Ionic Transport Behavior of Soft Nanochannels for Newtonian and Non-Newtonian Electrolytes

With the rapid progress in micro/nanofluidics, understanding the fundamental mechanisms of ionic transport, fluid behavior, and microsystem dynamics is more crucial than ever. Given the substantial expenses associated with manufacturing such systems, computational simulations offer a cost-effective avenue for advancing this industry sector while minimizing financial burdens. In this context, the current study explores the impact of electrolyte characteristics by numerically analyzing electroosmotic flow (EOF) in a conical nanochannel featuring charged slippery surfaces coated with a polyelectrolyte layer. Two types of electrolytic fluids, namely, water (representing a Newtonian fluid) and blood plasma (representing a non-Newtonian fluid), were investigated. The behavior of non-Newtonian electrolytes was modeled using the Bingham–Papanastasiou model. The governing equations of this nonlinear model, namely, the Poisson–Nernst–Planck and Navier–Stokes equations, were solved using the finite element method. Various parameters including slip length, surface charge density, soft layer charge density, and electrolyte concentration were systematically adjusted to assess three key aspects: EOF, ionic selectivity, and current rectification. The findings revealed that increasing the slip length significantly enhanced the EOF for both types of electrolytes. For instance, the EOF for platelets within the nanochannel core increased by 1.5 times with a slip length extension from 0 to 10 nm. Additionally, applying a positive voltage to the nanochannel amplified the EOF, particularly when the wall and soft layer charges were similar. For example, decreasing the wall charge density from 0 to −0.02 C/m2 while applying a positive voltage led to a 1.5-fold increase in platelet EOF, rising from 0.028 to 0.042 m/s.