Bubble formation in nanopores: a matter of hydrophobicity, geometry, and size

Abstract

This review focuses on the phase behaviour of liquids in nanoscale confinement, which promotes drying by a combination of hydrophobicity, small size, and high degree of confinement. In these conditions, the vapour phase can form at exceptionally large pressures or low temperatures as compared to bulk vaporisation, giving rise to the unexpected formation of bubbles. A general framework is introduced which allows to understand the main effects of confinement on the thermodynamics and on the kinetics of drying. The relevance of such phenomena is discussed in the realm of biological nanopores, specifically ion channels, and in nanoporous materials. The emergence of nanoscale effects not accounted for in macroscopic theories is discussed together with the open challenges in this rapidly expanding field.

Unveiling the Gating Mechanism of CRAC Channel: A Computational Study

“…This behaviour is not completely unexpected considering that in TMD the biasing potential is applied to the protein structure while water molecules redistribute spontaneously as a result of the changing chemical environment around them. In addition, the formation/destruction of the bubble is typically a first order transition, which, once triggered by structural changes, can be irreversible on the simulation timescale ( Giacomello and Roth, 2020 ); therefore very slow changes in the biasing potential are needed to avoid artifact. In this regard, it is also notable that the O → C simulation had to be 5 times longer than the C → O simulation.…”

Structure and dynamics of water confined in cylindrical nanopores with varying hydrophobicity

“…As is customary for the phase behaviour of water confined in this kind of system, depending on the pore hydrophobicity, one or two (meta)stable states of the system can exist, associated with wet and dry pores. The relative stability is highly dependent on the hydrophobicity, size of the pores and thermodynamic conditions [ 11 ]. Initializing the simulation in the wet state is typically sufficient in order to produce consistent sampling of the structure of confined liquid water, without observing evaporation events; yet more hydrophobic pores are characterized by low free-energy barriers for vapour bubble nucleation, making it possible to observe spontaneous vapour nucleation events during the computationally accessible simulation times.…”

“…The interest in the properties of confined water is further amplified by the extraordinary phenomenology (e.g. transport properties and phase behaviour) observed in a large class of technologically and biologically relevant systems, including (carbon) nanotubes [ 4 – 6 ], nanoporous materials [ 7 – 11 ] and ion channels [ 12 ].…”

Liquid intrusion in and extrusion from non-wettable nanopores for technological applications

“…Concerning further applications of liquid intrusion/extrusion, we focused on the narrow field related to energy and materials with negative compressibility. Actually, intrusion/extrusion of liquids into/from porous materials is of great importance for a much broader range of applications, e.g., liquid-phase chromatography, liquid separation, artificial and biological nanopores [13], and many more. Here, we refrain from discussing too many applications and aspects at the same time with the objective to give the theoretical and simulation fundamentals of intrusion/extrusion phenomena for researchers interested in the field.…”

“…Intrusion/extrusion of liquids in porous systems is important for many technological applications, among which the separation of liquids [1,2], liquid-phase chromatography [3,4], energy damping and storage [5,6], porosimetry for the characterization of the porous systems [7][8][9], biological and bioinspired channels [10][11][12][13], and many more. Intrusion/extrusion is important also for textured surfaces, i.e., surfaces presenting roughness that enhance their intrinsic lyophobicity, the property to repel a liquid (see below).…”