Thermocapillary actuation by optimized resistor pattern: bubbles and droplets displacing, switching and trapping

Area of Science:

• Microfluidics
• Surface Science
• Thermal Engineering

Background:

• Digital microfluidics enables precise control of discrete fluid volumes.
• The Marangoni effect, driven by surface tension gradients, offers a non-mechanical actuation method.
• Controlling bubble and droplet behavior is crucial for lab-on-a-chip applications.

Purpose of the Study:

• To present a novel method for bubble and droplet manipulation in microfluidic bifurcation channels.
• To utilize the thermal Marangoni effect for actuating elements.
• To demonstrate applications in displacement, switching, and trapping of microfluidic elements.

Main Methods:

• Utilized an optimized resistor pattern for controlled heating and a constant temperature gradient.
• Leveraged the thermal Marangoni effect to generate thermocapillary stresses on bubbles/droplets.
• Characterized element velocity dependence on cavity thickness and surface tension gradients.

Main Results:

• Demonstrated successful displacement, switching, and on-demand trapping of bubbles/droplets.
• Achieved element velocity increase with decreasing cavity thickness.
• Validated the method's effectiveness at flow velocities up to 1 cm/s.

Conclusions:

• The developed method offers a simple, integrated solution for microfluidic manipulation.
• Low power consumption (<0.4 W) and applied voltage (~10 V) make it energy-efficient.
• This technique provides precise control for digital microfluidics applications.