Imaging size-selective permeation through micropatterned thin films using scanning electrochemical microscopy

Area of Science:

• Electrochemistry
• Materials Science
• Chemical Engineering

Background:

• Investigating molecular transport through porous films is crucial for applications like filtration and sensing.
• Heterogeneous and patterned films present unique challenges for transport analysis.
• Scanning Electrochemical Microscopy (SECM) offers high spatial resolution for surface analysis.

Purpose of the Study:

• To develop and validate a new SECM-based approach for quantifying molecular transport rates through patterned porous films.
• To assess the molecular sieving capabilities of thin electropolymerized films.
• To determine permeation selectivity and diffusion coefficients within these films.

Main Methods:

• Utilized Scanning Electrochemical Microscopy (SECM) to image molecular sieving.
• Employed thin, electropolymerized films of Fe(5-amino-1,10-phenanthroline)3(2+) on patterned electrodes.
• Measured SECM tip currents for different redox probes to analyze transport.

Main Results:

• Demonstrated that films as thin as 12 nm can block larger molecules (>12 Å) while allowing smaller ones (5-8 Å) to permeate selectively.
• Observed a decrease in tip currents with increasing polymer thickness, consistent with partitioning and diffusion models.
• Quantitatively determined permeabilities within the poly[Fe(5-NH2-phen)3(2+)] films, showing excellent agreement with rotating-disk electrochemistry data.

Conclusions:

• The developed SECM methodology provides a versatile and quantitative approach for studying membrane transport.
• This technique allows for high lateral spatial resolution in analyzing permeation selectivity.
• The findings are applicable to understanding and designing advanced porous membrane systems.