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Cavitation is the formation of a vapor bubble in a metastable liquid. It occurs in numerous situations, ranging from engineering (ultrasonic cleaning, cavitation erosion) to the natural sciences (embolism in trees). Bulk cavitation is qualitatively well described by the Classical Nucleation Theory (CNT), provided that the dependence of surface tension on curvature is taken into account [1,2]. In contrast, in porous materials, cavitation should deviate from the bulk behavior if it occurs in pores of a size comparable to that of the critical bubble. This phenomenon is likely to occur in porous materials with nanometer-sized pores connected to the external gas reservoir through smaller apertures, such as in porous silicas with cage-like pores. Recent experimental studies suggest that confinement is at play when cavitation occurs in pores below 10 nm [3,4].
In the CNT picture, the energy barrier, entering the nucleation rate equation, corresponds to a saddle point, i.e. to the lowest energy conformation of the growing bubble. It is therefore generally assumed that the bubble is spherical, and located at the center of the pore [5,6]. However, the range of possible localizations of a confined gas bubble is governed by a free-energy landscape, resulting from the balance between energetic contributions, associated with interfacial free energy, and entropic-like contributions, due to the degrees of freedom related to position and shape of the bubble. There is therefore a non-negligible probability that the bubble nucleates away from the center [7]. Here, using molecular simulations in the canonical ensemble, we investigate the case of a nitrogen gas bubble confined within a filled spherical silica mesopore (mimicking SBA-16 cages). Further investigations in the grand canonical ensemble will also enable us to study the case of the spontaneous transient bubbles appearing in a metastable liquid [8]. This work is expected to provide an improved phenomenological model of nucleation barriers to interpret recent experimental data on cavitation under confinement and to probe nucleation beyond the predictions of the CNT [4].
| References | [1] M. Bossert, A. Grosman, I. Trimaille, F. Souris, V. Doebele, A. Benoit-Gonin, L. Cagnon, P. Spathis, P.-E. Wolf and E. Rolley, Evaporation Process in Porous Silicon: Cavitation vs Pore Blocking. Langmuir 37, 14419–14428 (2021). [2] M. Bossert, I. Trimaille, L. Cagnon, B. Chabaud, C. Gueneau, P. Spathis, P. E. Wolf and E. Rolley, Surface tension of cavitation bubbles. Proc. Natl. Acad. Sci. U. S. A. 120, e2300499120 (2023). [3] C. J. Rasmussen, A. Vishnyakov, M. Thommes, B. M. Smarsly, F. Kleitz and A. V. Neimark, Cavitation in Metastable Liquid Nitrogen Confined to Nanoscale Pores. Langmuir 26, 10147-10157 (2010). [4] E. Rolley et al., Cavitation in Confined Fluids, INTERPORE2026, abstract 605 [5] F. Bonnet, P.-E. Wolf, Thermally Activated Condensation and Evaporation in Cylindrical Pores. J. Phys. Chem. C 123, 1335-1347 (2019). [6] K. Morishige, Revisiting the Nature of Adsorption and Desorption Branches: Temperature Dependence of Adsorption Hysteresis in Ordered Mesoporous Silica. ACS Omega 6, 15964-15974 (2021). [7] J. Puibasset, Cavitation in Heterogeneous Nanopores: The Chemical Ink-Bottle. AIP Adv., 11, 095311 (2021). [8] J. Puibasset, Molecular-sized bubbles in a liquid: Free energy of formation beyond the capillarity approximation. J. Chem. Phys. 163, 034110 (2025). |
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| Country | France |
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