Field-Unmasked Surface Charge Enables Programmable Nanofluidics

Area of Science:

• Nanofluidics
• Surface Chemistry
• Electrokinetics

Background:

• Dynamic control of surface charge density is crucial for programmable nanofluidic devices.
• Current electrokinetics theory assumes surface charge is invariant under axial electric fields.

Purpose of the Study:

• To investigate a mechanism for dynamic surface charge modulation in nanofluidic systems using axial electric fields.
• To demonstrate real-time control over ionic conductance in nanofluidics.

Main Methods:

• Developed a modified Smoluchowski-Langevin framework to model ion-site equilibria.
• Conducted experiments on silicon nitride nanopores to measure ionic conductance.
• Utilized all-atom non-equilibrium molecular dynamics simulations to analyze interfacial phenomena.

Main Results:

• Discovered that axial electric fields can detrap counterions, exposing additional surface charges.
• Observed significant, real-time modulations in electroosmotic conductance exceeding classical predictions.
• Confirmed field-dependent modulation of ionic conductance in experimental nanopores.

Conclusions:

• Surface charge is not static but can be actively reshaped by electric fields in nanofluidic systems.
• Field-driven ion dynamics provide a new strategy for programmable control of ionic transport.
• Findings challenge existing electrokinetic paradigms and open avenues for advanced nanofluidic applications.