Structure and Dynamics of Water and Nonaqueous Solvents Confined in Extended Nanospaces Characterized by NMR Spectroscopy

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  • TSUKAHARA Takehiko
    Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
  • MORIKAWA Kyojiro
    Research Laboratory for Nuclear Reactors, Tokyo Institute of Technology
  • MAWATARI Kazuma
    Department of Applied Chemistry, School of Engineering, The University of Tokyo
  • KITAMORI Takehiko
    Department of Applied Chemistry, School of Engineering, The University of Tokyo

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Other Title
  • NMR分光法で見る拡張ナノ空間内における水及び非水溶媒の分子構造とダイナミクス
  • NMR ブンコウホウ デ ミル カクチョウ ナノ クウカン ナイ ニ オケル ミズ オヨビ ヒミズヨウバイ ノ ブンシ コウゾウ ト ダイナミクス

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Abstract

An extended nanospace (10—100 nm scale) makes it possible to induce unique physicochemical properties, because scientific and technological concepts in this region are shifted from the bulk condensed phase to single molecule, and from microfluidic technology to conventional nanotechnology, respectively. In this study, the molecular structure and dynamics of water and nonaqueous solvents confined in extended nanospaces on a fused-silica substrate were examined by using NMR chemical spectra, relaxation times, and so on. The results showed that the collective properties of molecular clusters with a size range from 10 to 100 nm in a liquid phase were characterized due to the effects of charged surface SiOH groups, and that unique properties differing from bulk water and surface-adsorbing water could appear in extended nanospaces. In particular, we found that (1) inhibition of molecular translational motions, (2) localization of proton charge distribution along a linear O···H–O hydrogen bonding chain, and (3) an enhancement of proton transfer of water due to the Grotthuss mechanism; (∫SiO−···H+···H2O) + H2O→∫SiO− + (H3O+ + H2O)→∫SiO− + (H2O + H3O+), were induced in extended nanospaces. Such changes appeared for sizes smaller than 800 nm. These results suggested that a proton transfer phase, in which water molecules are loosely coupled within about 50 nm from the surface, exists in extended nanospaces. This model could be qualitatively supported by a three-phase theory invoking the bulk, proton transfer, and surface-adsorbing phases.

Journal

  • BUNSEKI KAGAKU

    BUNSEKI KAGAKU 64 (4), 261-271, 2015

    The Japan Society for Analytical Chemistry

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