Relaxation amorphous ices

Therefore, experiments are performed on immobilized liquids , or in other words on amorphous water (also called vitreous water or glassy water). Currently, three structurally distinct amorphous states of water are known low- (LDA) , high- (HDA) and very high- (VHDA) density amorphous ice We emphasize that HDA is not a well defined state but rather comprises a number of substates. It has been suggested to use the nomenclature uHDA ( unrelaxed HDA ) ", eHDA ( expanded HDA ) " and/or rHDA ( relaxed HDA ) to account for this. Even though no signs of micro-crystallinity have been found in neutron or X-ray diffraction studies, it is unclear whether... 

The evolution of the piston displacement upon compressing the LDA sample is shown in Figure 5. For comparison, the results obtained upon PIA of ice Ih are included. The LDA-to-HDA transformation occurs at f 0.6 GPa, as indicated by the sudden change in d(/. This pressure is lower than the pressure at which ice Ih transforms to HDA ( 1 GPa). Still, the LDA-to-HDA transition is at least as sharp as the ice Ih-to-HDA transition and, thus, it also resembles a first-order transition in its volume change. We note that the density of HDA at 1 bar and T — 77K is, within error bars, the same density of the HDA samples obtained from PIA of ice Ih, 1.17 g cm . Moreover, the X ray diffraction patterns of HDA, obtained from ice Ih and LDA, are also very similar to each other [62]. Therefore, the HDA form obtained from LDA is apparently the same amorphous ice that results from PIA of Ih at r = 77K [24,62]. If the LDA to HDA transformation is indeed a true first-order transition, then one would expect to observe that HDA transforms back to LDA upon decompression. Otherwise, the LDA to HDA transformation could be interpreted as a simple relaxation effect of LDA. In this case, there would be a single amorphous phase of water (LDA), and HDA, instead of being a new amorphous phase different from LDA, would be a relaxed version of LDA [63]. Figure 5 shows... 

The difficulty of the experimental proof of the LLCP hypothesis, apart from the crystallization in NML, was that the amorphous ices were solid and not in the thermodynamical equilibrium. As for liquid, it was in the equilibrium and could be a sole state once pressure and temperature were fixed. Therefore, it would be possible to prove the discontinuity of the transition between two different liquids. However, regarding liquid water, LDL and HDL would crystallize immediately in NML, and we could not observe the LLT directly. In contrast, although we could observe the LDA HDA transition, the nonequilibrium nature of LDA and HDA threw doubt on the discontinuity of the transition logically. That is, the existence of the barrier in Fig. 5b was doubted the potential surface between LDA and HDA might be flat by nature. Then, the apparently discontinuous LDA-to-HDA transition (Fig. 7) might be, correctly, continuous or caused by unknown sticky relaxation of a nonequUibrium LDA state. If so, LLT of water would be continuous and LLCP would not exist. 

Guthrie M, Urquidi J, Tulk C, Benmore C, King D, Neuefeind J (2003) Direct structural measurements of relaxation processes during transformations in amorphous ice. Physical Review B 68(18) 1-5... 

Transitions. Samples containing 50 mol % tetrafluoroethylene with ca 92% alternation were quenched in ice water or cooled slowly from the melt to minimise or maximize crystallinity, respectively (19). Internal motions were studied by dynamic mechanical and dielectric measurements, and by nuclear magnetic resonance. The dynamic mechanical behavior showed that the CC relaxation occurs at 110°C in the quenched sample in the slowly cooled sample it is shifted to 135°C. The P relaxation appears near —25°C. The y relaxation at — 120°C in the quenched sample is reduced in peak height in the slowly cooled sample and shifted to a slightly higher temperature. The CC and y relaxations reflect motions in the amorphous regions, whereas the P relaxation occurs in the crystalline regions. The y relaxation at — 120°C in dynamic mechanical measurements at 1 H2 appears at —35°C in dielectric measurements at 10 H2. The temperature of the CC relaxation varies from 145°C at 100 H2 to 170°C at 10 H2. In the mechanical measurement, it is 110°C. There is no evidence for relaxation in the dielectric data. 

In conclusion, the deformation behavior of poly(hexamethylene sebacate), HMS, can be altered from ductile to brittle by variation of crystallization conditions without significant variation of percent crystallinity. Banded and nonbanded spherulitic morphology samples crystallized at 52°C and 60°C fail at a strain of 0.01 in./in. whereas ice-water-quenched HMS does not fail at a strain of 1.40 in./in. The change in deformation behavior is attributed primarily to an increased population of tie molecules and/or tie fibrils with decreasing crystallization temperature which is related to variation of lamellar and spherulitic dimensions. This ductile-brittle transformation is not caused by volume or enthalpy relaxation as reported for glassy amorphous polymers. Nor is a series of molecular weights, temperatures, strain rates, etc. required to observe this transition. Also, the quenched HMS is transformed from the normal creamy white opaque appearance of HMS to a translucent appearance after deformation. 

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