Nanoscale contact line visualization based on Total Internal Reflection Fluorescence Microscopy

Area of Science:

• Physics
• Surface Science
• Microscopy

Background:

• Studying droplet contact lines at the nanoscale is crucial for understanding wetting phenomena.
• Existing methods like conventional contact angle measurements lack spatial resolution, and Atomic Force Microscopy (AFM) is limited to specific droplet types.

Purpose of the Study:

• To develop and validate a novel, non-contact measurement method for studying droplet contact lines at the nanoscale.
• To accurately reconstruct the interface of partially wetting droplets using advanced microscopy techniques.

Main Methods:

• Utilizing Total Internal Reflection Fluorescence Microscopy (TIRFM) with an evanescent excitation field.
• Employing Atomic Force Microscopy (AFM) to determine the penetration depth of the evanescent field.
• Reconstructing droplet interfaces using fluorescent dye intensity distribution and measured penetration depth.

Main Results:

• Confirmed the exponential decay of the evanescent field intensity.
• Validated the penetration depth measurement against theoretical predictions.
• Demonstrated good agreement between TIRFM-reconstructed interfaces and those from AFM and conventional contact angle measurements.

Conclusions:

• The novel TIRFM-based method provides accurate nanoscale resolution for studying droplet interfaces.
• This non-contact technique overcomes limitations of existing methods, offering a versatile tool for stationary and dynamic wetting studies.