Kinetic Fragility Research Articles

Fast and direct determination of fragility in metallic glasses using chip calorimetry

We directly determine the thermodynamic fragility index of two metallic glasses (Mg65Cu25Gd10 and Au49Cu26.9Si16.3Ag5.5Pd2.3) from fictive temperature shifts induced by a variation of the quenching rate using fast differential scanning calorimetry (FDSC). Recent chip calorimeters are able to achieve the cooling rates necessary to perform such an evaluation. For the Mg65Cu25Gd10 and Au49Cu26.9Si16.3Ag5.5Pd2.3 metallic glasses studied, we find very good agreement of the kinetic fragility index with literature data obtained by conventional calorimetry and rheology. The thermodynamic fragility indices are m=25.5 ± 1.5 for Mg65Cu25Gd10 and m=50.3 ± 2.3 for Au49Cu26.9Si16.3Ag5.5Pd2.3, respectively. The FDSC method discussed here allows for fast and reliable determination of the kinetic fragility of metallic glasses, and is thus competitive with high-frequency methods.

Dynamical Correlations for Statistical Copolymers from High-Throughput Broad-Band Dielectric Spectroscopy.

Broad-band dielectric spectroscopy (BDS) provides a powerful method of characterizing relaxation dynamics in diverse materials. Here we describe and employ a novel instrument for high-throughput broad-band dielectric spectroscopy (HTBDS) that accelerates this capability, enabling simultaneous measurements of 48 samples. This capability is based around a coaxial switching system for rapid scanning between multiple samples on the same sample stage, coordinated with shared environmental control. We validate the instrument by measuring dielectric response in three polymers, distributed across 48 sample sites, and comparing results to measurements via a standard BDS instrument. Results are found to be reproducible and are in agreement with relaxation times from traditional BDS. We then employ HTBDS to establish mixing rules for glass transition temperatures, kinetic fragility indices, and segmental stretching exponents in a series of acrylate copolymers, a matter of considerable technological interest in a variety of technological applications. Results are consistent with the empirical Fox rule for the glass transition temperature Tg averaging in polymer blends, while they reveal a linear mixing rule for kinetic fragility indices. Finally, we test several proposed correlations between these distinct dynamical properties. These results demonstrate that HTBDS enables measurements of polymer relaxation at a throughput approximately 10 times higher than that of standard BDS approaches, opening the door to high-throughput materials design of dynamic response across a broad range of frequencies.

Reducing the Gap between the Activation Energy Measured in the Liquid and the Glassy States by Adding a Plasticizer to Polylactide.

The kinetic fragility of a glass-forming liquid is an important parameter to describe its molecular mobility. In most polymers, the kinetic fragility index obtained from the glassy state by thermally stimulated depolarization current is lower than the one determined in the liquid-like state by dielectric relaxation spectroscopy, as shown in this work for neat polylactide (PLA). When PLA is plasticized to different extents, the fragility calculated in the liquid-like state progressively decreases, until approaching the value of fragility calculated from the glass, which on the other hand remains constant with plasticization. Using the cooperative rearranging region (CRR) concept, it is shown that the decrease of the fragility in the liquid-like state is concomitant with a decrease of the cooperativity length. By splitting the fragility calculated in the liquid, in two contributions: volume and energetic, respectively, dependent and independent on cooperativity, we observed that the slope of the fragility plot in the glass is equivalent to the energetic contribution of the fragility in the liquid. It is then deduced that the difference between the slopes of the relaxation time dependence calculated in both glass and liquid is an indicator of the cooperative character of the segmental relaxation when transiting from liquid to glass. As the main structural consequence of plasticization lies in the decrease of interchain weak bonds, it is assumed that these bonds drive the size of the CRR. In contrast, the dynamics in the glass are independent on plasticization structural effects.

Development and crystallization kinetics of novel near-equiatomic high-entropy bulk metallic glasses

In this study, alloying method has been adopted to develop novel near-equiatomic high-entropy bulk metallic glasses (HE-BMGs) with high glass-forming ability (GFA). A class of quinary Zr31Ti27Be26Cu10M6 (M = Ag, Al, Ni, V, Cr, and Fe) and senary Zr28Ti24Be23Cu9Ni10N6 (NV, Cr, Fe, Ag, and Al) alloys were designed. Based on the phase formation rules of high entropy alloys (HEAs), all the developed compositions fall into the zone in which bulk metallic glasses will form. Accordingly, fully glassy rod samples with diameters ranging from 6 to 15 mm have been successfully prepared by copper mould casting. The developed HE-BMGs also possess high specific strength and certain compressive plasticity. Compared with the senary alloys, the quinary alloys possess higher GFA, better plasticity but lower strength. Among these alloys, Zr31Ti27Be26Cu10Ni6, Zr31Ti27Be26Cu10V6 and Zr31Ti27Be26Cu10Ag6 HE-BMGs have been chosen for further non-isothermal analyses according to their large glass forming ability. The apparent activation energies were calculated using Kissinger, Moynihan, Ozawa and Boswell methods. The local Avrami exponents and kinetic fragility were also studied. Based on the experimental results, we have discussed the high entropy effect on the GFA, mechanical properties and crystallization kinetics of developed HE-BMGs.

Correlation between the structure and structural relaxation data for (GeSe2)y(Sb2Se3)1-y glasses

Combined calorimetric and structural study, employing the techniques of differential scanning calorimetry and Raman spectroscopy, was performed to describe the enthalpy relaxation processes in the (GeSe2)y(Sb2Se3)1-y chalcogenide glasses. The full glass forming compositional region (y = 0.3–0.9) was explored. The enthalpy relaxation was described in terms of the phenomenological Tool-Narayanaswamy-Moynihan model. Compositional evolution of the glass transition temperatures and relaxation activation energies was explained based on the changing average bond energies and overall interconnectivity of the glassy matrices. Resemblance between the activation energies of the relaxation processes and viscous flow was confirmed for all studied glasses. Non-linearity and non-exponentiality of the enthalpy relaxation were found to be invariant with composition. The structural relaxation kinetics as well as kinetic fragilities determined for the present (GeSe2)y(Sb2Se3)1-y glassy system were very similar to the results obtained earlier for the (GeS2)y(Sb2S3)1-y glasses, which can be attributed to the similarly constrained topology of the pseudo-binary compositional lines.

A structural interpretation of the two components governing the kinetic fragility from the example of interpenetrated polymer networks

ABSTRACTKinetic fragility and cooperativity length, two major characteristics of the relaxation dynamics at the glass transition, are, respectively, investigated by dynamic mechanical analysis and modulated temperature differential scanning calorimetry in a series of interpenetrated polymer networks based on acrylate and epoxy systems. The relaxation dynamics are impacted by two variables: the rigidity of the network, and the structural heterogeneity resulting from blending. However, the fragility and the cooperativity do not vary similarly. The glass transition progressively broadens as the mass fractions of acrylate and epoxy become equivalent, leading to a strong decrease in cooperativity. On the other hand, under the same conditions, the fragility transitions between the lower value of pure acrylate and the higher value of pure epoxy. This divergence helps concluding that the variations in the temperature dependence of the relaxation time are not purely related to the more or less cooperative nature of the glass transition. By splitting the fragility index in a volume contribution and an energetic contribution, it is shown that the contribution of cooperativity to the variations of the relaxation time with temperature is increased under two structural conditions: low backbone rigidity and high intermolecular interactions. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1393–1403

Correlating ultrafast calorimetry, viscosity, and structural measurements in liquid GeTe and Ge15Te85

Two distinct trends in the temperature dependence of viscosity, measured directly and inferred from calorimetry by analyzing crystallization kinetics, can be correlated with the temperature evolution of the height of the first peak of the x-ray total structure factor for liquid GeTe and ${\mathrm{Ge}}_{15}{\mathrm{Te}}_{85}$. The phase-change chalcogenide GeTe is a high-fragility liquid with the kinetic fragility value of 76, at the glass-transition temperature, being between those for liquid (Ag,In)-doped ${\mathrm{Sb}}_{2}\mathrm{Te}$ and ${\mathrm{Ge}}_{2}{\mathrm{Sb}}_{2}{\mathrm{Te}}_{5}$. The viscosity of the high-temperature liquid shows Arrhenius kinetics on cooling to the melting point, and the structure factor conforms to the fragile liquid. For liquid ${\mathrm{Ge}}_{15}{\mathrm{Te}}_{85}$, the temperature evolution of the structure factor suggests a transition in the temperature range of about 100 K above the melting. The crystallization shows a wide range of Arrhenius kinetics in the supercooled liquid region. This finding combined with the dynamic viscosity measurements is interpreted by invoking a weak fragile-to-strong crossover on cooling the liquid ${\mathrm{Ge}}_{15}{\mathrm{Te}}_{85}$. The differences in structures and dynamics of liquid GeTe and ${\mathrm{Ge}}_{15}{\mathrm{Te}}_{85}$ appear closely correlated to their distinctly different crystallization mechanisms.

Glass formation, thermal and mechanical properties of ZrCuAlNi bulk metallic glasses

Abstract The glass forming ability, thermal and mechanical properties of some ZrCuAlNi bulk metallic glasses were analyzed. The compositions of the alloys were theoretically determined with the dense packing and kinetic fragility index models. Cylindrical and conical ingots were produced by copper mould suction-casting under Ar atmosphere. The conical ingots were characterized by means of X-ray diffraction in order to determine the glassy structure. It was found that both alloys have a critical glassy diameter, Dc, of 3 mm. Thermal behaviours were investigated by differential scanning calorimetry at heating rates of 0.5, 0.67 and 0.83 K/s. The gamma parameter γ, supercooled liquid region ΔTx, and reduced glass transition temperature Trg, of the experimentally obtained glasses indicated high glass forming ability. The glassy compositions showed a fragility index of ∼40 GPa. The compression test of the investigated alloys was carried out at a strain rate of 0.016 s−1, obtaining a elastic modulus of ∼83 GPa, total deformation of ∼5%, yield strength of 1.6 GPa and hardness of 4 GPa. It was concluded that the use of the dense packing and kinetic fragility index models helped to predict glass-forming compositions in the family alloy investigated.

A possible structural signature of the onset of cooperativity in metallic liquids.

It is widely, although not universally, believed that there must be a connection between liquid dynamics and the structure. Previous supporting studies, for example, have demonstrated a link between the structural evolution in the liquid and kinetic fragility. Here, new results are presented that strengthen the evidence for a connection. By combining the results from high-energy synchrotron X-ray scattering studies of containerlessly processed supercooled liquids with viscosity measurements, an accelerated rate of structural ordering beyond the nearest neighbors in the liquid is demonstrated to correlate with the temperature at which the viscosity transitions from Arrhenius to super-Arrhenius behavior. This is the first confirmation of predictions from several recent molecular dynamics studies.

Effects of solvents and solutes on glass-transition thermodynamics and kinetic fragility for amine and alcohol solutions of inorganic salts

We have used differential scanning calorimetry (DSC) to investigate the thermodynamic and kinetic properties of the glass transition of simple amine and alcohol solutions of inorganic salts. Although the glass-transition temperature (Tg) increases with the addition of salts, in common with other solutions, the concentration dependence of the heat-capacity change (∆Cp) at Tg and the kinetic fragility index (m) are quite different for the amine and alcohol solutions. The thermodynamic and kinetic properties depend more strongly on the solvents than on the solutes. By comparing the DSC data with Raman results, we suggest that the glass-transition thermodynamics and kinetics are controlled mainly by the strength or stability of hydrogen-bond structures and the properties of dominant intermolecular interactions in the solutions.

Kinetics of Glass Transition and Crystallization of a Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 Bulk Metallic Glass with High Mixing Entropy

The kinetics of glass transition and crystallization of a novel Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 bulk metallic glass (BMG) with high mixing entropy have been studied by differential scanning calorimetry (DSC) and X-ray diffraction (XRD). The continuous DSC curves show five stages of crystallization at lower heating rates (≤ 20 K/min). The activation energies of glass transition were determined by Moynihan and Kissinger methods, while the activation energies of crystallization were calculated utilizing Kissinger, Ozawa, and Boswell models. The crystalline phases corresponding to each crystallization step have been found out. The kinetic fragility of Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 BMG has also been evaluated. Based on the isothermal DSC curves, the Avrami exponent, evaluated from the Johnson–Mehl–Avrami equation, has been analyzed in detail. The current study reveals that the crystallization behavior of Zr40Hf10Ti4Y1Al10Cu25Ni7Co2Fe1 BMG exhibits characteristics of both the high entropy BMGs and traditional BMGs with a single principal element, leading to its high glass-forming ability.

Revealing the Link between Structural Relaxation and Dynamic Heterogeneity in Glass-Forming Liquids.

Despite the use of glasses for thousands of years, the nature of the glass transition is still mysterious. On approaching the glass transition, the growth of dynamic heterogeneity has long been thought to play a key role in explaining the abrupt slowdown of structural relaxation. However, it still remains elusive whether there is an underlying link between structural relaxation and dynamic heterogeneity. Here, we unravel the link by introducing a characteristic time scale hiding behind an identical dynamic heterogeneity for various model glass-forming liquids. We find that the time scale corresponds to the kinetic fragility of liquids. Moreover, it leads to scaling collapse of both the structural relaxation time and dynamic heterogeneity for all liquids studied, together with a characteristic temperature associated with the same dynamic heterogeneity. Our findings imply that studying the glass transition from the viewpoint of dynamic heterogeneity is more informative than expected.

Analysis of thermophysical properties of lead silicates in comparison to bulk metallic glasses

The equilibrium viscosity and the specific heat capacity of three lead silicate glass forming liquids (flint glasses) with low glass transition temperatures are experimentally measured and compared to the thermophysical properties of network glass-formers like SiO2 and GeO2 and of bulk metallic glasses. The data are analyzed using the Vogel–Fulcher–Tammann (VFT) equation, the Mauro–Yue–Ellison–Gupta–Allan (MYEGA) equation, and the Adam–Gibbs approach. The flint glasses depart from the Arrhenius equation in terms of liquid kinetics and their corresponding kinetic fragilities are intermediate between GeO2 and the bulk metallic glass-formers. Among the lead silicates the fragility increases with increasing content of network modifiers, as lead, sodium and potassium modify the silicate network by creating non-bridging oxygen that softens the network.

Kinetics, Thermodynamics, and Structure of Bulk Metallic Glass Forming Liquids

Bulk metallic glass forming melts are viscous liquids compared with pure metals and conventional alloys. They show intermediate kinetic fragility and low thermodynamic driving force for crystallization, leading to sluggish crystallization kinetics, leaving time for good glass forming ability and bulk casting thickness. We relate the kinetics to the thermodynamics of the supercooled liquid using the Adam–Gibbs equation. The kinetic fragility is also connected to the structural changes in the liquid and can be quantitatively linked to the robustness of medium-range order in the supercooled liquid with increasing temperature. Liquid–liquid transitions from fragile behavior at high temperature to strong behavior at low temperature in the supercooled liquid and in the vicinity of the glass transition emerge as a common phenomenon.

Synthesis and Characterization of Bio-Based Polyesters: Poly(2-methyl-1,3-propylene-2,5-furanoate), Poly(isosorbide-2,5-furanoate), Poly(1,4-cyclohexanedimethylene-2,5-furanoate).

In the present study, three new biobased furanoate polyesters with potential use in food packaging applications, named poly(isosorbide furanoate) (PIsF), poly(methyl-propylene furanoate) (PMePF) and poly(1,4-cyclohexane-dimethylene 2,5-furanoate) (PCHDMF) were synthesized. As monomers for the preparation of the polyesters, 2,5-furandicarboxylic acid (FDCA) and diols with irregular or complicated structure were used, including isosorbide (IS), 2-methyl-1,3-propanediol (MPD) and 1,4-cyclohexane-dimethanol (CHDM). The polymerization process was carried out via melt polycondensation method. The structural characteristics and thermal behavior of the polymers were studied. The kinetic fragility of the amorphous phase of the polymers was evaluated. The thermal degradation was studied by means of thermogravimetry and a pyrolysis Py-GC/MS (Pyrolysis-Gas Chromatography/Mass Spectroscopy) system to estimate the degradation mechanism.

Connecting diffusion and entropy of bulk water at the single particle level

The relation between the dynamic (e.g., diffusion) and thermodynamic (e.g., entropy) properties of water and water-like liquids has been an active area of research for a long time. Although several studies have investigated the diffusivity and entropy for different systems, these studies have probed either the configurational entropy or the excess entropy of the overall system. In this study, we focus on the entropy of water at a single molecule level at different temperatures. We have used a method developed in our group to calculate the translational and rotational entropy of individual water molecules at various temperatures. We find that the single water translational and rotational entropy exhibit a transition at around 240 K. The translational entropy of individual water molecules shows a consistent variation with change in temperature whereas the variation in the case of rotational entropy is much smaller at different temperatures. We have also calculated diffusion coefficients of water molecules at these temperatures. We find that diffusion also shows the well-known fragile to strong crossover transition at around the same temperature where transition in entropy values has been seen. We have calculated both kinetic and thermodynamic fragilities and crossover points using diffusion and single water translational entropy values. Finally, we correlate the diffusion and translational entropy of individual water molecules using an analog of the Adam-Gibbs relation. SYNOPSIS Translational and rotational entropy of individual water molecules have been calculated at different temperatures. The thermodynamic fragility in terms of translational entropy has been measured. The thermodynamics have been connected with the dynamics by correlating the diffusion coefficient with translational entropy at different temperatures by using analog of Adam-Gibbs relation.

From Glass Formation to Icosahedral Ordering by Curving Three-Dimensional Space.

Geometric frustration describes the inability of a local molecular arrangement, such as icosahedra found in metallic glasses and in model atomic glass formers, to tile space. Local icosahedral order, however, is strongly frustrated in Euclidean space, which obscures any causal relationship with the observed dynamical slowdown. Here we relieve frustration in a model glass-forming liquid by curving three-dimensional space onto the surface of a 4-dimensional hypersphere. For sufficient curvature, frustration vanishes and the liquid "freezes" in a fully icosahedral structure via a sharp "transition." Frustration increases upon reducing the curvature, and the transition to the icosahedral state smoothens while glassy dynamics emerge. Decreasing the curvature leads to decoupling between dynamical and structural length scales and the decrease of kinetic fragility. This sheds light on the observed glass-forming behavior in Euclidean space.

The kinetic fragility of Pt-P- and Ni-P-based bulk glass-forming liquids and its thermodynamic and structural signature

The thermodynamic and kinetic properties of Pt-P- and Ni-P-based bulk glass-forming liquids are investigated using differential scanning calorimetry and three-point beam bending. The kinetic fragility of the alloys is determined by measuring relaxation times and equilibrium viscosities. In the Pt-P-based alloy family a Pt-rich alloy is one of the most fragile bulk glass-forming liquids in the vicinity of the glass transition reported so far. The fragility parameter D∗ increases significantly with decreasing Pt-content, which is due to a more pronounced loss of excess entropy upon undercooling for the fragile liquids. Relying on previous observations made for Pd-P-based alloys, it is argued that a bifurcation of the P environment into Pt-Ni-P and Pt-Cu-P structural units stabilizes the deeply undercooled liquid due to formation of medium range order (MRO). This is supported by synchrotron X-ray scattering experiments, which reveal the formation of a pre-peak in the total structure factor with increasing fragility. Adapting a previously reported empirical correlation, we show that the more fragile liquid alloys are characterized by a more pronounced dilatation of atomic pair correlations on the length scale of 1 nm, corroborating the idea that the observed fragility behavior of Pt-P-based bulk glass-forming liquids is inherently related to structural changes on the length scale of MRO.

Thermodynamic and Kinetic Fragility of Freon 113: The Most Fragile Plastic Crystal.

We present a dynamic and thermodynamic study of the orientational glass former Freon 113 (1,1,2-trichloro-1,2,2-trifluoroethane, CCl_{2}F-CClF_{2}) in order to analyze its kinetic and thermodynamic fragilities. Freon 113 displays internal molecular degrees of freedom that promote a complex energy landscape. Experimental specific heat and its microscopic origin, the vibrational density of states from inelastic neutron scattering, together with the orientational dynamics obtained by means of dielectric spectroscopy have revealed the highest fragility value, both thermodynamic and kinetic, found for this orientational glass former. The excess in both Debye-reduced specific heat and density of states (boson peak) evidences the existence of glassy low-energy excitations. We demonstrate that early proposed correlations between the boson peak and the Debye specific heat value are elusive as revealed by the clear counterexample of the studied case.

Structure–properties relationships in fibre drawing of bioactive phosphate glasses

New bioactive phosphate glasses suitable for continuous fibre production are investigated in this work. The structure of both bulk and fibres from Na2O–CaO–MgO–P2O5 glasses has been studied by means of Raman and 31P and 23Na nuclear magnetic resonance spectroscopies, and the structural results have been correlated with the mechanical properties of the fibres and the dissolution rate of the bulk glasses. It has been observed that the mechanical properties of the phosphate glass fibres are influenced by the glass network connectivity, while the dissolution rates are governed by the Qi speciation of the PO4 units. As seen in previous studies, molar volume seems to play an important role in the fragility behaviour of phosphate glasses. Here, a lower molar volume resulting from the increase in the oxygen packing density hinders the cooperative flow of the PO4 units throughout the glass network and, therefore, causes a reduction in the kinetic fragility.