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separate overlapping transitions when one transition goes into the reversing signal and the other into the nonreversing signal. But what if both go into the reversing signal such as a melting transition overlapping a glass transition due to a phase

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glass transition kinetics of metallic alloys is of great importance to know its thermal stability, and finally to determine the useful range of operating temperatures for a specific technological application before the crystallization takes place [ 4

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study, we investigate the thermodynamic properties in the range of the glass transition temperature, T g . As reported, bound water plasticizes the silk fibroin films inducing a low T g during heating, and the water content within the silk film

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Abstract  

The definition of the glass transition temperature, T g, is recalled and its experimental determination by various techniques is reviewed. The diversity of values of T g obtained by the different methods is discussed, with particular attention being paid to Differential Scanning Calorimetry (DSC) and to dynamic techniques such as Dynamic Mechanical Thermal Analysis (DMTA) and Temperature Modulated DSC (TMDSC). This last technique, TMDSC, in particular, is considered in respect of ways in which the heterogeneity of the glass transformation process can be quantified.

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Abstract  

This personal review focuses on two aspects. First, glass transition dynamics and hence also calorimetry is connected to dynamic heterogeneity. This results in an interplay of the corresponding dynamic length scales and length scales from structural heterogeneities in polymeric samples. Second, the complexity of the dynamic glass transition itself results in different effects of this interplay for different experimental observables. Hence the comparison of results from calorimetry with other relaxation methods gives important clues to an understanding of the complex glass transition phenomenon.

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Abstract  

Thermal properties of industrial hydrolysis lignin (HL) obtained from bio-ethanol production plants were investigated by thermogravimetry and differential scanning calorimetry. Thermal decomposition of HL was observed in two stages suggesting coexisting carbohydrates. Glass transition temperature (T g) was observed in a temperature range from 248 to 363 K. T g values were lower than that of other industrial lignins, such as kraft lignin or lignosulfate. Enthalpy relaxation was observed as sub-T g, which is not as prominent as other industrial or laboratory scale isolated lignins. T g of HL decreased in the presence of water and saturated at water content (W c) of 0.18 (mass of water/mass of dry HL). The amount of bound water calculated from melting enthalpy of water and W c was ca. 0.18. Thermal decomposition and molecular motion of as obtained industrial HL are affected by coexisting carbohydrates.

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Abstract  

Relaxation times of bisphenol A polycarbonate around the glass transition temperature are estimated using the combination of differential scanning calorimetry (DSC) and thermostimulated depolarization currents (TSDC). These measurements are performed using samples with different thermal histories below and above the vitrification transformation. This protocol enables the extension of the range of equilibrium relaxation times measured by dielectric spectroscopy. By this mean we may recalculate the values of the Kauzmann temperature and fragility index.

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Journal of Thermal Analysis and Calorimetry
Authors: Marek Liška, Zdenek Černošek, Mária Chromčíková, Jana Holubová, Eva Černošková, and Libor Vozár

Abstract  

The results of StepScan DSC obtained for various oxides, chalcogenides, and organic glasses are discussed in connection with the commonly accepted theory of the glass transition. The new experimental features supporting the apparent idea of a reversible equilibrium being a part of the glass transition that is commonly interpreted as purely kinetic-relaxation phenomenon are discussed. Two alternative methods of the description of the reversible part of StepScan DSC record are compared:the empirical one using the exponential-power function [1 − exp(T/T g)n], and the second one based on the van’t Hoff’s equation describing the temperature dependence of equilibrium constant in terms of reaction enthalpy, ΔH. The adequacy of the empirical description is rationalized in the framework of the Tool–Narayanaswamy–Moynihan’s relaxation theory.

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Abstract  

The subjects of the paper are the mechanism of vitrification and the glass transition, and a definition of the temperature of the glass transition. A comprehensive description of the structural changes occurring in the amorphous phase (‘real’ and ‘semi-ordered’) in a vicinity of the glass transition is presented. One of the major motivation of our studies is to investigate the finite size effect of the glass transition that could be related to the cooperative motion in supercooled liquids. Also, new formula, describing the relaxation time temperature change, is applied in order to better reveal themechanismof the supermolecular formation under different internal and external factors. The results of the basic methods of thermal analysis, obtained for different polymeric systems, were used in this study. The proposed approach let us correlate the thermodynamic and the structural parameters, which are estimated from the experiments, and describe all well known shapes of the DSC traces, which can be recorded in the glass transition region. Based on positron annihilation lifetime spectroscopy and dilatometric results, the significance of the free and the specific volumes for the activation of the relaxing units is discussed.

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Abstract  

We have used molecular simulations to study the properties of nanocomposites formed by the chemical incorporation of polyhedral oligomeric silsesquioxane (POSS) particles in the cross-linked epoxy network. The particular POSS molecule chosen—glycidyloxypropyl-heptaphenyl POSS—can form only one bond with the cross-linker and thus was present as a dangling unit in the network. Four epoxy-POSS nanocomposites containing different fractions (up to 30 mass/%) of POSS particles were studied in this work. Well-relaxed atomistic model structures of the nanocomposites were created and then molecular dynamics simulations were used to characterize the density, glass transition temperature (T g), and the coefficient of volume thermal expansion (CVTE) of the systems. In addition to the effect of nanoparticle loading, the effect of nanoparticle chemistry on the nanocomposite properties was also characterized by comparing these results with our previous results (Lin and Khare, Macromolecules 42:4319–4327, 2009) on neat cross-linked epoxy and a nanocomposite containing a POSS nanoparticle that formed eight bonds with the cross-linked network. Our results showed that incorporation of these monofunctional POSS particles into cross-linked epoxy does not cause a measurable change in its density, glass transition temperature, or the CVTE. Furthermore, simulation results were used to characterize the aggregation of POSS particles in the system. The nanofiller particles in systems containing 11, 20, and 30 mass/% POSS were found to form small clusters. The cluster-size distribution of nanoparticles was also characterized for these systems.

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