Capillary rise of water in hydrophilic nanopores

Abstract

We report on the capillary rise of water in three-dimensional networks of hydrophilic silica pores with 3.5 nm and 5 nm mean radii, respectively (porous Vycor monoliths). We find classical square root of time Lucas-Washburn laws for the imbibition dynamics over the entire capillary rise times of up to 16 h investigated. Provided we assume two preadsorbed strongly bound layers of water molecules resting at the silica walls, which corresponds to a negative velocity slip length of -0.5 nm for water flow in silica nanopores, we can describe the filling process by a retained fluidity and capillarity of water in the pore center. This anticipated partitioning in two dynamic components reflects the structural-thermodynamic partitioning in strongly silica bound water layers and capillary condensed water in the pore center which is documented by sorption isotherm measurements.

Inhomogeneous relaxation dynamics and phase behaviour of a liquid crystal confined in a nanoporous solid

“…The entirely filled sample (fraction filling f =1.0) has been obtained by melt infiltration, that is capillaritydriven filling of the channels [8,[77][78][79]. To prepare the partially filled samples (0 < f < 1) we imbibed the porous matrix with binary 7CB/cyclohexane solutions of selected concentrations.…”

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

“…The first regime occurs in pores that are about 2 to 20 nm wide and results from "surface water" [water with structure and dynamics distinct from those of bulk liquid water, found within up to three statistical monolayers (~0.9 nm) from hydrophilic surfaces 34,35 ] constituting a nonnegligible part of the pore water 25,27,34 . In this regime, the average behavior of pore water is sometimes represented with a "core-shell" model, on which pore water is conceptually divided into a core of "free" water with bulk-liquid-like properties and a shell of "surface" water with distinct properties 25,27 . The second regime occurs in pores that are narrower than about 2 nm, where the bulk-liquid-like water core is absent 2,34 and surface water is influenced by confinement between two surfaces rather than by interaction with a single surface 26 .…”

“…Ice crystals formed in the free pore water in 2.4 nm diameter pores have a smaller lattice constant than those formed in 4.2 nm diameter pores, suggesting that confinement influences the structure of water even in the core region 29 . More recent research has concentrated on revealing the properties of ambient liquid water in silica nanopores including its structure 3,6,31 , vibrational 5 dynamics 4 , diffusivity 2,32 , and viscosity 25 . These studies showed that the first one or two statistical water monolayers on the silica surface are ordered and much less mobile than the rest of the pore water 3,25,37 .…”

“…Studies of water in hydrophilic nanopores carried out with a range of techniques (thermoporometry 1,24 , capillary imbibition 25 , surface force apparatus 22,26 , infrared and Raman spectroscopy 4,17,18,21,27 , NMR spectroscopy 28 , X-ray and neutron diffraction 6,[29][30][31] , quasi-elastic neutron 4 scattering 2,32 , molecular dynamics simulations 26,[33][34][35][36] ) show that this failure occurs in pores narrower than ~20 nm and can be classified into two regimes. The first regime occurs in pores that are about 2 to 20 nm wide and results from "surface water" [water with structure and dynamics distinct from those of bulk liquid water, found within up to three statistical monolayers (~0.9 nm) from hydrophilic surfaces 34,35 ] constituting a nonnegligible part of the pore water 25,27,34 . In this regime, the average behavior of pore water is sometimes represented with a "core-shell" model, on which pore water is conceptually divided into a core of "free" water with bulk-liquid-like properties and a shell of "surface" water with distinct properties 25,27 .…”

Communication: Slow proton-charge diffusion in nanoconfined water

“…The precise confinement volume below which such collective dynamics, and thus proton-charge diffusion, slows down may be system dependent, and may be slightly larger in systems in which (unlike reverse micelles) more than one water monolayer is immobilized by surface binding. 48 In view of the above-discussed relation between protoncharge diffusion and water dynamics, it is interesting to investigate whether a correlation exists between the average reorientation rate of the water molecules in the nanodroplets and the diffusion constant of the proton. We indeed find (Fig.…”