Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Structural recovery asymmetry

The glassy state is nonequilibrium in nature and exhibits a tendency to rmdergo structural relaxation toward equilibrium. This tendency of the glassy state to relax structurally toward equilibrium is often referred to as structural recovery. It was observed, however, that the progress towards structural recovery with time varies significantly between a down-quench and an up-quench. This is referred to as asymmetry of structural recovery. The norrlinearlty of the process is described by the following equation [16] ... [Pg.22]

Explain structural recovery and the asymmetry of structural recovery. [Pg.62]

This asymmetry in the recovery means that the structural-relaxation time depends not only on the temperature but also on the instantaneous structure. In particular, when the approach toward equilibrium is from above, the initial structure of the material will have a higher molecular mobility than that of the equilibrium structure, although the difference decreases as the departure from equiUbrium decreases. On the other hand, the opposite is true when the approach toward equilibrium is from below. This feature of isothermal structural relaxation is sometimes referred to in the literature as the nonlinearity of the process, in the sense that the structural relaxation cannot be described by the linear differential equation... [Pg.82]

Our focus has been the elucidation of specific features of the model which give rise to the most important aspects of glass transition behavior. Thus time dependence arises naturally from a consideration of the molecular aspects of the overall phenomena involved. The pronounced nonlinearity and asymmetry of behavior result from the structure dependency of the individual retardation times introduced in the model. In fact, our analysis shows that, on a time scale appropriately compensated to take account of structural dependence, non-linearity and asymmetry vanish. The existence of a multiplicity of recovery times in the model leads to memory, which is observed in real systems. [Pg.294]

The asymmetry of approaching equilibrium demonstrates a relaxation process subject to more complex thermal histories. That is, the material is initially equilibrated at temperature To that departs AT from the test temperature Ti, i.e.. To = Ti + AT or To = Ti - AT, in cases of down-jump or up-jump, respectively. Subsequently, the temperature is controlled to jump to Ti, where the volumetric evolution is then measured in the relaxation induced from the temperature jump. Although the magnitude of the temperature jump AT in both cases of the up-jump and down-jump is the same, the volume recovery towards equilibrium is found to be much faster in the down-jump experiment (Ti < To) than in the up-jump experiment (Ti > To). This result indicates the inherent nonlinearity of the structural relaxation process and has been widely used to determine that the aging response depends upon the instantaneous state of the material. [Pg.53]


See other pages where Structural recovery asymmetry is mentioned: [Pg.8]    [Pg.81]    [Pg.84]    [Pg.176]    [Pg.2225]    [Pg.133]    [Pg.756]    [Pg.756]    [Pg.62]    [Pg.61]    [Pg.421]    [Pg.342]   
See also in sourсe #XX -- [ Pg.81 ]




SEARCH



Asymmetrie

Asymmetry

Structural recovery

© 2024 chempedia.info