Evaluation of Acoustophoretic and Dielectrophoretic Forces for Droplet Injection in Droplet-Based Microfluidic...

Area of Science:

• Microfluidics
• Acoustofluidics
• Dielectrophoresis

Background:

• Acoustophoretic forces are used in microfluidic devices, often generated by piezoelectric substrates like lithium niobate (LiNbO3).
• These devices can also generate electrical fields, leading to dielectrophoretic forces.
• Distinguishing between acoustophoretic and dielectrophoretic forces is crucial for optimizing microfluidic device performance.

Purpose of the Study:

• To design microfluidic devices with a droplet injection module.
• To experimentally determine the contribution of acoustophoretic versus dielectrophoretic forces to droplet injection.
• To establish a methodology for pinpointing dominant forces in droplet manipulation within acoustomicrofluidics.

Main Methods:

• Fabrication of polydimethylsiloxane (PDMS)-based microfluidic devices with integrated electrodes (embedded liquid metal interdigitated transducers - elmIDTs).
• Comparison of devices on piezoelectric (LiNbO3) and non-piezoelectric (glass) substrates.
• Characterization using laser Doppler vibrometry (LDV), infrared imaging, and evaluation of droplet injection under varying operational parameters (frequency, voltage, polarity).

Main Results:

• Devices on LiNbO3 substrates generated acoustic fields.
• Droplet injection was observed in both LiNbO3 and glass substrate devices.
• Droplet injection was solely attributed to dielectrophoretic forces, independent of acoustic field generation.

Conclusions:

• Droplet injection in the studied microfluidic devices is driven by dielectrophoretic forces from elmIDTs, not acoustophoretic forces.
• The methodology successfully differentiates the contributions of acoustophoretic and dielectrophoretic forces.
• This work provides a framework for understanding and optimizing force contributions in droplet-based microfluidic systems.