Ultra-slow dynamics in low density amorphous ice revealed by deuteron NMR: indication of a glass transition

Abstract

The postulated glass-liquid transition of low density amorphous ice (LDA) is investigated with deuteron NMR stimulated echo experiments. Such experiments give access to ultra-slow reorientations of water molecules on time scales expected for structural relaxation of glass formers close to the glass-liquid transition temperature. An involved data analysis is necessary to account for signal contributions originating from a gradual crystallization to cubic ice. Even if some ambiguities remain, our findings support the view that pressure amorphized LDA ices are of glassy nature and undergo a glass-liquid transition before crystallization.

NMR studies on the temperature-dependent dynamics of confined water

“…Upon further cooling, T 1,l decreases, as anticipated for fast dynamics (ω 0 τ ≪ 1) in liquid water inside the pores, while T 1,s o rises, as expected for slow dynamics (ω 0 τ ≫1) in an ice phase outside the pores. A comparison with T 1 values for bulk ice (I h ) 44 supports the latter assignment. Near 225 K, T 1,s o becomes too long for a reliable determination in a reasonable amount of time, whereas T 1,l passes a minimum, indicating that confined water exhibits correlation times τ ≈ 1/ω 0 ≈ 1 ns.…”

Possible relations between supercooled and glassy confined water and amorphous bulk ice

“…However, although this crossover scenario to a low temperature b-relaxation is consistent with most experimental observations it should be noted that there are also results in the literature that contradict the possibility that water becomes a solid material only slightly below 228 K. Attempts have been made to measure the viscosity of LDA in the temperature range between the believed glass transition temperature at 136 K and the crystallization temperature at 150 K, 87 and more long-range diffusional motions, typical of liquids, have been claimed to occur in this temperature range. 27,[88][89][90] However, these results are neither uncontroversial nor internally consistent since they predict different temperature dependences of the viscosity or diffusivity of the claimed deeply supercooled water. There seem to be two main problems to distinguish between a true glass-to-liquid transition and an unfreezing of local molecular reorientations.…”

2H NMR study on temperature-dependent water dynamics in amino-acid functionalized silica nanopores

“…62 internal ice in the native pore, whereas they are much shorter than those reported for external ice, which amount to about 1000 s at 200 K, 62 and also much shorter than those of hexagonal and cubic ices in the bulk. 95,96 These discrepancies mean that the internal ice can be clearly distinguished from external and bulk ice phases in the 2 H SLR analyses. Moreover, it implies that water reorientation is faster for the confined ice than for hexagonal or cubic bulk ices, possibly as a consequence of a perturbed ice structure under nanoscale geometrical restriction.…”