Viscoelectric effect on the chemiosmotic flow in charged soft nanochannels

Abstract

The charged nanochannel surface and pH-sensitive grafted polyelectrolyte layer (PEL) play a critical role in the design of devices aimed at controlling nanofludic flow. They enable the manipulation of ionic transport by influencing the electric-double (EDL) layers that overlap. Additionally, the viscoelectric effect, amplified by a strong EDL electric field, may enhance the activation energy and viscosity of liquids. Motivated by this, we conducted a numerical investigation using a finite element method-based solver, COMSOL, to examine the effects of the viscoelectric effect on concentration-gradient-driven chemiosmotic flow in a charged soft nanochannel with grafted pH-sensitive polyelectrolyte layer on the inner wall surfaces. It is important to note that the nanochannel is positioned between two reservoirs with different pH values and bulk-ionic concentrations. The PEL is sensitive to protonic association–dissociation due to the presence of carboxylic and amine groups in monomeric units. In our study, we comprehensively demonstrate variations in key variables characterizing the underlying flow. These variations include changing the solute concentration in the left side reservoir within the range of 0.1–5 mol m−3, adjusting the pH of the right-side reservoir (pHR) within the range of 3–10, and varying the viscoelectric coefficient. The viscoelectric effect significantly raises viscosity near the wall due to the stronger EDL electric field generated at the left-side reservoir resulting from the higher solute concentration. On the other hand, viscosity tends to decrease with lower pHR values and remains unaffected by changes at higher pHR values. The average flow velocity shows an increasing–decreasing pattern as the concentration of the right-side reservoir is enhanced. Additionally, the decrease in flow velocity becomes noticeably more pronounced with higher solute concentrations in the right-side reservoir when accounting for the viscoelectric effect. The findings of the present study have practical implications for novel nanofluidic devices, frequently employed in various engineering applications to control flow.