0000000000512757
AUTHOR
Fabio Bruni
Dynamic properties of solvent confined in silica gels studied by broadband dielectric spectroscopy
Abstract We report the results of a broadband (10−2–107 Hz) dielectric spectroscopy study on a solvent system (glycerol–water solution) confined in a porous silica matrix. The dielectric relaxation of the system is studied as a function of both temperature (120–280 K) and solvent composition (0–36 glycerol molar percentage), at constant matrix composition. Our data show that glycerol–water systems confined inside silica gel are characterized by a very complex dynamics quite different from that observed in solution, thus indicating that confinement may deeply modify solvent dynamics. Indeed in addition to the relaxation processes similar to those occurring in bulk samples, new dielectric rel…
Study of percolation and clustering in supercritical water-CO2 mixtures
The microscopic structure of supercritical water-CO(2) mixture is investigated by neutron diffraction experiments exploiting the isotopic HD substitution. The investigated water reach mixtures are in the liquidlike region of the phase diagram, according to the behavior of the radial distribution functions, yet a reduction of the average number of hydrogen bonds, compared to equivalent states of pure water, is found. As a consequence, the average dimension of water clusters is reduced and the system stays below the percolation threshold. These results, along with the shift of the main peaks of the site-site radial distribution functions, suggest that the excess volume in these supercritical …
Structure and dynamics of water confined in silica hydrogels: X-ray scattering and dielectric spectroscopy studies.
We have used a sol-gel technique to obtain optically transparent hydrogels in which water is confined within a 3D silica matrix. In this work we report X-ray scattering and dielectric spectroscopy measurements on samples having different aging times and compare them with previously obtained results with near-infrared (NIR) absorption spectroscopy. X-ray scattering at room temperature enables to characterize the structure and size of the matrix pores and the non-uniform distribution of water inside the hydrogel. Broad band dielectric spectroscopy in the temperature range 130-280 K enables to study water dynamics. In aged hydrogels two relaxations are clearly evident and show characteristic t…
CO(2)-water supercritical mixtures: Test of a potential model against neutron diffraction data
Abstract A neutron diffraction experiment on supercritical mixtures of water and CO 2 at two concentrations is presented. Data are analyzed within the EPSR framework and the water–water and water–CO 2 radial distribution functions are compared with those calculated by a Molecular Dynamics simulation performed by using the TIPS2 and EPM-M potential models for water and CO 2 respectively. It is found that the Molecular Dynamics simulation reproduces the overall shape of the site–site radial distribution functions, although missing a few subtle changes brought along when the CO 2 concentration is increased.
Dielectric Relaxations in Confined Hydrated Myoglobin
In this work we report the results of a broadband dielectric spectroscopy study on the dynamics of a globular protein, myoglobin, in confined geometry, i.e. encapsulated in a porous silica matrix, at low hydration levels, where about only one or two water layers surround the proteins. In order to highlight the specific effect of confinement in the silica host, we compared this system with hydrated myoglobin powders at the same hydration levels. The comparison between the data relative to the two different systems indicates that geometrical confinement within the silica matrix plays a crucial role in protein-water dielectric relaxations, the effect of sol-gel encapsulation being essentially …