The Role of Re-Entrant Microstructures in Modulating Droplet Evaporation Modes.

Area of Science:

• Surface science and microfluidics
• Materials science and engineering
• Physics of soft matter

Background:

• Re-entrant microstructures enhance non-wettability by trapping air, crucial for microfluidics, thermal management, and self-cleaning surfaces.
• Understanding droplet evaporation dynamics on these structures is key to optimizing surface performance.

Purpose of the Study:

• To investigate the evaporation of water droplets on silicon carbide (SiC) and silicon dioxide (SiO2) re-entrant microstructures.
• To analyze the influence of material composition (SFE) and structural geometry (solid area fraction) on evaporation dynamics.

Main Methods:

• Experimental examination of sessile droplet evaporation on SiC and SiO2 re-entrant surfaces.
• Analysis of volume reduction, contact angle changes, and evaporation modes.
• Correlation of wettability (via SFE) and structural parameters (solid area fraction) with evaporation kinetics.

Main Results:

• Lower surface free energy (SFE) of SiC surfaces leads to quicker contact line depinning and retraction compared to SiO2.
• The constant contact line (CCL) phase is shorter on SiC (55-59%) than on SiO2 (51-68%), indicating faster evaporation.
• Increased solid area fraction (narrower pillar gaps) stabilizes droplets, extending both CCL and constant contact angle (CCA) phases, while wider gaps promote faster evaporation.

Conclusions:

• Hydrophobicity and structural geometry are critical factors controlling microscale liquid behavior.
• Design of re-entrant surfaces can be tailored by adjusting material SFE and solid area fraction for optimized liquid management and evaporation control.