Sonoluminescence and sonochemiluminescence from a microreactor

TL;DR

This study investigates how microfabricated pits on a substrate influence sonoluminescence and sonochemiluminescence in ultrasonic fields, revealing that multiple pits enhance light emission and bubble cloud formation, with implications for microreactor design.

Contribution

It demonstrates that microfabricated pits significantly intensify sonoluminescence and sonochemiluminescence, and explores bubble dynamics and radical production in microreactor environments.

Findings

SL intensity increases with number of pits

Bubble clouds form from multiple pits at high pressure

Radical production confirmed via luminol SCL emission

Abstract

Micromachined pits on a substrate can be used to nucleate and stabilize microbubbles in a liquid exposed to an ultrasonic field. Under suitable conditions, the collapse of these bubbles can result in light emission (sonoluminescence, SL). Hydroxyl radicals (OH*) generated during bubble collapse can react with luminol to produce light (sonochemiluminescence, SCL). SL and SCL intensities were recorded for several regimes related to the pressure amplitude (low and high acoustic power levels) at a given ultrasonic frequency (200 kHz) for pure water, and aqueous luminol and propanol solutions. Various arrangements of pits were studied, with the number of pits ranging from no pits (comparable to a classic ultrasound reactor), to three-pits. Where there was more than one pit present, in the high pressure regime the ejected microbubbles combined into linear (two-pits) or triangular (three-pits) bubble clouds (streamers). In all situations where a pit was present on the substrate, the SL was intensified and increased with the number of pits at both low and high power levels. For imaging SL emitting regions, Argon (Ar) saturated water was used under similar conditions. SL emission from aqueous propanol solution (50 mM) provided evidence of transient bubble cavitation. Solutions containing 0.1 mM luminol were also used to demonstrate the radical production by attaining the SCL emission regions.