5 years ago

Threshold for Vapor Nanobubble Generation Around Plasmonic Nanoparticles

Threshold for Vapor Nanobubble Generation Around Plasmonic Nanoparticles
Samy Merabia, Thierry Biben, Julien Lombard
Vapor nanobubbles are transient bubbles that are generated by plasmonic nanoparticles illuminated by a pulsed laser and that have been proposed for cancer therapy. Their physical properties are, however, poorly understood. In this article, we discuss the conditions of appearance of these nanobubbles, on the basis of a hydrodynamics phase field model. In particular, we critically assess the role of the Laplace pressure which was invoked to control the onset of nanobubble production. We clearly demonstrate that capillary effects have only a mild effect on the process of nanoscale vaporization. We also characterize the threshold of nanoscale boiling under different conditions of nanoparticle size and contact angle. We conclude that a very thin shell of liquid water should be brought at the spinodal temperature Tspin ≃ 550 K, which gives upper bounds for the shell assumption of Katayama et al. ( Langmuir 2014, 30, 9504), who consider that a finite volume should be heated at Tspin to create a nanobubble. The existence of a finite thermal resistance at the interface between the particle and water controls the vaporization kinetics, and severly delays vapor nanobubble generation in the vicinity of the corresponding threshold. Finally, we compare the predictions of the hydrodynamic model to available experimental data, corresponding to respectively nanoseconds and femtoseconds pulses. The hydrodynamic simulations are in good agreement with the experimental results of Siems et al. ( New J. Phys. 2011, 13, 043018) and Katayama et al., provided that the possibility of gold nanoparticle melting is taken into account. All these considerations help in building a simple thermal diffusive model that may reproduce both the threshold and the kinetics of nanobubble generation, depending on the nanoparticle size and the laser pulse duration, without any fitting parameter.

Publisher URL: http://dx.doi.org/10.1021/acs.jpcc.7b01854

DOI: 10.1021/acs.jpcc.7b01854

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