Direct Observation of Homogeneous Cavitation in Nanopores

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Direct Observation of Homogeneous Cavitation in Nanopores

V. Doebele, A. Benoit-Gonin, F. Souris, L. Cagnon, P. Spathis, P. E. Wolf, A. Grosman, M. Bossert, I. Trimaille, and E. Rolley

Phys. Rev. Lett. 125, 255701 – Published 15 December 2020

Abstract

We report on the evaporation of hexane from porous alumina and silicon membranes. These membranes contain billions of independent nanopores tailored to an ink-bottle shape, where a cavity several tens of nanometers in diameter is separated from the bulk vapor by a constriction. For alumina membranes with narrow enough constrictions, we demonstrate that cavity evaporation proceeds by cavitation. Measurements of the pressure dependence of the cavitation rate follow the predictions of the bulk, homogeneous, classical nucleation theory, definitively establishing the relevance of homogeneous cavitation as an evaporation mechanism in mesoporous materials. Our results imply that porous alumina membranes are a promising new system to study liquids in a deeply metastable state.

Received 9 July 2020
Revised 16 October 2020
Accepted 30 October 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.255701

Physics Subject Headings (PhySH)

Cavitation Confinement Desorption Nucleation

Drops & bubbles Gas-liquid interfaces Nanostructures Porous materials

Film deposition Optical interferometry Static light scattering

Condensed Matter, Materials & Applied PhysicsPolymers & Soft MatterStatistical Physics & Thermodynamics

Authors & Affiliations

V. Doebele¹, A. Benoit-Gonin ¹, F. Souris ¹, L. Cagnon ¹, P. Spathis ¹, P. E. Wolf ^1,†, A. Grosman^2,*, M. Bossert², I. Trimaille², and E. Rolley ^3,‡

¹Université Grenoble Alpes, CNRS, Institut Néel, F-38042 Grenoble, France
²Sorbonne Université, CNRS, Institut des NanoSciences de Paris, INSP, F-75005 Paris, France
³Laboratoire de Physique de l’Ecole Normale Supérieure, ENS, Université PSL, CNRS, Sorbonne Université, Université de Paris, F-75005 Paris, France

^*Deceased.
^†pierre-etienne.wolf@neel.cnrs.fr
^‡rolley@phys.ens.fr

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Vol. 125, Iss. 25 — 18 December 2020

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Images

Figure 1
Cavitation in an ink-bottle geometry. (a) Straight cylindrical pore opened to a vapor reservoir, which empties through recession of the liquid-vapor meniscus. The smaller the pore diameter, the smaller the evaporation pressure. (b,c) Two possible evaporation mechanisms for a cavity ended by a cylindrical constriction. In panel (b), the constriction empties at its equilibrium pressure, triggering further evaporation in the wider cavity through meniscus recession; in panel (c), if the constriction is narrow enough for its evaporation pressure to lie below the cavitation threshold, the cavity empties by cavitation, while the constriction remains filled with liquid.
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Figure 2
Cavitation in an alumina membrane. Starting from a native alumina membrane with 60-nm-diameter pores (a), successive 2-nm-thick alumina layers are deposited at the mouth of the pore, reducing the pore aperture [(b), 8 layers]. Sorption isotherms of hexane are measured at $18 ° C$ (c) as described in the text. The membrane fluid content is deduced from $Δ n$ , the change of the membrane optical index with respect to the empty state. The (superimposed) dashed curves are the condensation isotherms, and the continuous lines are the evaporation isotherms, for increasing deposits of alumina at the pore mouth (black is for native, green for 8 layers, blue for 10 layers, and red for 12 layers). For intermediate coatings, the noise is due to a loss of contrast of the interference pattern (resulting from a strong light scattering [20]). The sharp drop at $- 20 MPa$ is the signature of cavitation.
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Figure 3
Evaporation in porous silicon ink bottles. (a) Isotherms for an alumina-coated poSi sample [left part of panel (c)]. Superimposed dashed lines correspond to condensation and solid lines to evaporation. Black lines are poSi as prepared ( $⟨ d ⟩ = 26 nm$ , pore length $l = 20 μ m$ ); green/blue/red lines are poSi coated by $2 / 6 / 8$ alumina layers. For as-prepared poSi, the condensation isotherm is much less steep than in the case of poAl, reflecting the wider distribution of pore diameters. (b) Isotherms obtained on a duplex-layer sample formed by successively electro-etching a top layer with small pores $⟨ d ⟩ = 12 nm$ and a bottom layer with large pores $⟨ d ⟩ = 26 nm$ [right part of panel (c)]. The contributions of the two layers are plotted separately in black for the top layer and in red for the bottom layer. (c) Binarized transmission electron microscopy (TEM) images of the cross section of cavities ( $⟨ d ⟩ = 26 nm$ , red) and of the constrictions of the duplex sample ( $⟨ d ⟩ = 12 nm$ , black).
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Figure 4
Cavitation rate $Γ$ at 19°C as a function of liquid pressure $P_{L}$ for poAl membranes with average pore diameters $d = 60 nm$ and $d = 25 nm$ . Here, $Γ$ is measured from the exponential decay of the number of filled pores following a quench of the pressure reservoir from 60 mb down to a lower pressure ranging between 52 and 55 mbar, as illustrated in the inset for the 60-nm membrane. The fraction of filled pores $ϕ$ is measured through the logarithm of the optical transmission and normalized to its value at time $t = 0$ , corresponding to a 10% transmission [20]. The cavitation rate per unit volume $Γ$ is deduced by dividing the decay rate by the pore volume, which is computed using $d = 56 nm$ and $d = 27 nm$ . These values lie within the error bars of the measured values above and are such that $Γ (P_{L})$ is identical for the two membranes. Lines correspond to the CNT predictions for different values of the attempt rate or the surface tension (see text).
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