Glass transitions in quasi-two-dimensional suspensions of colloidal ellipsoids

We observed a two-step glass transition in monolayers of colloidal ellipsoids by video microscopy. The glass transition in the rotational degree of freedom was at a lower density than that in the translational degree of freedom. Between the two transitions, ellipsoids formed an orientational glass. Approaching the respective glass transitions, the rotational and translational fastest-moving particles in the supercooled liquid moved cooperatively and formed clusters with power-law size distributions. The mean cluster sizes diverge in power law as they approach the glass transitions. The clusters of translational and rotational fastest-moving ellipsoids formed mainly within pseudonematic domains and around the domain boundaries, respectively.     

Observation and analysis of a glass transition in amorphous frozen solutions of iron-II chloride

This paper deals with Mössbauer investigations, X-ray diffraction studies and differential calorimetric measurements of the amorphous state of frozen solutions of FeCl₂ in water. This glassy state persists from at least ?180 °C until ?90 °C. All three experimental methods reveal the existence of a glass transition at ?110 °C from an amorphous state to a supercooled liquid. It is shown that for such transitions important conclusions can be drawn from a comparison between the Mössbauer and X-ray diffraction Debye-Waller factor respectively by determining the transmitted Mössbauer intensity far off resonance. Out of the analysis we conclude that the glassy state of quenched ice is due to the hexaquo complexes as implanted impurities which prevail their surrounding from a regular crystallisation. These impurities are also responsible for the glass transition into a supercooled liquid state by releasing new degrees of freedom as e.g. hindered rotational modes.     

Universal nature of particle displacements close to glass and jamming transitions

We examine the structure of the distribution of single particle displacements (van Hove function) in a broad class of materials close to glass and jamming transitions. In a wide time window comprising structural relaxation, van Hove functions reflect the coexistence of slow and fast particles (dynamic heterogeneity). The tails of the distributions exhibit exponential, rather than Gaussian, decay. We argue that this behavior is universal in glassy materials and should be considered the analog, in space, of the stretched exponential decay of time correlation functions. We introduce a dynamical model that describes quantitatively numerical and experimental data in supercooled liquids, colloidal hard spheres, and granular materials. The tails of the distributions directly explain the decoupling between translational diffusion and structural relaxation observed in glassy materials.     

Studies on magnetic-field-induced first-order transitions

We shall discuss magnetization and transport measurements in materials exhibiting a broad first-order transition. The phase transitions would be caused by varying magnetic field as well as temperature, and we concentrate on ferro- to antiferromagnetic transitions in magnetic materials. We distinguish between metastable supercooled phases and metastable glassy phase.     

Metallic glassy fibers

A review on the formation and unique physical and mechanical properties of metallic glassy fibers (MGFs) with the diameter ranging from micro to nano scales fabricated by a supercooled liquid extraction method (SLEM) is given. The SLEM method, through driving metallic glass rods in their supercooled liquid region via superplasticity, can fabricate MGFs with precisely designed and controlled size and properties, high structural uniformity and surface smoothness and extreme flexibility. The SLEM method is efficient and the MGFs can be continuously prepared by this method. A parameter f based on the thermal and rheological properties of MG-forming alloys is proposed to control the preparation and size of the fibers. We show that the novel MGFs with superior properties may attract intensive scientific interests and propel more engineering and functional applications.     

Role of unstable directions in the equilibrium and aging dynamics of supercooled liquids

The connectivity of the potential energy landscape in supercooled atomic liquids is investigated through a calculation of the instantaneous normal modes spectrum and a detailed analysis of the unstable directions in configuration space. We confirm the hypothesis that the mode-coupling critical temperature is the T at which the dynamics crosses over from free to activated exploration of configuration space. We also observe changes in the local connectivity of configuration space sampled during aging, following a temperature jump from a liquid to a glassy state.     

Atomic mechanism of glass formation in supercooled monatomic liquids

Atomic mechanism of glass formation in supercooled monatomic liquids is monitored via analyzing the spatial arrangement of solid-like atoms. The supercooled states are obtained by cooling from the melt using molecular dynamics (MD) simulation. Solid-like atoms, detected via Lindemann-like freezing criterion, are found throughout the liquid. Their number increases with decreasing temperature and they form clusters. In the deeply supercooled region, all solid-like atoms form a single percolation cluster which spans throughout the system. The number of atoms in this cluster increases steeply with further cooling. Glass formation in supercooled liquids occurs when a single percolation cluster of solid-like atoms involves the majority of atoms in the system to form a relatively rigid glassy solid. By analyzing the temperature dependence of static and dynamic properties, we identify three characteristic temperatures of glass formation in supercooled liquids including the Vogel–Fulcher temperature.     

Fast interfacial ionic conduction in nanostructured glass ceramics

The hopping movements of mobile ions in a nanostructured LiAlSiO4 glass ceramic are characterized by time-domain electrostatic force spectroscopy (TDEFS). While the macroscopic conductivity spectra are governed by a single activation energy, the nanoscopic TDEFS measurements reveal three different dynamic processes with distinct activation energies. Apart from the ion transport processes in the glassy and crystalline phases, we identify a third process with a very low activation energy, which is assigned to ionic movements at the interfaces between the crystallites and glassy phase. Such interfacial processes are believed to play a key role for obtaining high ionic conductivities in nanostructured solid electrolytes.     

Anomalous electrical conductivity behavior at elevated pressure in the protic ionic liquid procainamide hydrochloride

Using broadband dielectric spectroscopy, we investigated the effect of hydrostatic pressure on the conductivity relaxation time τ{σ} of the supercooled protic ionic liquid, procainamide hydrochloride, a common pharmaceutical. The pressure dependence of τ{σ} exhibited anomalous behavior in the vicinity of the glass transition T{g}, manifested by abrupt changes in activation volume. This peculiar behavior, paralleling the change in temperature dependence of τ{σ} near T{g}, is a manifestation of the decoupling between electrical conductivity and structural relaxation. Although the latter effectively ceases in the glassy state, free ions retain their mobility but with a reduced sensitivity to thermodynamic changes. This is the first observation of decoupling of ion migration from structural relaxation in a glassy conductor by isothermal densification.     

Crystallization Kinetics of Co48Cr15Mo14C15BaEr2 Bulk Metallic Glass with High Thermal Stability

We investigate the crystallization kinetics of Co48Cr15Mo14C15B6Er2 bulk metallic glass. It is found that Co48Cr15Mo14C15B6Er2 alloy shows extraordinary glass-forming ability, and a fully glassy rod with a diameter of 10mm can be formed, Thermal analysis exhibits that this glassy alloy has a high thermal stability, Johnson-Mehl-Avrami analysis of isothermal differential scanning calorimetry demonstrates that the crystalline phases homogeneously nucleates at a constant rate and grows linearly at a constant rate in three dimensions in the supercooled liquid of the glassy alloy.     

The Boson peak interpretation and evolution in confined amorphous water

We study the evolution of the Boson peak for water confined in cement paste obtained by means of Inelastic Neutron Scattering from room temperature to the deep supercooled regime. We analyze the data in terms of a universal-like model, developed for glass forming liquids in the frame of the energy landscape. In such a way it is possible to discriminate between the fragile and strong glass forming character of supercooled liquids and the dynamical crossover, fragile to strong, between them. Hence, we confirm the link between the Boson peak and the water polymorphism. In particular, the main result is represented by a crossover from a local energetic minima configuration to that characteristic of saddle points on going towards the deep supercooled regime up to the dynamical arrest.     

Out of Equilibrium Dynamics of the Toy Model with Mode Coupling and Trivial Hamiltonian

We extend our previous analysis of the toy model that mimics the mode coupling theory of supercooled liquids and glass transitions to the out of equilibrium dynamics. We derive a self-consistent set of equations for correlation and response functions.     

Liquid-liquid transition in the molecular liquid triphenyl phosphite

We found both nucleation-growth-type and spinodal-decomposition-type transformation from one liquid state to another in a "molecular liquid," triphenyl phosphite (TPP). Binodal and spinodal temperatures of this transition at ambient pressure were determined by the characteristics of morphological evolution, domain-growth kinetics, and rheological evolution. Furthermore, a distinct thermal signature of the glass transition of a second liquid was also detected in addition to that of an ordinary liquid. These findings strongly suggest the existence of a liquid-liquid transition; more precisely, a transformation of one supercooled liquid to a glassy state of another liquid, in TPP.     

Mössbauer label and radiothermoluminescence methods for the study of low-temperature polymorphism and dynamic properties of metastable phases of thermotropic liquid crystals

The Mössbauer label and the radiothermoluminescence (RTL) methods were used for the study of low-temperature polymorphism of thermotropic liquid crystals (LC) possessing glassy and supercooled mesophases as well as solid metastable phases. The dynamic properties of unstable LC phases are also investigated. The activation energies for various types of molecular and fragmental movements in these mesophases are estimated from their RTL spectra. From Mössbauer spectra, the diffusional characteristics of different low-temperature mesophases are obtained.     

Force Distributions near Jamming and Glass Transitions

We calculate the distribution of interparticle normal forces P(F) near the glass and jamming transitions in model supercooled liquids and foams, respectively. P(F) develops a peak that appears near the glass or jamming transitions, whose height increases with decreasing temperature, decreasing shear stress and increasing packing density. A similar shape of P(F) was observed in experiments on static granular packings. We propose that the appearance of this peak signals the development of a yield stress. The sensitivity of the peak to temperature, shear stress, and density lends credence to the recently proposed generalized jamming phase diagram.     

Atomic mechanism of vitrification process in simple monatomic nanoparticles *

Glass formation in simple monatomic nanoparticles has been studied by molecular dynamics simulations in spherical model with a free surface. Models have been obtained by cooling from the melt toward glassy state. Atomic mechanism of glass formation was monitored via spatio-temporal arrangement of solid-like and liquid-like atoms in nanoparticles. We use Lindemann freezing-like criterion for identification of solid-like atoms which occur randomly in supercooled region. Their number grows intensively with decreasing temperature and they form clusters. Subsequently, single percolation solid-like cluster occurs at temperature above the glass transition. Glass transition occurs when atoms aggregated into this single percolation cluster are in majority in the system to form relatively rigid glassy state. Solid-like domain is forming in the center of nanoparticles and grows outward to the surface. We found temperature dependence of potential energy, mean-squared displacement (MSD) of atoms, diffusion constant, incoherent intermediate scattering function, radial distribution function (RDF), local bond-pair orders detected by Honeycutt-Andersen analysis, radial density profile and radial atomic displacement distributions in nanoparticles. We found that liquid-like atoms in models obtained below glass transition have a tendency to concentrate in the surface layer of nanoparticles. However, they do not form a purely liquid-like surface layer coated nanoparticles.     

Indication for hyperdeformed cluster states in <Superscript>233</Superscript>Th

An activation technique was used to investigate relative yields of fission products from the reaction ²³²Th(n, f ) for neutron energies between 1.3 and 1.8MeV covering the region around the first hyperdeformed resonances. Intensities of characteristic γ-ray transitions were analyzed to search for changes in the mass distribution for neutron energies corresponding to the resonances and below the resonances. Relative increases in yield between 7 and 23% are observed for A ≈ 100 and 132 in the resonance region around 1.6MeV. It is proposed that the yield enhancement of daughter nuclei of the preformed fragments ¹³²Sn and ¹⁰¹Zr arises from cold fission of a di-cluster configuration. The experimental results support theoretical predictions for the existence of hyperdeformed octupole shapes based on the di-nuclear configuration ¹³²Sn + ¹⁰¹Zr.     

Mössbauer studies of polymers in the glassy state and near their glass transition

Mössbauer absorption spectra of glassy block and copolymers with lowT _G containing ferrocene have been recorded in a wide temperature range (4–330 K) to investigate the dynamical processes of the system, in the glassy state and around the glass transition. An inhomogeneous broadening due to conformational substates with different hyperfine parameters found at lower temperatures becomes motionally narrowed above 40 K. Whereas in the glassy state both the block and the copolymers reveal the same vibrational behaviour, we found differences in the vicinity of their respective glass transitions. For the block polymer an anomalous decrease of the recoilfree fractionf _A was found above the static glass transition. In agreement with neutron data on other polymers we attribute this behaviour to an onset of motions of the ferrocene units of higher than 10¹⁰ Hz. For the copolymers, however, a departure of lnf _A from linearity was detected already far below the staticT _G. We propose that this is caused by residual solvents which allow an easier cooperative rearrangement of the segments even belowT _G. First attempts to interpret the Mössbauer data by means of the predictions of the mode coupling theory are reported.     

Oxidation of Zr 55 Cu 30 Al 10 Ni 5 bulk metallic glass in the glassy state and the supercooled liquid state

The oxidation behavior of Zr₅₅Cu₃₀Al₁₀Ni₅ bulk metallic glass in air in the glassy state and the supercooled liquid state was studied using a thermogravimetric analyzer, X-ray diffraction and scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy. It was found that the isothermal oxidation kinetics of the glass in both states follows a two-step parabolic law. The oxidation process is governed by the inward diffusion of oxygen and the outward diffusion of Cu, with the first being dominant. The faster diffusion of atoms in the supercooled liquid state led to a network precipitation of crystalline Cu, and the crystallization that occurred in this state in the later stage of oxidation caused a reduction in the rate of oxidation. Two types of Zr oxides, i.e. t-ZrO₂ and m-ZrO₂, were formed in the oxidation process in both the glassy and supercooled liquid states. t-ZrO₂ mainly formed in the outer layer of the oxide scale, while m-ZrO₂ tended to form in the inner layer. The formation of m-ZrO₂ is possibly activated by the crystallization of the glass near the interface of the oxide scale and the substrate alloy. In addition, oxidation also has a substantial effect on the formation of crystallized phases. The formation of a Cu-rich phase of Cu₁₀Zr₇ occurred in the oxidizing atmosphere. However, the formation of a Zr-rich phase of Zr₂(Ni, Cu) mainly took place in a vacuum environment. PACS 81.05.Kf; 81.65.Mq; 64.60.-i     

Colloidal glass transition observed in confinement

We study a colloidal suspension confined between two quasiparallel walls as a model system for glass transitions in confined geometries. The suspension is a mixture of two particle sizes to prevent wall-induced crystallization. We use confocal microscopy to directly observe the motion of colloidal particles. This motion is slower in confinement, thus producing glassy behavior in a sample which is a liquid in an unconfined geometry. For higher volume fraction samples (closer to the glass transition), the onset of confinement effects occurs at larger length scales.