Abstract
Structural transformations originating from diverse rearrangements of the hydrogen bonding in water create various phases. Although most phases have been well investigated down to the molecular level, the molecular structure of the nanomeniscus, a ubiquitous form of nanoscale water in nature, still remains unexplored. Here, we demonstrate that the water nanomeniscus exhibits the stable, ice-VII-like molecular structure in ambient condition. Surface-enhanced Raman spectroscopy on trace amounts of water, confined in inter-nanoparticle gaps, shows a narrowed tetrahedral peak at 3340 cm-1 in the OH-stretching band as well as a lattice-vibrational mode at 230 cm-1. In particular, the ice-VII-like characteristics are evidenced by the spectral independence with respect to temperature variations and differing surface types including the material, size and shape of nanoparticles. Our results provide un unambiguous identification of the molecular structure of nanoconfined water, which is useful for understanding the molecular aspects of water in various nanoscale, including biological, environments.
Highlights
Structural transformations originating from diverse rearrangements of the hydrogen bonding in water create various phases
By using the natural confinement system of dried silver nanoparticulate we have succeeded in demonstrating its molecular structure by a common analyzing technique of Raman spectroscopy, showing that the water nanomeniscus has the similar hydrogenbonding character of ice-VII even in ambient conditions
We have repeatedly performed precipitation and dispersion of the solution to decrease the concentration of impurities below 1 nM to maximize the impregnation possibility of pure water in the nanogaps within the silver nanoparticulates when dried in ambient condition
Summary
Structural transformations originating from diverse rearrangements of the hydrogen bonding in water create various phases. 1234567890():,; There has been increasing interest in how water changes its structure and properties when confined at nanoscale[1], for example, in the low-dimensional confinement in graphene[2,3,4] or carbon nanotubes[5,6,7,8] Unlike such artificially prepared nanostructures, water nanomenisci are naturally and prevalently formed by capillary condensation between nearby surfaces or by ambient drying in micro- and nano-particulates, such as in wet sand[9], sticky flour[10], swelling clay[11] and frictional material[12]. The unique phase of ice-VII has been investigated widely in geology and planetary science, because it serves as an indicator for the existence of water or ice in inaccessible frontiers, such as Earth’s deep mantle and extra-terrestrial outer space[15,16,17] This is because the temperature and pressure ranges in the phase fields of the bulk ice-VII match those found in such extreme environments. Our optical spectroscopic findings show that iceVII-like molecular structure can exist as a highly stable state of water even in normal terrestrial ambient conditions
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