Metastable Supercooled Liquid State Research Articles

Lower Temperature Soldering Using Supercooled Liquid Metal

Lead-free solder metal alloys can be formed into supercooled liquid metal microcapsules and used to create solid full metal interconnects at dramatically lower processing temperatures. These alloys can be made with or without bismuth. The technology encapsulates known and established RoHS compliant solder alloys inside a thin oxide/organic shell nanofilm that keeps the metal in a metastable supercooled liquid state at ambient temperatures. The thin oxide/organic shell can be mechanically broken or chemically dissolved to release the liquid metal that then rapidly solidifies all without requiring heat. The novel solder interconnect technology avoids thermal damage to components and materials, or quality issues caused by coefficient of thermal expansion mismatch.

Effect of loading rate on crystallization of metallic glass supercooled liquids

Metallic glasses exhibit unique thermoplastic processing capability, which is enabled by their metastable supercooled liquid state below the crystallization temperature. The thermoplastic processing critically depends on the crystallization time (processing time window), temperature (viscosity), applied load, and strain-rate. Among these parameters, the effects of crystallization time and processing temperature have been extensively studied. However, the effects of load and loading rate have not been thoroughly investigated. In this work, we performed a systematic study of load on the supercooled liquid state of three metallic glass formers: Pt-based, Zr-based, and Pd-based. The results show that the load-response of a metallic glass supercooled liquids is strongly composition dependent. The onset temperature of crystallization decreases with increasing load in Pt-based metallic glass whereas for Zr-based and Pd-based metallic glasses the onset temperature remains unchanged. The crystallization peak time is reduced for all three metallic glasses after thermoplastic forming. The results are discussed in terms of nucleation and growth of crystallites in metallic glasses.

Hierarchical aging pathways and signatures of thermodynamic transition in molecular glasses

When a liquid is supercooled, its structural equilibration time τeq increases sharply approaching the glass transition temperature Tg, below which it is kinetically arrested in the out of equilibrium glassy state. Upon annealing below Tg, such glassy state relaxes toward the equilibrium state. There is growing evidence that such relaxation process is quite complex, influenced by the complexity of the potential energy landscape. Here we report the observation of a hierarchical aging pathway in the process of the glass-to-supercooled liquid transition in various molecular glass forming systems. Differential scanning calorimetry reveals that the glassy state upon annealing below Tg firstly enters a transient metastable supercooled liquid state with slightly higher enthalpies than that of the equilibrium supercooled liquid state when extrapolated to below Tg. This observation is also confirmed by structural measurements via Raman scattering. The dynamics of the transient metastable-to-stable supercooled liquid transition exhibits characteristics of thermodynamic transition at spinodal temperature Tsp slightly above Tg, leading to anomalous behaviors such as the appearance of a transition-like behavior in the plot of fragility measurements. These observations imply that the free energy landscape of the supercooled liquid develops complexity with qualitative changes approaching Tg and could have strong influence on the process of the glass transition.

Glass relaxation and hysteresis of the glass transition by molecular dynamics simulations

As out-of-equilibrium materials, glasses continually tend to relax toward the metastable supercooled liquid state. Glass relaxation can result in a nonreversible glass transition upon a cooling/reheating cycle. Here, based on molecular dynamics simulations, we present a methodology combining thermal cycles and inherent configuration analysis to investigate the features of relaxation and glass transition reversibility. By considering three archetypical silicate glasses, viz., silica, sodium silicate, and calcium aluminosilicate, we show that, for all the glasses considered herein, the enthalpy relaxation can be well described by mode-coupling theory. Further, we demonstrate the existence of a decoupling between enthalpy and volume relaxation. Finally, we show that enthalpy relaxation results in a nonreversible glass transition---the degree of nonreversibility being strongly system-specific.

Response to comment on “The glassy state of matter: Its definition and ultimate fate”

The comment by Popov raises two questions related to (a) whether the glassy state can more appropriately be described as metastable or unstable and (b) whether the supercooled liquid state exists below the glass transition temperature, Tg. We argue that the glassy state is thermodynamically unstable, as it continuously and spontaneously relaxes toward the metastable supercooled liquid state at any nonzero temperature. Moreover, the supercooled liquid state—the target for the glass relaxation process—exists at any temperature below the liquidus temperature of a system. There is no problem with having a missing target for the glass relaxation process, since this metastable supercooled liquid state can always be defined.

Vibrational dynamics of glass forming: 2-phenylbutan-1-ol (BEP), 2-(trifluoromethyl)phenethyl alcohol (2TFMP) and 4-(trifluoromethyl)phenethyl alcohol (4TFMP) in their thermodynamic phases

ABSTRACTThe complex polymorphism and vibrational dynamics of three glass-forming single-phenyl-ring alcohols (with and without fluorine atoms) have been studied by complementary methods. Glass of isotropic liquid phase and cold crystallization of metastable supercooled liquid state were detected. Temperature investigations of vibrational motions show important role of hydrogen bonds in interactions between molecules. Theoretical calculations for isolated molecule, as well as dimer- and tetramer-type aggregates of non-covalently bound molecules, allow for a good description of experimental spectra. Intermolecular interactions of molecules with ortho and para positions of CF3 group in phenyl ring have a similar influence on the spectra observed.

Development of sodium acetate trihydrate-ethylene glycol composite phase change materials with enhanced thermophysical properties for thermal comfort and therapeutic applications

The heat packs using phase change materials (PCMs) are designed for possible applications such as body comfort and medical applications under adverse situations. The development and performance of such heat packs rely on thermophysical properties of PCMs such as latent heat, suitable heat releasing temperature, degree of supercooling, effective heat releasing time, crystallite size, stability against spontaneous nucleation in metastable supercooled liquid state and thermal stability during heating and cooling cycles. Such PCMs are rare and the available PCMs do not exhibit such properties simultaneously to meet the desired requirements. The present work reports a facile approach for the design and development of ethylene glycol (EG) and aqueous sodium acetate trihydrate (SAT) based composite phase change materials, showing these properties simultaneously. The addition of 2–3 wt% EG in aqueous SAT enhances the softness of SAT crystallites, its degree of supercooling and most importantly the effective heat releasing time by ~10% with respect to aqueous SAT material. In addition, the maximum heat releasing temperature of aqueous SAT has been tailored from 56.5 °C to 55 °C, 54.9 °C, 53.5 °C, 51.8 °C and 43.2 °C using 2%, 3%, 5%, 7% and 10 wt% EG respectively, making the aqueous SAT-EG composite PCMs suitable for desired thermal applications.

Variability in the relaxation behavior of glass: Impact of thermal history fluctuations and fragility.

Glasses are nonequilibrium materials that continuously relax toward the metastable supercooled liquid state. As such, the properties of a glass depend on both its composition and thermal history. When an initially cooled glass is subjected to additional thermal cycles, relaxation during the heat treatment is accelerated, leading to changes in the macroscopic properties of the glass. This relaxation behavior is intrinsic to the glassy state and of critical interest to the high-tech glass industry. In many practical cases, the magnitude of the relaxation is less important than the variability of the relaxation effects due to slight variations in the thermal history experienced by the glass. These fluctuations in thermal history can occur either during the initial glass formation or during the subsequent heat treatment cycle(s). Here we calculate the variation in relaxation behavior using a detailed enthalpy landscape model, showing that the relaxation variability can be reduced dramatically by increasing the fragility of the system.

Crystallization Behavior and Relaxation Dynamics of Supercooled S-Ketoprofen and the Racemic Mixture along an Isochrone

In this paper, we study crystallization behavior and molecular dynamics in the supercooled liquid state of the pharmaceutically important compound ketoprofen at various thermodynamic conditions. Dielectric relaxation for a racemic mixture was investigated in a wide range of temperatures and pressures (up to 350 MPa), whereas crystallization kinetics for racemic and single enantiomers was studied along a (T, p) curve characterized by the same structural relaxation time, τα ≅ 10–6 s, a so-called isochrone. The aim was to investigate the effect of pressure on the crystallization tendencies of pure enantiomers and their 50–50 equimolar mixture in the metastable supercooled liquid state. Crystallization kinetic studies revealed that at the same isochronal conditions the behavior of the S-enantiomer and R,S-racemic mixture of ketoprofen is entirely different. This was examined in the context of previous results and in view of the possibility of inducing changes in the enantiomeric composition or enantiomers separation from a racemic mixture as the effect of high pressure.

Atypical gelation in gelatin solutions probed by ultra-fast calorimetry

This paper describes the first application of ultrafast scanning calorimetry to the process of gelation in concentrated (40 wt%) aqueous gelatin solutions. It demonstrates that the regular gelation that occurs on cooling can be outrun at sufficiently fast cooling rates (≥500 K s−1) so that the solution reaches a metastable supercooled liquid state. Successive heating of the supercooled solution reveals an atypical process of gelation that takes place while continuously raising the temperature. Isoconversional kinetic analysis is applied to treat the atypical gelation process and to compare it with regular gelation on cooling. Although atypical and regular gelation occur on significantly different time scales they appear to have common dynamics.

Estimation of Relative Glass Forming Abilities of Multicomponent Alloy Systems

A thermodynamic calculation scheme based on a CALPHAD method has been studied to evaluate the relative glass forming abilities (GFAs) of multicomponent alloy systems. The concept of the normalized driving force has been developed for estimation of the relative GFAs of different alloy systems. Driving forces of formation of crystalline phases under metastable supercooled liquid state have been calculated for different alloy systems to predict the possible crystalline phases and the maximum driving forces normalized by the respective melting temperatures are correlated with the experimentally obtained GFAs of the alloys. It shows that the estimated relative GFAs of different alloy systems based on the normalized driving forces agree well with the experimental results.

Slow relaxations in salicylsalicylic acid studied by dielectric techniques

The dielectric techniques of Thermally Stimulated Depolarization Currents (TSDC) and Dielectric Relaxation Spectroscopy (DRS) were used in order to study the low frequency molecular motions in salicylsalicylic acid. Since this substance is a very effective glass-former, the molecular mobility was analyzed in the glassy state, in the metastable supercooled liquid state, and in the crystal. Four different kinds of motion have been detected and characterized: one in the crystal, two in the glass (α and β-relaxations) and one in the metastable liquid. Salicylsalicylic acid appears as a very strong glass former (fragility index m=31 on the Angell scale). In addition, the thermally stimulated depolarization current technique used in the study proved to be a very powerful tool to study slow molecular motion in this particular system.

An Interstitialcy Theory of Structural Relaxation and Related Viscous Flow of Glasses

A theory of isothermal structural relaxation and creep of glasses below the glass transition temperature is given. According to the interstitialcy theory, the supercooled liquid state does not exist below a Kauzmann "pseudocritical" temperature T(k), which lies above the temperature T(K), commonly called the "Kauzmann temperature." Structural relaxation is simply a reduction with time of the interstitialcy concentration to the crystalline state for T<T(k), and to the metastable supercooled liquid state for T>T(k). The predicted viscosity eta is universal, given by eta=eta(0) + eta(T)t, in agreement with experiment. eta is continuous in T, with eta discontinuous at T(k) but linear in 1/T above and below T(k). The dependence of eta on the shear modulus directly connects kinetic and thermodynamic properties of glasses and liquids.

Thermal hysteresis in dithiadiazolyl and dithiazolyl radicals induced by supercooling of paramagnetic liquids close to room temperature: a study of F3CCNSSN and an interpretation of the behaviour of F3CCSNSCCF3.

The trifluoromethyl-substituted dithiadiazolyl and dithiazolyl radicals, F3CCNSSN (1) and F3CCSNSCCF3 (2) associate through pi*-pi* covalent and electrostatic S delta+...N delta- interactions in the solid state, but melt with a dramatic volume increase to generate paramagnetic liquids; these radicals exhibit thermal hysteresis, which arises through a meta-stable super-cooled liquid state, close to room temperature.

Glass transition, structural relaxation, and theories of viscosity: a molecular dynamics study of amorphous CaAl2Si2O8

Molecular dynamics (MD) simulation provides a unique window into the dynamics of amorphous silicates of geochemical importance. Of special interest are theories of the glass transition and viscosity when an equilibrium liquid passes through the metastable supercooled liquid state to become a nonequilibrium glass. Viscosity increases enormously in a small temperature range around the glass transition temperature. Twenty MD simulations utilizing 1300 particles were conducted for CaAl2Si2O8 at temperatures in the range 1700 to 5000 K along the ∼ 1 GPa isobar. A pairwise potential with Coulombic and Born-Mayer interaction was used in the evaluation of forces. Simulation durations range from 50 to 150 ps. Previously, structures, thermodynamic properties, and tracer diffusivities were determined as a function of temperature for liquid and glass (Morgan and Spera, 2001). Here, the focus is upon atomic cooperative motion at the nanometer scale and theories of viscosity illuminated by correlation analysis and tagged particle dynamics. Dramatic differences in the dynamics of particles monitored by the nongaussian component of atom self-diffusivity, the van Hove correlation function and the intermediate scattering function appear near the (computer) glass transition temperature Tg = 2800 K. At T < Tg, the van Hove correlation function for oxygen and calcium exhibits a double-peaked structure characteristic of hopping diffusion through correlated jumps involving neighboring particles to nearest neighbor sites in an otherwise “frozen” structure. The crossover between continuous (hydrodynamic-like) motion and hopping motion shows up in the time dependence of the mean square displacement as a function of temperature and in the temporal decay of microscopic density fluctuations given by the intermediate scattering function. A particle and its neighbors remain trapped for a finite waiting time before undergoing a cooperative thermally activated rearrangement that is based on an elementary hop. The waiting time distribution is strongly temperature dependent and related to the dramatic increase in structural relaxation time as temperature approaches Tg. Three models for the glass transition—the Adam-Gibbs configurational entropy model, mode-coupling theory, and the stochastic trapping diffusion model—are discussed in light of the MD simulations. Although each model offers novel insight into the glass transition and the relationship between structural relaxation and atomic-scale dynamics, no single model is complete. The MD simulations are consistent with a picture of “dynamic heterogeneity” as the cause of the sluggish dynamics as an equilibrium liquid becomes deeply supercooled. At some temperature above the Kauzmann temperature (TK) where the extrapolated entropy of supercooled liquid equals that of crystalline solid, long-lived, highly cooperative, collective particle motions take place in restricted regions of three-dimensional space. Subsets of particles exhibit faster or slower than average relaxation rates. The relationship of dynamic heterogeneity viewed in three-dimensional Euclidean space to its analog in 6N-dimensional-phase space remains to be elucidated. Specifically, the lifetime and sizes of cooperatively rearranging regions as a function of temperature needs further study. Self-organization of cooperatively rearranging regions demands further investigation as well.

The kinetic glass transition of the Zr46.75Ti8.25Cu7.5Ni10Be27.5 bulk metallic glass former-supercooled liquids on a long time scale

Viscosity and enthalpy relaxation from the amorphous state into the supercooled liquid state was investigated in the bulk metallic glass forming Zr46.75Ti8.25Cu7.5Ni10Be27.5 alloy below the calorimetric glass transition. At different temperatures, the viscosities relax into states that obey the same Vogel–Fulcher–Tammann relation as the data obtained at higher temperatures in the supercooled liquid. Enthalpy recovery experiments after relaxation in the same temperature range show that the enthalpy of the material reaches values that also corresponds to the supercooled liquid state. The glass relaxes into a metastable supercooled liquid state, if it is observed on a long time scale. Equilibration is possible far below the calorimetric glass transition and very likely even below the isentropic temperature.

The Supercooled Liquid of the Bulk Metallic Glass Forming Zr&lt;sub&gt;46.25&lt;/sub&gt;Ti&lt;sub&gt;8.25&lt;/sub&gt;Cu&lt;sub&gt;7.5&lt;/sub&gt;Ni&lt;sub&gt;10&lt;/sub&gt;Be&lt;sub&gt;27.5&lt;/sub&gt; Alloy on Long Time Scales

The relaxation from the amorphous state into the supercooled liquid state was investigated in the bulk metallic glass forming Zr 46.75 Ti 8.25 Cu 7.5 Ni 10 Be 27.5 alloy. Viscosity relaxation as well as enthalpy recovery after isothermal annealing were measured at temperatures below the calorimetrically observed glass transition. The viscosity relaxes into states that obey the same Vogel-Fulcher-Tammann relation as the data obtained at higher temperatures in the supercooled liquid. On a time scale longer than the relaxation time the alloy reaches the supercooled liquid state below the calorimetric glass transition. Enthalpy recovery experiments after relaxation in the same temperature range show that the enthalpy of the material also reaches a value that corresponds to the supercooled liquid state. The observed glass transition in this strong liquid is of purely kinetic nature and reflects the increasing relaxation time with undercooling. A metastable amorphous equilibrium state could not be observed in this strong liquid but a metastable supercooled liquid state on a long time scale.

Crossover relaxation of the viscosity of Pd 40Ni 40P 19Si 1 near the glass transition

Tensile creep experiments on melt-spun ribbons of Pd 40Ni 40P 19Si 1 were performed near the glass transition temperature. Changes in the shear viscosity during relaxation were measured and equilibration of the glass to the metastable super-cooled liquid state was observed. The relaxation behavior varied considerably, depending on the thermal history of the sample: monotonie increases and decreases as well as crossover changes in the viscosity were measured. The results are interpreted with phenomenological and atomistic models for flow, and a qualitative modification of the atomistic defect model is suggested to account for the crossover behavior.