High-ionic-strength electroosmotic flows in uncharged hydrophobic nanochannels

Area of Science:

• Physical Chemistry
• Nanotechnology
• Computational Science

Background:

• Electroosmotic flow (EOF) is typically observed in charged nanochannels.
• Previous theoretical work suggested the possibility of EOF in uncharged nanochannels under specific conditions.

Purpose of the Study:

• To investigate high-ionic-strength electroosmotic flows within uncharged nanochannels using molecular dynamics simulations.
• To analyze the resulting fluid velocity profiles, apparent zeta potential, and molecular behavior.

Main Methods:

• Molecular dynamics simulations were employed to model fluid behavior.
• Analysis included computing velocity profiles, polarization density, and ion distributions.
• The Helmholtz-Smoluchowski relation was used to determine the apparent zeta potential.

Main Results:

• Simulations demonstrated a net electroosmotic flow with maximum velocities reaching approximately 2 m/s.
• An apparent zeta potential of -29.7 ± 6.8 mV was calculated, consistent with experimental findings.
• Water molecule orientation exhibited field-aligned behavior in the bulk and oscillatory patterns near the wall.
• Chloride ions concentrated near water molecules, while sodium ions showed diffuse distribution.

Conclusions:

• Molecular dynamics simulations confirm the occurrence of significant electroosmotic flow in uncharged nanochannels at high ionic strengths.
• The findings provide insights into the complex interplay of electric fields, ions, and water at the nanoscale.
• This work contributes to understanding non-equilibrium phenomena in confined systems.