Abstract
When ultrasound is irradiated into the liquid, positive and negative pressure are alternately applied to the gas molecules in the liquid, and as the bubbles repeatedly compress and expand to about several μm to 100 μm, at the limit of high pressure during compression. Micro bubbles bursts, resulting in”shock wave” and ”local high temperature and high pressure field”. This is called ultrasonic cavitation. At this time, ”physical action by shock wave” and ”chemical action by OH radical generated by thermal decomposition of water at local high temperature and high pressure field” occur. On the other hand, in recent years, ultrafine bubbles have been paid attention which are bubbles of 10 to 100 nm size. Unlike microbubbles of 1 μm size or more, this ”nanobubble” exists stably in water. We set up a working hypothesis that this ultrafine bubble will be the core of ultrasound cavitation. We hypothesize that combination of ultrafine bubbles and ultrasound irradiation can synergistically increase ”physical effect by shock wave” and ”chemical effect by OH radical generated by thermal decomposition of water in a local high temperature and high pressure field” upon ultrasonic cavitation. The combination of ultrafine bubble and ultrasound synergistically improved the generation of OH radicals and the inactication of E. coli.
