Neutron Scattering Study on Dynamics of Water Molecules in MCM-41

Takahara, S; M, Nakano; Kittaka, Shigeharu; Kuroda, Yasushige; Mori, T.; Hamano, Hideaki; Yamaguchi, Toshio

doi:10.1021/jp984136j

Cited by 179 publications

(235 citation statements)

References 10 publications

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“…The success (even for pore diameters as low as 1 nm) of this very simple core-shell conceptual model is remarkable in view of the fact that the actual decrease in water mobility near hydrophilic surfaces occurs gradually over two or three water layers and that the first water layer is not really and MD simulation studies 38,43 , but it supports recent MD simulation results by Lerbret et al 37 . Our results on water diffusion are consistent with QENS data 32,96,97 (yielding a measure of confidence in the quality of our MD simulations) and can be described with a very simple "core-shell" conceptual model on which the first water monolayer is immobile on diffusive time scales while the rest of the pore water diffuses as fast as bulk liquid water.…”

Section: Water Density Distributionsupporting

confidence: 87%

“…4 by calculating the slope of MSD(τ) from τ = 2 to 10 ps and by using a MSD(τ) function calculated either in the xy plane or in the z direction, whichever was parallel to the nearest surface. Our predicted D nanopore values are compared in Figure 8 with experimental results obtained by quasi-elastic neutron scattering (QENS) 32,96,97 . Most models used to interpret QENS data treat a small portion of the pore water as immobile.…”

Section: Water Density Distributionmentioning

confidence: 99%

“…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 . Studies of water in hydrophilic nanopores carried out with a range of techniques (thermoporometry 1,24 , capillary imbibition 25 , surface force apparatus 22,26 , infrared and Raman spectroscopy 4,17,18,21,27 , NMR spectroscopy 28 , X-ray and neutron diffraction 6,[29][30][31] , quasi-elastic neutron 4 scattering 2,32 , molecular dynamics simulations 26,[33][34][35][36] ) show that this failure occurs in pores narrower than ~20 nm and can be classified into two regimes. The first regime occurs in pores that are about 2 to 20 nm wide and results from "surface water" [water with structure and dynamics distinct from those of bulk liquid water, found within up to three statistical monolayers (~0.9 nm) from hydrophilic surfaces 34,35 ] constituting a nonnegligible part of the pore water 25,27,34 .…”

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

2012

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We present molecular dynamics (MD) simulations of water-filled silica nanopores such as those that occur in ordered oxide ceramics (MCM-41, SBA-15), controlled pore glasses (such as Vycor glass), mesoporous silica, bioglasses, and hydrous silica gel coatings of weathered minerals and glasses. Our simulations overlap the range of pore diameters (1 to 4 nm) where confinement causes the disappearance of bulk-liquid-like water. In ≥ 2 nm diameter pores, the silica surface carries three statistical monolayers of density-layered water, interfacial water structure is independent of confinement or surface curvature, and bulk-liquid-like water exists at the center of the pore (this last finding contradicts assumptions used in most previous neutron diffraction studies and in several MD simulation studies of silica nanopores). In 1 nm diameter pores, bulk-liquidlike water does not exist and the structural properties of interfacial water are influenced by confinement. Predicted water diffusion coefficients in 1 to 4 nm diameter pores agree with quasi-elastic neutron scattering (QENS) data and are roughly consistent with a very simple "core-shell" conceptual model whereupon the first statistical water monolayer is immobile and the rest of the pore water diffuses as rapidly as bulk liquid water.

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Section: Water Density Distributionsupporting

confidence: 87%

Section: Water Density Distributionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

2012

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“…[21][22][23][24][25] The slowing down of both rotational and/or translational motions of confined water molecules has been also verified to be promoted with decreasing pore sizes and temperatures. [26][27][28][29] These results have suggested that the specific hydrogen bonding network of water layer on surfaces differing from bulk water, i.e., the adsorbed water phase, is responsible for causing the freezing behavior of confined water in the supercooled state.…”

Section: Introductionmentioning

confidence: 98%

Temperature and Size Effects on Structural and Dynamical Properties of Water Confined in 1 – 10 nm-scale Pores Using Proton NMR Spectroscopy

et al. 2017

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We were able to fill 1 -10 nm-scale silica pores with water by vapor condensation, and examined the freezing phenomena, structures, and molecular motions of the confined water in the temperature range from 293 to 188 K by 1 H-NMR spectroscopy. The results showed that almost all water molecules confined in 10 nm-scale pores were frozen and that approximately half of the water confined in 1 nm-scale pores existed in the liquid state even below the freezing point. The water adsorbed on the pore surfaces was estimated as a monolayer in 2.58 nm pores and bi-and tri-layers in 6.48 nm and larger pores, respectively. Furthermore, it was clarified from the proton relaxation rate ( 1 H-1/T1) measurements that the molecular motions of adsorbed water itself were restricted by nanoconfinement and were extremely dependent on the conditions of proton exchange and hydrogen bond rearrangements of the adsorbed water.

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“…Quasi-elastic neutron scattering measurements demonstrated the strong confinement effect on translational diffusion of water molecules to decrease, while rotational motion was not affected remarkably. 37 Neutron spin echo analysis, however, indicated clear difference in dynamic nature between monolayer water and central bulky water in the pore. 20 Poor interconnection between both phases has been substantiated by DSC analysis of freezing-melting of pore water.…”

Section: -9mentioning

confidence: 97%

Dielectric study on two dynamic phases of 1-propanol confined in mesopores of MCM-41

2013

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Two dynamic phases were recognized on the 1-propanol molecules confined in MCM-41 with pore diameters d = 2.1, 2.4, 2.7 and 3.6 nm by dielectric measurements, in which two types of confined states of liquid were investigated: surface-adsorbed (sa) and pore-filled (pf) liquid. The dielectric measurements in the frequency range 103–107 Hz and temperature range 120–300 K showed that the molecular motions became slower in the following order: bulk, pf and sa liquid, which is the same order as for methanol and ethanol confined in MCM-41 reported previously. For pf samples, two relaxation components, which correspond to molecules near the pore surface and at the center of the pores, were observed separately. This is somewhat different from the behavior of methanol and ethanol confined as pf state in which two relaxation components were also detected but a clear separation between them was not observed. This implies that 1-propanol molecules near the pore wall interact weakly with those at the central part of the pores. For the MCM-41 sample with the smallest pore diameter (d = 2.1 nm), however, the dielectric spectra of the pf sample were very similar to those of the sa sample. That is, the dynamic motion of molecules in the pf sample was inhibited by narrow space surrounded by monolayer molecules similarly to that in the sa sample

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Neutron Scattering Study on Dynamics of Water Molecules in MCM-41

Cited by 179 publications

References 10 publications

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

Molecular Dynamics Simulations of Water Structure and Diffusion in Silica Nanopores

Temperature and Size Effects on Structural and Dynamical Properties of Water Confined in 1 – 10 nm-scale Pores Using Proton NMR Spectroscopy

Dielectric study on two dynamic phases of 1-propanol confined in mesopores of MCM-41

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