Controlled directional water-droplet spreading on a high-adhesion surface

Area of Science:

• Materials Science
• Surface Chemistry
• Fluid Dynamics

Background:

• Controlling droplet behavior on surfaces is crucial for microfluidics.
• Existing methods often lack precise control over directional spreading.

Purpose of the Study:

• To develop a method for controlled directional spreading of droplets on smart surfaces.
• To investigate the relationship between wettability gradients and droplet movement.

Main Methods:

• Utilizing anodic oxidation to create tunable wettability gradients on conductive substrates.
• Precisely controlling oxidation conditions to achieve gradient values from 0.14 to 3.38° mm⁻¹.
• Observing water droplet behavior on surfaces with linear, V-shaped, and inverse-V-shaped wettability gradients.

Main Results:

• Achieved controlled, directional spreading of water droplets solely based on the wettability gradient.
• Demonstrated that droplet movement is predominantly along the gradient, even on inverted surfaces.
• Successfully created surfaces with designed V- and inverse-V-shaped gradients, directing droplet interactions.

Conclusions:

• Anodic oxidation offers a versatile method for fabricating surfaces with tailored wettability gradients.
• This technique enables precise control over droplet spreading directionality.
• The developed smart surfaces show significant potential for applications in microfluidic devices and lab-on-a-chip systems.