Knowing the pressure dependence of glass forming liquids is important in various contexts. Here, we study the case of supercooled water, which has at least two different amorphous states with different densities. The pressure dependencies of the two glass transitions are predicted to show opposite behaviour, crossing in the P-T plane at elevated pressure. The experimental identification of the glass transition at elevated pressure and cryo-conditions is technically difficult. Moreover, in the case of amorphous ices, the glass transition is interrupted by crystallization, which makes it even more challenging. We show the feasibility of performing X-ray photon correlation spectroscopy experiments at elevated pressure using a diamond anvil cell at cryogenic temperatures. We observe two dynamic components when approaching the glass transition temperature. For high-density amorphous ice at a pressure of around (0.08 ± 0.02) GPa we determine the glass transition to be at higher temperatures compared to ambient conditions.

Here, we investigate the hypothesis that despite the existence of at least two high-density amorphous ices, only one high-density liquid state exists in water. We prepared a very-high-density amorphous ice (VHDA) sample and rapidly increased its temperature to around 205 ± 10 K using laser-induced isochoric heating. This temperature falls within the so-called “no-man’s land” well above the glass-liquid transition, wherein the IR laser pulse creates a metastable liquid state. Subsequently, this high-density liquid (HDL) state of water decompresses over time, and we examined the time-dependent structural changes using short x-ray pulses from a free electron laser. We observed a liquid–liquid transition to low-density liquid water (LDL) over time scales ranging from 20 ns to 3 μs, consistent with previous experimental results using expanded high-density amorphous ice (eHDA) as the initial state. In addition, the resulting LDL derived both from VHDA and eHDA displays similar density and degree of inhomogeneity. Our observation supports the idea that regardless of the initial annealing states of the high-density amorphous ices, the same HDL and final LDL states are reached at temperatures around 205 K.

Hydrated proteins undergo a transition in the deeplysupercooledregime, which is attributed to rapid changes in hydration water andprotein structural dynamics. Here, we investigate the nanoscale stress-relaxationin hydrated lysozyme proteins stimulated and probed by X-ray PhotonCorrelation Spectroscopy (XPCS). This approach allows us to accessthe nanoscale dynamics in the deeply supercooled regime (T = 180 K), which is typically not accessible through equilibriummethods. The observed stimulated dynamic response is attributed tocollective stress-relaxation as the system transitions froma jammed granular state to an elastically driven regime. The relaxationtime constants exhibit Arrhenius temperature dependence upon coolingwith a minimum in the Kohlrausch-Williams-Watts exponentat T = 227 K. The observed minimum is attributedto an increase in dynamical heterogeneity, which coincides with enhancedfluctuations observed in the two-time correlation functions and amaximum in the dynamic susceptibility quantified by the normalizedvariance chi( T ). The amplification offluctuations is consistent with previous studies of hydrated proteins,which indicate the key role of density and enthalpy fluctuations inhydration water. Our study provides new insights into X-ray stimulatedstress-relaxation and the underlying mechanisms behind spatiotemporalfluctuations in biological granular materials.

Unraveling the mechanism of water’s glass transition and the interconnection between amorphous ices and liquid water plays an important role in our overall understanding of water. X-ray photon correlation spectroscopy (XPCS) experiments were conducted to study the dynamics and the complex interplay between the hypothesized glass transition in high-density amorphous ice (HDA) and the subsequent transition to low-density amorphous ice (LDA). Our XPCS experiments demonstrate that a heterodyne signal appears in the correlation function. Such a signal is known to originate from the interplay of a static component and a dynamic component. Quantitative analysis was performed on this heterodyne signal to extract the intrinsic dynamics of amorphous ice during the HDA–LDA transition. An angular dependence indicates non-isotropic, heterogeneous dynamics in the sample. Using the Stokes–Einstein relation to extract diffusion coefficients, the data are consistent with the scenario of static LDA islands floating within a diffusive matrix of high-density liquid water.

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.

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 (similar to 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. Subsequently, we capture the recrystallization of the liquid domains, which occurs on microsecond timescales due to the cooling by heat dissipation and results to a decrease of the average liquid domain size.

Studying protein interactions at low temperatures hasimportantimplications for optimizing cryostorage processes of biological tissue,food, and protein-based drugs. One of the major issues is relatedto the formation of ice nanocrystals, which can occur even in thepresence of cryoprotectants and can lead to protein denaturation.The presence of ice nanocrystals in protein solutions poses severalchallenges since, contrary to microscopic ice crystals, they can bedifficult to resolve and can complicate the interpretation of experimentaldata. Here, using a combination of small- and wide-angle X-ray scattering(SAXS and WAXS), we investigate the structural evolution of concentratedlysozyme solutions in a cryoprotected glycerol-water mixturefrom room temperature (T = 300 K) down to cryogenictemperatures (T = 195 K). Upon cooling, we observea transition near the melting temperature of the solution (T & AP; 245 K), which manifests both in the temperaturedependence of the scattering intensity peak position reflecting protein-proteinlength scales (SAXS) and the interatomic distances within the solvent(WAXS). Upon thermal cycling, a hysteresis is observed in the scatteringintensity, which is attributed to the formation of nanocrystallitesin the order of 10 nm. The experimental data are well described bythe two-Yukawa model, which indicates temperature-dependent changesin the short-range attraction of the protein-protein interactionpotential. Our results demonstrate that the nanocrystal growth yieldseffectively stronger protein-protein attraction and influencesthe protein pair distribution function beyond the first coordinationshell.

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. 

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 + v₂, 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.

Amorphous solid water plays an important role in our overall understanding of water's phase diagram. X-ray scattering is an important tool for characterising the different states of water, and modern storage ring and XFEL facilities have opened up new pathways to simultaneously study structure and dynamics. Here, X-ray photon correlation spectroscopy (XPCS) was used to study the dynamics of high-density amorphous (HDA) ice upon heating. We follow the structural transition from HDA to low-density amorphous (LDA) ice, by using wide-angle X-ray scattering (WAXS), for different heating rates. We used a new type of sample preparation, which allowed us to study μm-sized ice layers rather than powdered bulk samples. The study focuses on the non-equilibrium dynamics during fast heating, spontaneous transformation and crystallization. Performing the XPCS study at ultra-small angle (USAXS) geometry allows us to characterize the transition dynamics at length scales ranging from 60 nm–800 nm. For the HDA-LDA transition we observe a clear separation in three dynamical regimes, which show different dynamical crossovers at different length scales. The crystallization from LDA, instead, is observed to appear homogenously throughout the studied length scales.