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

Abstract

We report a detailed study of the main structural and dynamical features of water confined in model Lennard–Jones nanopores with tunable hydrophobicity and finite length ( L = 26 Å). The generic model of cylindrical confinement used is able to reproduce the wetting features of a large class of technologically and biologically relevant systems spanning from crystalline nanoporous materials, to mesoporous silica and ion channels. The aim of this work is to discuss the influence of parameters such as wall hydrophobicity, temperature, and pore size on the structural and dynamical features of confined water. Our simulation campaign confirmed the existence of a core domain in which water displays bulk-like structural features even in extreme ( R = 7.0 Å) confinement, while dynamical properties were shown to depend non-trivially on the size and hydrophobicity of the pores. This article is part of the theme issue ‘Progress in mesoscale methods for fluid dynamics simulation’.

Mechanism of Water Intrusion into Flexible ZIF-8: Liquid Is Not Vapor

“…However, attention has recently turned toward the investigation of the microscopic mechanism of hydrophobic ZIF wetting . Deepening the understanding of hydrophobic wetting has been the main goal of several groups in the scientific community in recent years, exploring the effects of confining water in hydrophobic nanopores, the interactions of water with different hydrophobic surfaces, and the liquid and vapor interfaces in nanoconfinement under hydrostatic pressure. − In a recent work, Sun et al, proposed the intrusion of ZIF-8 to be governed by the condensation of vapor present in the nanoscale cages, postulating that the kinetics of the intrusion process is determined by the intrinsic length (single nanometer) and time scales (nanoseconds) necessary for critical water clusters to nucleate inside individual cages.…”

Local grafting heterogeneities control water intrusion and extrusion in nanopores

“…For extrusion, on the other hand, simulations show that local accumulations of hydrophobic material and constrictions act as nucleation seeds for vapor bubbles. These effects were not accessible by previous simulation efforts on idealized hydrophobic nanopores without explicit functionalization 18,23 .…”

Reversible Surface Energy Storage in Molecular-Scale Porous Materials

“…Figure 5 shows the dependence of simulated intrusion and expulsion pressures, P in and P ex , on the pore diameter h. The increased volatility of confined water observed upon the reduction of pore diameter conforms to intensified depletion of the overall hydrogen bonding and concomitant structural changes as hydration water becomes the majority component in the system [38]. The observed variation of P in can be approximated by the macroscopic relation P in ∼ = of the pores.…”

“…Figure5shows the dependence of simulated intrusion and expulsion pressu and Pex, on the pore diameter h. The increased volatility of confined water observed the reduction of pore diameter conforms to intensified depletion of the overall hyd bonding and concomitant structural changes as hydration water becomes the m component in the system[38]. The observed variation of Pin can be approximated macroscopic relation 𝑃 ≅ ∆ , where ∆𝛾 represents the wetting free energy of th and ℎ ≈ ℎ − 𝜎 is the water-accessible width of the pore obtained by subtract diameter of CHn groups (𝜎 = 3.74 Å for the given model) from the C-C dista across the pore.…”