Method to determine the effective ζ potential in a microchannel with an embedded gate electrode

Abstract

We present a theoretical model to determine the effective zeta potential ζ(eff) in microfluidic channels where an embedded, insulated gate electrode allows for external tuning of a portion of the channel surface charge. In addition, we derive a method to determine ζ(eff) in such channels, for any value of salt concentration, using the solution displacement technique. To do so, we simulate typical current-monitoring measurements using our model, and highlight the experimental parameters that lead to inaccurate results using this procedure with an heterogenous channel. Our method corrects for such inaccuracies by using our model with experimental data to find the correct value of ζ(eff) . Finally, we perform experiments to demonstrate our method and the use of our model with a silica-PMDS microchannel system with an embedded Ti-Au-Ti gate electrode that covers 50% of the bottom surface of the channel. We show that our theory captures the salient features of our experiments, thereby offering a useful tool to predict effective zeta potential in channels with a nonuniform zeta potential.

Ion Correlations in Nanofluidic Channels: Effects of Ion Size, Valence, and Concentration on Voltage- and Pressure-Driven Currents

“…These parameters were chosen to encompass the values of real devices (e.g., the use of trivalent ions by van der Heyden et. al 7 and high surface charges in electrode-embedded devices 30,31 ).…”

“…The calculations were performed for nanoslit devices with a height of 50 or 100 nm, a length of 5 mm, and a width of 50 μm. These parameters were chosen to encompass the values of real devices (e.g., the use of trivalent ions by van der Heyden et al and high surface charges in electrode-embedded devices , ).…”

Ionic Origin of Electro-osmotic Flow Hysteresis

“…Previous investigations on EOF involving solutions with different concentrations 19 20 21 22 only focus on the behavior of the main constituent ionic species (such as K + and Cl − ions in KCl solutions) and fail to capture the main effect of EOF hysteresis. Similarly, the conventional analyses of EOF in microchannel with heterogeneous zeta potential 23 24 only consider the distribution of main constituent ionic species.…”

Electroosmotic shear flow in microchannels

“…However, the PB coated glass carries not the expected positive charge as measured in a fully coated channel: þ18 AE 4 mC=m 2 (to determine the surface charge in this channel we used the solution displacement method [18,29]). Actually it carries only a less negative charge compared to the bare glass, because the PB coated glass slides were rinsed in DI water such that most of the PB was washed away.…”

“…For most materials the intrinsic zeta potential is negative, but it can be decreased or even reversed to positive by coating the channel wall with a cationic polymer. This technique was first introduced in capillary electrophoresis to improve protein analyses [14] and is applied by several other authors [15][16][17][18][19]. Stroock et al calculated, and verified experimentally, the flow profile in microchannels with oppositely charged surfaces [20].…”