Electroosmotic Flow of Viscoelastic Fluid in a Nanochannel Connecting Two Reservoirs

Abstract

: Electroosmotic flow (EOF) of viscoelastic fluid with Linear Phan-Thien-Tanner (LPTT) constitutive model in a nanochannel connecting two reservoirs is numerically studied. For the first time, the influence of viscoelasticity on the EOF and the ionic conductance in the micro-nanofluidic interconnect system, with consideration of the electrical double layers (EDLs), is investigated. Regardless of the bulk salt concentration, significant enhancement of the flow rate is observed for viscoelastic fluid compared to the Newtonian fluid, due to the shear thinning effect. An increase in the ionic conductance of the nanochannel occurs for the viscoelastic fluid. The enhancement of the ionic conductance is significant under the overlapping EDLs condition.

Keywords: electrical double layer; electroosmotic flow; ionic conductance; nanofluidics; viscoelastic fluid.

Figure 1

Schematic diagram of a nanochannel connecting two reservoirs at both ends. Uniform negative surface charges are distributed on the nanochannel wall and the adjacent walls of reservoirs. An external electric field is applied by a potential bias between the inlet (Anode) and outlet (Cathode).

Figure 2

Distribution of the dimensionless axial velocity at the center of the nanochannel for bulk salt concentrations C₀ = 0.5 mM, 5 mM, and 50 mM: symbols (OpenFOAM) and lines (Comsol).

Figure 3

Variation of volume flow rate with the Weissenberg number for bulk concentration C₀ = 0.5 mM, 5 mM, and 50 mM.

Figure 4

Variation of ionic conductance with Weissenberg number for C₀ = 0.5 mM, 5 mM, and 50 mM.

Figure 5

Percentage of the convective and migrative ionic conductance components for Newtonian and viscoelastic fluids of Wi = 200 for C₀ = 0.5 mM, 5 mM, and 50 mM, respectively. For clarity, the percentage of the components for viscoelastic fluid is shown with respect to the Newtonian fluid under the same bulk salt concentration. Thus, the total height for viscoelastic fluid becomes 127%, 120%, and 103% for C₀ = 0.5 mM, 5 mM, and 50 mM, respectively.

Figure 6

The variation of $\frac{\mathbf{\partial }{\varnothing }^{\prime }}{\mathbf{\partial }{\mathit{y}}^{\prime }}$ along the symmetry axis of the nanochannel for C₀ = 0.5 mM.