Assessing the Thickness-Permeation Paradigm in Nanoporous Membranes

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Engineering

Background:

• Membrane nanofabrication aims for thinner materials to enhance permeation.
• Thinner membranes present challenges in mechanical stability and defect control.
• Understanding viscous transport mechanisms is crucial for optimizing membrane performance.

Purpose of the Study:

• Investigate the impact of membrane thickness on viscous transport mechanisms in nanopores.
• Study liquid permeation across double-layer graphene membranes with varying pore sizes and thicknesses.
• Determine the role of entrance resistance in limiting permeation through atomically thin nanoporous membranes.

Main Methods:

• Synthesized double-layer graphene membranes with nanopores (6–1000 nm diameter).
• Fabricated nanoporous membranes up to 90 nm thick using atomic layer deposition.
• Investigated liquid permeation across a range of viscosities and pressures.

Main Results:

• Entrance resistance dominates viscous transport for aspect ratios up to one.
• Liquid permeation is limited by viscous dissipation at the pore entrance.
• Entrance resistance acts as a universal upper bound for viscous transport, independent of membrane thickness.

Conclusions:

• Membrane permeation is fundamentally limited by pore entrance resistance.
• Rational selection of membrane thickness based on target solute size is crucial for optimizing performance.
• The study provides a new perspective on membrane nanofabrication, emphasizing optimized thickness over extreme thinness.