Water dynamics in controlled pore silica glasses

Bordallo, H. N.; Herwig, K. W.; Dozier, W. D.; Drake, F.

doi:10.1051/jp4:2000741

Cited by 5 publications

(6 citation statements)

References 4 publications

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“…The D t 3D diffusion coefficients and τ 0 residence times obtained are shown in Table 2 together with the values for supercooled bulk water taken from Teixeira et al [1984]. We can see that the residence time τ 0 in the soot micropores is larger than that of bulk water as was observed for water in porous Vycor glasses [ Bellissent‐Funel et al , 1995; Bordallo et al , 2000]. Moreover, we see that the residence time increases with decreasing temperature as was observed in porous Vycor glass [ Bellissent‐Funel et al , 1995].…”

Section: Resultsmentioning

confidence: 62%

“…In previous observations of water diffusion in porous glasses the jump translation diffusion model for bulk water was used [ Bellissent‐Funel et al , 1995; Bordallo et al , 2000]. So it is worth comparing our 2‐D translation diffusion coefficients to those obtained for the 3‐D bulk water.…”

Section: Resultsmentioning

confidence: 99%

“…In the most currently used models [ Chen and Teixeira , 1986; Bordallo et al , 2000] the translational component of the scattering law S t ( Q , ω) is described by a Lorentzian curve with a HWHM Γ(Q)

For two‐dimensional adsorbates on surfaces the Brownian diffusion model provides

where D t 2D is the 2D translational diffusion coefficient, θ is the angle between the normal to the surface and the scattering vector Q. In the case of adsorbed water inside the soot micropores we have to integrate with over the isotropic distribution of soot powder.…”

Section: Quasielastic Neutron Scattering: Methods Of Analysismentioning

confidence: 99%

“…Then the parameters D t , D r and the liquid fraction are tested for the higher Q values and are considered as representative of the actual experimental values when the agreement between the experimental QENS spectra and the model spectra is good for all 10 values of Q using the same set of parameters. The mean displacement 〈u 2 〉 in the Debye‐Waller factor is taken equal to 0.2 at T above 273 K [ Bordallo et al , 2000] and to 0.1 at T less then 273 K to take into account the reduction of the vibrational amplitude with decreasing T. It should be pointed out that the analysis of the QENS spectra is not very sensitive to the value of 〈u 2 〉.…”

Section: Quasielastic Neutron Scattering: Methods Of Analysismentioning

confidence: 99%

“…In order to understand the soot ice nucleation properties, it is worthwhile to determine the dynamics and the structure of condensed water on the exhaust soot surface. The quasielastic neutron scattering (QENS) technique has been used to measure the water dynamics in the water‐filled porous glasses [ Bordallo et al , 2000] and powders of graphitized carbon black [ Maruyama et al , 1992], as well as water confined in micropores of Vycor glass [ Bellissent‐Funel et al , 1995]. QENS is well suited for measuring the translational diffusion coefficient of mobile water molecules and determining the adsorbate liquid‐like fraction of a water/ice mixture [ Maruyama et al , 1992].…”

Section: Introductionmentioning

confidence: 99%

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Water adsorption and dynamics on kerosene soot under atmospheric conditions

et al. 2002

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[1] Morphology, microstructure and surface chemistry of laboratory made kerosene soot used as an aircraft soot surrogate have been studied to establish the correlation between the porosity and the mechanism of water adsorption on the soot surface. The quasielastic neutron scattering (QENS) technique has been used to characterize the dynamics of water confined in the soot pores network. Spectra above and below the water triple point T m describe the translational and rotational diffusion of water molecules adsorbed in 0.5 nm micropores, 2 nm supermicropores and !2 nm mesopores. Below T m an appreciable amount of liquid water exists in the soot micropores down to the lowest tropospheric temperatures. The depression in freezing temperature is related to the pore dimension. Water confined in the micropores appears to freeze completely only at T below 200 K showing that the nucleation process depends on the specific microporosity. At the saturation plume conditions ffi30% of adsorbed water has been transformed into ice. These results show that, in the upper troposphere, soot particles presenting the above-mentioned properties will contain stable water/ice components inside the pores with 25% of unfrozen water.

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Section: Resultsmentioning

confidence: 62%

Section: Resultsmentioning

confidence: 99%

For two‐dimensional adsorbates on surfaces the Brownian diffusion model provides

Section: Quasielastic Neutron Scattering: Methods Of Analysismentioning

confidence: 99%

Section: Quasielastic Neutron Scattering: Methods Of Analysismentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Water adsorption and dynamics on kerosene soot under atmospheric conditions

et al. 2002

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Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering

2006

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Portland cement reacts with water to form an amorphous paste through a chemical reaction called hydration. In concrete the formation of pastes causes the mix to harden and gain strength to form a rock-like mass. Within this process lies the key to a remarkable peculiarity of concrete: it is plastic and soft when newly mixed, strong and durable when hardened. These qualities explain why one material, concrete, can build skyscrapers, bridges, sidewalks and superhighways, houses, and dams. The character of the concrete is determined by the quality of the paste. Creep and shrinkage of concrete specimens occur during the loss and gain of water from cement paste. To better understand the role of water in mature concrete, a series of quasielastic neutron scattering (QENS) experiments were carried out on cement pastes with water/cement ratio varying between 0.32 and 0.6. The samples were cured for about 28 days in sealed containers so that the initial water content would not change. These experiments were carried out with an actual sample of Portland cement rather than with the components of cement studied by other workers. The QENS spectra differentiated between three different water interactions: water that was chemically bound into the cement paste, the physically bound or "glassy water" that interacted with the surface of the gel pores in the paste, and unbound water molecules that are confined within the larger capillary pores of cement paste. The dynamics of the "glassy" and "unboud" water in an extended time scale, from a hundred picoseconds to a few nanoseconds, could be clearly differentiated from the data. While the observed motions on the picosecond time scale are mainly stochastic reorientations of the water molecules, the dynamics observed on the nanosecond range can be attributed to long-range diffusion. Diffusive motion was characterized by diffusion constants in the range of (0.6-2) 10(-9) m(2)/s, with significant reduction compared to the rate of diffusion for bulk water. This reduction of the water diffusion is discussed in terms of the interaction of the water with the calcium silicate gel and the ions present in the pore water.

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Quasi-elastic neutron scattering study of dimethyl-sulfoxide–water mixtures: Probing molecular mobility in a nonideal solution

Bordallo

Herwig

Luther

et al. 2004

The Journal of Chemical Physics

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The translational and rotational motions of water and dimethyl sulfoxide, [DMSO, (CH(3))(2)SO] have been investigated using quasi-elastic neutron scattering. Water-DMSO mixtures at five DMSO mole fractions, chi(DMSO), ranging from 0 to 0.75, were measured. Hydrogen-deuterium substitution was used to extract independently the water proton dynamics (d-DMSO-H(2)O), the DMSO methyl proton dynamics (h-DMSO-D(2)O) and to obtain background corrections (d-DMSO-D(2)O). The translational diffusion of water slows down significantly compared to bulk water at all chi(DMSO)>0. The rotational time constant for water exhibits a maximum at chi(DMSO)=0.33 that corresponds to the observed maximum of the viscosity of the mixture. Data for DMSO can be analyzed in terms of a relatively slow tumbling of the molecule about its center-of-mass in conjunction with random translational diffusion. The rotational time constant for this motion exhibits some dependence on chi(DMSO), while the translational diffusion constant shows no clear variation for chi(DMSO)>0. The results presented reinforce the idea that due to the stronger associative nature of DMSO, DMSO-water aggregates are formed over the whole composition range, disturbing the tetrahedral natural arrangement of the water molecules. As a consequence adding DMSO to water causes a drastic slowing down of the dynamics of the water molecule, and vice versa.

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Water dynamics in controlled pore silica glasses

Cited by 5 publications

References 4 publications

Water adsorption and dynamics on kerosene soot under atmospheric conditions

Water adsorption and dynamics on kerosene soot under atmospheric conditions

Water Dynamics in Hardened Ordinary Portland Cement Paste or Concrete: From Quasielastic Neutron Scattering

Quasi-elastic neutron scattering study of dimethyl-sulfoxide–water mixtures: Probing molecular mobility in a nonideal solution

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