Unusual Relaxation Behavior of Water Inside the Sodalite Cages of Faujasite-Type Molecular Sieves

Abstract

Broad-band dielectric spectroscopy (10-2 to 109 Hz) is applied to investigate the molecular dynamics of NaY, a zeolite of faujasite structure. A dc conductivity contribution and three relaxation processes were revealed in the dielectric spectra. The relaxation process in the high-frequency range ascribed to orientational fluctuations of water molecules inside the sodalite cages is studied in detail. As a main result it is found that its mean relaxation time has an unusual saddle-like temperature dependence, which obeys neither an Arrhenius nor a Vogel−Fulcher−Tammann law. A quantitative description was given on the basis of a model recently developed by Feldman et al. (J. Phys. Chem. B 2001, 105, 1845) to analyze the dynamics of water confined in nanoporous glasses. Reasonable values for the activation energies of orientational fluctuations and of defect formation as well as for the defect concentration were obtained.

Water-Triggered Conduction Mediated by Proton Exchange in a Hygroscopic Fulleride and Its Hydrate

“…As visible in panels a and d of Figure 3, upon raising the temperature the loss feature is observed to shift to lower frequencies while the conductivity decreases. Such temperature dependence of the loss feature is anomalous (the characteristic frequency should increase with temperature due to the higher thermal energy), and resembles that observed in other hydrated systems such as organic 10 and inorganic 2,[23][24][25] porous materials. The origin of this effect has been the object of controversy, and has been related either to a reduction of the available free volume per defect in the hydrogen-bond network of interstitial water upon heating, 10,23,24,33 or to a Maxwell-Wagner-Sillar polarization effect due to the strong increase of the static permittivity of a porous sample when water adsorbs onto inner surfaces.…”

“…14 The non-monotonic temperature-dependence of σ dc and of the frequency of the loss maximum observable in Figure 2 may be at first surprising, as one expects both the conductivity and the characteristic loss frequency to increase with temperature. 18 However, such behavior is not uncommon in water containing porous systems near the water desorption temperature, 1,2,10,[23][24][25][26] as will be discussed in Section 3.b. Given the complexity of the results and the presence of two modalities of hydration in the as-stored powder (Figure 1c), we have probed separately the effect of the structural and surface hydration water.…”

Comment on “Investigating hydration dependence of dynamics of confined water: Monolayer, hydration water, and Maxwell–Wagner processes” [J. Chem. Phys. 128, 154503 (2008)]

“…The subject of water in confined porous matrices has been an area of our interests for about a decade. [2][3][4][5][6] Therefore, the study of Sjöström et al 1 attracted our attention and we would like to point out some questionable, from our point of view, aspects of their investigation.…”

“…In general, it is believed that the Johari-Goldstein relaxation is a precursor of glassy dynamics but no glass transition is detected in the system. In literature [2][3][4][5][6]8,9 this low temperature process is usually ascribed to the icelike behavior of water molecules.…”

Dehydration-rehydration induced structural changes in pristine and composite layered double hydroxides

“…The dielectric spectrum of the pristine CaFe-LDH is similar in appearance to other watercontaining materials, such as zeolites [130], clay minerals [131], etc. At this temperature, three relaxations can be identified.…”