Towards a phase diagram for the process of acoustic droplet vaporization

Abstract

The phase-change of a liquid droplet exposed to an oscillating acoustic field is known as “acoustic droplet vaporization.” It potentially represents a versatile tool for medical applications. In an attempt to understand the complex mechanisms that drive the vaporization process, a theoretical and numerical model is developed to describe the time evolution of a three-phase phase model, made of an initial (nucleus) bubble of vapor perfluorocarbon, at the center of a liquid droplet of the same perfluorocarbon immersed in water. The effect of an encapsulating layer can also be taken into account. The model is solved numerically to compute the vapor bubble and liqud droplet evolution with time. The dynamics are sorted into six different regimes depending on their characteristics and on the system ultimate fate. Those regimes can be organized within a phase diagram that synthesizes all the possible dynamics, predicting whether the complete vaporization occurs or not depending on the two control parameters, the amplitude and the frequency of the driving acoustical field. In particular, the dependance of the vaporization threshold with frequency is discussed with two different behaviors at low or high frequency.