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Nucleation of Bubbles in Perfluoropentane Droplets Under Ultrasonic Excitation

Excerpt

Lipid coated perfluorocarbon (PFC) nanodroplets can be vaporized by an external ultrasound pulse to generate bubbles. These bubbles produced in situ have potential applications in tumor imaging and drug delivery. Here we employ the classical nucleation theory (CNT) to investigate the peak negative pressure required to induce acoustic droplet vaporization (ADV). The theoretical analysis predicts that the ADV threshold increases with increasing surface tension of the droplet core and increasing excitation frequency. It decreases with increasing temperature and droplet size. The predictions are in qualitative agreement with experimental observations. We also estimate and discuss the energy required to form critical cluster to argue that nucleation occurs inside the droplet, as was also observed by high-speed cameras. To find the stability of these PFC droplets to temperature fluctuations, their limit of superheat was also calculated. These CNT based theoretical predictions prove to be a promising tool to design phase-shift nano emulsions with low threshold pressures.

Introduction
Background Classical Nucleation Theory
Nucleation of Bubble Inside the Droplet Using Acoustic Waves
Threshold Pressure Criterion
Estimation of Effective Volume of Nucleation
Estimation of Time Scale of Nucleation
Acoustic Droplet Vaporization Threshold Pressure
Nucleation at a Liquid-Liquid Interface
Nucleation in a Binary Mixture of Perfluorocarbons
Kinetic Limit of Superheat
ADV Threshold and Limit of Superheat: Comparison of Theoretical Predictions with Experiments
Conclusion
References
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