Ionic dispersion in nanofluidics

Abstract

An analytical solution for dispersion of ionic and neutral solutes in nanoscale channels is presented. Results suggest that in the presence of relatively thick electrical double layers (EDLs) characteristic of nanofluidics, the dispersion of ionic solutes differs from that of neutral solutes on which previous theory is based. Ionic dispersion for circular cross-section channels is quantified as a function of a valance parameter, the relative EDL thickness, and the form of the velocity profile. Two unique mechanisms governing ionic dispersion in both pressure- and electrokinetically driven flows are identified. The results of the analytical solution, employing the linearized form of the Poisson-Boltzmann equation, are supported and extended by the results of an independent computational model employing the nonlinear Poisson-Boltzmann equation. Applicability of the computational results is not limited by the Debye-Hückel approximation. Collectively, these results indicate that dispersion of ionic species in nanoscale channels is markedly charge dependent, and substantially deviates from that of neutral solutes in the same flow.

Effects of Stern layer conductance on electrokinetic energy conversion in nanofluidic channels

“…It is important to note that for a given fluid and channel combination, z will, in general, vary with the nondimensional channel height K = kh. One option to address this is to use a surface-charge based potential parameter for scaling instead of zeta potential [13,16,17,32]. In this work and other studies [3, 4, 9-12, 15, 21, 26, 27, 33, 34], the zeta potential is used directly, as it may be readily determined through experiment and provides a direct measure of the electroosmotic mobility.…”

Dispersion of charged tracers in charged porous media

“…Thus the corresponding components reduce to the same components of the diffusion tensor. If the tracers can explore the whole slit section, the dispersion factor can be expressed as [12] f (αL, q) = − (10b) where the deviation from the average velocity g q (ξ) = [u y (ξ) + βDqE y − v y,q ]/u ref depends on both the charge q of the tracer and αL via the local velocity u y .…”

Dispersion of protein bands in a horseshoe microchannel during IEF

“…However, in a microfluidic chip, Joule heating is not a major source of dispersion because of the large channel surface-tovolume ratio [23]. Dispersion due to extended double-layers can be very high in a nanofluidic application [20], but its contribution will be negligible in the case of a microfluidic channel (10-100 mm) [18]. However, dispersion due to complex channel shapes is very important in all devices, especially in an integrated lab-on-a-chip device because multi-dimensional separations require complex geometries.…”

“…The primary sources of solute band dispersions are Joule heating [19], extended electric double-layers [20] and complex channel shapes such as dog legs [15] or cross-channels [12]. In a traditional, large-scale separation, Joule heating effect cannot be neglected because high voltages induce nonuniform temperature in a separation channel [21,22].…”