Water properties under nano-scale confinement

Abstract

Water is the universal solvent and plays a critical role in all known geological and biological processes. Confining water in nano-scale domains, as encountered in sedimentary rocks, in biological, and in engineered systems, leads to the deviations in water’s physicochemical properties relative to those measured for the non-confined phase. In our comprehensive analysis, we demonstrate that nano-scale confinement leads to the decrease in the melting/freezing point temperature, density, and surface tension of confined water. With increasing degree of spatial confinement the population of networked water, as evidenced by alterations in the O-H stretching modes, increases. These analyses were performed on two groups of mesoporous silica materials, which allows to separate pore size effects from surface chemistry effects. The observed systematic effects of nano-scale confinement on the physical properties of water are driven by alterations to water’s hydrogen-bonding network—influenced by water interactions with the silica surface — and has implications for how we understand the chemical and physical properties of liquids confined in porous materials.

Anomalously High Proton Conduction of Interfacial Water

“…The effective thickness h of the interfacial water layer is limited by a few nanometers 12,36 . Therefore, the enhanced conductivity of confined water observed in our experiment can be explained by the cumulative effect of the interfacial water with high ionic conductivity σi, and the water with bulk conductivity σw 37 .…”

Ionic liquids under nanoscale confinement

“…There is increasing evidence that extreme confinement of ILs can lead to a change of the freezing-melting temperature. The change in the melting point of a liquid in a confined geometry is described by the Gibbs-Thomson equation [64], which usually accounts for the depression of the freezingmelting point of the liquid (as in the case of water [65]) into a pore. This equation predicts a reduction of the freezing-melting temperature inversely proportional to the pore dimension and proportional to the difference Δγ=γ wl −γ ws between the wall-liquid surface energy γ wl and the wall-solidified liquid surface energy γ ws .…”

Porous versus Dense ‐ Effect of Silica Coating on Contrast Enhancement of Iron Carbide Nanoparticles in T2‐Weighted Magnetic Resonance Imaging

“…recently showed that the water existing in nanoscale confinement behaves more like ice in a mesoporous silica system. Due to increased impact of surface water‐silanol interactions, the ice like effects are more significant when mesopores are smaller than 5 nm . Therefore, high transverse relaxivity of mesoporose silica coated iron carbide NPs can be explained by the effect of hydrophilic mesoporous shell which increases the capability of trapping large amounts of ice‐like water with high T 2 relaxation rate …”