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Abstract  

The calorimetric glass transition and dielectric dynamics of -relaxation in propylene glycol (PG) and its five oligomers (polypropylene glycol, PPG) have been investigated by the modulated differential scanning calorimetry (MDSC) and the broadband dielectric spectroscopy. From the temperature dependence of heat capacity of PPGs, it is clarified that the glass transition temperature (T g) and the glass transition region are affected by the heating rate. The kinetic changes of PG and PPGs near T g strongly depend on the underlying heating rate. With increasing the molecular mass of PPGs, the fragility derived from the relaxation time against temperature also increases. The PG monomer is stronger than its oligomers, PPGs, because of the larger number density of the —OH end group which tends to construct the intermolecular network structure. Adam-Gibbs (AG) theory could still hold for MDSC results due to the fact that the dielectric relaxation time can be related to the configurational entropy.

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Abstract  

Calorimetry is the method first used by Jackson and McKenna to study the effect of finite-size on the molecular dynamics of glass-formers confined in nano-meter scale pores. It was found that the glass transition is shifted to lower temperature as pore size decreases. Since then, other spectroscopic techniques have corroborated this finding and given more information on the molecular dynamics. These results are used to compare with the predictions of several theories of glass transition, and in particular the coupling model of the author.

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temperature around T g and is given [ 34 , 35 ] by: 20 where E g is the apparent activation energy for the glass transition. According to Viglis [ 36 ] glass forming liquids that exhibit an approximate Arrhenius temperature dependence are defined as

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Abstract  

The thermal behaviour of salicylsalicylic acid (CAS number 552-94-3) was studied by differential scanning calorimetry (DSC). The endothermic melting peak and the fingerprint of the glass transition were characterised at a heating rate of 10C min-1. The melting peak showed an onset at T on = 144C (417 K) and a maximum intensity at T max = 152C (425 K), while the onset of the glass transition signal was at T on = 6C. The melting enthalpy was found to be ΔmH = 28.90.3 kJ mol-1, and the heat capacity jump at the glass transition was ΔC P = 108.10.1 J K-1mol-1. The study of the influence of the heating rate on the temperature location of the glass transition signal by DSC, allowed the determination of the activation energy at the glass transition temperature (245 kJ mol-1), and the calculation of the fragility index of salicyl salicylate (m = 45). Finally, the standard molar enthalpy of formation of crystalline monoclinic salicylsalicylic acid at T = 298.15 K, was determined as ΔfHm o(C14H10O5, cr) = - (837.63.3) kJ mol-1, by combustion calorimetry.

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Abstract  

We investigated the features of the glass transition relaxation of two room temperature ionic liquids using DSC. An important observation was that the heat capacity jump, that is the signature of the glass transition relaxation, shows a particularly strong value in this type of new and promising materials, candidates for a range of applications. This suggests a high degree of molecular mobility in the supercooled liquid state. The study of the influence of the heating rate on the temperature location of the glass transition signal, allowed the determination of the activation energy at the glass transition temperature, and the calculation of the fragility index of these two ionic glass-formers. It was concluded that this kind of materials belong to the class of relatively strong glass-forming systems.

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The glass transition temperatures of sorbitol and fructose were characterized by four points determined on DSC heating thermograms (onset, mid-point, peak and end-point), plus the limit fictive temperature. The variations of these temperature values, observed as functions of cooling and heating rates, were used to determine the fragility parameter, as defined by Angell [1] to characterize the temperature dependence of the dynamic behavior of glass-forming liquids in the temperature range above the glass transition.

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Abstract  

We have studied the temperature dependence of the viscosity of some polymeric materials by using both, the bond-strength-coordination number fluctuation model and the random walk model. The results reveal that both models show an excellent agreement with the experimental data. For the random walk model, two equations corresponding to two temperature regimes (low-T and high-T) separated by the critical temperature T c, which is difficult to determine, are needed to describe the temperature dependence of the viscosity of a fragile system, whereas for the bond-strength-coordination number fluctuation model, a single equation with clear physical meaning describes the temperature dependence of the viscosity of both, the fragile and strong systems. We have also studied the relationship between the normalized temperature range of cooperativity and the fragility index. A theoretical expression for the relationship has been derived based on the bond-strength-coordination number fluctuation model. The comparison with the experimental data shows a good agreement, leading to the conclusion that the kinetic properties of glass forming liquids and the cooperativity of molecular relaxations are correlated.

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, structural relaxation and visco-elastic behavior of non-crystalline materials, and highly supercooled glass-forming liquids, nanostructured oxidic materials, and phase change materials, with more than 110 papers published. In 2000, he was awarded D.Sc. degree

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temperature. The value of F ≈ 16 defined as the strong glass-forming liquids [ 26 ], while a high value of F ≈ 200 represents the fragile glass-forming liquid [ 27 ]. In our investigated system, the values of F vary from ≈16 to 28 means strong glass

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remarkable property of certain glass-forming liquids is that a fast mode of crystal growth is activated near the glass transition temperature T g and continues in the glassy state. The kinetic parameters of glass transition in glassy Se–In system are

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