Tribo-Charge Induced Wetting (TCW): A New Wettability Control Mechanism for Electric-Free Droplet Manipulation

Area of Science:

• Surface science and microfluidics
• Materials science and engineering

Background:

• Electrowetting-on-dielectric (EWOD) controls microfluidics using electric fields but requires power and complex circuitry.
• Existing methods limit device simplicity, portability, and cost-effectiveness for widespread applications.

Purpose of the Study:

• Introduce tribo-charge driven wetting (TCW) as a novel, electric-free mechanism for active wettability control.
• Demonstrate the feasibility of TCW for core digital microfluidics operations.
• Explore the potential of TCW for resource-limited and point-of-care applications.

Main Methods:

• Utilized contact electrification to generate surface charges for wettability modulation.
• Employed a tribo-actuator to induce charge density (σ = -12.61 µC m⁻²) for contact angle modulation (Δθ = 44.4°±1.1).
• Performed experimental and numerical analyses to understand TCW performance scaling with actuator area and charge density.

Main Results:

• Achieved significant contact angle modulation without external power or electrodes.
• Demonstrated droplet transport, merging, and generation at speeds up to 40 mm s⁻¹ using TCW.
• Showcased fingertip-controlled droplet manipulation, highlighting simplicity and user-interactivity.

Conclusions:

• TCW provides a fundamentally new, electric-free paradigm for active droplet control in digital microfluidics.
• The technology is scalable, cost-effective, and suitable for portable, resource-limited lab-on-a-chip and point-of-care devices.
• TCW advances the fundamental understanding of charge-driven wettability and opens new avenues for microfluidic applications.