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The structural relaxation dynamics of conventionally prepared bulk glass of N,N′-bis(3-methylphenyl)-N,N′-diphenyl-benzidine (TPD) was measured by differential scanning calorimetry. The calorimetric data were quantitatively described in terms of the Tool–Narayanaswamy–Moynihan (TNM) model. The TNM parameters were evaluated using a combination of linearization and non-linear optimization methodologies: h*/R = 109.5 kK, ln(A/s) = −321, β = 0.37, x = 0.64. In addition, the TNM phenomenology was used to describe recently reported normalized thickness data of stable and aged thin TPD films measured by ellipsometry. The structural relaxation was found to proceed at a markedly higher rate in these thin films prepared by the physical vapor deposition compared to that of conventional bulk glass. This feature appears to be associated with the significantly narrower distribution of relaxation times (β ≅ 0.8) observed for stable thin film in "as-deposited" form with uniquely dense molecular packing. Interestingly, very similar attributes of the relaxation kinetics were also found in the aged thin film with a previously erased thermal history associated with the deposition. [ABSTRACT FROM AUTHOR]

The self‐plasticization, i.e., the increase in the polymer chains' mobility by including its monomer, has a major impact on a polymer's structural, thermal, and mechanical properties. In this study, differential scanning calorimetry (DSC), optical and Raman microscopies, thermo‐mechanical analysis (TMA), size exclusion chromatography equipped with a multi‐angle light scattering detector (SEC‐MALS), and X‐ray diffraction analysis (XRD) are used to investigate the effect of thermally induced self‐plasticization of poly‐(p‐dioxanone), PDX, on the crystal growths from the amorphous and molten states. Significant changes in the crystallization behavior and mechanical properties of PDX are found only for samples self‐plasticized at the depolymerization temperature (Td) above 150 °C. The intense self‐plasticization leads to the decrease of the crystallization temperature, increase of the crystal growth rapidity, disappearance of the distinct α→α’ polymorphic transition, reduction of the overall melting temperature, and segregation of the redundant monomer. Although the morphology of the crystalline phase has a major impact on the mechanical properties of PDX, the self‐plasticization itself does not seem to result in any major changes in the magnitude, localization, or morphology of formed crystallites (these are primarily driven by the temperature of crystal growth). The manifestation of the variable activation energy concept is discussed for the present crystallization data. [ABSTRACT FROM AUTHOR]

The processes of structural relaxation, crystal growth, and thermal decomposition were studied for amorphous griseofulvin (GSF) by means of thermo-analytical, microscopic, spectroscopic, and diffraction techniques. The activation energy of ~395 kJ·mol−1 can be attributed to the structural relaxation motions described in terms of the Tool–Narayanaswamy–Moynihan model. Whereas the bulk amorphous GSF is very stable, the presence of mechanical defects and micro-cracks results in partial crystallization initiated by the transition from the glassy to the under-cooled liquid state (at ~80 °C). A key aspect of this crystal growth mode is the presence of a sufficiently nucleated vicinity of the disrupted amorphous phase; the crystal growth itself is a rate-determining step. The main macroscopic (calorimetrically observed) crystallization process occurs in amorphous GSF at 115–135 °C. In both cases, the common polymorph I is dominantly formed. Whereas the macroscopic crystallization of coarse GSF powder exhibits similar activation energy (~235 kJ·mol−1) as that of microscopically observed growth in bulk material, the activation energy of the fine GSF powder macroscopic crystallization gradually changes (as temperature and/or heating rate increase) from the activation energy of microscopic surface growth (~105 kJ·mol−1) to that observed for the growth in bulk GSF. The macroscopic crystal growth kinetics can be accurately described in terms of the complex mechanism, utilizing two independent autocatalytic Šesták–Berggren processes. Thermal decomposition of GSF proceeds identically in N2 and in air atmospheres with the activation energy of ~105 kJ·mol−1. The coincidence of the GSF melting temperature and the onset of decomposition (both at 200 °C) indicates that evaporation may initiate or compete with the decomposition process. [ABSTRACT FROM AUTHOR]

The CaO-SiO₂ glass forming system is a typical example of a situation when the Shakhmatkin and Vedishcheva thermodynamic model cannot explain the experimentally determined Q-units distribution. As the system components are determined as stable crystalline phases found in the equilibrium phase diagram, the reason of the model failure is the missing system component representing the Q³ structural unit. We suggested a solution to the problem by adding an artificial CaO∙2SiO₂ component and we proposed a method of estimating the Gibbs energy of this component. The method is based on the linear relationship found between the reaction Gibbs energy of the formation of the system components representing the different Qn units (n = 3, 2, 1, 0) divided by the number of non-bridging oxygen atoms in this particular component (i.e., 4-n) on one side and the n value on the other side. The method was qualified by the good coincidence of the model results with the MAS NMR experimentally determined Q-distribution. Moreover, the estimated value of Gibbs energy practically coincides with the optimised value obtained by minimising the sum of the squares of the deviations between the experimental and calculated Q-distribution with respect to the molar Gibbs energy of CaO∙2SiO₂.