Ultrafast dynamics of the acoustic vaporization of phase-change microdroplets.
Acoustically sensitive emulsions are a promising tool for medical applications such as localized drug delivery. The physical mechanisms underlying the ultrasound-triggered nucleation and subsequent vaporization of these phase-change emulsions are largely unexplored. Here, the acoustic vaporization of individual micron-sized perfluoropentane (PFP) droplets is studied at a nanoseconds timescale. Highly diluted emulsions of PFP-in-water and oil-in-PFP-in-water droplets, ranging from 3.5 to 11 μm in radius, were prepared and the nucleation and growth of the vapor bubbles was imaged at frame rates of up to 20 Mfps. The droplet vaporization dynamics was observed to have three distinct regimes: (1) prior to nucleation, a regime of droplet deformation and oscillatory translations within the surrounding fluid along the propagation direction of the applied ultrasound; (2) a regime characterized by the rapid growth of a vapor bubble enhanced by ultrasound-driven rectified heat transfer; and (3) a final phase characterized by a relatively slow expansion, after ultrasound stops, that is fully dominated by heat transfer. A method to measure the moment of inception of the nucleation event with respect to the phase of the ultrasound wave is proposed. A simple physical model captures quantitatively all of the features of the subsequent vapor bubble growth.
Physics of Fluids Group and MIRA Institute for Biomedical Technology and Technical Medicine, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands. o.shpak@utwente.nl
Oleksandr
O
Shpak
Tom J A
TJ
Kokhuis
Ying
Y
Luan
Detlef
D
Lohse
Nico
N
de Jong
Brian
B
Fowlkes
Mario
M
Fabiilli
Michel
M
Versluis
D004337:Drug Carriers; D016503:Drug Delivery Systems / Q000379:methods*; D004655:Emulsions; D004735:Energy Transfer; D005466:Fluorocarbons / Q000737:chemistry*; D006358:Hot Temperature; D033401:Microscopy, Acoustic; D008956:Models, Chemical; D009038:Motion; D009991:Oscillometry; D010316:Particle Size; D013016:Sound; D013024:Soybean Oil / Q000737:chemistry; D013997:Time Factors; D014465:Ultrasonics / Q000379:methods*; D014835:Volatilization; D014867:Water / Q000737:chemistry; D010420:Pentanes
D004337:Drug Carriers; D004655:Emulsions; D005466:Fluorocarbons; D013024:Soybean Oil; D014867:Water; C008806:perfluoropentane; D010420:Pentanes