title: A model for acoustic vaporization of encapsulated droplets.
abstract: The use of encapsulated liquid nanoparticles is currently largely investigated for medical applications, mainly because their reduced size allows them to enter targeted areas which cannot be reached by large microbubbles (contrast agents). Low-boiling point perfluorocarbon droplets can be vaporized on-site under the action of the ultrasonic field, in order to turn them into echogeneous-eventually cavitating-microbubbles. This paper presents a theoretical model describing this phenomenon, paying particular attention to the finite size of the droplet and its encapsulation by a thin viscoelastic layer. Numerical simulations are done for droplets of radii 1 and 10 μm and for frequencies of 1-5 MHz. Results reveal that droplet surface tension and shell rigidity are responsible for an increase of the acoustic droplet vaporization threshold. Furthermore, this threshold does not vary monotonically with frequency, and an optimal frequency can be found to minimize it. Finally, the role of some physical properties on the dynamics of the particle is analyzed, such as the contrast of inner and outer liquids densities and the mechanical properties of the shell.
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d'Alembert, F-75005 Paris, France.
authors.forename: Matthieu
authors.initials: M
authors.lastname: Guédra
authors.affiliation: Sorbonne Universités, UPMC Univ Paris 06, CNRS, UMR 7190, Institut Jean Le Rond d'Alembert, F-75005 Paris, France.
authors.forename: François
authors.initials: F
authors.lastname: Coulouvrat
mesh_terms: D003198:Computer Simulation; D004548:Elasticity; D004655:Emulsions; D005466:Fluorocarbons / Q000737:chemistry*; D045423:Microbubbles; D008962:Models, Theoretical; D053758:Nanoparticles; D009716:Numerical Analysis, Computer-Assisted; D010316:Particle Size; D011312:Pressure; D013499:Surface Properties; D044366:Transition Temperature; D000069453:Ultrasonic Waves; D014465:Ultrasonics / Q000379:methods*; D014783:Viscosity; D014835:Volatilization
chemical_list: D004655:Emulsions; D005466:Fluorocarbons