Thermocapillary Droplet Actuation: Effect of Solid Structure and Wettability

Area of Science:

• Fluid Dynamics
• Surface Science
• Microfluidics

Background:

• Thermocapillary flow drives droplet motion on heated surfaces.
• Patterned surfaces introduce complexities like contact angle hysteresis.
• Controlling droplet dynamics is crucial for microfluidic applications.

Purpose of the Study:

• To investigate thermocapillary-driven droplet flow on nonuniformly heated patterned surfaces.
• To understand the role of substrate wettability and contact angle hysteresis in droplet migration.
• To explore methods for manipulating droplet dynamics, including motion control and mixing.

Main Methods:

• Utilized a sharp-interface finite element scheme for 2D and 3D simulations.
• Simulated droplet behavior across a range of substrate wettabilities (hydrophilic to superhydrophobic).
• Analyzed the interplay between mechanical forces and thermocapillary flow.

Main Results:

• Contact angle hysteresis is critical for enabling droplet migration beyond a specific thermal gradient.
• Droplet migration velocity and direction are influenced by net mechanical forces and thermocapillary flow.
• Demonstrated the ability to control droplet motion along predefined paths and entrap droplets using wetting defects.

Conclusions:

• Substrate design, including wettability and hysteresis, allows for manipulation of droplet dynamics.
• Precise control over droplet movement and enhanced internal mixing are achievable.
• Findings offer pathways for advanced microfluidic device design and operation.