Electroosmotic transport and current rectification of viscoelastic electrolyte in a conical pore nanomembrane

Abstract

Nanomembranes have received a wide range of applications in water treatment, gas separation, molecular and supramolecular separations. Nanopores offer the separation of the components even at nano- or picomolar concentrations. In addition, DNA translocation, DNA sequencing of nucleotides, single molecular analyses for biomedical nanoscopic devices are perhaps the unique feature of nanomembranes that convectional membranes may not achieve. Despite such an overwhelming application, the theoretical understanding of electroosmotic transport in nanopores is still in infancy and it is limited to simple Newtonian-like fluids. This work has numerically investigated the ionic current rectification (ICR) in a conical nanopore filled with viscoelastic electrolyte. ICR quantifies the unequal upstream and downstream ionic flow rates during the forward and reverse potential bias. This is similar to a semiconductor transistor's current potential (I−V) response. The ICR exhibits several potential applications in the design of biosensors for the measurement and analysis of biofluids such as blood, lymph, and plasma, micro-scale pumping devices, ion-selective membranes, etc. The electroosmotic flow (EOF) in the conical nanopore of Carreau fluid is investigated by solving a set of Poisson, Nernst–Planck, and momentum equations to account for the electric potential, transport of ionic species, and velocity field. The behaviors of ICR in Carreau fluid are examined by varying the shear-thinning index (0.6≤n≤1), Debye length (1≤κRt≤50), Deborah number (1≤De≤100), and applied electric potential (−50≤V≤50). The electroosmotic flow is observed to be significantly stronger in shear-thinning fluids. All else being equal, the volumetric flow rate increases several folds in shear-thinning fluids. Shear-thinning fluid behavior enhances the magnitude of the current in the conical nanopore.