title: The lifetime evaluation of vapourised phase-change nano-droplets.
abstract: Phase-change nano-droplets (PCNDs) are sub-micron particles that are coated with phospholipid and contain liquid-state perfluorocarbons such as perfluoropentane (boiling point=29°C) and perfluorohexane (boiling point=57°C), which can vapourise upon application of ultrasound. The bubbles generated by such reactions can serve as ultrasound contrast agents or HIFU sensitisers. However, the lifetime of bubbles generated from PCNDs on μs-order is not well known. Knowledge of the condition of PCND-derived bubbles on μs-order is essential for producing bubbles customised for specific purposes. In this study, we use an optical measurement system to measure the vapourisation and stability of the bubbles (bubble-lifetime) as well as the stability-controlling method of the nucleated bubbles on μs-order while changing the internal composition of PCNDs and the ambient temperature. PCND-derived bubbles remain in a bubble state when the boiling point of the internal composition is lower than the ambient temperature, but lose their optical contrast after approximately 10μs by re-condensation or dissolution when the boiling point of the internal composition is higher than the ambient temperature. We reveal that the superheating condition significantly affects the fate of vapourised PCNDs and that the bubble-lifetime can be controlled by changing both the ambient temperature conditions and the internal composition of PCNDs.
authors.affiliation: Department of Precision Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan.
authors.forename: Ayumu
authors.initials: A
authors.lastname: Ishijima
authors.affiliation: Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan.
authors.forename: Jun
authors.initials: J
authors.lastname: Tanaka
authors.affiliation: Department of Bioengineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan. Electronic address: azuma@fel.t.u-tokyo.ac.jp.
authors.forename: Takashi
authors.initials: T
authors.lastname: Azuma
authors.affiliation: Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan.
authors.forename: Kosuke
authors.initials: K
authors.lastname: Minamihata
authors.affiliation: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Yamaguchi
authors.affiliation: Department of Precision Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan.
authors.forename: Etsuko
authors.initials: E
authors.lastname: Kobayashi
authors.affiliation: Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan.
authors.forename: Teruyuki
authors.initials: T
authors.lastname: Nagamune
authors.affiliation: Department of Precision Engineering, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo, Tokyo, Japan.
authors.forename: Ichiro
authors.initials: I
authors.lastname: Sakuma
keywords: Acoustic droplet vapourisation; Bubble-lifetime; High-speed imaging; Perfluorocarbon; Phase-change nano-droplet; Vapourisation