Droplet Wetting Propagation on a Hybrid-Wettability Surface

Area of Science:

• Fluid dynamics
• Surface science
• Materials science

Background:

• Understanding droplet behavior on surfaces with varying wettability is crucial for microfluidics and material design.
• Hybrid-wettability surfaces, combining hydrophilic and hydrophobic regions, present unique challenges and opportunities for fluid manipulation.

Purpose of the Study:

• To experimentally and numerically investigate droplet dynamics on hybrid-wettability surfaces.
• To analyze the interfacial evolution, spreading-receding behavior, and migration mechanisms of droplets.
• To elucidate the influence of surface energy imbalance and fluid parameters on droplet migration.

Main Methods:

• Experimental observation of droplet impingement and interaction with hybrid-wettability boundaries.
• Numerical simulations employing the single variable method to isolate parameter effects.
• Analysis of pressure fields and contact angles to understand migration drivers.

Main Results:

• Droplets exhibit spreading-receding behavior in hydrophobic regions before migrating towards hydrophilic areas due to unbalanced surface energy.
• Increasing Weber number enhances spreading and migration in hydrophobic regions but reduces migration in hydrophilic regions.
• An unsymmetrical pressure field is identified as a primary driver for droplet migration.
• Hydrophilic contact angle significantly influences droplet migration, increasing the pressure gradient in hydrophobic regions.

Conclusions:

• The study provides fundamental insights into droplet migration on hybrid-wettability surfaces.
• Understanding these dynamics is essential for designing advanced microfluidic devices and functional materials.
• The findings highlight the role of surface energy gradients and pressure fields in directing droplet movement.