The electroosmotic flow (EOF) of viscoelastic fluid in a long nanoslit is numerically studied to investigate the rheological property effect of Linear Phan-Thien-Tanner (LPTT) fluid on the fully developed EOF. The non-linear Poisson-Nernst-Planck equations governing the electric potential and the ionic concentration distribution within the channel are adopted to take into account the effect of the electrical double layer (EDL), including the EDL overlap. When the EDL is not overlapped, the velocity profiles for both Newtonian and viscoelastic fluids are plug-like and increase sharply near the charged wall. The velocity profile resembles that of pressure-driven flow when the EDL is overlapped. Regardless of the EDL thickness, apparent increase of velocity is obtained for viscoelastic fluid of larger Weissenberg number compared to the Newtonian fluid, indicating the shear thinning behavior of the LPTT fluid. The effect of the Weissenberg number on the velocity distribution is less significant as the degree of EDL overlapping increases, due to the overall decrease of the shear rate. The increase (decrease) of polymer extensibility (viscosity ratio) also enhances the EOF of viscoelastic fluid.
Keywords: Linear Phan-Thien-Tanner (LPTT) model; electrical double layer; electroosmotic flow; nanoslit; viscoelastic fluid.