Migration Mechanism Regulated by the Coupling between Ions and Charged Nanoparticles in Janus Nanochannels

Charged nanoparticle migration through asymmetric nanochannels is important for particle separation, nanoscale drug delivery, and nanofluidic regulation. However, in electrolyte solutions, particle transport is governed not only by the applied electric field or fixed channel charges but also by local ion distributions, particle counterion clouds, and electro-osmotic responses. Here, a Janus nanochannel model was constructed, and molecular dynamics simulations investigated the translocation of positively charged nanoparticles through an asymmetric fixed-charge channel. Increasing the positive charge at the right end increased particle residence time near the Janus interface and positively charged gating region, promoted counterion enrichment around the particle, and weakened local water flow assistance. Increasing the salt concentration enhanced particle-local counterion enrichment and altered gating-region charge compensation; the associated nonmonotonic migration response is consistent with competition between these effects. A stronger applied electric field accelerated translocation and reduced particle-local counterion screening but did not eliminate the retardation effect of the right-half gating region. Particle-free channel simulations further revealed ion enrichment and spatially nonuniform ion and water transport near the fixed-charge polarity transition. These results suggest that fixed-charge gating, particle-local screening, gating-region charge compensation, and local electro-osmotic response jointly influence charged particle migration in Janus nanochannels.