Unidirectional Self-Driving Liquid Droplet Transport on a Monolayer Graphene-Covered Textured Substrate

Area of Science:

• Materials Science
• Microfluidics
• Surface Science

Background:

• Controllable directional transport of liquid droplets on surfaces is crucial for microfluidics.
• Existing methods often require external energy sources, posing limitations.
• Understanding self-driving mechanisms is key for biological process modeling and microfluidic device design.

Purpose of the Study:

• To design a novel surface microstructure for unidirectional self-driving liquid mercury (Hg) droplet transport.
• To investigate the physical mechanisms underlying spontaneous droplet movement on functionalized surfaces.
• To explore the role of graphene and surface texturing in droplet dynamics.

Main Methods:

• Fabrication of a three-dimensional grooved copper (Cu) substrate covered with a monolayer graphene.
• Experimental observation of liquid Hg droplet movement on the functionalized surface.
• Classical molecular dynamics simulations to analyze droplet behavior and energy landscapes.

Main Results:

• Demonstrated spontaneous, unidirectional transport of liquid Hg droplets on the graphene-covered Cu substrate without external forces.
• Molecular dynamics revealed distinct acceleration, deceleration, and return stages of Hg droplet movement.
• Hg droplets achieved continuous unidirectional motion by overcoming energy barriers at step junctions between unit cells.

Conclusions:

• The novel zigzag textured surface, coated with graphene, effectively facilitates self-driving droplet transport.
• Monolayer graphene reduces droplet pinning and substrate friction, enabling continuous movement.
• This research provides a new platform for exploring graphene-based functional surfaces for droplet manipulation and understanding self-driving mechanisms.