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.

Highlights

  • Water is the universal solvent and plays a critical role in all known geological and biological processes

  • The physicochemical properties of water are controlled by the hydrogen- (H) bonding network, which is comprised of intermolecular interactions of water molecules[1]

  • Spatial confinement leads to deviations in the thermodynamic and physical properties of water, compared to those observed in the bulk non-confined phase

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Summary

Methods

The BET surface area for each mesoporous silica was obtained using Micrometrics Tristar 3000 Sorptometer or an Autosorb iQ2-Chemi instrument (Quantachrome Instruments, Boynton Beach, Florida, USA) following a procedure described previously[46]. The procedure on both instruments was the same. Samples were degassed under vacuum at 300 °C for 20 hours This information was used, along with the N2 BET data, to calculate the density and surface tension of water in the pores, based off the calculations from Takei et al.[7].

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