Structure Of Supercooled Liquids Research Articles

Dimensionality reduction of local structure in glassy binary mixtures.

We consider unsupervised learning methods for characterizing the disordered microscopic structure of supercooled liquids and glasses. Specifically, we perform dimensionality reduction of smooth structural descriptors that describe radial and bond-orientational correlations and assess the ability of the method to grasp the essential structural features of glassy binary mixtures. In several cases, a few collective variables account for the bulk of the structural fluctuations within the first coordination shell and also display a clear connection with the fluctuations of particle mobility. Fine-grained descriptors that characterize the radial dependence of bond-orientational order better capture the structural fluctuations relevant for particle mobility but are also more difficult to parameterize and to interpret. We also find that principal component analysis of bond-orientational order parameters provides identical results to neural network autoencoders while having the advantage of being easily interpretable. Overall, our results indicate that glassy binary mixtures have a broad spectrum of structural features. In the temperature range we investigate, some mixtures display well-defined locally favored structures, which are reflected in bimodal distributions of the structural variables identified by dimensionality reduction.

Identifying structural signature of dynamical heterogeneity via the local softness parameter.

In this work we study the relationship between the softness of a mean-field caging potential and dynamics at the local level. We first describe the local softness, which shows a distribution, thus identifying structural heterogeneity. We show that the lifetime of the softness parameter is connected to the lifetime of the well-known cage structure in supercooled liquids. Finally, our theory predicts that the local softness and the local dynamics is causal below the onset temperature where there is a decoupling between the short and long time dynamics, thus allowing a static description of the cage. With the decrease in temperature, the correlation between structure and dynamics increases. The study shows that at lower temperatures, the structural heterogeneity increases, and since the structure becomes a better predictor of the dynamics, it leads to an increase in the dynamical heterogeneity. We also find that the softness of a hard, immobile region evolves with time and becomes soft and eventually mobile due to the rearrangements in the neighborhood, confirming the well-known facilitation effect.

Dynamical time scales of friction dynamics in active microrheology of a model glass.

Owing to the local/heterogeneous structures in supercooled liquids, after several decades of research, it is now clear that supercooled liquids are structurally different from their conventional liquid counterparts. Accordingly, an approach based on a local probe should provide a better understanding about the local mechanical properties as well as heterogeneous structures. Recently, the superiority of active microrheology over global rheology has been demonstrated [Yu et al., Sci. Adv., 2020, 6, 8766]. Here, we elaborate this new avenue of research and provide more evidence for such superiority. We report on the results of an extensive molecular dynamics simulation of active microrheology of a model glass. We identify several time scales in time series of friction, and detect a transition in dynamical behavior of friction. We discuss the possible relation to structural heterogeneities-a subject of considerable interest in glass physics.

Autonomously revealing hidden local structures in supercooled liquids

Few questions in condensed matter science have proven as difficult to unravel as the interplay between structure and dynamics in supercooled liquids. To explore this link, much research has been devoted to pinpointing local structures and order parameters that correlate strongly with dynamics. Here we use an unsupervised machine learning algorithm to identify structural heterogeneities in three archetypical glass formers—without using any dynamical information. In each system, the unsupervised machine learning approach autonomously designs a purely structural order parameter within a single snapshot. Comparing the structural order parameter with the dynamics, we find strong correlations with the dynamical heterogeneities. Moreover, the structural characteristics linked to slow particles disappear further away from the glass transition. Our results demonstrate the power of machine learning techniques to detect structural patterns even in disordered systems, and provide a new way forward for unraveling the structural origins of the slow dynamics of glassy materials.

Glass structure and crystallization via two distinct thermal histories: Melt crystallization and glass crystallization

This study focuses on the effect of structural inhomogeneity of 44.4CaO-33.2SiO2-8.8Na2O-6.2Al2O3-7.4B2O3 glass on its crystallization behavior. The crystallization behavior of the investigated lime-sodium aluminoborosilicate glass system is explored for the two thermal histories of melt crystallization and the heat treatment of quenched glass. The results show that sodium melilite (CaNaAlSi2O7) and larnite (β-Ca2SiO4) are the dominant crystalline phases during heating (glass crystallization) and cooling (melt crystallization), respectively. In the glass structure from the heat treatment at 610 °C, both Si2O7 and AlO4 units (i.e., four-coordinated Al) are dominant. This may induce sodium melilite (CaNaAlSi2O7) crystallization, connecting Si2O7 and AlO4 units with O and linking Ca and Na between interlayers. The melt structure, meanwhile, has more SiO4 and AlO6 units in its silicate and aluminate. Therefore, larnite (β-Ca2SiO4) crystallizes on cooling by combining SiO4 units and Ca. The crystallization behavior is further discussed considering the inhomogeneity structure of supercooled liquids before nucleation.

Role of structure in the α and β dynamics of a simple glass-forming liquid.

The elusive connection between dynamics and local structure in supercooled liquids is an important piece of the puzzle in the unsolved problem of the glass transition. The Johari-Goldstein β relaxation, ubiquitous in glass-forming liquids, exhibits mean properties that are strongly correlated to the long-time α dynamics. However, the former comprises simpler, more localized motion, and thus has perhaps a more straightforward connection to structure. Molecular dynamics simulations were carried out on a two-dimensional, rigid diatomic molecule (the simplest structure exhibiting a distinct β process) to assess the role of the local liquid structure on both the Johari-Goldstein β and the α relaxation. Although the average properties for these two relaxations are correlated, there is no connection between the β and α properties of a given (single) molecule. The propensity for motion at long times is independent of the rate or strength of a molecule's β relaxation. The mobility of a molecule averaged over many initial energies, a measure of the influence of structure, was found to be heterogeneous, with clustering at both the β and α time scales. This heterogeneity is less extended spatially for the β than for the α dynamics, as expected; however, the local structure is the more dominant control parameter for the β process. In the glassy state, the arrangement of neighboring molecules determines entirely the relaxation properties, with no discernible effect from the particle momenta.

Effect of Nb addition on Fe-Ni-B-Si amorphous and crystalline composite coatings by laser processing

The effect of Nb addition on Fe–Ni–B–Si amorphous and crystalline composite coatings was studied. Firstly, the coatings with different forms of Nb were investigated by X-ray Diffractometry (XRD) and Scanning Electron Microscopy (SEM) tests. It was found that ferroniobium can increase the glass forming ability (GFA) of the coatings and large negative mixing enthalpies of elements are helpful to form an amorphous phase in coatings. A precipitation phase with complex structure in supercooled liquid is helpful to form an amorphous phase. Secondly, the coatings with different amounts of Nb were investigated, too. It was found that one stage crystallization reaction happened in Fe31Ni31Si18B18Nb2 coating with low Nb content and two stage crystallization reactions in Fe30Ni30Si18B18Nb4 and Fe28Ni28Si18B18Nb8 coatings by laser processing. The thickness of amorphous and crystalline composite layer of coatings is about 0.4mm. The hardness of composite layer is higher than that in the clad layer. Breaking off of hard phases in high Nb content coatings will increase the mass loss in wear tests.

Communication: Crystallite nucleation in supercooled glycerol near the glass transition

Heterogeneity and solid-like structures found near the glass transition provide a key to a better understanding of supercooled liquids and of the glass transition. However, the formation of solid-like structures and its effect on spatial heterogeneity in supercooled liquids is neither well documented nor well understood. In this work, we reveal the crystalline nature of the solid-like structures in supercooled glycerol by means of neutron scattering. The results indicate that inhomogeneous nucleation happens at temperatures near T(g). Nevertheless, the thermal history of the sample is essential for crystallization. This implies such structures in supercooled liquids strongly depend on thermal history. Our work suggests that different thermal histories may lead to different structures and therefore to different length and time scales of heterogeneity near the glass transition.

In situ measurement of the structure of supercooled oxide liquids

This paper will describe the results of in situ high-energy X-ray measurements performed on stable and supercooled oxide liquids using containerless techniques. As will be discussed in the companion paper (Weber et al.), the use of an aerodynamic levitator furnace with laser heating allows the structures of refractory oxide liquids to be probed. Because of the contactless nature of this sample environment liquids can be deeply supercooled, and this provides opportunities to study the metastable structures of supercooled liquids. Of particular interest are the so-called fragile liquids that depart from Arrhenius-law viscosity behaviour and that, by definition, have temperature-dependent structures. The focus of this paper is the study of two oxide systems, MgO–SiO2 and Al2O3–SiO2. These two liquids have highly disordered stable liquid structures that differ substantially from the structures of the equivalent glasses. We present data showing how these structures change when supercooled and demonstrate dramatic changes in short-range (coordination number) and intermediate-range order during vitrification. These data have been collected by isothermal measurement and also fast quenching methods using the recently developed method of rapid acquisition using a Perkin Elmer amorphous silicon flat panel detector; this gives a large Q coverage for incident energies of >115 keV. The rapid data acquisition enables the vitrification process to be observed directly.

A new threshold of uncovering the nature of glass transition: The slow ß relaxation in glassy states

The glass transition involves more than one dynamic relaxation mechanisms in supercooled liquids, such as α relaxation, slow s relaxation and fast s relaxation and so on. For the traditional theoretical system, α relaxation is believed mainly responsible for the nature of the glass transition as the beginning of the phenomenon. This idea, however, has been open to a big challenge since recent studies have indicated that slow s relaxation closely relates to α relaxation. Slow s relaxation determines the characteristics of α relaxation and is the precursor and the more microscopic base of glass transition behavior. In order to illuminate the significance of slow s relaxation in the fields of the glass transition and the structure of supercooled liquids, the accomplished progress is summarized from different aspects such as on the correlation between α relaxation and slow s relaxation, on the manner of α-slow s relaxation merging, on the energy landscape, on the excess wing and on the thermodynamically phenomenological models. The tendency of investigation in slow s relaxation is also evaluated.

Acoustic levitator for structure measurements on low temperature liquid droplets

A single-axis acoustic levitator was constructed and used to levitate liquid and solid drops of 1-3 mm in diameter at temperatures in the range -40 to +40 degrees C. The levitator comprised (i) two acoustic transducers mounted on a rigid vertical support that was bolted to an optical breadboard, (ii) an acoustic power supply that controlled acoustic intensity, relative phase of the drive to the transducers, and could modulate the acoustic forces at frequencies up to 1 kHz, (iii) a video camera, and (iv) a system for providing a stream of controlled temperature gas flow over the sample. The acoustic transducers were operated at their resonant frequency of approximately 22 kHz and could produce sound pressure levels of up to 160 dB. The force applied by the acoustic field could be modulated to excite oscillations in the sample. Sample temperature was controlled using a modified Cryostream Plus and measured using thermocouples and an infrared thermal imager. The levitator was installed at x-ray beamline 11 ID-C at the Advanced Photon Source and used to investigate the structure of supercooled liquids.

Icosahedral Order, Frustration, and the Glass Transition: Evidence from Time-Dependent Nucleation and Supercooled Liquid Structure Studies

One explanation for the glass transition is a geometrical frustration owing to the development of non-space-filling short-range order (icosahedral, tetrahedral). However, experimental demonstrations of this are lacking. Here, the first quantitative measurements of the time-dependent nucleation rate in a Zr59Ti3Cu20Ni8Al10 bulk metallic glass are combined with the first measurements of the evolution of the supercooled liquid structure to near the glass transition temperature to provide strong support for an icosahedral-order-based frustration model for the glass transition in Zr-based glasses.

The structure of supercooled liquids and glasses as Skyrmionic texture

A re-appraisal of the frustration models for glass-forming and supercooled liquids is presented. It is shown that the elasticity theory expressed by covariant derivatives with respect to an ideal template on a three-sphere S3 allows for the formation of localized soft Skyrmion states. Owing to the homomorphism between the proper rotation group SO(4) for the symmetry of S3 and the SU(2) group for the unitary 2×2 matrices, the simplest version of the frustration models contain Skyrme’s hedgehog solution stabilized by the fixed gauge background from the covariant derivatives. The structure of glasses and supercooled liquids can be rendered as dense Skyrmionic matter which reproduces geometric frustration at larger length scales in an orientable continuum.

Quantitative Link between Single-Particle Dynamics and Static Structure of Supercooled Liquids

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionQuantitative Link between Single-Particle Dynamics and Static Structure of Supercooled LiquidsJeetain Mittal, Jeffrey R. Errington, and Thomas M. TruskettCite this: J. Phys. Chem. B 2007, 111, 19, 5531Publication Date (Web):April 24, 2007Publication History Published online24 April 2007Published inissue 1 May 2007https://doi.org/10.1021/jp072284gCopyright © 2007 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views227Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (3 KB) Get e-Alerts Get e-Alerts

Quantitative Link between Single-Particle Dynamics and Static Structure of Supercooled Liquids

We present evidence via molecular simulation that the supercooled fluid states of SPC/E water as well as the "repulsive" and "attractive" supercooled fluid states of a recently introduced model for colloids with short-ranged attractions are characterized by the same functional relationship between self-diffusivity and the pair correlation function. We discuss how this simple relationship connects to an earlier finding that the temperature dependency of a supercooled fluid's single-particle dynamics tracks that of its excess entropy (relative to ideal gas). The generality of this observed structure-property relationship is supported by its ability to successfully describe the nontrivial behaviors of these very different types of model systems.

Relating nucleation to dynamical and structural heterogeneity in supercooled liquid metal

Molecular dynamics (MD) simulation has been adopted to study the dynamical properties and structural transition of supercooled liquid Ni near the crystalline temperature. Dynamical heterogeneity properties have been investigated by characterizing relaxation time dependence of the dynamics parameter such as mean square displacement (MSD) or non-Gaussian parameter (NGP). After undergoing the first plateau, MSD curve shows a second plateau that emerges at the temperature of 1090 K. The non-diffusive rearrangement suggests the nuclei forming and crystalline growth. The pair analysis (PA) technique as well as visual inspection has been performed to explore the structure of nuclei. We found the face centered cubic (FCC) cluster made up of twelve 1421 bonded pairs plays an important role in the nucleation and crystalline growth. Our simulation provides an atomistic understanding on how the dynamics and structure of supercooled liquids evolves in the crystalline formation.

Liquid fragility—A key to going deep into materials of glassy states

“Liquid fragility” is a concept that has been widely used in the investigation on the glass community, though it was presented less than two decades ago. The concept enables the comparison between the glass-forming liquids with different dynamic characters by using a general criterion, in which the temperature scale is reduced by the glass transition temperature. In order to illuminate the significance of the concept in the fields of the glass transition, structural relaxation process and the structure of supercooled liquids, the accomplished progress and the faced challenges are summarized from different aspects such as on the correlation between dynamics and thermodynamic characters of condensed matters, on the energy landscape, on the nonexponential relaxation and on the theoretical model of microstructure and medium-range order. The tendency of investigation in “liquid fragility” is also evaluated.

Devitrification of the Zr 41.2Ti 13.8Cu 12.5Ni 10.0Be 22.5 bulk metallic glass studied by XRD, SANS, and NMR

The crystallization process of the Zr 41.2Ti 13.8Cu 12.5Ni 10.0Be 22.5 bulk metallic glass was investigated by X-ray diffraction (XRD), small-angle neutron scattering, and 9Be nuclear magnetic resonance. Upon annealing near the glass transition and up to a temperature near 673 K, a Be-containing crystalline phase forms after sufficient decomposition of the supercooled liquid. The XRD pattern of this Be-containing phase is consistent with icosahedral symmetry. The small length scale of the decomposed supercooled liquid structure limits the grain size of this phase, which gives rise to broad XRD peaks. Above 673 K, annealing produces Be 2Zr and Zr 2Cu, along with other crystalline phases.

Thermodynamic Properties of Inhomogeneous Structures in Supercooled Liquids

The weighted density-functional theory is applied to investigate the free-energy landscape of dense supercooled liquids. Metastable states intermediate to the liquid and crystal phases are found, which can be identified with the supercooled states seen in computer simulations. These states are marked by a lower degree of mass localization as compared to the highly localized state termed as "hard-sphere glass" found in earlier studies. We evaluate the free energy using the modified weighted density approximation (MWDA), as formulated by Denton and Ashcroft (1989) Phys. Rev. A , 39 , 4701. The inhomogeneous density is parametrized in terms of Gaussian profiles centered around random lattice sites. The effects of heterogeneity coming from a fluctuation of the width of these Gaussian profiles show that the free energy of the system increases with increase in the fluctuations and, finally, the metastable minima disappear with growing fluctuations.

Dynamics of inherent structure in supercooled liquids near kinetic glass transition.

We present a description of the dynamics of a supercooled binary Lennard-Jones liquid in term of the potential landscape of the system. The slowing down of the dynamics in supercooled liquids near the kinetic glass transition is related to the existence of basins in the potential landscape. The inherent structures that are the local potential minima in the configuration space obtained by a quench process are employed to represent the configurations of the basins. We present time correlation functions of the inherent structure, both the self and the coherent part, as a function of wave vector. We also calculated the mean-square displacement, and the non-Gaussian parameter of the van Hove self-correlation function. Compared with the dynamics of original configurations, the short-time relaxation has almost been eliminated by the quench process. However, the long-time alpha relaxations remain essentially the same. We conclude that the long-time alpha relaxation is the result of cross-basin transition in the potential landscape in the configuration space.