Relaxation dynamics structural glasses

Various types of power law relaxation have been observed experimentally or predicted from models of molecular motion. Each of them is defined in its specific time window and for specific molecular structure and composition. Examples are dynamically induced glass transition [90,161], phase separated block copolymers [162,163], polymer melts with highly entangled linear molecules of uniform length [61,62], and many others. A comprehensive review on power law relaxation has been recently given by Winter [164],... 

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. 

The AG model [48] for the dynamics of glass-forming liquids essentially postulates that the drop in S upon lowering temperature is accompanied by collective motion and that the fluid s structural relaxation times r are activated with a barrier height that is proportional [80] to the number z of polymer... 

In determining the dynamic structure factor, the value of Do (7o) is needed to be specified. Here the decoupling is studied as a function of the change of density. A noticeable long-time tail in density relaxation appears only very near to the glass transition line. This makes the choice of 7o or p0 rather easy. It is found that, for the reduced temperature, T = 0.8, the reduced density is 0.91. 

Below Tg, structural relaxation is too slow to be observable, but secondary processes persist, which determine, e.g., the mechanical and dielectric properties of glasses. These processes have been extensively studied for polymers, where they are usually associated with polymer-specific dynamics such as side-group motion. From the point of view of glass physics, it is more interesting to investigate secondary relaxation processes in glasses comprised of rigid molecules, i.e., molecules without... 

Study the chain dynamics in the amorphous polymer atactic polypropylene. " The arrest of the structural relaxation above the glass-transition temperature Tg was investigated using ID and 2D deuteron NMR spectra. 

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