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 (Tg) and the glass transition region are affected by the heating rate. The kinetic changes of PG and PPGs near Tg 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.
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.
Authors:S. K. Tripathi, Balbir Singh Patial, and Nagesh Thakur
temperature around T g and is given [ 34 , 35 ] by:
where E g is the apparent activation energy for the glass transition. According to Viglis [ 36 ] glassformingliquids that exhibit an approximate Arrhenius temperature dependence are defined as
Authors:Hermínio Digo, Susana Pinto, and Joaquim Moura Ramos
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 Ton = 144C (417 K) and a maximum intensity at Tmax = 152C (425 K), while the onset of the glass transition signal was at Ton = 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 ΔCP = 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 ΔfHmo(C14H10O5, cr) = - (837.63.3) kJ mol-1, by combustion calorimetry.
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.
Authors:D. Simatos, G. Blond, G. Roudaut, D. Champion, J. Perez, and A. L. Faivre
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  to characterize the temperature dependence of the dynamic behavior of glass-forming liquids in the temperature range above the glass transition.
Authors:Jean Ndeugueu, Masahiro Ikeda, and Masaru Aniya
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 Tc, 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.
, structural relaxation and visco-elastic behavior of non-crystalline materials, and highly supercooled glass-formingliquids, nanostructured oxidic materials, and phase change materials, with more than 110 papers published. In 2000, he was awarded D.Sc. degree
Authors:Rajneesh Kumar, Pankaj Sharma, and V. S. Rangra
temperature. The value of F ≈ 16 defined as the strong glass-formingliquids [ 26 ], while a high value of F ≈ 200 represents the fragile glass-formingliquid [ 27 ]. In our investigated system, the values of F vary from ≈16 to 28 means strong glass
remarkable property of certain glass-formingliquids 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