Dynamics of Glass Forming Ammonia Hydrates

Abstract

The dielectric relaxation of ammonia-water mixtures was studied for a range of NH3 mole fractions x. For 0.01 ≤ x < 0.33, the samples can be supercooled relatively easily. In this composition range, the relaxation strength is proportional to x. The dielectric relaxation times display a super-Arrhenius behavior, are independent of the NH3 content in the specified range, and, for T > 250 K, line up smoothly with those of pure water. The relaxation behavior of glass forming ammonia hydrates was also investigated using nuclear magnetic resonance techniques including deuteron relaxometry and stimulated-echo spectroscopy, as well as static field-gradient proton diffusometry. These experiments yielded additional insights into the rotational and translational dynamics of ammonia hydrates.

Deeply supercooled aqueous LiCl solution studied by frequency-resolved shear rheology

“…The solid lines guide the eye. (c) Data for hexagonal ice as compiled from work by Kawada, 55 Johari and Whalley, 56 Tyagi and Murthy, 57 Didzoleit et al, 58 Sasaki et al, 59 and Popov et al 60 For comparison, we include the line from frame (b) which represents the data of the CO 2 -filled Sχ clathrate hydrate. even under high-vacuum conditions.…”

“…5(c), we summarize data for single-and poly-crystalline hexagonal ice from various sources. [55][56][57][58][59][60] Depending on the preparation route and presumably also affected by the number of unintentionally implemented impurities, at a given temperature, the time scale of this ice phase strongly varies. Yet, the most extensive data set for the relaxation times in that figure, reported by Johari and Whalley, 56 is again close to that of LDA.…”

“…53 Further comparison is made with dielectric data reported for various crystalline ices, again, without intentional impurity doping. While numerous results are available for ices studied under high pressure, 40 here we focus on ambientpressure data for hexagonal ice [54][55][56][57][58][59][60] and phases that were prepared under high-pressure conditions. The present compilation includes previously published results for ice V 51 and ice XII, 50 as well as data on the ices IV, VI, and the CO 2 -filled Sχ clathrate hydrate.…”

Dynamics in Glass Forming Sulfuric and Nitric Acid Hydrates

“…For visual clarity, only the fits to the overall relaxation time traces (such as for SA3H) are shown. Furthermore, literature data on aqueous solutions of H 2 O 2 and N 2 H 4 (ref ) as well as of NH 3 (ref ) and KOH (ref ) are included. (b) T g,cal scaled Arrhenius plot of the motional correlation times that were determined using various NMR techniques (open symbols from diffusion data; filled symbols for τ < 10 –5 s from T 1 ; longer τ from F 2 ).…”

“…For the present work, we examined the dynamical properties of several glass forming nitric and sulfuric acid hydrates using dielectric spectroscopy and various nuclear magnetic resonance (NMR) techniques. One of the motivations for our study is that mixtures of relatively simple (inorganic) water additives such as, e.g., N 2 H 4 , H 2 O 2 , NH 3 , or KOH, sometimes present only in subpercent amounts, are effective in suppressing the crystallization in the resulting aqueous solutions. The extent to which such studies can teach us something about the glass formation of H 2 O itself, a question which has been explored since long, is of vital importance in view of the ongoing debate regarding water’s glass transition with its numerous ramifications. ,− …”