On the acoustic vaporization of micrometer-sized droplets

Abstract

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 micros tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 microm, independent of droplet diameter which ranged from 5 to 27 microm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet's imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.

Microscale acoustofluidics: Microfluidics driven via acoustics and ultrasonics

“…Barreras et al (2002) found a similar phenomenon in a detailed experimental study using a piston ultrasonic atomizer, effectively capturing a number of images that indicated the length scales of each of the instabilities giving rise to the drops. Other means for generating micron-sized drops are described in the literature, and the article by Kripfgans et al (2004) is especially thorough in describing how atomization produces small drops from a fluid jet that is subsequently exposed to intense ultrasound. Elrod et al (1989) made use of a piston transducer with a concave cup milled into the irradiating end; when submerged in water by a distance corresponding to the focal length of the concavity, the cup focused the ultrasound to a small region at the fluid surface and allowed the ejection of single drops.…”

Towards Aberration Correction of Transcranial Ultrasound Using Acoustic Droplet Vaporization

“…Figure 1 shows the setup used to perform transcranial ADV. The procedure for creating droplets for vaporization has been described by Kripfgans et al (2004). Droplets were vaporized using a 550 kHz, 70 mm diameter, 100 mm focal-length, air-backed, lead zirconate titanate (PZT-4) transducer (Channel Industries, Santa Barbara, CA, USA).…”

“…ADV is a technique whereby liquid droplets are phase transitioned into gas bubbles using an acoustic disturbance (Apfel, 1998). The liquid droplets employed and their manufacturing are described in detail elsewhere (Kripfgans et al, 2004). The droplets' core, dodecafluoropentane (DDFP) (Strem Chemicals, Newburyport, MA, USA), has a bulk fluid boiling point of 29 °C, which is less than normal body temperature (37 °C).…”

“…The DDFP droplet is stabilized in a superheated state by an albumin shell. In vitro studies have elucidated the values of parameters (such as pulse length, pulse amplitude, presence of nucleation sites) for controlling ADV (Kripfgans et al, 2000;Giesecke and Hynynen, 2003;Kripfgans et al, 2004;Lo et al, 2007). Of these, it has also been found that the vaporization threshold decreases with increasing insonification frequency for short insonification pulses.…”

Phase-transition Perfluorocarbon Nanoparticles for Ultrasound Molecular Imaging and Therapy

“…From then award, ADV has been profoundly investigated in the group works of Michigan University with albumin coated perfluoropentane (PFP) nanoparticles, which illustrated substantially applications PFC nanoparticles with ADV in terms of drug delivery, thrombolysis, and gas embolism, etc. [33][34][35][36][37][38][39][40][41][42][43]. Table 1 lists some parameters of candidate perfluorocarbons.…”