Liquid-Cell Electron Microscopy of Adsorbed Polymers

Area of Science:

• Polymer Science
• Materials Science
• Microscopy

Background:

• Visualizing individual macromolecules in solution is challenging due to electron beam damage and background scattering.
• Graphene liquid cells offer a potential solution by providing thin windows and a protective environment.

Purpose of the Study:

• To demonstrate the visualization of individual polystyrene sulfonate and poly(ethylene oxide) molecules in aqueous solution using transmission electron microscopy.
• To analyze polymer adsorption, desorption, conformational fluctuations, and projected sizes.
• To evaluate the advantages of graphene liquid cells for polymer imaging.

Main Methods:

• Transmission electron microscopy (TEM) imaging of aqueous polymer solutions.
• Utilizing creased graphene sheets to create liquid pockets for sample containment.
• Employing a liquid cell approach with graphene windows to minimize electron scattering and sample degradation.
• Imaging at 0.3 s per frame to capture molecule dynamics.

Main Results:

• Individual polymer molecules (polystyrene sulfonate, poly(ethylene oxide)) were successfully visualized at nanometer resolution.
• The graphene liquid-cell approach reduced sample degradation from incident electrons and minimized background scattering.
• Analysis of projected sizes, conformational fluctuations, and adsorption-desorption events of polymers was achieved without metal-ion labeling.
• Statistical analysis of hundreds of images confirmed observations across varying polymer types, molecular weights, and salt concentrations.

Conclusions:

• Graphene liquid-cell TEM is a viable method for observing individual polymer molecules in solution.
• This technique offers advantages in reducing sample damage and background noise, facilitating detailed molecular analysis.
• The approach is applicable to various polymers and experimental conditions, using standard TEM equipment.