Nanochannel Electroosmosis: Debye Layer Overlap & Ion Selectivity

This simulator solves the linearized Poisson–Boltzmann and Stokes-flow equations for a slit nanochannel between two charged walls, then renders the result as a live 3D particle field. Cations and anions are placed with Boltzmann-weighted density across the channel height and drift along the channel at the local electroosmotic velocity u(y) — so as you shrink the channel or dilute the electrolyte, you can watch the electric double layers on each wall grow until they physically overlap: the flat "plug" flow of a wide, high-salt channel collapses into a slower, parabolic-like profile, and the channel becomes visibly ion-selective as co-ions are expelled from the entire cross-section. This double-layer-overlap regime is exactly what separates nanofluidics from microfluidics, and underlies real devices such as nanofluidic diodes and ion-current-rectifying pores.