 
Summary: Ion concentrations and velocity profiles in nanochannel
electroosmotic flows
R. Qiao and N. R. Alurua)
Beckman Institute for Advanced Science and Technology, University of Illinois at UrbanaChampaign,
Urbana, Illinois 61801
Received 12 August 2002; accepted 11 December 2002
Ion distributions and velocity profiles for electroosmotic flow in nanochannels of different widths
are studied in this paper using molecular dynamics and continuum theory. For the various channel
widths studied in this paper, the ion distribution near the channel wall is strongly influenced by the
finite size of the ions and the discreteness of the solvent molecules. The classical Poisson
Boltzmann equation fails to predict the ion distribution near the channel wall as it does not account
for the molecular aspects of the ionwall and ionsolvent interactions. A modified Poisson
Boltzmann equation based on electrochemical potential correction is introduced to account for
ionwall and ionsolvent interactions. The electrochemical potential correction term is extracted
from the ion distribution in a smaller channel using molecular dynamics. Using the electrochemical
potential correction term extracted from molecular dynamics MD simulation of electroosmotic
flow in a 2.22 nm channel, the modified PoissonBoltzmann equation predicts the ion distribution
in larger channel widths e.g., 3.49 and 10.00 nm with good accuracy. Detailed studies on the
velocity profile in electroosmotic flow indicate that the continuum flow theory can be used to
predict bulk fluid flow in channels as small as 2.22 nm provided that the viscosity variation near the
