Glasses can be formed by many routes. In some cases, distinct polyamorphic forms are found. The normal mode of glass formation is cooling of a viscous liquid. Liquid behavior during cooling is classified between "strong" and "fragile," and the three canonical characteristics of relaxing liquids are correlated through the fragility. Strong liquids become fragile liquids on compression. In some cases, such conversions occur during cooling by a weak first-order transition. This behavior can be related to the polymorphism in a glass state through a recent simple modification of the van der Waals model for tetrahedrally bonded liquids. The sudden loss of some liquid degrees of freedom through such first-order transitions is suggestive of the polyamorphic transition between native and denatured hydrated proteins, which can be interpreted as single-chain glass-forming polymers plasticized by water and cross-linked by hydrogen bonds. The onset of a sharp change in d dT( is the Debye-Waller factor and T is temperature) in proteins, which is controversially indentified with the glass transition in liquids, is shown to be general for glass formers and observable in computer simulations of strong and fragile ionic liquids, where it proves to be close to the experimental glass transition temperature. The latter may originate in strong anharmonicity in modes ("bosons"), which permits the system to access multiple minima of its configuration space. These modes, the Kauzmann temperature T(K), and the fragility of the liquid, may thus be connected.

https://science.sciencemag.org/content/sci/267/5206/1924.full.pdf

Formation of glasses from liquids and biopolymers.

REVIEW ARTICLE: Glassy metals

Water is the most abundant liquid on earth and also the substance with the largest number of anomalies in its properties. It is a prerequisite for life and as such a most important subject of current research in chemical physics and physical chemistry. In spite of its simplicity as a liquid, it has an enormously rich phase diagram where different types of ices, amorphous phases, and anomalies disclose a path that points to unique thermodynamics of its supercooled liquid state that still hides many unraveled secrets. In this review we describe the behavior of water in the regime from ambient conditions to the deeply supercooled region. The review describes simulations and experiments on this anomalous liquid. Several scenarios have been proposed to explain the anomalous properties that become strongly enhanced in the supercooled region. Among those, the second critical-point scenario has been investigated extensively, and at present most experimental evidence point to this scenario. Starting from very low ...

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Water: A Tale of Two Liquids

Viscosity of liquid silica, silicates and alumino-silicates

Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments / Albert Rimola;Dominique Costa;Mariona Sodupe;Jean-François Lambert;Piero Ugliengo. In: CHEMICAL REVIEWS. ISSN 0009-2665. STAMPA. 113:6(2013), pp. 4216-4313. Original Citation: Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

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Silica Surface Features and Their Role in the Adsorption of Biomolecules: Computational Modeling and Experiments

Some applications of molecular dynamics calculations to the vitreous state have been examined for simple ionic MX and MX2 type glasses. The MX system which corresponds to a hypothetical vitreous and supercooled amorphous KCl is found to undergo an isobaric transition in the region of 0.3 Tf and an isothermal transition at around 35 kbar (T=Tf). The transition is evidenced by a discontinuity in second order thermodynamic properties and may be associated with a virtual disappearance of translational diffusion. By employing a variety of irreversible stress histories, the vitreous state in this case is shown to be insensitive to the thermodynamic stress history up to a maximum computationally permissible relaxation time of around 10−10 sec. Simulations are also reported for some ionic liquids of MX2 stoichiometry which, in contrast with KCl, have glass‐forming ability (BeF2, ZnCl2, and SiO2). Although the relaxation times involved in laboratory glass formation far exceed the long‐time limit of computer ’’expe...

Molecular dynamics studies of the vitreous state: Simple ionic systems and silica

Molecular dynamics computations are reported for systems of soft repulsive discs of the inverse twelfth‐power potential and for Lennard‐Jones atoms in two dimensions. In the case of soft discs the melting transition is obtained by assuming a first‐order transition and subsequent application of Ross’s melting rule. The assumption is vindicated by additional computations for the 2‐D L‐J model in which the melting and freezing parameters are determined by direct MD computation along the isotherm T=0.8 e/k and the isochore ρr20=1.0079. The results reaffirm the presence of first‐order phase boundaries and refute the postulated existence of a ’’hexatic mesophase’’ bounded by second‐order transitions. These two‐dimensional models are seen to have much smaller discontinuities in density and entropy than their three‐dimensional counterparts and to exhibit more pronounced premelting increases in the heat capacity. This is interpreted to be a consequence of the proximity of the mechanical instability points to the f...

Melting in two dimensions: Determination of phase transition boundaries

Molecular dynamics calculation of phase coexistence properties: The soft-sphere melting transition

Pressure and self-diffusion calculations for a model fluid system of parallel hard cubes are reported. When viewed alongside equations of state incorporating the known coefficients in the virial expansion (b 2 to b 7), a weak phase change is postulated around 1/4 close-packing. Changes in behaviour are also seen at the same density for the self-diffusion coefficient and an associated single-particle free volume. It is conjectured that a transition may be identifiable with the low-density percolation transition that occurs in all hard-core fluids when the single particle configurational volume becomes extensive. If the hard-sphere model were to behave similarly, the observations may have implications for the general development of liquid-state theory.

Percolation Transition in the Parallel Hard-cube Model Fluid

Transport properties of simple liquids (the Lennard-Jones model) have been determined, from stress correlation functions, for both the homogeneous liquid and in narrow pores of molecular dimensions. Viscosity profiles are defined by means of a resolution of the total stress tensor and its autocorrelation function into auto- and cross-components of single molecules. This enables a precise definition of viscosity profiles and provides a method of determination from molecular dynamics (MD) simulations of the interfacial regions. Preliminary shear viscosity profiles for liquids in periodic rectangular cavities (between two semi-infinite walls) have been obtained for both the transverse and longitudinal components. Profiles of these transport coefficients have no direct experimentally accessible counterparts, but could be useful for bulk fluid mechanics predictions. Results are presented for (i) a hard, elastic wall–molecule interaction and (ii) a Lennard-Jones (10–4) cohesive wall. Elongational viscosities, which have not previously been investigated via MD correlation functions have also been computed for the homogeneous fluid and the interfacial system. The results are discussed in relation to current experimentation on interfacial viscosities (including recent non-equilibrium molecular dynamics studies).

Leslie V. Woodcock

Papers

Molecular dynamics studies of the vitreous state: Simple ionic systems and silica

Melting in two dimensions: Determination of phase transition boundaries

Molecular dynamics calculation of phase coexistence properties: The soft-sphere melting transition

Percolation Transition in the Parallel Hard-cube Model Fluid

Interfacial viscosities via stress autocorrelation functions