Charge localization, rectification, and transport in electrolyte patchy nanochannels

We study ionic charge localization and transport in electrolyte-filled nanochannels with heterogeneous walls. Localized charged patches at the channel boundaries trap counterions, enabling controlled charge accumulation in otherwise straight channels. Combining lattice-Boltzmann simulations with analytical modeling, we show that the stability and mobility of these charge clouds result from a balance between electrostatic forces, hydrodynamic drag, and diffusion. Under applied electric fields and pressure gradients, localized charge produces diode-like rectification. Pressure-driven flow shifts the dissociation threshold of the counterion cloud, yielding strongly asymmetric current-voltage characteristics. A minimal force-balance model quantitatively captures the rectification window and its linear dependence on the pressure gradient, demonstrating rectification in the absence of geometric asymmetry. We further examine dynamic control using moving wall patches. In the linear electrostatic regime, charge responds diffusively to patch motion, while strong wall potentials induce a strong colocalization and active charge transport. We identify drift- and diffusion-dominated transport regimes and a critical patch velocity beyond which charge localization fails. These results establish patchy wall potentials as a minimal mechanism for controlling ionic localization, rectification, and transport in nanochannels.