Ionic current rectification properties of power-law fluids in a nanochannel with non-uniform surface charge density

The exploration of ion transport properties in nanochannels with non-uniform surface charge density is imperative to enhance comprehension of the ionic current rectification phenomenon and to broaden the implementation of the rectification effect. However, the majority of research in this domain is confined to Newtonian fluids. In this study, the Poisson–Nernst–Planck equation is employed to address the electro-osmotic flow of power-law fluids in a nanochannel. The impact of the charging conditions of the nanochannel wall and the fluid properties on the ion concentration, ionic current, and velocity is investigated through numerical simulations. It is observed that when the length of the high surface charge density wall is increased from 10 to 40 nm, the ratio of the maximum to minimum concentrations on the central axis increases from 5.5 to 9.1. An increase in the power-law index, from 0.9 to 0.95, results in a 45% rise in the maximum total ion concentration along the central axis. In addition, both decreasing the low surface charge density and increasing the power-law index can effectively improve the rectification ratio of the nanochannel with non-uniform surface charge density. Specifically, a 38% enhancement in the ionic current rectification ratio (CRR) is observed when the low surface charge density is reduced from −5 to −1.7 mC/m2. Furthermore, a 42% increase in the CRR is attained by increasing the power-law index from 0.9 to 1.0.