion of solutes is highly dependent upon the flow field, bringing in the importance of surface property. For instance, liquid slip at the wall increases zeta potential, which consequently changes the shape of the flow profile. The increased dispersion by virtue of higher momentum transport may be helpful for mixing and detection schemes. To emphasize such characteristics, in this study, we have analyzed the transient dynamics of Maxwell fluids and solute dispersion characteristics in a microchannel with slip-dependent zeta potential. A semi-analytical approach based on the Concentrated Matrix Exponential method has been employed to study the flow characteristics, accounting for the form of the time-periodic electric field and viscoelastic properties of the Maxwell fluid. The Taylor–Aris moment analysis is employed to evaluate the dispersion coefficient, centroid motion, skewness, and kurtosis. Full-sinusoidal forcing couples smoothly with viscoelastic relaxation and generally provides the highest instantaneous throughput. Rectangular forcing performs poorly at larger relaxation times due to abrupt field reversals. Wall slip and fluid elasticity enlarge the time-periodic axial dispersion and strengthen transient deviations from Gaussian statistics. Non-sinusoidal pulses create sharper oscillations in the dispersion coefficient than the sinusoidal waveform. Axial spreading of the mean concentration increases with Péclet number, relaxation time, and wall slip due to advection, viscoelastic memory, and slip-enhanced shear. These results may enlighten about the applicability of time-periodic flows and wall properties in the development of electrokinetic microfluidic devices conveying viscoelastic fluids.