Creation of cavitation activity in a microfluidic device through acoustically driven capillary waves

Area of Science:

• Microfluidics
• Acoustics
• Materials Science

Background:

• Microfluidic devices offer precise control over fluid dynamics.
• Acoustic cavitation is a phenomenon with various applications, but achieving high intensity in micro-devices is challenging.
• Polydimethylsiloxane (PDMS) is a common material for microfluidic device fabrication.

Purpose of the Study:

• To investigate the generation of intense acoustic cavitation in PDMS-based microfluidic devices.
• To explore the role of ultrasonic vibrations and gas-liquid interfaces in cavitation.
• To characterize the generated cavitation bubble clusters.

Main Methods:

• Utilizing a piezoelectric transducer to induce oscillations in a glass slide bonded to a PDMS microfluidic device.
• Operating the transducer at 100 kHz with varying driving voltages (20-230 V).
• Measuring pressure and vibration amplitudes near the glass surface.
• Employing high-speed photography (up to 250,000 frames/s) to record cavitation dynamics.
• Sustaining cavitation clusters via continuous gas injection through a T-junction.

Main Results:

• Observed nonlinear surface waves at gas-liquid interfaces under strong forcing.
• Identified gas pocket entrapment at interfaces as nuclei for inertial cavitation.
• Recorded cavitation bubble clusters with void fractions exceeding 50%.
• Demonstrated sustained cavitation through continuous gas supply.

Conclusions:

• Ultrasonic vibrations can effectively generate intense acoustic cavitation in PDMS microfluidic devices.
• Nonlinear surface waves and gas entrapment are key mechanisms for cavitation initiation.
• The developed method allows for sustained, high-void-fraction cavitation clusters, opening possibilities for microfluidic applications.