Cavitation and Confinement – CAVCONF

In order to observe cavitation, the easier process of surface evaporation has to be impeded. Both in simulations and experiments, this is achieved by using an ink bottle geometry, where a cavity of tunable diameter is connected to an outer vapor reservoir through a narrow nanometric constriction, thus stabilizing the liquid inside the cavity.

Using molecular dynamics, we study the statistics of bubble formation in tens of successive simulation runs in a single pore. Experimentally, we achieve a similar goal in single shot experiments, by studying billions of ink bottles etched in silicon or alumina where cavitation unfolds independently and in parallel. Interferometric or volumetric measurements of the fluid mass inside the membranes as the pressure is decreased allow us to directly determine the relationship between pressure and nucleation rate, and to compare it to CNT or to the result of molecular dynamics.

Key results are obtained for both simulations and experiments. First, the ink bottle geometry does indeed allow to obtain homogeneous cavitation - i.e. the bubble appears away from the walls -, and to study its statistics.
Second, when the fluid-wall interaction is negligible, CNT quantitatively describes the measured cavitation rates provided the reduction of the surface tension for nanometric bubbles is accounted for.
Last, as expected, decreasing the cavity radius reduces the cavitation rate for a fixed pressure.

Key results are obtained for both simulations and experiments. First, the ink bottle geometry does indeed allow to obtain homogeneous cavitation - i.e. the bubble appears away from the walls -, and to study its statistics.
Second, when the fluid-wall interaction is negligible, CNT quantitatively describes the measured cavitation rates provided the reduction of the surface tension for nanometric bubbles is accounted for. Last, as expected, decreasing the cavity radius reduces the cavitation rate for a fixed pressure.

To go further, we aim to extend our measurements of cavitation to alumina membranes with smaller cavities (< 5 nm) than obtained up to now.
We also plan to extend the existing collaboration in partnership with B. Lebeau's team at Haute-Alsace University. This will allow us to study confinement in mesoporous silicas. These materials present networks of ink-bottles with narrower constrictions than presently achieved with alumina.
We expect that such measurements should allow us to decipher the influence of confinement, not only on the energy barrier for nucleation, but laos on the prefactor of the Arhenius law.

Thèses

[1] V. Doebele, Condensation et évaporation de l'hexane dans les membranes d'alumine poreuse. Thèse de doctorat, Université Grenoble Alpes (2019).

[2] M. Bossert, Étude expérimentale de la cavitation dans les milieux mésoporeux. Thèse de doctorat, Sorbonne Université (2022).

Articles

[1] Doebele V., Benoit-Gonin A., Souris F., Cagnon L., Spathis P., Wolf P. E., Grosman A., Bossert M., Trimaille I. and Rolley E., Direct Observation of Homogeneous Cavitation in Nanopores. Physical Review Letters 125, 25, 255701 (2020) [editor’s choice] .

[2] Bossert, M., Grosman A., Trimaille and Rolley E., Stress or Strain Does Not Impact Sorption in Stiff Mesoporous Materials,. Langmuir 36 (37) 11054-11060 (2020).

[3] Bossert, M., Grosman A., Trimaille I., Souris F., Doebele V., Benoit-Gonin A., Cagnon L., Spathis P., Wolf P.E. and Rolley E., Evaporation Process in Porous Silicon: Cavitation vs Pore Blocking,. Langmuir 37(49) 14419-14428 (2021).

[4] Puibasset, J. , Cavitation in heterogeneous nanopores: The chemical ink-bottle, AIP Advances 11, 9, 095311 (2021).

[5] M. Bossert I. Trimaille, L. Cagnon, B. Chabaud, C. Gueneau, P. Spathis, P. E. Wolf, and E. Rolley, Surface tension of cavitation bubbles, PNAS, 120 (15), pp.e2300499120 (2023)

[6] Puibasset, J., A General Relation Between the Largest Nucleus and All Nuclei Distributions for Free Energy Calculations, J. Chem. Phys, 157, 191102 (2022).

Cavitation, i.e. the formation of a vapor bubble in a stretched liquid, is of fundamental interest and plays a central role in many technologies and natural science. For decades, the consensus has been that, in bulk liquid, cavitation occurs via the stochastic formation of a bubble nucleus as described by the Classical Nucleation Theory (CNT). Whether the same could also happen in liquid confined inside a nanopore has only been recently considered. A few experiments, some of them performed by members of the consortium, suggest that liquids in nanoporous materials can indeed evaporate through cavitation. However, results are scarce, contradictory and no coherent picture has yet emerged.

In this project, the main issue is to elucidate if and how cavitation occurs in nanopores: what is the influence of fluid-wall interaction, of the temperature? Is nucleation homogeneous or heterogeneous? To this aim, we propose to explore the behavior of different fluids at variable temperatures in tailored nanomaterials with pores having a so-called ink-bottle geometry.

Another issue, and a pre-requisite for the study of confined cavitation, is to test accurately the relevance of the CNT to bulk, homogeneous, cavitation. To shed light on current issues in the field, we propose to use simple liquids (helium, nitrogen, and argon) as benchmark to perform bulk cavitation experiments using the so-called 'synthetic tree' developed at Cornell University.

The last issue concerns very small closed systems: it was recently predicted that the constraint of mass conservation could inhibit cavitation and lead to a superstabilization of a stretched liquid. We will carry out the first experimental study of this phenomenon to confirm, or rule out, its existence.

Our ambitious project is based on the complementary expertise from four laboratories : Institut Néel (NEEL), Institut des NanoSciences de Paris (INSP), Laboratoire de Physique Statistique de l'Ecole Normale Supérieure (LPSENS), and Interfaces, Confinement, Matériaux et Nanostructures, (ICMN). It gathers a unique ensemble of skills and know-how with several original features and challenges.

A first one is to use a large variety of fluids, going from simple cryogenic liquids (helium, argon, nitrogen) to more complex room temperature liquids (alkanes and water). Helium, a perfectly wetting fluid, will be a benchmark for purely homogeneous cavitation. Comparison with the other fluids will reveal the influence of the fluid structure and the nature of the fluid-wall interaction on cavitation.

A second original feature is to use cryogenic liquids up to their critical temperature, giving access to the region where cavitation is expected to be the mechanism of evaporation in porous materials.

A third one is to master the elaboration of porous silicon and porous alumina membranes with a controlled ink-bottle geometry allowing unambiguous detection of cavitation.

A fourth original feature is the joint approach coupling experiments and theoretical analysis, based on either a generalization of the CNT to a confined geometry or direct molecular simulations. These theoretical approaches will be compared together, and will help to rationalize our experimental results.

By exploring a large range of physical parameters such as the liquid-vapor surface energy or the fluid-wall interactions, together with the expected progresses in its theoretical numerical modeling, our project will bring unprecedented experimental information on cavitation, both in bulk and confined geometries. Beyond their expected large impact in the adsorption community, our results will be relevant for other fields of physics such as statistical or soft matter physics. They may also have implications in interdisciplinary fields such as geophysics or biophysics.