Cavitation and Confinement – CAVCONF

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.