Dynamic aspects of electroosmotic flow in a cylindrical microcapillary

Transient electro-osmotic flow in cylindrical microcapillaries containing salt-free medium

“…Theoretical results are presented for the effect of various parameters including the total surface charge per unit length ͑or zeta potential͒, the Debye length, and the radius of cylinder on the characteristics of the transient EOF. Although the general behavior of transient electroosmotic flow in a cylindrical tube is similar to that observed in a microchannel containing an electrolyte solution, 13,14,19 the Debye length has no effect on such a transient behavior for the case of constant surface charge density, and the steady-state electro-osmotic flow significantly deviates from the typical plug flow for high surface charge. Furthermore, the electro-osmotic mobility increases nonlinearly with the total surface charge; however, the increase in this mobility is considerably suppressed because the counterion condensation occurs at higher surface charge.…”

“…These transient EOF behaviors were also observed in a microchannel containing an electrolyte solution. 13,14,19 When the steady state is reached, however, even at higher Q the fluid velocity distribution strongly deviates from the typical plug-like flow pattern observed in an electrolyte solution. This result is expected since the shape of steady-state EOF is only determined by the electric potential difference field, which exhibits a completely different behavior on Q as compared with that observed in an electrolyte solution ͑see Fig.…”

“…Note that the counterions are distributed so that the electroneutrality of the whole system is satisfied. Because the time scale related to electromigration in the electric double layer ͑EDL͒, which is of order 10 −8 -10 −7 s, 20 is at least two orders smaller than that associated with the evolution of EOF, which is of order 10 −5 -10 −3 s, 13,14 the transient effect of the EDL can then be neglected and the local volumetric charge density e ͑r͒ can be described by the Poisson equation 21 1 r…”

“…However, in practical situation, the efficiency of electrophoretic separation in an electrolyte solution has been observed to strongly depend on the duration of sample injection, 11 which in turn is related to the unsteady electro-osmotic flow ͑EOF͒ field. [12][13][14] Further, the cylindrical capillary has been widely used in biological chips such as micropumps, 15 capillary electrophoretic devices for separation of proteins, 16 and coaxial jet mixing devices used in chemical analysis and biomedical diagnostics. 17,18 Therefore, it is necessary to study the transient response of EOF in a cylindrical microcapillary containing a salt-free medium.…”

Transient electroosmotic flow of general Maxwell fluids through a slit microchannel

“…Recently, time-dependent EOF has been attracting growing attention as an alternative mechanism of microfluidic transport [11][12][13][14][15][16][17]. All the papers indicated above deal with Newtonian fluids.…”