Particle migration and sorting in microbubble streaming flows.

Area of Science:

• Fluid dynamics
• Acoustic manipulation
• Microfluidics

Background:

• Microbubble-driven streaming flows are generated using ultrasonic excitation.
• These flows exhibit robustness across a broad spectrum of driving frequencies.
• Microfluidic devices often rely on passive techniques for particle sorting, which can be limited by throughput and feature size requirements.

Purpose of the Study:

• To develop and demonstrate novel methods for size-sensitive particle sorting and trapping in microchannels.
• To investigate the combination of microbubble streaming flows and Poiseuille flows for particle manipulation.
• To establish a predictive mechanism for particle behavior based on channel and flow geometry.

Main Methods:

• Utilizing semicylindrical microbubbles driven by ultrasound to generate strong streaming flows.
• Integrating these streaming flows with Poiseuille flow within microchannels.
• Employing experimental observations and asymptotic theory, modified for 3D effects, to model flow characteristics and particle trajectories.

Main Results:

• Two distinctive, highly tunable methods for size-sensitive particle sorting and trapping were achieved.
• The developed method allows for higher throughput compared to traditional passive sorting techniques.
• A simple mechanism based on channel and flow geometry reliably predicts sorting behavior.
• Asymptotic theory accurately models key flow features, including peak speeds and particle trajectories, when accounting for 3D effects.

Conclusions:

• Ultrasonic microbubble streaming flows provide an effective platform for advanced particle manipulation in microfluidics.
• The combined flow approach offers a tunable and high-throughput solution for size-sensitive particle sorting.
• The proposed theoretical framework accurately describes and predicts the observed particle sorting and trapping phenomena.