The phase transition between water and ice is ubiquitous and one of the most important phenomena ... more The phase transition between water and ice is ubiquitous and one of the most important phenomena in nature. Here, we performed time-resolved x-ray scattering experiments capturing the melting and recrystallization dynamics of ice. The ultrafast heating of ice I is induced by an IR laser pulse and probed with an intense x-ray pulse which provided us with direct structural information on different length scales. From the wide-angle x-ray scattering (WAXS) patterns, the molten fraction, as well as the corresponding temperature at each delay, were determined. The small-angle x-ray scattering (SAXS) patterns, together with the information extracted from the WAXS analysis, provided the time-dependent change of the size and the number of liquid domains. The results show partial melting (~13%) and superheating of ice occurring at around 20 ns. After 100 ns, the average size of the liquid domains grows from about 2.5 nm to 4.5 nm by the coalescence of approximately six adjacent domains. Subs...
High-density (HDA) and low-density amorphous ices (LDA) are believed to be counterparts of the hi... more High-density (HDA) and low-density amorphous ices (LDA) are believed to be counterparts of the high-and low-density liquid phases of water, respectively. In order to better understand how the vibrational modes change during the transition between the two solid states, we present infrared spectroscopy measurements, following the change of the decoupled OD-stretch (v OD) (∼2460 cm −1) and OH-combinational mode (v OH + v 2 , v OH + 2v R) (∼5000 cm −1). We observe a redshift from HDA to LDA, accompanied with a drastic decrease of the bandwidth. The hydrogen bonds are stronger in LDA, which is caused by a change in the coordination number and number of water molecules interstitial between the first and second hydration shell. The unusually broad uncoupled OD band also clearly distinguishes HDA from other crystalline high-pressure phases, while the shape and position of the in situ prepared LDA are comparable to those of vapor-deposited amorphous ice.
Recent experiments continue to find evidence for a liquid-liquid phase transition (LLPT) in super... more Recent experiments continue to find evidence for a liquid-liquid phase transition (LLPT) in supercooled water, which would unify our understanding of the anomalous properties of liquid water and amorphous ice. These experiments are challenging because the proposed LLPT occurs under extreme metastable conditions where the liquid freezes to a crystal on a very short time scale. Here, we analyze models for the LLPT to show that coexistence of distinct high-density and low-density liquid phases may be observed by subjecting low-density amorphous (LDA) ice to ultrafast heating. We then describe experiments in which we heat LDA ice to near the predicted critical point of the LLPT by an ultrafast infrared laser pulse, following which we measure the structure factor using femtosecond x-ray laser pulses. Consistent with our predictions, we observe a LLPT occurring on a time scale < 100 ns and widely separated from ice formation, which begins at times >1 μs.
Using time-resolved wide-angle X-ray scattering, we investigated the early stages (10 μs−1 ms) of... more Using time-resolved wide-angle X-ray scattering, we investigated the early stages (10 μs−1 ms) of crystallization of supercooled water, obtained by the ultrafast heating of high-and low-density amorphous ice (HDA and LDA) up to a temperature T = 205 K ± 10 K. We have determined that the crystallizing phase is stacking disordered ice (I sd), with a maximum cubicity of χ = 0.6, in agreement with predictions from molecular dynamics simulations at similar temperatures. However, we note that a growing small portion of hexagonal ice (I h) was also observed, suggesting that within our timeframe, I sd starts annealing into I h. The onset of crystallization, in both amorphous ice, occurs at a similar temperature, but the observed final crystalline fraction in the LDA sample is considerably lower than that in the HDA sample. We attribute this discrepancy to the thickness difference between the two samples.
In Newtonian gravity it is a moot question whether energy should be localized in the field or ins... more In Newtonian gravity it is a moot question whether energy should be localized in the field or inside matter. An argument from relativity suggests a compromise in which the field energy is positive definite. We show that the same compromise is implied by Noether’s theorem applied to a variational principle for perfect fluids, if we assume Dirichlet boundary conditions on the potential. We then analyse a thought experiment due to Bondi and McCrea that gives a clean example of inductive energy transfer by gravity. Some history of the problem is included.
Experimental observation of the liquid-liquid transition in bulk supercooled water under pressure
Science
We prepared bulk samples of supercooled liquid water under pressure by isochoric heating of high-... more We prepared bulk samples of supercooled liquid water under pressure by isochoric heating of high-density amorphous ice to temperatures of 205 ± 10 kelvin, using an infrared femtosecond laser. Because the sample density is preserved during the ultrafast heating, we could estimate an initial internal pressure of 2.5 to 3.5 kilobar in the high-density liquid phase. After heating, the sample expanded rapidly, and we captured the resulting decompression process with femtosecond x-ray laser pulses at different pump-probe delay times. A discontinuous structural change occurred in which low-density liquid domains appeared and grew on time scales between 20 nanoseconds to 3 microseconds, whereas crystallization occurs on time scales of 3 to 50 microseconds. The dynamics of the two processes being separated by more than one order of magnitude provides support for a liquid-liquid transition in bulk supercooled water.
Amorphous ice is commonly used as a noncrystalline matrix for protecting sensitive biological sam... more Amorphous ice is commonly used as a noncrystalline matrix for protecting sensitive biological samples in cryogenic electron microscopy (cryo-EM). The amorphization process of water is complex, and at least two amorphous states of different densities are known to exist, high-and lowdensity amorphous ices (HDA and LDA). These forms are considered to be the counterparts of two distinct liquid states, namely, high-and low-density liquid water. Herein, we investigate the HDA to LDA transition using electron diffraction and cryo-EM. The observed phase transition is induced by the impact of electrons, and we discuss two different mechanisms, namely, local heating and beam-induced motion of water molecules. The temperature increase is estimated by comparison with X-ray scattering experiments on identically prepared samples. Our results suggest that HDA, under the conditions used in our cryo-EM measurements, is locally heated above its glass-transition temperature.
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Papers by Tobias Eklund