Glass Transition Kinetics Research Articles

Analyses of kinetic glass transition in short-range attractive colloids based on time-convolutionless mode-coupling theory.

For short-range attractive colloids, the phase diagram of the kinetic glass transition is studied by time-convolutionless mode-coupling theory (TMCT). Using numerical calculations, TMCT is shown to recover all the remarkable features predicted by the mode-coupling theory for attractive colloids: the glass-liquid-glass reentrant, the glass-glass transition, and the higher-order singularities. It is also demonstrated through the comparisons with the results of molecular dynamics for the binary attractive colloids that TMCT improves the critical values ofthe volume fraction. In addition, a schematic model of three control parameters is investigated analytically. It is thus confirmed that TMCT can describe the glass-glass transition and higher-order singularities even in such a schematic model.

Glass transition kinetics and thermal stability of Se82 − xTe18Sbx (x = 0, 4, 8 and 12 at %) glassy alloys

Glass transition kinetics of Se82−xTe18Sbx (x = 0, 4, 8 and 12 at.%) glassy alloys has been studied using differential scanning calorimetry (DSC). DSC runs were taken at different heating rates (5, 10, 15 and 20 K/min) for each samples. Heating rate dependence of glass transition temperature (Tg) has been studied using Lasocka empirical relation. Activation energy of glass transition (Eg) has been determined using Kissinger and Moynihan’s relation. Effect of Sb concentration on glass transition temperature and activation energy has been studied. Thermal stability of Se82 − xTe18Sbx glassy alloys has also been investigated using Dietzal relation, Saad and Poulin relation, Hurby parameter (Hr) and Lie and Liu parameter (γ). Compositional dependence of parameters investigated for thermal stability has also been studied.

On the possibility of modeling of polymers glass transition in a wide range of cooling and heating rates

The presented work continues the investigation of the problems connected with modeling of the kinetics of polymers glass transition in a wide range of temperature change rates. In our previous work Tropin et al. (2015) , an attempt to model a big set of heat capacity curves of polystyrene glass transition has been made, and the inability of the common methods to do this within a single set of parameters has been demonstrated. To go a step further, in this work we proceed with the common and several novel methods of modeling. To normalize the models with each other, a fit of the 10K/min cooling/heating DSC curves of polystyrene is made, and the literature model parameters readjusted. Further, the modeling of the reduced heat capacity curves at the cooling and heating rates in a wide range of q=10−6–106K/s with a logarithmic step is performed. The comparison of Tg(q) behavior with lately measured data for polystyrene is made. It is shown, that the methods need some modifications to qualitatively describe details of the glass transition kinetics in a wide range of q. Some of the possibilities to advance the models are discussed.

Se-doped GeTe4 glasses for far-infrared optical fibers

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study thermokinetic behavior of Ge21SeyTe79−y infrared glasses (for y up to 8 at.% of Se). Glass transition kinetics was described in terms of the Tool-Narayanaswamy-Moynihan model and the relaxation motions were interpreted using Raman spectroscopy data. Both enthalpy and volume relaxation kinetics were found to be uninfluenced by Se addition. On the other hand, DSC crystallization behavior changed significantly with increasing Se content: initial addition of Se partially delays and decelerates both the initial Te precipitation and the consequent volume-located crystallization of GeTe and Te; additional increase of Se content then further delays and separates the volume-located crystallization processes but the initial surface Te precipitation is no longer affected. From this point of view the fine compositional tuning of basic thermal stability of GeTeSe infrared glasses appears meaningless. On the contrary, glass workability window (determined by means of the TMA crystallization experiments) was found to be significantly affected by Se addition, emphasizing the importance of this type of measurements for the glass technology and material science. The 4 at.% Se content was found optimal with respect to fiber-drawing procedure.

Study of Glass Transition Kinetics of Ge25–xSe75Sbx (x = 12, 15 and 18) Glassy Alloys by Differential Scanning Calorimetery

Study of Glass Transition Kinetics of Ge_{25–<i>x</i>}Se₇₅Sb_<i>x</i> (<i>x</i> = 12, 15 and 18) Glassy Alloys by Differential Scanning Calorimetery

On the nature of the liquid-to-glass transition equation

Within the model of delocalized atoms, it is shown that the parameter δTg, which enters the glasstransition equation qτg = δTg and characterizes the temperature interval in which the structure of a liquid is frozen, is determined by the fluctuation volume fraction \({f_g} = {\left( {{{\Delta {V_e}} \mathord{\left/ {\vphantom {{\Delta {V_e}} V}} \right. \kern-\nulldelimiterspace} V}} \right)_{T = {T_g}}}\) frozen at the glass-transition temperature Tg and the temperature Tg itself. The parameter δTg is estimated by data on fg and Tg. The results obtained are in agreement with the values of δTg calculated by the Williams–Landel–Ferry (WLF) equation, as well as with the product qτg—the left-hand side of the glass-transition equation (q is the cooling rate of the melt, and τg is the structural relaxation time at the glass-transition temperature). Glasses of the same class with fg ≈ const exhibit a linear correlation between δTg and Tg. It is established that the currently used methods of Bartenev and Nemilov for calculating δTg yield overestimated values, which is associated with the assumption, made during deriving the calculation formulas, that the activation energy of the glass-transition process is constant. A generalized Bartenev equation is derived for the dependence of the glass-transition temperature on the cooling rate of the melt with regard to the temperature dependence of the activation energy of the glasstransition process. A modified version of the kinetic glass-transition criterion is proposed. A conception is developed that the fluctuation volume fraction f = ΔVe/V can be interpreted as an internal structural parameter analogous to the parameter ξ in the Mandelstam–Leontovich theory, and a conjecture is put forward that the delocalization of an active atom—its critical displacement from the equilibrium position—can be considered as one of possible variants of excitation of a particle in the Vol’kenshtein–Ptitsyn theory. The experimental data used in the study refer to a constant cooling rate of q = 0.05 K/s (3 K/min).

Crystallization kinetics and glass transition kinetics of iron borophosphate glass and CeO2-doped iron borophosphate compounds

Effects of CeO2 doping and the preexisting formed CePO4 crystallite on the crystallization kinetics and glass transition kinetics of the 36Fe2O310B2O354P2O5 glass (IBP glass) have been investigated by differential thermal analysis (DTA). The results reveal that a well defined glass transition peak and two crystallization peaks are observed in DTA curve of the IBP glass. The crystallization activation energies for the first crystallization peak (Ec for P1) and the second crystallization peak (Ec for P2) of the IBP glass are 211.77 KJ mol−1 and 564.31 KJ mol−1 respectively. And CeO2 doping insignificantly affects the Ec for P1 but increases the Ec for P2. Moreover, the preexisting CePO4 crystallite increases the Ec for P1 and the activation energies of glass transition peak (Eg). However, the CePO4 crystallite obviously decreases the Ec for P2. In addition, the crystal growth in the IBP glass occurs in two dimensions. Due to the preexisting CePO4, the dimensions of crystal growth in CeO2-doped IBP compounds change to three. The conclusions offer some useful information for the disposal of high-level radioactive wastes using iron borophosphate glasses and iron borophosphate based glass-ceramics.

Investigation of glass transition kinetics in C60-doped carbazole-based photorefractive polyacrylates

Abstract This article describes the fabrication of C60-doped carbazole-based bi-functional photorefractive polyacrylates, the C60-doped concentrations are 0.0, 0.2, 0.5, 0.7 and 1.0 wt.-%, respectively. For these photorefractive polyacrylates, differential scanning calorimetric runs have been taken under nonisothermal conditions at different heating rates. The result indicates that the glass transition temperature Tg first increases and then decreases with increasing of C60 content. Tg of the same sample increases with increasing heating rate. The activation energy of glass transition (Eg) has been evaluated based on the Moynihan and Kissinger model. The results showed that both Eg values obtained from Kissinger's and Moynihan's relations are in good agreement.

Glass formability in medium-sized molecular systems/pharmaceuticals. I. Thermodynamics vs. kinetics.

Scrutinizing critical thermodynamic and kinetic factors for glass formation and the glass stability of materials would benefit the screening of the glass formers for the industry of glassy materials. The present work aims at elucidating the factors that contribute to the glass formation by investigating medium-sized molecules of pharmaceuticals. Glass transition related thermodynamics and kinetics are performed on the pharmaceuticals using calorimetric, dielectric, and viscosity measurements. The characteristic thermodynamic and kinetic parameters of glass transition are found to reproduce the relations established for small-molecule glass formers. The systematic comparison of the thermodynamic and kinetic contributions to glass formation reveals that the melting-point viscosity is the crucial quantity for the glass formation. Of more interest is the finding of a rough correlation between the melting-point viscosity and the entropy of fusion normalized by the number of beads of the pharmaceuticals, suggesting the thermodynamics can partly manifest its contribution to glass formation via kinetics.

Effect of Sn additive on the structure and crystallization kinetics in Ge–Se alloy

The structure of Ge20Se80−xSnx glassy alloys and crystallization phases are identified using the X-ray diffraction (XRD) and Scanning Electron Microscope (SEM). The glass transition kinetics and the crystallization mechanism of the system are studied using Differential Scanning Calorimeter (DSC) under non-isothermal condition. The results reveal that glass transition temperature (Tg) increases with increasing Sn content which is attributed to the increase in the coordination number. The increase of the glass transition activation energy (Eg) with increasing Sn content is attributed to the decrease in the internal energy of the system as Sn increases. The compositional dependence of both glass forming ability and thermal stability are studied. From the experimental data, the thermal stability parameter (S) is found to be maximum for Ge20Se78Sn2 alloy, which indicates that this alloy is thermally more stable in the composition range under investigation. The effect of composition on the crystallization mechanism is discussed using different kinetic models. The crystallization activation energy (Ec) decreases with increasing Sn. This is attributed to the addition of Sn increases the tendency of crystallization. The calculated values of Avrami exponent (n) indicates the crystallization process occurs in one-and two dimensions for Sn is less than or equals 12 at%, respectively.

Role of Bi incorporation on glass transition kinetics in glassy Se78Te20Sn2 alloy

ABSTRACTIn this communication, we report the results of calorimetric measurements on the samples of recently synthesized multi-component glassy alloys of Se78−xTe20Sn2Bix (0 ≤ x ≤ 6) system. For calorimetric study of glass transition kinetics, differential scanning calorimetry (DSC) technique has been used in non-isothermal mode. Peak glass transition temperature (Tg) is determined using the DSC scans. Kinetic parameters A and B of glass transition are determined using heating rate dependence of Tg. Activation energy of glass transition (Eg) has been calculated using Moynihan and Kissinger methods. Glass-forming ability and thermal stability are also determined using Hurby and Saad–Poulin relations, respectively.

Thermal behavior of Se-rich GeSb2Se(4-y)Tey (glassy) system

The thermokinetic behavior of the GeSb2Se(4-y)Tey glassy chalcogenide system (a compositional analog of the famous GST-124 PCM material) was thoroughly investigated. Regarding the glass transition kinetics, the substitution of Se by Te was found to lead to looser structural packing resulting in lower activation energy and more independent relaxation movements. On the other hand, in the case of cold crystallization (studied in dependence on particle size) the addition of Te led to the formation of different crystalline phases with higher activation energy of the crystallization process. In addition, based on the description in terms of the Johnson-Mehl-Avrami nucleation-growth kinetics it was found that the Te addition resulted in prioritization of the volume-located 3D crystal growth. Furthermore, P-type heat capacity dependence was found to occur in the present chalcogenide system, where the Te addition led to an increase of the Cp-T curvature in the undercooled liquid. Concerning the overall thermokinetic characterization, the effect of Se↔Te substitution on glass-stability and glass-forming ability was discussed.

Kinetics of glass transition, negative magnetization and exchange bias effects in Sm1−xBixCrO3

DC magnetization and magnetic relaxation studies of polycrystalline Sm1−xBixCrO3 (x = 0, 0.1) demonstrated the kinetics of magnetic glass behaviour in SmCrO3: the frozen antiferromagnetic state was dominant to the glassy transition state.

Glass transition kinetics measured by fast scanning calorimetry

Enthalpy relaxation data obtained for amorphous selenium by means of fast scanning calorimetry were described in terms of Tool–Narayanaswamy–Moynihan model. The effect of thermal gradients formed within the measured sample was found to explain the marked difference between the FSC and conventional DSC data obtained for a-Se. If the influence of thermal gradients is accounted for, the similar set of TNM parameters as obtained for a-Se from conventional DSC can be used to describe the FSC data. Temperature profiles of the thermal gradients as well as sources of additional uncertainties occurring within the introduced conception are discussed in detail. In addition, a normalization procedure accounting for the difference between the slopes of heat capacity in the glass and undercooled liquid regions was introduced. Correct data preparation was found to have a critical influence on the applied enthalpy relaxation evaluation procedures. Due to the unresolved issue of the prediction of manifesting thermal gradients found in case of the recent study on amorphous selenium, the FSC technique appears, for the time being, to have limited usage for enthalpy relaxation studies.

Evolution of structural (α) relaxation time anomalies in GexSe1−x chalcogenide glasses

We examine enthalpy relaxation across the chalcogenide glass series GexSe1−x, prepared over close-by compositions using conventional melt-quenching technique. We estimate the timescale τ(Tg) characterizing enthalpic relaxation near the kinetic glass transition temperature, using the non-reversing heat-flow data obtained from modulated differential scanning calorimetry measurements over a wide range of compositions (2.1 ≤ r ≤ 2.8, r = 2x + 2). Anomalies in the enthalpy-relaxation characteristic-times τg(r) are identified with three rigidity-transitions encountered in successive Ge-doping of polymeric selenium chains.

Thermal characterization of Se–Te thin films

The thermal behavior of thin selenium–tellurium (Se–Te) films was studied under non-isothermal conditions using differential scanning calorimetry; full binary compositional range was investigated. Based on the glass transition, crystallization and melting data the decreasing glass-forming ability in the Se–Te chalcogenide system was described by using a novel glass-forming ability (GFA) criterion. The glass transition kinetics of the as-prepared thin films was found to change with increasing Te content; namely the activation energy of structural relaxation processes decreased from 355 to 245kJmol−1 within the given compositional region. In the glass-forming region (at approx. 0–30% Te) the GFA and relaxation data obtained for the thin films correlated very well with the results for bulk glasses. Furthermore, the kinetics of crystallization were studied and described in terms of the Johnson–Mehl–Avrami nucleation-growth model. The apparent activation energy of crystallization was found to increase with Te content, changing from 115 to 170kJmol−1 in the given compositional range. Two-dimensional growth of crystallites, consistent with the idea of sterically restricted crystallization in a thin layer, was confirmed for the Se-rich compositional region. Further addition was found to lead to increased process complexity due to the formation of smaller, volume-located crystallites. In the glass-forming region, the crystallization kinetics of thin films corresponded to that determined for very fine Se–Te powders.

Structure and thermal analysis of Se100 − x(SbSn)x chalcogenide glasses

Se100−x(Sb0.5Sn0.5)x (3≤x≤12at.%) glassy alloys were prepared using the melt quenching technique. The amorphous nature of the as-prepared samples was confirmed by scanning electron microscope (SEM) and X-ray diffraction (XRD) and the effect of the addition of Sb0.5Sn0.5 content on the glass transition and crystallization kinetics of amorphous Se has been studied. The glass transition temperature (Tg) was increased with increasing content of Sb0.5Sn0.5. This behaviour was discussed in terms of glass density (ρ), cohesive energy (CE) and the overall mean bond energy <E>. The values of the activation energy of crystallization were increased with increasing Sb0.5Sn0.5 content that was confirmed by increasing the Hruby's parameter (Krg) with the increase of Sb0.5Sn0.5 content. Furthermore, the difference between Tc and Tg was increased due to the delay in nucleation process. This leads to the enhancement of the thermal stability and consequently the glass forming ability.

Influence of pH on mechanical relaxations in high solids LM-pectin preparations

The influence of pH on the mechanical relaxation of LM-pectin in the presence of co-solute has been investigated by means of differential scanning calorimetry, ζ-potential measurements and small deformation dynamic oscillation in shear. pH was found to affect the conformational properties of the polyelectrolyte altering its structural behavior. Cooling scans in the vicinity of the glass transition region revealed a remarkable change in the viscoelastic functions as the polyelectrolyte rearranges from extended (neutral pH) to compact conformations (acidic pH). This conformational rearrangement was experimentally observed to result in early vitrification at neutral pH values where dissociation of galacturonic acid residues takes place. Time–temperature superposition of the mechanical shift factors and theoretical modeling utilizing WLF kinetics confirmed the accelerated kinetics of glass transition in the extended pectin conformation at neutral pH. Determination of the relaxation spectra of the samples using spectral analysis of the master curves revealed that the relaxation of macromolecules occurs within ∼0.1s regardless of the solvent pH.

Viscosity of Se–Te glass-forming system

Abstract This work is focused on viscosity of chalcogenide system Se–Te. Viscosity values of four glass-forming compositions in this system (containing 5, 10, 20 and 30 at.% of tellurium) were measured by penetration and parallel-plate method in the region of undercooled melt and glass. These results are combined with literature data for melt region. The kinetic fragility and viscosity glass transition temperature values obtained by different methods are calculated from measured data.

Kinetics of glass transition of La65Al20Co15 metallic glass

The glass transition kinetics of melt-spun La65Al20Co15 amorphous alloy ribbons has been investigated using differential scanning calorimetry (DSC) technique with continuous heating of the sample at different heating rates. The dependence of the glass transition temperature (Tg) on the heating rate (β) has been determined by Lasocka’s relationship. The activation energy (E) of the glass transition has been obtained by employing Moynihan and Kissinger methods, respectively. It is found that the glass transition process cannot be described in terms of single activation energy. The variation of E with the extent of conversion (α) is further analyzed by using two iso-conversional methods. It is observed that the E of glass transition demonstrates a significant increase with the extent of conversion from amorphous to supercooled liquid phase of La65Al20Co15 metallic glass.