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Hierarchical Multiscale Simulation of Electrokinetic Transport in Silica Nanochannels at the Point of Zero Charge

Summary: Hierarchical Multiscale Simulation of Electrokinetic Transport in
Silica Nanochannels at the Point of Zero Charge
Sony Joseph and N. R. Aluru*
Department of Mechanical Science and Engineering, Beckman Institute for AdVanced Science and
Technology, UniVersity of Illinois at Urbana-Champaign, Urbana, Illinois 61801
ReceiVed April 13, 2006. In Final Form: August 6, 2006
Effects of nanoscale confinement and partial charges that stem from quantum calculations are investigated in silica
slit channels filled with 1 M KCl at the point of zero charge by using a hierarchical multiscale simulation methodology.
Partial charges of both bulk and surface atoms from ab initio quantum calculations that take into account bond
polarization and electronegativity are used in molecular dynamics (MD) simulations to obtain ion and water concentration
profiles for channel widths of 1.1, 2.1, 2.75, and 4.1 nm. The interfacial electron density profiles of simulations matched
well with that of recent X-ray reflectivity experiments. By simulating corresponding channels with no partial charges,
it was observed that the partial charges affect the concentration profiles and transport properties such as diffusion
coefficients and mobilities up to a distance of about 3 O-O from the surface. Both in uncharged and partially charged
cases, oscillations in concentration profiles of K+ and Cl- ions give rise to an electro-osmotic flow in the presence
of an external electric field, indicating the presence of an electric double layer at net zero surface charge, contrary
to the expectations from classical continuum theory. I-V curves in a channel-bath system using ionic mobilities from
MD simulations were significantly different for channels with and without partial charges for channel widths less than
4.1 nm.
I. Introduction


Source: Aluru, Narayana R. - Department of Mechanical and Industrial Engineering, University of Illinois at Urbana-Champaign


Collections: Engineering; Materials Science