4 research outputs found
Electroosmotic flow reversal outside glass nanopores.
We report observations of a striking reversal in the direction of electroosmotic flow (EOF) outside a conical glass nanopore as a function of salt concentration. At high ionic strengths (>100 mM), we observe EOF in the expected direction as predicted by classical electrokinetic theory, while at low salt concentrations (<1 mM) the direction of the flow is reversed. The critical crossover salt concentration depends on the pore diameter. Finite-element simulations indicate a competition between the EOF generated from the inner and outer walls of the pore, which drives flows in opposite directions. We have developed a simple analytical model which reveals that, as the salt concentration is reduced, the flow rates inside the pore are geometrically constrained, whereas there is no such limit for flows outside the pore. This model captures all of the essential physics of the system and explains the observed data, highlighting the key role the external environment plays in determining the overall electroosmotic behavior
A Landau-Squire nanojet
Fluid jets are found in nature at all length scales, from microscopic to
cosmological. Here we report on an electroosmotically driven jet from a single
glass nanopore about 75 nm in radius with a maximum flow rate ~15 pL/s. A novel
anemometry technique allows us to map out the vorticity and velocity fields
that show excellent agreement with the classical Landau-Squire solution of the
Navier Stokes equations for a point jet. We observe a phenomenon that we call
flow rectification: an asymmetry in the flow rate with respect to voltage
reversal. Such a nanojet could potentially find applications in
micromanipulation, nanopatterning, and as a diode in microfluidic circuits.Comment: 20 pages, 4 figure
A Landau–Squire Nanojet
Fluid jets are found in nature at
all length scales from microscopic to cosmological. Here we report
on an electroosmotically driven jet from a single glass nanopore about
75 nm in radius with a maximum flow rate ∼15 pL/s. A novel
anemometry technique allows us to map out the vorticity and velocity
fields that show excellent agreement with the classical Landau–Squire
solution of the Navier–Stokes equations for a point jet. We
observe a phenomenon that we call flow rectification: an asymmetry
in the flow rate with respect to voltage reversal. Such a nanojet
could potentially find applications in micromanipulation, nanopatterning,
and as a diode in microfluidic circuits