Researchers at Osaka Metropolitan University have elucidated a longstanding enigma in sonochemistry: the reason chemical reactions decelerate when ultrasonic power is very high. Their discoveries facilitate more intelligent use of ultrasound in scientific and industrial contexts, including environmental remediation and the synthesis of beneficial nanoparticles.

Science Behind Ultrasound and Chemical Reactions

Despite being imperceptible to the human ear, ultrasonography significantly influences sonochemistry. Ultrasonic waves applied to a liquid produce small bubbles that swiftly expand and disintegrate, a phenomenon known as acoustic cavitation. The collapse generates energy bursts that temporarily attain temperatures akin to that of the sun’s surface, instigating chemical processes.

“Typically, increasing ultrasonic output speeds up the reaction,” stated Takuya Yamamoto. He is an associate professor at Osaka Metropolitan University’s Graduate School of Engineering and the lead author of this study. “But once the output exceeds a certain level, the reaction rate rapidly drops. That paradox has puzzled researchers for years.”

This paradoxical phenomena represents a significant hurdle in the advancement of effective industrial applications for ultrasound.

Multi-Method Approach to Understanding the Reversal

To elucidate the mechanism underlying this “ultrasonic reversal,” the team performed six experimental types, encompassing bubble imaging, sonochemiluminescence observations, and sound pressure measurements, with three numerical simulations that modeled bubble dynamics and internal temperatures.

Their findings indicated that excessive ultrasonic power causes vigorous bubble movement, which distorts the ultrasonic waves. This distortion inhibits bubble formation and significantly diminishes the quantity of active bubbles that might facilitate chemical reactions, hence decelerating the total reaction rate.

The researchers observed three separate zones of ultrasonic reactions, each defined by unique wave patterns and bubble dynamics. These insights elucidate how the speeds of chemical reactions, bubble proliferation, acoustic streaming, and degassing behavior vary with ultrasound intensity.

“Our study helps demystify a complex phenomenon during which sound waves, fluid motion, and bubble physics are all interacting,” Yamamoto stated.

Understanding the balance is a key to making sonochemistry more predictable and scalable for real-world use.

“We hope this result will open the door to broader industrial applications of ultrasonic technology, from synthesizing nanoparticles to breaking down persistent pollutants like PFAS, the so-called ‘forever chemicals’,” Yamamoto stated.

About OMU 

OMU is established in Osaka as one of the largest public universities in Japan. Osaka Metropolitan University is dedicated to shaping the future of society through the “Convergence of Knowledge” and the advancement of world-class research.

Original Publication
Authors: Ryota Aoki, Kanji D. Hattori and Takuya Yamamoto.
Journal: Ultrasonics Sonochemistry
DOI: 10.1016/j.ultsonch.2025.107419
Method of Research: Experimental study
Subject of Research: Not applicable
Article Title: Revisit to the mechanism of quenching: Power effects for sonochemical reactions
Article Publication Date: 6-Jun-2025
COI Statement: The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Takuya Yamamoto reports financial support was provided by Japan Science and Technology Agency. If there are other authors, they declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.