Visualizing ion transport in polymers via ion-chromic indicators.

Area of Science:

• Polymer Science
• Materials Science
• Electrochemistry

Background:

• Polymers with high ionic conductivity are crucial for energy storage devices like batteries and fuel cells.
• Accurate measurement of ion diffusion in polymers is essential but often requires complex methods.
• Existing techniques for studying ion transport in polymer electrolytes can be time-consuming and instrument-intensive.

Purpose of the Study:

• To present a straightforward and accessible strategy for quantifying ion diffusion in polymer networks.
• To utilize an ion-chromic spiropyran as a visual indicator for ion transport.
• To demonstrate the method's applicability to common ions (LiTFSI, KTFSI, NaTFSI) and polymers (poly(ethylene oxide)-based).

Main Methods:

• Employed ion-chromic spiropyran as a colorimetric probe for ion diffusion.
• Investigated the diffusion of lithium, potassium, and sodium bis(trifluoromethanesulfonyl)imide salts in poly(ethylene oxide) polymer films.
• Monitored the spatial-temporal evolution of the spiropyran isomerization product via optical tracking.
• Applied diffusion equations to the observed colorimetric changes to calculate diffusion coefficients.

Main Results:

• Successfully demonstrated a colorimetric method for measuring ion diffusion coefficients in polymer films.
• The spiropyran indicator undergoes a distinct color change upon interaction with specific ions, enabling quantitative analysis.
• The method allows for the determination of diffusion coefficients for LiTFSI, KTFSI, and NaTFSI in poly(ethylene oxide)-based polymers.
• The optical tracking and data fitting approach provides a simple yet effective way to study ion transport.

Conclusions:

• The developed ion-chromic spiropyran method offers a simple, optical approach to study ion diffusion in polymers.
• This technique is versatile and not limited to energy storage applications, applicable under various conditions like different temperatures and macroscopic deformation.
• The simplicity of the method makes it a valuable tool for researchers investigating ion transport phenomena in polymeric materials.