Joule heating in nanofluidic membranes: Influence of soft surface layer charge distribution and implications for ion selectivity, ionic current rectification and electroosmotic flow

Nanofluidic systems hold promise for applications in water purification, energy conversion, and molecular sensing, yet Joule heating often limits their performance. This study numerically investigates how the charge distribution within polyelectrolyte layers (PEL) on cylindrical nanochannel walls influences thermal dissipation and key electrokinetic properties. Three configurations: unipolar, bipolar, and tripolar, are examined using coupled Poisson–Nernst–Planck, Navier–Stokes, and energy equations under steady-state conditions. The results evidence that bipolar nanochannels exhibit superior thermal management compared to unipolar and tripolar configurations. Specifically, at an electrolyte concentration ratio ${\lambda }_c=100$ across the channel and for an applied lateral voltage $V_{\text{app}}=5V$, Joule heating in bipolar nanochannels was 523 nW, a 22.5% reduction compared to the 675 nW obtained for both unipolar and tripolar cases. Given that Joule heating values exceeding 500 nW are substantial in nanofluidic systems, this reduction highlights the effectiveness of bipolar nanochannels in mitigating thermal dissipation. Furthermore, bipolar nanochannels enhanced EOF velocity, achieving a maximum value of 9.83 × 10⁻³ m/s at ${\lambda }_c=10$, which significantly exceeds the performance of unipolar and tripolar designs with maximum EOF velocities of 2.39 × 10⁻³ m/s and 2.85 × 10⁻³ m/s, respectively. This is attributed to the bipolar configuration’s ability to better regulate internal electric fields and enhance ion mobility. Bipolar nanochannels further exhibited superior ionic current rectification, making them suitable for applications in ionic transistors and nanofluidic diodes. These findings suggest that bipolar charge modulation offers an effective strategy for mitigating thermal effects and optimizing nanofluidic device performance. This study contributes to the rational design of energy-efficient nanofluidic membranes for desalination, ionic gating, and related technologies.