Deuteron nuclear magnetic resonance and dielectric study of host and guest dynamics in KOH-doped tetrahydrofuran clathrate hydrate

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

“…81 This behavior prevails until a partial transformation to another state sets in upon heating, 81 eventually leading to the emergence of a two-component spectrum. 82 As mentioned near the end of Sec. III B, a two-phase mixture is indeed expected to occur for the presently studied CO 2 -filled Sχ clathrate hydrate which thus may rationalize the appearance of the high-frequency feature.…”

Doping-enhanced dipolar dynamics in ice V as a precursor of hydrogen ordering in ice XIII

“…This figure contains data on KOH-doped ice I h /XI [64,65], KOD-doped ice I h /XI [16], RbOH-doped ice I h /XI [14], HCl-doped ice V/XIII from this paper, and HCl-doped ice XII/XIV [53]. The data on the potassium hydroxide doped clathrate hydrates refer to the guest molecules THF (tetrahydrofuran, doped with KOH [18,70] or KOD [20]), ACE (acetone, with KOH) [21], or TMO (trimethylene oxide, with KOH) [21]. The arrows indicate the phase transition temperatures.…”

“…Table I further summarizes parameters like activation energy E, phase transition temperature T c , and relaxation time τ , measured just above and below T c . The table also includes data on various KOH-doped clathrate hydrates, which at high temperatures crystallize in the cubic structure sII and which can display (at least partial) proton ordering at low temperatures when containing tetrahydrofuran (THF) [69][70][71][72], acetone (ACE), or trimethylene oxide (TMO) as guests [18][19][20][21][22]. These clathrates may currently be considered as closest reference systems for an empty structure sII clathrate hydrate, i.e., for ice XVI for which a hydrogen ordered companion phase was not observed experimentally so far [7].…”

“…Ice [18,19] 7.4 -61.9 0.0006* THF(KOD) [20] 7.4 -67 ± 4 0.008-0.5 acetone(KOH) [21] 8.5 -46.6 0.001-0.2* TMO(KOH) [21] 9.0 -34.5 30-300* to identify a well-defined relaxation time at which an orderdisorder phase transition is expected. While fast dipolar relaxation seems to be a necessary condition for the occurrence of thermally driven [74] hydrogenordering phase transitions in the ices, this condition is not sufficient as the case of KOH-doped ice V suggests.…”

“…For hexagonal ice (ice I h ) [11][12][13][14][15][16][17] and for related systems such as the sII clathrate hydrates [18][19][20][21][22], it has long been shown that alkali hydroxide doping can lead to a lowtemperature orientational ordering [23]. Despite occasional other suggestions [24], dopants such as alkali or hydrogen halides, earth alkali hydroxides, or ammonia are ineffective in catalyzing a hydrogen ordered low-temperature phase [11].…”