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Water confined in a sol-gel network has been characterized by x-ray and neutron diffraction for two samples of mesoporous silica: one with a hydrophilic character (a nonmodified one) and another with a hydrophobic character (a modified one with a methylated internal pore surface). The pore size has been previously characterized [J.Jelassi et al., Phys. Chem. Chem. Phys. 134, 1039 (2010)] to have a mean pore diameter of approximately 55 Å. The diffraction measurements presented in this paper have been made at room temperature [293 K] for a filling factor of 0.45, giving a mean thickness of 8-9 Å for the water layer. The results show that the local order of the confined water molecules in the intermediate region of 3-6 Å is significantly different from that of the bulk water and also for the two different environments. For the hydrophilic sample, the siloxyl groups at the surface modify the water structure through the effects of interfacial hydrogen-bonding, which influences the orientational configuration of local water molecules and creates a modified spatial arrangement in the pore. In the case of the hydrophobic sample, there is no specific interaction with the pore wall, which is primarily van der Waals type, and the water molecules at the interface are differently oriented to create a hydrogen-bonded network linked more directly to the rest of the water volume. In the present circumstances, the thickness of the water layer has a relatively small dimension so that the interpretation of the measured diffraction pattern is not as straightforward as for the bulk liquids, and it is necessary to consider the effects of diffraction-broadening from a distributed sample volume and also the contribution from cross-terms that remain after conducting a 'wet-minus-dry' analysis procedure. These analytic difficulties are discussed in the context of the present measurements and compared with the work of other groups engaged in the study of water confined in different environments. The present results, again, emphasize the complexity influencing the properties of water in a confined geometry and the strong influence of surface interactions on its behavior. [ABSTRACT FROM AUTHOR]

We present a study of the dynamical behavior of trehalose, a cryoprotecting agent, in concentrated aqueous solutions. Dynamics in a wide time range from picoseconds to nanoseconds has been observed using both neutron time of flight and neutron spin-echo techniques. Fast dynamics has been described using a simple diffusion model, while dynamical processes at longer times show a more complex behavior, described by a stretched exponential decay. Obtained relaxation times show a good agreement with data from viscosity measurements on aqueous trehalose solutions by Magazu et al. [Branca, Magazu, Maisano et al., J. Phys.: Condens. Matter 11, 3823 (1999)]. Experimental data provide us with some insight into the cryoprotecting properties and processes of trehalose. We conclude that an increase of the solvent viscosity in embedded biological material due to the production or the presence of trehalose might prevent biomolecules from damage. © 2005 American Institute of Physics. [ABSTRACT FROM AUTHOR]

A structural investigation of liquid D2O was performed by neutron scattering at pressures up to 6 kbar and in a range of temperatures from 53 down to -65 °C. Some comparison is made with Monte Carlo (MC) and molecular dynamics (MD) simulations. In particular, the results are used to test some recent MD simulations leading to a phase diagram which provides a complete picture of the stable and metastable behavior of water and incorporates the two amorphous ices of water. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

In order to study the structural properties of water at interfaces, we performed neutron scattering experiments of water confined inside interconnected pores of Vycor glass. The structure factors and the corresponding radial distribution functions of the confined water have been determined as a function of temperature from 35 °C down to -100 °C and for two levels of hydration of the glass (full and partial hydration). At 27 °C, the structure factor of confined water is very similar to that of bulk water. When decreasing the temperature, we show that it is possible to supercool water inside pores of Vycor but not to the extent expected for such a small confining space. In fact the presence of large hydrophilic silica interface enhances the nucleation of ice. The observed phase of ice is the cubic ice which appears at about -18 °C in the full hydrated Vycor. The other interesting observation is a greater degree of supercooling of water in partially hydrated samples of Vycor compared to fully hydrated ones. Moreover, the presence of a small amount of liquid water down to -40 °C is identified. [ABSTRACT FROM AUTHOR]

X-ray and neutron diffraction measurements were performed on glassy water prepared by rapid cooling of water droplets on a cryoplate. Structure factors and radial distribution functions were found to be nearly identical to those obtained from amorphous ice formed either by vapor deposition onto substrates cooled at 77 K or after heating the high-density amorphous ice. [ABSTRACT FROM AUTHOR]

High-density amorphous water is studied by neutron scattering in a Q range extending to 16 Å-1. The low density form of amorphous water is also analyzed and compared with previous results. There are very important differences in the composite pair correlation functions of the two forms of amorphous ice, in particular beyond the first nearest-neighbors distance. We conclude that the hydrogen bond network is strongly deformed in a manner analogous to that found in water at high temperature. This is in contrast with the behavior of the pair correlation function of low-density amorphous water, which is closer to that of supercooled water. [ABSTRACT FROM AUTHOR]

The first order difference method of neutron diffraction and isotopic substitution has been applied to the Ni2+ and Cl- ions in a 2 m nickel chloride heavy water solution at 100 °C and 1000 bar, and at 300 °C and 1000 bar. The results show that both the Ni2+ and the Cl- hydration shell become progressively weakened with increasing temperature. The hydration number of Ni2+ drops from ∼6 under ambient conditions to ∼5.4 at 100 °C and to ∼4.5 at 300 °C. The hydration number of Cl- at 100 °C (6.9) is similar to the value under ambient conditions (6.4) and reduces to ∼4.9 at 300 °C. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Quasielastic neutron scattering spectra were measured for pure acetonitrile at 25 °C. In the framework of a simple model of translation and rotation, it was found that the short-time self-diffusion coefficient of liquid acetonitrile is similar to the long-time one measured by NMR. As far as the rotational motion is concerned, the characteristic time was found to be close to the typical value of the molecule spinning motion. The complete inelastic and quasielastic spectra may be further used to check the results of molecular dynamics simulations of acetonitrile. [ABSTRACT FROM AUTHOR]

Quasielastic neutron scattering (QENS) spectra were measured for a 0.43 M solution of n-tetrapentylammonium bromide in deuterated acetonitrile at 25 °C, 5 °C, and -15 °C. Values of the translational diffusion coefficient of the cations were inferred from these data using a simple model of translation and rotation. These values are significantly higher than the ones obtained by nuclear magnetic resonance (NMR) spin–echo measurements. The difference can be explained by the different time scales covered by QENS and NMR. QENS shows essentially the contribution of a second order electrophoretic effect to the diffusion coefficient whereas NMR encompasses both electrophoretic and relaxation effects. Consequently, the combination of both techniques allows the two effects to be separated. The relaxation contribution to the diffusion coefficient was calculated by brownian dynamics simulation and compared to the experimental results. The solvent-averaged ion pair potentials used for this computation were simultaneously adjusted to the thermodynamic and to the small-angle neutron scattering data by means of hypernetted chain (HNC) calculations. [ABSTRACT FROM AUTHOR]

The structure around lithium counterions in polyacrylate solutions has been investigated by neutron diffraction, and it is concluded that small cations remain hydrated when they accumulate around a highly charged polymer. Interactions between the polyion and the counterions over a range outside the hydration shell are also observed. The relaxation rate of 7Li due to dipolar coupling to 17O was obtained by nuclear magnetic resonance. The results indicate that the polyion exerts a moderate influence on the reorientational dynamics of the lithium aqua-ion. [ABSTRACT FROM AUTHOR]