A trapped water network in nanoporous material: the role of interfaces

Abstract

The infrared spectra of water confined in well controlled pore glasses were recorded as a function of the pore size ranging from 8 to 320 nm and in the 30-4000 cm(-1) spectral range using the ATR technique. The experiments prove that even in the large pores, the water network is significantly perturbed. The energy of the connectivity (or hindered translation) band (around 150 cm(-1)) is found to increase when the pore size decreases, indicating that confinement increases the H-bonding between neighbouring water molecules. Moreover, a drastic decrease of the FWHM of the connectivity band was observed upon confinement. This can be related to some ordering induced by the rigid walls of the pores. Furthermore, the partial filling of pores causes a significant modification to the water network, resembling heating of the trapped liquid and suggesting a role played by the water/air interface.

Infra-red imaging of bulk water and water–solid interfaces under stable and metastable conditions

“…However, the measurements gained throughout this study are not sufficient to establish a firm conclusion on the exact role played by the interfaces to stabilize the entrapped liquid. It is noteworthy to stress that we are not able to separate the potential mixed effects between the interfacial role and the confinement, possibly acting also in solids in the thinnest part (50-500 nm 28,29 ) of the cavities. In parallel,…”

“…We confirm the surprising ability of vibrational spectroscopy to get insights the H-bond networking at the sub-wavelength scale. Le Caer et al 29 observed the effects of confinement over hundreds of nanometers, and also were able to record the appearance of liquid-air interfaces during drying experiments. The present work is a further encouraging step in the same direction, to use the IR micro-spectroscopy in studying the versatility of the liquid water properties.…”

“…Actually, the inward unbalanced forces which make up the specificity of the interfacial region 28 ), or even 320 nm (far-and mid-infrared spectroscopy 29 ).…”

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

“…This fundamental question has implications for the utility of synthetic nanoporous silicates such as ordered oxide ceramics (MCM-41, SBA-15) [1][2][3] , controlled pore glasses (CPG, including Vycor glass) 1,4 , mesoporous silica 5,6 , and bioglasses 7 . In geochemistry, it determines the influence of hydrous silica gel coatings on the long-term weathering rates of silicate glasses and minerals 8,9 , these rates being important unknowns in studies of soil formation 10 and global carbon cycling 11 and in predicting the fate of CO 2 12,13 and high-level radioactive waste in geological repositories 14,15 .…”

“…In geochemistry, it determines the influence of hydrous silica gel coatings on the long-term weathering rates of silicate glasses and minerals 8,9 , these rates being important unknowns in studies of soil formation 10 and global carbon cycling 11 and in predicting the fate of CO 2 12,13 and high-level radioactive waste in geological repositories 14,15 . From a theoretical perspective, the question is compelling because hydrophilic silica nanopores can be readily fabricated with well-controlled structural features (the materials listed above have an amorphous SiO 2 matrix, silanol surface functional groups, cylindrical pores, and pore diameters that can be varied from about 1 nm to more than 100 nm [1][2][3][4]6 ) for probing the new physics of water that occur due to finite-size effects, a frontier research area with broad implications in catalysis 16 , biology 17,18 , nanofluidics 19,10 , membrane science 2`, and the geosciences [21][22][23] . Theoretical models of transport and chemistry in water-filled nanopores routinely rely on the simplifying approximation that water properties are not modified by confinement 19 , but this approximation is expected to fail in nanoporous media where pore size approaches the diameter of a water molecule 20 .…”