A simple approach for local contact angle determination on a heterogeneous surface

Area of Science:

• Surface Science
• Materials Science
• Physical Chemistry

Background:

• Measuring local contact angles on heterogeneous surfaces is challenging.
• Distinguishing between different surface chemistries (hydrophobic/hydrophilic) is crucial for surface characterization.

Purpose of the Study:

• To present a straightforward method for quantifying local contact angles on surfaces with mixed hydrophobic and hydrophilic patches.
• To enable the derivation of line tension from contact angle measurements on such heterogeneous surfaces.

Main Methods:

• Utilized confocal microscopy for high-resolution imaging.
• Employed a low concentration of Rhodamine-B (RB) dye (2 × 10⁻⁷ mol/L).
• Leveraged RB's aggregation at specific interfaces (air-liquid, solid-liquid on hydrophobic patches) for enhanced contrast.

Main Results:

• Rhodamine-B fluorescence effectively delineated liquid-solid and hydrophobic-hydrophilic interfaces.
• Local contact angles were successfully measured on the heterogeneous surface.
• Line tension was derived from the contact angle data, yielding a value of (-2.06 ± 1.53) × 10⁻⁶ J/m.

Conclusions:

• The developed method provides a simple yet effective approach for contact angle measurement on complex surfaces.
• The use of fluorescent dyes offers a practical way to visualize and differentiate surface interfaces.
• The study successfully quantifies line tension, offering insights into interfacial phenomena on heterogeneous materials.