Relaxation Processes Associated with Crystallization and Glass Transition in Amorphous 5PbO·3GeO2

1985 ◽  
Vol 24 (Part 1, No. 4) ◽  
pp. 397-400 ◽  
Author(s):  
Masaki Maeda
Keyword(s):  
Glass Transition ◽  
Relaxation Processes

Relaxation processes and intermolecular interactions in PVME hydrogels in sub-zero temperatures: Glass transition and pre-melting of ice

Polymer ◽  
2012 ◽  
Vol 53 (1) ◽  
pp. 161-168 ◽  
Author(s):  
Marcin Pastorczak ◽  
Michael Wübbenhorst ◽  
Gustavo Dominguez-Espinosa ◽  
Lidia Okrasa ◽  
Marek Pyda ◽  
...  
Keyword(s):  
Glass Transition ◽  
Intermolecular Interactions ◽  
Relaxation Processes

Glass Transition and Relaxation Processes in Supercooled Water

2004 ◽  
Vol 93 (24) ◽  
Author(s):  
Silvina Cerveny ◽  
Gustavo A. Schwartz ◽  
Rikard Bergman ◽  
Jan Swenson
Keyword(s):  
Glass Transition ◽  
Supercooled Water ◽  
Relaxation Processes

scholarly journals Pharmaceutical Amorphous Organic Materials Characterization by Using the Differential Scanning Calorimetry and Dynamic Mechanical Analysis

2011 ◽  
Vol 6 (2) ◽  
pp. 91-95
Author(s):  
Ion Dranca ◽  
Igor Povar ◽  
Tudor Lupascu
Keyword(s):  
Differential Scanning Calorimetry ◽  
Glass Transition ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Dynamic Mechanical Analysis ◽  
Mechanical Analysis ◽  
Relaxation Processes ◽  
Scanning Calorimetry ◽  
Dynamic Mechanical ◽  
Β Relaxation

This research has been carried out in order to demonstrate the use of differential scanning calorimetry (DSC) in detecting and measuring α- and β-relaxation processes in amorphous pharmaceutical systems. DSC has been employed to study amorphous samples of poly (vinylpyrrolidone) (PVP), indomethacin (InM), and ursodeoxycholic acid (UDA) that are annealed at temperature (Ta) around 0.8 of their glass transition temperature (Tg). Dynamic mechanical analysis (DMA) is used to measure β- relaxation in PVP. Yet, the DSC has been used to study the glassy indomethacin aged at 0 and -10 oC for periods of time up to 109 and 210 days respectively. The results demonstrate the emergence of a small melting peak of the α-polymorph after aging for 69 days at 0°C and for 147 days at -10°C (i.e., ~55°C below the glass transition temperature) that provides evidence of nucleation occurring in the temperature region of the β-relaxation.

scholarly journals PACMAN PERCOLATION AND THE GLASS TRANSITION

Fractals ◽  
2013 ◽  
Vol 21 (03n04) ◽  
pp. 1350021 ◽  
Author(s):  
RAFFAELE PASTORE ◽  
MASSIMO PICA CIAMARRA ◽  
ANTONIO CONIGLIO
Keyword(s):  
Monte Carlo ◽  
Relaxation Time ◽  
Glass Transition ◽  
Monte Carlo Simulations ◽  
Relaxation Process ◽  
Time Scales ◽  
Relaxation Processes ◽  
Percolation Transition ◽  
Glass Model ◽  
Different Time Scales

We investigate via Monte Carlo simulations the kinetically constrained Kob-Andersen lattice glass model showing that, contrary to current expectations, the relaxation process and the dynamical heterogeneities seems to be characterized by different time scales. Indeed, we found that the relaxation time is related to a reverse percolation transition, whereas the time of maximum heterogeneity is related to the spatial correlation between particles. This investigation leads to a geometrical interpretation of the relaxation processes and of the different observed time scales.

scholarly journals Microscopic-Phenomenological Model of Glass Transition and Temperature Dependence of Viscosity—Part I: Foundations of the Model

Ceramics ◽  
2021 ◽  
Vol 4 (2) ◽  
pp. 302-330
Author(s):  
Karl Günter Sturm
Keyword(s):  
Glass Transition ◽  
Cross Section ◽  
Molecular Vibration ◽  
Glass Temperature ◽  
Relaxation Processes ◽  
Axis Orientation ◽  
Distribution Width ◽  
Adjacent Element ◽  
The Cross ◽  
Simple Molecules

The glass transition is described as a time- and history-independent singular event, which takes place in an interval dependent on the distribution width of molecular vibration amplitudes. The intrinsic glass transition is not seen as a relaxation phenomenon, but is characterized by a fixed volumetric state at the glass temperature Tg0. The relaxation behavior of the transport properties depends on the distance to Tg0. Free volume is redefined and its generation is the result of the fluctuating transfer of thermal energy into condensed matter and the resulting combined interactions between the vibration elements. This creates vacancies between the elements which are larger than the cross-section of an adjacent element or parts thereof. Possible shifts of molecules or molecular parts through such apertures depend on the size and axis orientation and do not require further energetic activation. After a displacement, additional volume is created by delays in occupying abandoned positions and restoring the energetic equilibrium. The different possibilities of axis orientation in space result in the different diffusive behavior of simple molecules and chain molecules, silicate network formers, and associated liquids. Glass transformation takes place at a critical volume Vg0 when the cross-section of apertures becomes smaller than the cross-section of the smallest molecular parts. The glass transition temperature Tg0 is assigned to Vg0 and is therefore independent of molecular relaxation processes. Tg0 is well above the Kauzmann and Vogel temperatures, usually just a few degrees below the conventionally measured glass temperature Tg(qT). The specific volume at the two temperatures mentioned above cannot be achieved by a glass with an unordered structure but only with aligned molecular axes, i.e. in a crystalline state. Simple liquids consisting of non-spherical molecules additionally alter their behavior above Vg0 at Vglwhere the biggest gaps are as small as the largest molecular diameter. Tgl is located in the region of the crystalline melting point Tm. Both regions, above and below Tm, belong to different physical states and have to be treated separately. In the region close to Vg0 respectively Tg0, the distribution of vibration amplitudes has to be taken into account. The limiting volume Vg0 and the formation of apertures larger than the cross-section of the vibrating elements or parts thereof, in conjunction with the distribution width of molecular vibrations as Vg0 is approached, and the spatial orientation of the molecular axes is key to understanding the glass transition.

Insights into the Structural Dynamics of PLGA at Terahertz Frequencies

2018 ◽  
Author(s):  
Talia A. Shmool ◽  
J. Axel Zeitler
Keyword(s):  
Glass Transition ◽  
Relaxation Process ◽  
Free Volume ◽  
Variable Temperature ◽  
Dipole Moments ◽  
Relaxation Processes ◽  
Segmental Motion ◽  
Terahertz Time Domain Spectroscopy ◽  
Free Volume Theory ◽  
Terahertz Frequencies

The mechanical properties of an amorphous copolymer are directly related to the dynamic processes occurring at the molecular level. Poly lactic-co-glycolic acid (PLGA) is a biodegradable co-polymer, and in this work we investigate the dynamics of PLGA and its glass transition behaviour by performing variable temperature terahertz time-domain spectroscopy (THz-TDS) experiments. We correlate PLGA dynamics, as measured at terahertz frequencies, their temperature dependence, molecular weight (MW), lactide to glycolide ratio, and free volume. The THz-TDS data can be used to detect two distinct glass transition processes, T<sub>g,α</sub> and T<sub>g,β</sub>. To complement our analysis, we use dynamic mechanical analysis (DMA) to probe the β- and α-relaxation processes in PLGA, and compare the results obtained from the DMA experiments with those obtained using THz-TDS. We attribute T<sub>g,β</sub> to the change in dipole moments associated with the β-relaxation process, originating from the local rotation of C-O macromolecular chain segments, and T<sub>g,α</sub> to the change in dipole moments due to large segmental motion of the copolymer backbone associated with the α-relaxation process. We connect our experimental results to the free volume theory proposed by Fox and Flory, and demonstrate our results are consistent with the relationship between the experimentally determined T<sub>g,β</sub> and T<sub>g,α</sub> and free volume and PLGA dynamics.

Investigation of Dipolar Relaxation Processes in a Side-Chain Nonlinear Optical Polymer

1996 ◽  
Vol 446 ◽  
Author(s):  
Z. -Y. Cheng ◽  
R. S. Katiyar ◽  
S. Bauer ◽  
S. Bauer-Gogonea
Keyword(s):  
Glass Transition ◽  
Dielectric Spectroscopy ◽  
Nonlinear Optical ◽  
Side Chain ◽  
Relaxation Processes ◽  
Dipolar Relaxation ◽  
Depolarization Current ◽  
Chain Polymer ◽  
Optical Polymer ◽  
Nonlinear Optical Polymer

AbstractAmorphous thin films of a typical side-chain nonlinear optical polymer were investigated by means of dielectric spectroscopy and thermally stimulated depolarization current (TSDC) within the temperature range -40°C to 230°C. Three distinct relaxation processes, labelled α, β and γ were observed. The α-relaxation, associated with the glass transition, is well described by the Vogel-Fulcher relation, while the sub glass transition β and γ-relaxation follow Arrhenius relations. The advantage of TSDC over dielectric spectroscopy is demonstrated for the investigation of the weak β-relaxation in the side-chain polymer. Furthermore, the β -relaxation is responsible for the initial, fast decay of the electro-optical response of the side-chain polymer at room temperature.

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