Small-angle water reorientations in KOH doped hexagonal ice and clathrate hydrates

Abstract

Using deuteron nuclear magnetic resonance and dielectric spectroscopy KOH doped tetrahydrofuran clathrate hydrates and KOH doped hexagonal ice are studied at temperatures above 60 and 72 K, respectively. Below these temperatures proton order is established on the lattice formed by the water molecules. In the clathrate hydrate a new type of small-angle motion is discovered using deuteron spin-spin relaxation, line-shape analysis, and stimulated-echo experiments. Based on the latter results a model is developed for the local proton motion that could successfully be tested using random-walk simulations. It is argued that the newly identified small-angle motion, obviously absent in undoped samples, is an important feature of the mechanism which accompanies the establishment of proton order not only in doped clathrate hydrates but also in doped hexagonal ice. Specific motions of OH(-) defects are demonstrated to explain the experimentally observed behavior. The relative importance of localized versus delocalized OH(-) defect motions is discussed.

Electrical properties of methane hydrate + sediment mixtures

“…Most impurities that are dissolved in water become excluded during ice crystallization, with the exception of a few acids (HF and HCl), ammonia (NH 3 ), alkalis (KOH and NaOH), and their derivatives (NH 4 F or KCl) that drastically change the protonic carrier concentration [e.g., Petrenko and Whitworth , ]. KOH inclusion into THF hydrate has also been demonstrated to trigger formation of charge carriers, Bjerrum and protonic defects, and could also affect mobilities of other point defects [ Nelson et al , ]. If CH 4 hydrate behaves similar to ice, then the sand may have contributed KOH and its derivative KCl during synthesis, which is consistent with IC detection of both K + water melted from samples containing sand (runs 5 and 6), but not in those containing glass beads (run 7) or in those that did contain any sediment (run 3) (Table S1).…”

Molecular Motions in Supercooled and Glassy Ibuprofen: Deuteron Magnetic Resonance and High-Resolution Rheology Study

“…Furthermore, the local minimum spin–spin relaxation time, T 2,min ∼ 180 μs, observed in the glassy state is much longer than expected for an isotropic reorientation process for that calculations show that the minimum deuteron T 2,iso (relating to correlation times of about 1 μs) should also be on the order of 1 μs . The jump angle Δφ characterizing ibuprofen’s anisotropic motion can roughly be approximated as Δφ ∼ 2/3­( T 2,iso / T 2,min ) 1/2 . From the given T 2 minimum, one thus estimates Δφ ∼ 3°.…”

“…In analogy to eq , the M (Δ) data were described using a stretched exponential function thus yielding the temperature-dependence of T 2 , as shown in Figure c. For both isotopomers, a broad minimum appears near ∼154 K. A theoretical approach, which is detailed elsewhere, allows one to estimate the associated molecular timescale, τ 2 glass ≈ 35 μs . Furthermore, the local minimum spin–spin relaxation time, T 2,min ∼ 180 μs, observed in the glassy state is much longer than expected for an isotropic reorientation process for that calculations show that the minimum deuteron T 2,iso (relating to correlation times of about 1 μs) should also be on the order of 1 μs .…”

Dynamic signatures of the transition from stacking disordered to hexagonal ice: Dielectric and nuclear magnetic resonance studies

“…Immersed in liquid nitrogen the tubes were inserted in the sample coil of the probe head which was then transferred into a cryostat precooled to 77 K. Deuteron NMR spin-lattice relaxation experiments were conducted at a Larmor frequency of ω L = 2π × 55 MHz by applying the saturation recovery technique and recording the longitudinal magnetization recoveries; see Ref. 35 for further details.…”