Measurement of electroosmotic and electrophoretic velocities using pulsed and sinusoidal electric fields

Abstract

In this work, we explore two methods to simultaneously measure the electroosmotic mobility in microchannels and the electrophoretic mobility of micron‐sized tracer particles. The first method is based on imposing a pulsed electric field, which allows to isolate electrophoresis and electroosmosis at the startup and shutdown of the pulse, respectively. In the second method, a sinusoidal electric field is generated and the mobilities are found by minimizing the difference between the measured velocity of tracer particles and the velocity computed from an analytical expression. Both methods produced consistent results using polydimethylsiloxane microchannels and polystyrene micro‐particles, provided that the temporal resolution of the particle tracking velocimetry technique used to compute the velocity of the tracer particles is fast enough to resolve the diffusion time‐scale based on the characteristic channel length scale. Additionally, we present results with the pulse method for viscoelastic fluids, which show a more complex transient response with significant velocity overshoots and undershoots after the start and the end of the applied electric pulse, respectively.

Electroosmotic flow of non‐Newtonian fluids in a constriction microchannel

“…This is surprising considering the fact that the viscosities of the two viscoelastic solutions are both significantly larger than that of the buffer solution (Table ). One potential reason is the polymer‐induced variation of zeta potential , and another is the formation of near‐wall polymer‐depleted skimming layer .…”

Measurement of the amplitude and phase of the electrophoretic and electroosmotic mobility based on fast single‐particle tracking

“…In this work, we have carried out accurate measurements of the electrophoretic mobility of individual microparticles by measuring particles in the middle of a microchannel and applying an AC electric field of a high frequency such that EO can be ignored. Similar methods can be found in the literature with distinct advantages and disadvantages, including that developed by Sadek [ 7 ], Ikeda [ 10 ], or more extensive approaches such as the one presented by Oddy and Santigo [ 8 ] in which probability density functions for particle mobilities are reported. Despite sharing some underlying principles, the advantage of our approach is that a single measurement (at a single AC frequency) is sufficient to obtain an accurate value of the electrophoretic mobility including phase information.…”

“…However, only the absolute values of mobilities are measured (neglecting the sign of the electrophoretic particle mobility) because phase information is discarded. Alternatively, in [7], Sadek et al. use a similar method that relies on fitting theory to data obtained at three frequencies to obtain and , as well as a pulsed‐ field approach.…”

“…Other techniques focus on electrophoretic measurements on a particle‐to‐particle basis, either based on optical detection with a camera [ 7 , 8 , 9 , 10 , 11 ], employing optical trapping [ 12 , 13 ], or more advanced laser scanning systems [ 14 ]. The advantage of a single‐particle measurements is that polydisperse samples can be measured accurately and that detailed phenomena, for example, single charging events [ 11 ] or single binding events can be observed.…”

Effect of skimming layer in an electroosmotically driven viscoelastic fluid flow over charge modulated walls

“…These devices need accurate flow control for the effective transport of fluids, which requires efficient flow driving mechanics in the miniaturized scale. The advantages of electrically driven flows make it a lucrative method to adopt for species transport in microfluidic devices [5–8]. Electrically driven flow takes advantage of the electro‐kinetic phenomenon, and the process of driving fluid is commonly known as electroosmosis.…”