Electroosmotic shear flow in microchannels

Abstract

We generate and study electroosmotic shear flow in microchannels. By chemically or electrically modifying the surface potential of the channel walls a shear flow component with controllable velocity gradient can be added to the electroosmotic flow caused by double layer effects at the channel walls. Chemical modification is obtained by treating the channel wall with a cationic polymer. In case of electric modification, we used gate electrodes embedded in the channel wall. By applying a voltage to the gate electrode, the zeta potential can be varied and a controllable, uniform shear stress can be applied to the liquid in the channel. The strength of the shear stress depends on both the gate voltage and the applied field which drives the electroosmotic shear flow. Although the stress range is still limited, such a microchannel device can be used in principle as an in situ micro-rheometer for lab on a chip purposes.

Electrokinetic Control of Bacterial Deposition and Transport

“…The shear forces F HF and F EOF 4,21 acting on a bacterium located at h s were calculated from the shear rates (σ), 22 induced by the velocity of hydraulic (υ HF ) and the electroosmotic (υ EOF ) water flow using…”

“…The shear forces F HF and F EOF , acting on a bacterium located at h s were calculated from the shear rates (σ), induced by the velocity of hydraulic (υ HF ) and the electroosmotic (υ EOF ) water flow using F H F , h s = σ H F , h s * η * A b / 2 = υ H F , h h s * η * A b / 2 and F E O F , h s = σ E O F , h s * η * A b / 2 = υ E O F , h h s * η * A b / 2 where η is the viscosity of the liquid (η = 3.19 kg m –1 h –1 ), and A b /2 ( A b /2 = 6.3 × 10 –12 m 2 ) is the effective surface of the adhered bacterium, i.e. assuming that half of the cell surface area is subject to the shear flow.…”

Capillary electrophoresis analysis of different variants of the amyloidogenic protein β2‐microglobulin as a simple tool for misfolding and stability studies

“…The identification of the precise factor that, along the electrophoretic separation, promotes the misfolding of variant is extremely difficult. The magnitude of the electroosmotic shear flow must be negligible under these conditions ; however, we can speculate that a nonzero shear component may well exist and contribute, in this particular case, to exert a misfolding effect on the protein molecules, over the migration time window inside the capillary. Finally, the role that protein interaction with hydrophilic surfaces such as an array of negative charges may have in conformational rearrangements should not be overlooked, as recently reported for wtβ 2 ‐m .…”

Generalized Taylor dispersion for translationally invariant microfluidic systems

“…In the absence of potential difference, the flow is nearly constant at distances greater than the Debye length from the surface and is referred to as a plug flow. Differing zeta potentials can be generated by using different or treated surfaces [32]. If we assume that the electrolyte can be treated in the weak coupling regime where βqφ is sufficiently small (and so in particular the surface potential is weak), the Poisson-Boltzmann equation can be linearized giving the Debye-Hückel approximation…”