title: Investigating the Existence of Bulk Nanobubbles with Ultrasound.
abstract: Nanobubbles are expected to dissolve in milliseconds. Experimental evidence of nanobubbles that were stable for days had thus been first received with circumspection. If the large number of experimental confirmations has now made clear that surface nanobubbles could exist, bulk nanobubbles are still subject to debate. When observations are reported, the main problem is to make sure the observed particles are really made of gas. We show that ultrasound is an ideal tool for investigating the existence of bulk nanobubbles: 1) it is sensitive to minute quantities of gas, 2) it allows one to determine the bubble size distribution, 3) it discriminates unambiguously between gaseous and solid/liquid inclusions. To illustrate the efficiency of ultrasonic detection, we performed size measurements of bubbles produced by a commercial nano-/microbubble generator. No nanobubble was detected with this device. It would be insightful to use ultrasonic detection in experimental situations for which stable nanobubbles were reported.
authors.affiliation: Department of Macromolecular Science and Engineering, Graduate School of Science & Technology, Kyoto Institute of Technology Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan. valentin.leroy@univ-paris-diderot.fr.|Laboratoire Matière et Systèmes Complexes, Université Paris-Diderot, CNRS (UMR 7057), 75205, Paris, France. valentin.leroy@univ-paris-diderot.fr.
authors.forename: Valentin
authors.identifier: http://orcid.org/0000-0003-1449-5422
authors.initials: V
authors.lastname: Leroy
authors.affiliation: Department of Macromolecular Science and Engineering, Graduate School of Science & Technology, Kyoto Institute of Technology Matsugasaki, Sakyo-ku, Kyoto, 606-8585, Japan. nori@kit.jp.
authors.forename: Tomohisa
authors.initials: T
authors.lastname: Norisuye
keywords: bulk nanobubbles; liquids; nanobubbles; surface nanobubbles; ultrasound