Hydrodynamic dispersion due to combined pressure-driven and electroosmotic flow through microchannels with a thin double layer.

Abstract

The hydrodynamic dispersion of a nonadsorbed and nonelectrolyte solute is considered for the case of a flow driven through a straight microchannel by pressure and electric potential differences. The analysis is conducted using a thin double layer approximation developed in the previous paper (Zholkovskij, E. K.; Masliyah, J. H.; Czarnecki, J. Anal. Chem. 2003, 75, 901-909). On the basis of this approach, an expression is derived to address the dispersion coefficient for arbitrary electrokinetic potential, electrolyte type, and cross-section geometry. In the derived expression, the influence of cross-section geometry manifests itself through the channel hydrodynamic radius and through three dimensionless geometrical factors. The procedure for obtaining the geometrical factors is presented for an arbitrary cross-section geometry. The geometrical factors are evaluated for several examples of cross section: (i) unbounded parallel planes; (ii) circle; (iii) annulus; (iv) ellipse; (v) rectangle. The dependency of the dispersion coefficient on different parameters is discussed. It is shown that the dependencies are substantially affected by the cross-section geometry, electrolyte type, and electrokinetic potential.