Studies of Water Adsorbed in Porous Vycor Glass

Hirama, Yasuko; Takahashi, Tomiki; Hino, Masao; Sato, Toshio

doi:10.1006/jcis.1996.0629

Cited by 63 publications

(54 citation statements)

References 17 publications

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“…Nonbridging oxygens (NBO's) are bonded to only one silicon atom and are saturated with a hydrogen atom. The number density of the hydroxyl groups in our samples is 2.5 nm −2 , in good agreement with the experimentally determined value [15]. The second species of surface oxygen atoms are bridging oxygens (BO's), which are connected to two silicon atoms.…”

Section: Model For the Vycor Pore And Molecular Dynamics Calculationssupporting

confidence: 91%

Modifications of the hydrogen bond network of liquid water in a cylindrical SiO2 pore

Hartnig

Witschel

Spohr

et al. 2000

Journal of Molecular Liquids

108

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We present results of molecular dynamics simulations of water confined in a silica pore. A cylindrical cavity is created inside a vitreous silica cell with geometry and size similar to the pores of real Vycor glass. The simulations are performed at different hydration levels. At all hydration levels water adsorbs strongly on the Vycor surface; a double layer structure is evident at higher hydrations. At almost full hydration the modifications of the confinement-induced site-site pair distribution functions are in qualitative agreement with neutron diffraction experiment. A decrease in the number of hydrogen bonds between water molecules is observed along the pore radius, due to the tendency of the molecules close to the substrate to form hydrogen-bonds with the hydrophilic pore surface. As a consequence we observe a substrate induced distortion of the H-bond tetrahedral network of water molecules in the regions close to the surface.

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Section: Model For the Vycor Pore And Molecular Dynamics Calculationssupporting

confidence: 91%

Modifications of the hydrogen bond network of liquid water in a cylindrical SiO2 pore

Hartnig

Witschel

Spohr

et al. 2000

Journal of Molecular Liquids

108

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“…At the end of this process the cell contains 6400 silica atoms, 12500 bO and 230 nbO. This last number yields a surface density of acidic hydrogen of 2.5 nm −2 in good agreement with the 2.3 nm −2 obtained in the experiments [18]. The simulations have been performed in the NVE ensemble introducing water molecules into the pore.…”

Section: Model and Simulation Detailssupporting

confidence: 76%

Single particle slow dynamics of confined water

Gallo

2000

Phys. Chem. Chem. Phys.

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Molecular dynamics simulations of SPC/E water confined in a Silica pore are presented. The simulations have been performed at different hydration levels and temperatures to study the singleparticle dynamics. Due to the confinement and to the presence of a hydrophilic surface, the dynamic behaviour of the liquid appears to be strongly dependent on the hydration level. On lowering temperature and/or hydration level the intermediate scattering function displays a double-step relaxation behaviour whose long time tail is strongly non-exponential. At higher hydrations two quite distinct subsets of water molecules are detectable. Those belonging to the first two layers close to the substrate suffer a severe slowing down already at ambient temperature. While the behaviour of the remaining ones is more resemblant to that of supercooled bulk SPC/E water. At lower hydrations and/or temperatures the onset of a slow dynamics due to the cage effect and a scenario typical of supercooled liquids approaching the kinetic glass transition is observed. Moreover, for low hydrations and/or temperatures, the intermediate scattering function clearly displays an overshoot, which can be assigned to the so called "Boson Peak".

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“…The observed relaxation rate corresponds to the weighted average of the relaxation rates of the water molecules in the different layers. The exchange rate is therefore faster than the NMR time scale (25-30 μs) as observed with Vycor glass (Hirama et al, 1996) and porous silica gels , Porion et al 1998, but contrary to that observed with some biological materials such as starch (Le Botlan et al, 1998) or membranes by a femtosecond timeresolved study (Ghosh, 2007). This phenomenon was not foreseeable from the studies on water-rich gels of Kunigel-V1 bentonite (Nakashima, 2004) the external surface would correspond to about 27 g of water per kg of dry clay i.e.…”

Section: Nmr Results On Hydrated Samplesmentioning

confidence: 87%

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

Montavon

Guo

Tournassat

et al. 2009

Geochimica et Cosmochimica Acta

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. Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study. Geochimica et Cosmochimica Acta, Elsevier, 2009, 73 (24) AbstractThe aim of the present work was to quantify accessible porosities for iodide and for a water tracer (HTO) on water-saturated compacted clay samples (illite, montmorillonite and MX-80 bentonite) and to relate these macroscopic values to the forms of water in these porosities (surface/bulk water, external/internal water). Low field proton NMR was used to characterize and quantify the forms of water. This enabled the three different populations (structural OH, external surface and internal surface water) to be differentiated on hydrated clays by considering the difference in proton mobility. An accurate description of the water forms within the different populations did not appear possible when water molecules of these populations were in contact because of the occurrence of rapid exchange reactions. For this 2 reason, it was not possible to use the low resolution NMR method to quantify external surface and bulk water in fully water-saturated compacted clay media at room temperature. This latter information could however be estimated when analyzing the samples at -25°C. At this temperature, a distinction based on the difference in mobility could be made since surface water remained in a semi-liquid state whereas bulk water froze. In parallel, accessible porosities for anions and HTO were determined by an isotopic dilution method using capillaries to confine the materials. HTO was shown to probe the whole pore volume (i.e. the space made of surface and bulk water). When the surface water volume was mainly composed of interlayer water (case of montmorillonite and bentonite), iodide was shown to be located in the pore space made of bulk water. When the interlayer water was not present (case of illite), the results showed that iodide could access a small fraction of the surface water volume localized at the external surface of the clay particles.

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Studies of Water Adsorbed in Porous Vycor Glass

Cited by 63 publications

References 17 publications

Modifications of the hydrogen bond network of liquid water in a cylindrical SiO2 pore

Modifications of the hydrogen bond network of liquid water in a cylindrical SiO2 pore

Single particle slow dynamics of confined water

Porosities accessible to HTO and iodide on water-saturated compacted clay materials and relation with the forms of water: A low field proton NMR study

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