Amorphous ices low-density

More recently, simulation studies focused on surface melting [198] and on the molecular-scale growth kinetics and its anisotropy at ice-water interfaces [199-204]. Essmann and Geiger [202] compared the simulated structure of vapor-deposited amorphous ice with neutron scattering data and found that the simulated structure is between the structures of high and low density amorphous ice. Nada and Furukawa [204] observed different growth mechanisms for different surfaces, namely layer-by-layer growth kinetics for the basal face and what the authors call a collected-molecule process for the prismatic system. 

Amorphous water (also called glassy water or amorphous ice) can form when the temperature is decreased extremely rapidly below the glass transition temperature (Tg) of water (about 130 K at 0.1 MPa) (Mishima and Stanley, 1998). There are three types of amorphous ice low-density amorphous ice (LDA), high-density amorphous ice (HDA), and very high-density amorphous ice (VHDA), with VHDA being discovered most recently (Finney et al., 2002). 

Low-Density Amorphous Ice (LDA). Upon heating HDA to T > 115 K or very high density amorphous ice (VHDA) to T > 125 K at ambient pressure, the structurally distinct amorphous state LDA is produced. Alternatively, LDA can also be produced by decompressing HDA or VHDA in the narrow temperature range of 139-140 K to ambient pressure [153-155]. The density of this amorphous state at 77 K and 1 bar is 0.93 g/cm3 [152]. These amorphous-amorphous transitions are discussed in Sections III.C and III.D. 

Results relative to a 25% hydrated Vycor sample indicates that at room temperature interfacial water has a structure similar to that of bulk supercooled water at a temperature of about 0°C, which corresponds to a shift of about 25 K [40]. The structure of interfacial water is characterized by an increase of the long-range correlations, which corresponds to the building of the H-bond network as it appears in low-density amorphous ice [41 ]. There is no evidence of ice formation when the sample is cooled from room temperature down to -196°C (liquid nitrogen temperature). 

Neutron scattering methods have been used in the past primarily to explore both the structural and dynamic properties of bulk water. One example is a study in which the two phases of the water polymorphism were described, that is, the LDL and the HDL [42]. These experiments were on compressed water in a temperature regime in which the anomalous properties of water are most visible, that is, close to the ice I/ice III triple point (T = 251K, P = 209 MPa). The 00, OH, and HH partial structure factors and the site site radial distribution function between distinct atoms were extracted from the diffraction data. If we assume that the structure of water can be represented as a linear combination of the structures of the end points, that Is, the HDL and LDL structures, we obtain two values for the densities /Ohdl = L20 g cm (0.0402 molecules A ) and pldl = 0.88 g cm (0.0295 molecules/A ). These values are close to the reported densities of high-density and low-density amorphous ice [97]. 

At temperatures lower than 150K, the existence of the low-density amorphous ice (LDA) has been known since 1935. LDA was made by the deposition of water vapor onto a cold substrate [3] or by the extremely rapid cooling, 10 Ks , of micrometer-size droplets of liquid water [4]. Water molecules of LDA were located disorderly like those of liquid water. However, LDA was solid, and its density, 0.94 g cm , was as low as that of ice Ih. Although we might regard LDA as vitrified water [5,6], the relationship between LDA and the high temperature liquid water was unknown due to NML. 

T. Loerting, W. Schustereder, K. Winkel, C. G. Salzmann, I. Kohl, E. Mayer, Amorphous ice Stepwise formation of very-high-density amorphous ice from low-density amorphous ice at 125 K, Phys. Rev. Lett. 96 (2006) 025702. 

There exist different types of ice (see also Fig. 1.12). The ice we know from everyday live (also snow) has a hexagonal structure. At higher temperatures and pressures ice can also form a cubic structure 4). Other forms of ice are called II, III, V, VI, VII, VIII, IX and X. The difference between these forms is their crystalline structure. One also speaks of low-density amorphous ice (LDA), high-density amorphous ice (HDA), very high-density amorphous ice (VHDA) and hyperquenched glassy water (HGW). 

Abstract Neutron scattering data for low-density amorphous ice, produced by low-temperature and low-rate vapour deposition, shows that the dynamical properties of the vapour deposited amorphous ice are different from other low-density ices. 

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