Dynamic phenomena glass

It is not clear, whether the experimentally observed random local freezing of the deuterons in the O-D—O bonds in deuteron glasses corresponds to a true thermodynamic phase transition or whether one deals with a dynamic phenomenon which only seems static because of the finite observation time of the experimental techniques. The recently observed42 splitting between the field-cooled and zero-field dielectric susceptibilities below an instability temperature Tf seems to speak for the occurrence of an Almeida-Thouless-like thermodynamic phase transition in deuteron glasses. It is well known that ID NMR and EPR allow a direct measurement of the Edwards-Anderson order parameter qEA only on time scales of 10 3-10 8 s and 2D exchange NMR possibly seems to be a better technique for such slow motions. 

Our overall conclusion, therefore, is that for mesoporous glasses adsorption, hysteresis is a dynamic phenomenon that is not simply related to a capillary vapor-liquid phase transition. Slow dynamics for long times makes the states accessible in experiments in the hysteresis loop appear equilibrated and quite reproducible. Mean field theory and Monte Carlo simulations in the grand ensemble provide a physically realistic description of these phenomena. 

It is important to mention at this point that, in the solid state, some of the above spectral parameters are not only determined by molecular motions, but also by the dynamics of the spin system. As a consequence, in bulk polymers at temperatures below the glass-transition temperature, the competition between molecular dynamics and spin dynamics may introduce some difficulties in the data interpretation. On the other hand, the spin dynamics phenomenon itself can be a most useful tool for studying the solid-state organization of heterogeneous materials. 

The three polymers studied display remarkable physical aging effects [24], with a strong increase of modulus and changes in the location and intensity of the glass transition. This phenomenon is exemplified in Fig. 17 where the changes of dynamic moduli in a PDEB sample aged for 14 months are very apparent. 

Thereby, the features of the a-relaxation observed by different techniques are different projections of the actual structural a-relaxation. Since the glass transition occurs when this relaxation freezes, the investigation of the dynamics of this process is of crucial interest in order to understand the intriguing phenomenon of the glass transition. The only microscopic theory available to date dealing with this transition is the so-called mode coupling theory (MCT) (see, e.g. [95,96,106] and references therein) recently, landscape models (see, e.g. [107-110]) have also been proposed to account for some of its features. 

An intense femtosecond laser spectroscopy-based research focusing on the fast relaxation processes of excited electrons in nanoparticles has started in the past decade. The electron dynamics and non-linear optical properties of nanoparticles in colloidal solutions [1], thin films [2] and glasses [3] have been studied in the femto- and picosecond time scales. Most work has been done with noble metal nanoparticles Au, Ag and Cu, providing information about the electron-electron and electron-phonon coupling [4] or coherent phenomenon [5], A large surface-to-volume ratio of the particle gives a possibility to investigate the surface/interface processes. 

As a general comment about the dynamic mechanical relaxational behavior of this polymer, the results are consistent with dielectric data [210] and with the fact that no glass transition phenomenon is observed, at least in the range of temperature studied. This is striking in an amorphous polymer. It is likely that the residual part of the molecule mechanically active above the temperature of the ft relaxation is only a small one, and this is the reason for the low loss observed in the a zone. 

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