  Recent experimental work has suggested that electroosmotic flows (EOF)
through conical nanopores exhibit rectification in the opposite sense to the
well-studied effect of ionic current rectification. A positive bias voltage
generates large EOF and small current, while negative voltages generate small
EOF and large current. Here we systematically investigate this effect using
finite-element simulations. We find that inside the pore, the electric field
and salt concentration are inversely correlated, which leads to the inverse
relationship between the magnitudes of EOF and current. Rectification occurs
when the pore is driven into states characterized by different salt
concentrations depending on the sign of the voltage. The mechanism responsible
for this behaviour is concentration polarization, which requires the pore to
exhibit the properties of permselectivity and asymmetry.
