Field‐Unmasked Surface Charge Enables Programmable Nanofluidics

ABSTRACT A central challenge in the development of programmable nanofluidic devices lies in achieving dynamic control over surface charge density, which governs ionic conductance at the nanoscale. A prevailing view in electrokinetics is that the surface charge density remains invariant under axial electric fields of varying magnitudes. Here, we report a mechanism by which axial electric fields actively reshape interfacial charge in nanofluidic systems through field‐driven detrapping of wall‐bound counterions, exposing additional surface charges. This reversible unmasking of hidden charges triggers large, real‐time modulations in electroosmotic conductance, far exceeding classical electrokinetic expectations. By accounting for the discrete origin of the charge sites on ionizable surfaces, we demonstrate the field‐coupled nature of the ion‐site equilibria. A modified Smoluchowski–Langevin framework quantitatively captures this emergent behavior. Experiments on silicon nitride nanopores confirm the field‐dependent modulation of ionic conductance, while all‐atom non‐equilibrium molecular dynamics reveal the underlying coupling between solvent structuring, ion adsorption, and surface heterogeneity. By overturning the long‐held view of surface charge as a static property, our findings establish field‐programmable nanofluidics as a powerful strategy for dynamic control of ionic transport, without chemical modification or complex nanofabrication.