Structure Of Amorphous Ice Research Articles

Pair Distribution Function from Electron Diffraction in Cryogenic Electron Microscopy: Revealing Glassy Water Structure.

In recent years, cryogenic electron microscopy (Cryo-EM) has revolutionized the structure determination of wet samples and especially that of biological macromolecules. The glassy-water medium in which the molecules are embedded is considered an almost in vivo environment for biological samples. The local structure of amorphous ice is known from neutron- and X-ray-diffraction studies, techniques appropriate for much larger volumes than those used in cryo-EM. We here present a first study of the pair-distribution function g(r) of glassy water under cryo-EM conditions using electron diffraction data. We found g(r) to be between that of low-density amorphous ice and that of supercooled water. Under electron exposure, cubic-ice regions were found to nucleate in thicker glassy-water samples. Our work enables to obtain quantitative structural information using g(r) from cryo-EM.

Dynamics of hydration water in gelatin and hyaluronic acid hydrogels.

We employed broadband dielectric spectroscopy (BDS), for the investigation of the water dynamics in partially hydrated hyaluronic acid (HA), and gelatin (Gel), enzymatically crosslinked hydrogels, in the water fraction ranges [Formula: see text]. Our results indicate that at low hydrations ([Formula: see text]), where the dielectric response of the hydrogels is identical during cooling and heating, water plasticizes strongly the polymeric matrix and is organized in clusters giving rise to [Formula: see text]-process, secondary water relaxation and to an additional slower relaxation process. This later process has been found to be related with the dc charge conductivity and can be described in terms of the conduction current relaxation mechanism. At slightly higher hydrations, however, always below the hydration level where ice is formed during cooling, we have recorded in HA hydrogel a strong water dielectric relaxation process, [Formula: see text], which has Arrhenius-like temperature dependence and large time scale resembling relaxation processes recorded in bulk low density amorphous solid water structures. This relaxation process shows a strong-to-fragile transition at [Formula: see text]C and our data suggest that the VTF-like process recorded at [Formula: see text]C is controlled by the same molecular process like long range charge transport. In addition, our data imply that the crossover temperature is related with the onset of structural rearrangements (increase in configurational entropy) of the macromolecules. In partially crystallized hydrogels ([Formula: see text]) HA exhibits at low temperatures the ice dielectric process consistent with the bulk hexagonal ice, whereas Gel hydrogel exhibits as main low temperature process a slow relaxation process that refers to open tetrahedral structures of water similar to low density amorphous ice structures and to bulk cubic ice. Regarding the water secondary relaxation processes, we have shown that the [Formula: see text]-process and the [Formula: see text] process are activated in water hydrogen bond networks with different structures.

Large-Scale Structure and Hyperuniformity of Amorphous Ices.

We investigate the large-scale structure of amorphous ices and transitions between their different forms by quantifying their large-scale density fluctuations. Specifically, we simulate the isothermal compression of low-density amorphous ice (LDA) and hexagonal ice to produce high-density amorphous ice (HDA). Both HDA and LDA are nearly hyperuniform; i.e., they are characterized by an anomalous suppression of large-scale density fluctuations. By contrast, in correspondence with the nonequilibrium phase transitions to HDA, the presence of structural heterogeneities strongly suppresses the hyperuniformity and the system becomes hyposurficial (devoid of "surface-area fluctuations"). Our investigation challenges the largely accepted "frozen-liquid" picture, which views glasses as structurally arrested liquids. Beyond implications for water, our findings enrich our understanding of pressure-induced structural transformations in glasses.

Highly confined water: two-dimensional ice, amorphous ice, and clathrate hydrates.

Understanding phase behavior of highly confined water, ice, amorphous ice, and clathrate hydrates (or gas hydrates), not only enriches our view of phase transitions and structures of quasi-two-dimensional (Q2D) solids not seen in the bulk phases but also has important implications for diverse phenomena at the intersection between physical chemistry, cell biology, chemical engineering, and nanoscience. Relevant examples include, among others, boundary lubrication in nanofluidic and lab-on-a-chip devices, synthesis of antifreeze proteins for ice-growth inhibition, rapid cooling of biological suspensions or quenching emulsified water under high pressure, and storage of H2 and CO2 in gas hydrates. Classical molecular simulation (MD) is an indispensable tool to explore states and properties of highly confined water and ice. It also has the advantage of precisely monitoring the time and spatial domains in the sub-picosecond and sub-nanometer scales, which are difficult to control in laboratory experiments, and yet allows relatively long simulation at the 10(2) ns time scale that is impractical with ab initio molecular dynamics simulations. In this Account, we present an overview of our MD simulation studies of the structures and phase behaviors of highly confined water, ice, amorphous ice, and clathrate, in slit graphene nanopores. We survey six crystalline phases of monolayer (ML) ice revealed from MD simulations, including one low-density, one mid-density, and four high-density ML ices. We show additional supporting evidence on the structural stabilities of the four high-density ML ices in the vacuum (without the graphene confinement), for the first time, through quantum density-functional theory optimization of their free-standing structures at zero temperature. In addition, we summarize various low-density, high-density, and very-high-density Q2D bilayer (BL) ice and amorphous ice structures revealed from MD simulations. These simulations reinforce the notion that the nanoscale confinement not only can disrupt the hydrogen bonding network in bulk water but also can allow satisfaction of the ice rule for low-density and high-density Q2D crystalline structures. Highly confined water can serve as a generic model system for understanding a variety of Q2D materials science phenomena, for example, liquid-solid, solid-solid, solid-amorphous, and amorphous-amorphous transitions in real time, as well as the Ostwald staging during these transitions. Our simulations also bring new molecular insights into the formation of gas hydrate from a gas and water mixture at low temperature.

Pressure-induced structural change from low-density to high-density amorphous ice by molecular-dynamics simulations

We have investigated the pressure dependence of the structure of amorphous ices by molecular-dynamics simulations to clarify the characteristic features of the structural change from the low-density amorphous (LDA) ice to the high-density amorphous (HDA) ice. We have found that, with increasing pressure at the temperature of 77 K, (1) the mean-square-displacement and its fluctuation as a function of time decrease, (2) the second peak of the oxygen–oxygen (O O) correlation function g ( r ) shifts to shorter distances and changes its shape drastically, e.g. it splits into two peaks, though the first peak remains almost same, (3) the average coordination number estimated from the first peak of g ( r ) increases from 4 to 5, (4) the broad peak of the O O O bond-angle distribution around 110° decreases and shifts towards 60°. From these results we conclude that the four-fold coordinated tetrahedral local structure in LDA ice changes to the five-fold coordinated structure in HDA ice, where the ‘fifth’ neighboring water molecule corresponds to the ‘interstitial’ water molecule.

Transient Pronounced Density Variation in Amorphous Ice Structures

Abstract The structural transformation of different high-density amorphous (HDA) ice modifications into the low-density amorphous (LDA) ice is studied by small-angle neutron scattering (SANS) techniques. All experiments have been performed at stationary conditions allowing to collect detailed information not only on the SANS formfactor but also on its time evolution and, hence, the kinetics governing the transformation process. A parametrization of the SANS formfactor by a superposition of the Debye-Bueche formfactor, characterizing a non-particulate two phase mixture, and a Porod-limit scattering formfactor is carried out successfully. The Porod-limit scattering indicates the presence of sharp interfaces and surfaces present in the sample material. Interpreting this signal as due to a grainy consistency of the amorphous samples grain sizes of the order of at least some micrometers can be approximated. The Debye-Bueche ansatz accounts for the formation of a transient pronounced signal on mesoscopic length scales. Its analysis results in an average domain size of 12–16 Å characterizing a hypothetical two phase mixture in its state of strongest intermixture, i.e., strongest heterogeneity. Interpretation of the Debye-Bueche formfactor by the Porod invariant results in a sample contrast that is by a factor of about 4 smaller than a hypothetical first-order transition between any modification of HDA and LDA. This statement is valid for an unstrained two-phase system separated by sharp interfaces. A detailed discussion is given which tries to set the present results into a more realistic context.

Vibrational dynamics of amorphous ice structures studied by high-resolution neutron spectroscopy

The dynamics of amorphous water ice structures of different densities have been studied by high-resolution neutron time-of-flight and backscattering spectroscopy. An accurate determination of the vibrational density of states $G(\ensuremath{\omega})$ in the energy range of phonons $\ensuremath{\hbar}\ensuremath{\omega}\ensuremath{\lesssim}40\text{ }\text{meV}$ of a many fold of structures comprising the low-density amorphous (LDA, $\ensuremath{\rho}\ensuremath{\approx}31\text{ }\text{molecules}/{\text{nm}}^{3}$), high-density amorphous (HDA, $\ensuremath{\rho}\ensuremath{\approx}39\text{ }\text{molecules}/{\text{nm}}^{3}$), very-high-density amorphous (vHDA, $\ensuremath{\rho}\ensuremath{\approx}41\text{ }\text{molecules}/{\text{nm}}^{3}$) and modifications of intermediate density in respect to HDA and vHDA has been achieved. Unlike the $G(\ensuremath{\omega})$ of high-density crystalline phases IX, V, and XII, which have been measured as reference systems, the $G(\ensuremath{\omega})$ of all high-density amorphous counterparts proves to be textureless except for a predominant peak at low energies. In vHDA this peak is centered at about 10 meV and redshifted upon density decrease to 7 meV in LDA. A concomitant upshift of the low-energy librational band edge from 34 to 45 meV is detected in deuterated samples. Mean-square displacement and Debye temperatures ${T}_{D}$ for vHDA, ${\mathrm{HDA}}^{\ensuremath{'}}$---a structure obtained as a transient product of the temperature induced vHDA to LDA transformation---and LDA are extracted from the highest resolution backscattering experiments. ${T}_{D}$ values indicate the absence of a dominant excess of low-energy modes in $G(\ensuremath{\omega})$, referred to as boson peak in the literature, being in agreement with the $G(\ensuremath{\omega})$ properties directly monitored by the time-of-flight technique. Having applied deuterated sample material we are able to display phase coherence effects within the phonon system in the second and third pseudo-Brillouin zone $(1\text{ }{\text{\AA{}}}^{\ensuremath{-}1}\ensuremath{\le}Q\ensuremath{\le}5\text{ }{\text{\AA{}}}^{\ensuremath{-}1})$ of the amorphous samples. A phase coherent signal from acoustic phonons can be followed up to energies of at least 15 meV.

Link between the diversity, heterogeneity and kinetic properties of amorphous ice structures

Based on neutron wide-angle diffraction and small-angle neutron scattering experiments, we show that there is a correlation between the preparational conditions of amorphous ice structures, their microscopic structural properties, the extent of heterogeneities on a mesoscopic spatial scale and the transformation kinetics. There are only two modifications that can be identified as homogeneous disordered structures, namely the very high-density vHDA and the low-density amorphous LDA ice. Structures showing an intermediate static structure factor with respect to vHDA and LDA are heterogeneous phases. This holds independently from their preparation procedure, i.e. either obtained by pressure amorphization of ice Ih or by heating of vHDA. The degree of heterogeneity can be progressively suppressed when higher pressures and temperatures are applied for the sample preparation. In accordance with the suppressed heterogeneity the maximum of the static structure factor displays a pronounced narrowing of the first strong peak, shifting towards higher Q-numbers. Moreover, the less heterogeneous the obtained structures are the slower is the transformation kinetics from the high-density modifications into LDA. The well known high-density amorphous structure HDA does not constitute any particular state of the amorphous water network. It is formed due to the preparational procedure working in liquid nitrogen as thermal bath, i.e. at about 77K.

Evolution of the structure of amorphous ice - from LDA through HDA to VHDA

Evolution of the structure of amorphous ice - from LDA through HDA to VHDA

Modelling of the structure and vibrational properties of LDA, HDA, and VHDA amorphous ices

The models of three known amorphous ice structures—low-density (LDA), high-density (HDA) and very-high-density (VHDA) amorphous ices have been obtained using sequential steps of molecular dynamics simulation and the additional optimization scheme within the lattice dynamics approach at the different cell parameters. It has been shown that this combined approach leads to a more accurate and detailed structural description of HDA and LDA ices and yields results that are in excellent agreement with experiment. The dynamic properties of obtained structures have been analyzed within the lattice dynamics approach. It has been shown that in all considered structures there exist some extended vibrational modes, which involve up to 70% of molecules. These modes apparently are a consequence of existence of hydrogen bonds network in amorphous ices.

Evolution of the structure of amorphous ice: From low-density amorphous through high-density amorphous to very high-density amorphous ice

We report results of molecular dynamics simulations of amorphous ice for pressures up to 22.5 kbar. The high-density amorphous ice (HDA) as prepared by pressure-induced amorphization of I(h) ice at T=80 K is annealed to T=170 K at various pressures to allow for relaxation. Upon increase of pressure, relaxed amorphous ice undergoes a pronounced change of structure, ranging from the low-density amorphous ice at p=0, through a continuum of HDA states to the limiting very high-density amorphous ice (VHDA) regime above 10 kbar. The main part of the overall structural change takes place within the HDA megabasin, which includes a variety of structures with quite different local and medium-range order as well as network topology and spans a broad range of densities. The VHDA represents the limit to densification by adapting the hydrogen-bonded network topology, without creating interpenetrating networks. The connection between structure and metastability of various forms upon decompression and heating is studied and discussed. We also discuss the analogy with amorphous and crystalline silica. Finally, some conclusions concerning the relation between amorphous ice and supercooled water are drawn.

High density amorphous ices: Disordered water towards close packing

The structure of amorphous ice under pressure has been studied by molecular dynamics at 160 K. The starting low-density phase undergoes significant changes as the density increases, and at rho=1.51 g/cm(3) our calculated g(OO)(r) is in excellent agreement with in situ neutron diffraction data obtained at 1.8 GPa and 100 K on very high density amorphous ice made at 150 K. As the system is further compressed, in the theoretical simulations, up to rho=1.90 g/cm(3), the structural modifications are continuous up to the highest density. The analysis of orientational distributions reveals that dense amorphous ice is characterized by major distortions of the tetrahedral geometry, and that the pressure structural changes, already observed experimentally at lower densities, can be interpreted as a trend towards a disordered closed-packed structure.

Local structure of amorphous ice as revealed by O K-edge EXAFS.

The oxygen K-edge extended X-ray absorption fine structure (EXAFS) spectrum of an ice film prepared by deposition of water vapor on a substrate at 100 K was measured in the surface-sensitive Auger yield mode. Five distinct peaks are revealed in the Fourier transform spectrum of the EXAFS data. The peaks are attributed to O-H bonds (with overlapping contributions from intramolecular covalent and intermolecular hydrogen bonds) as well as to intermolecular O...O scattering paths in the distance range of 1-7 A. The pattern of the longer O...O distances resembles that of a high-pressure crystalline modification of ice (ice II).

Condensation and structure of amorphous ices: A computational study

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Modelling of the structure of amorphous ice

The structure of amorphous solid water was simulated using hand-built models and a computer relaxation procedure. The structure of high temperature amorphous ice was reproduced by a continuous random network model of tetrahedrally bonded water molecules with 5, 6, 7 and 8-fold rings of oxygen atoms and a small amount of 4-fold rings. The structure of the low-temperature form of amorphous ice was reproduced in the framework of a model containing only 6 and 8-fold rings of atoms. In this model Van der Waals forces between the oxygen atoms must be also introduced.

ChemInform Abstract: THE STRUCTURAL MODEL OF WATER. II. THE STRUCTURE OF AMORPHOUS ICE AND STRUCTURAL RELATIONS BETWEEN WATER AND SOME ICE POLYMORPHS ON THE BASIS OF THE TETRAGONAL CLUSTER MODEL

Chemischer InformationsdienstVolume 9, Issue 36 Physical Inorganic Chemistry ChemInform Abstract: THE STRUCTURAL MODEL OF WATER. II. THE STRUCTURE OF AMORPHOUS ICE AND STRUCTURAL RELATIONS BETWEEN WATER AND SOME ICE POLYMORPHS ON THE BASIS OF THE TETRAGONAL CLUSTER MODEL F. HAJDU, F. HAJDUSearch for more papers by this author F. HAJDU, F. HAJDUSearch for more papers by this author First published: September 5, 1978 https://doi.org/10.1002/chin.197836011AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat No abstract is available for this article. Volume9, Issue36September 5, 1978 RelatedInformation

Electron diffraction study of the structure of amorphous ice

Electron diffraction study of the structure of amorphous ice