Electrokinetic ion transport and liquid flux across<br/><br/>nanochannels

Wednesday, December 9, 2009 - 3:20pm - 4:00pm
EE/CS 3-180
Hsueh-Chia Chang (University of Notre Dame)
Keywords: electrokinetics, nanoscience, limiting current, Donnan potential, ion selectivity, Warburg Impedance

Abstract: With the advent of nanofabrication technologies,
nano-channels with dimensions smaller than the Debye screening
layer can now be fabricated to allow scrutiny of the various
anomalous DC and AC I-V characteristics of ion-selective
membranes at the single-pore level — such knowledge is
essential for rapid DNA sequencing, single-molecule
sensing/identification and plasmonic imaging in nanoscience.
Combining theoretical analyses of the underlying ion/solvent
fluxes and confocal imaging of velocity and ion concentration
fields, we explore the fundamental mechanisms behind non-ideal
selectivity, Donnan potential, asymmetric depletion/enrichment
layer formation, limiting and overlimiting-current, diode-like
rectification, Warburg impedance response, inter-channel
communication etc. Curiously, hydrodynamic effects at the
depletion end of the channel is found to control many of the
non-Ohmic behavior at higher voltages. Interfacial vortices
created by an osmotic pressure driven instability (first
predicted by I. Rubinstein) and induced charges at the corners
of nanopores are found to specify the overlimiting current, the
rectification factor and inter-pore communication. The
intensity of these vortices and their influence on the
ion-carried currents are found to be strongly dependent on the
pore/reservoir geometries and can be described by limiting
fundamental solutions of the Laplace and Stokes equations due
to severe electric and flow field focusing into the
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