In Situ Droplet Microgoniometry Using Optical Microscopy.

Area of Science:

• Surface Science
• Materials Science
• Physical Chemistry

Background:

• Solid-liquid interactions, crucial in nature and industry, are governed by surface properties like chemical heterogeneity and physical roughness.
• Contact angle measurement, characterizing wettability, is typically performed using goniometry or the Wilhelmy plate method.
• Existing methods struggle with microdroplets, local wetting variations, non-circular contact lines, and in situ measurements during dynamic processes like condensation.

Purpose of the Study:

• To develop novel, simple, and powerful contact angle measurement techniques for microscale droplets.
• To overcome the limitations of conventional methods in characterizing wettability, especially for microdroplets and heterogeneous surfaces.
• To enable in situ contact angle measurements during experiments.

Main Methods:

• Utilized conventional optical microscopy combined with focal plane shift imaging.
• Applied principles of ray optics and wave interference for precise measurements.
• Investigated a wide range of water droplet sizes (10 μm < D < 600 μm) and apparent contact angles (0° ≤ θapp ≤ 180°).

Main Results:

• Successfully developed and validated new contact angle measurement techniques.
• Demonstrated the capability to accurately characterize microscale droplet advancing and receding contact angles.
• Showcased the method's effectiveness across diverse droplet sizes and wettability conditions.

Conclusions:

• The developed optical microscopy techniques offer a significant advancement in contact angle measurement.
• This method provides a more accessible, rapid, and versatile tool for studying microscale wetting phenomena.
• The findings facilitate a deeper understanding of solid-liquid interactions in various scientific and industrial applications.