Pore conductivity control at the hundred-nanometer scale: an experimental and theoretical study

Area of Science:

• Materials Science
• Physical Chemistry
• Nanotechnology

Background:

• Conductivity in nanoporous membranes is crucial for separation technologies.
• Understanding ion transport mechanisms at the nanoscale is essential for designing advanced materials.

Purpose of the Study:

• To investigate the mechanism controlling ion conductivity at the 100-nm scale in track-etched polycarbonate membranes.
• To explore the influence of pH, ionic strength, and surface modifications on ion transport.

Main Methods:

• Conductivity measurements using absorption spectroscopy.
• Transport experiments with charged molecular ions (methyl viologen and naphthalene disulfonate).
• Theoretical modeling to analyze electric field effects and surface interactions.

Main Results:

• Observed pH-dependent conductivity changes for both positively and negatively charged ions.
• Demonstrated that surface trapping of mobile ions (e.g., Cl-, Na+) governs conductivity, not pore-scale electric fields.
• Identified opposite conductivity trends for cations and anions at different pH levels.

Conclusions:

• The study reveals an unexpected surface-driven mechanism controlling ion transport in nanopores.
• This finding challenges conventional understanding based solely on electric fields at the nanoscale.
• Potential applications include high-throughput separation of large molecules and biological entities.