Ionic Transport and Selectivity of Electrokinetically-Actuated Non-Newtonian Flows within a pH-Regulated Rectangular Nanochannel.
2021
In the present study, the ionic transport and selectivity of
electrokinetically-driven flow of power-law fluids in a long pH-regulated
rectangular nanochannel are analyzed. The electrical potential and momentum
equations are numerically solved through a finite difference procedure for a
non-uniform grid. Non-linear Poisson-Boltzmann equation along with the
association/dissociation reactions on the surface is considered. In addition,
numerical simulations with the finite element method in 3D space are performed
to compare the results with those obtained from 2D analysis. Moreover, an
analytical solution under Debye-H\"uckel approximation for the limiting case of
a slit nanochannel is derived and its results are compared with those obtained
from numerical simulations. It is shown that the channel aspect ratio can
influence all the physicochemical parameters. It is observed that the mean
velocity and the convective ionic conductance are strong descending functions
of the flow behavior index. By investigating the non-Newtonian fluid behavior
effect, it is revealed that its impact on the ionic conductance becomes
significant at high values of the solution pH and its variation can alter the
anionic transport direction inside the nanochannel. Moreover, it is shown the
flow behavior index can strongly influence the ion selectivity of the
nanochannel and its variation can be used to let the selectivity go through its
maximum as a function of pH.
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