Glass transition temperature structural-relaxation time

Concentration of locally favoured structures Structural relaxation time Glass transition temperature Two Order Parameters (Model)... 

The solidity of gel electrolytes results from chain entanglements. At high temperatures they flow like liquids, but on cooling they show a small increase in the shear modulus at temperatures well above T. This is the liquid-to-rubber transition. The values of shear modulus and viscosity for rubbery solids are considerably lower than those for glass forming liquids at an equivalent structural relaxation time. The local or microscopic viscosity relaxation time of the rubbery material, which is reflected in the 7], obeys a VTF equation with a pre-exponential factor equivalent to that for small-molecule liquids. Above the liquid-to-rubber transition, the VTF equation is also obeyed but the pre-exponential term for viscosity is much larger than is typical for small-molecule liquids and is dependent on the polymer molecular weight. 

In the discussion on the dynamics in the bead-spring model, we have observed that the position of the amorphous halo marks the relevant local length scale in the melt structure, and it is also central to the MCT treatment of the dynamics. The structural relaxation time in the super-cooled melt is best defined as the time it takes density correlations of this wave number (i.e., the coherent intermediate scattering function) to decay. In simulations one typically uses the time it takes S(q, t) to decay to a value of 0.3 (or 0.1 for larger (/-values). The temperature dependence of this relaxation time scale, which is shown in Figure 20, provides us with a first assessment of the glass transition... 

Table 4.1 Parameters related to the structural relaxation for the polymers investigated by NSE glass transition temperature Tg, position of the first static structure factor peak Qmax> shape parameter magnitude considered to perform the scaling of the NSE data, and temperature dependence of the structural relaxation time...

Indirect evidence of nonequilibrium flucmations due to CRRs in structural glasses has been obtained in Nyquist noise experiments by Ciliberto and co-workers. In these experiments a polycarbonate glass is placed inside the plates of a condenser and quenched at temperatures below the glass transition temperature. Voltage fluctuations are then recorded as a function of time during the relaxation process and the effective temperature is measured ... 

Figure 7 Compari.son of structural relaxation times for fragile and strong glasses with glass transition temperatures of 70°C. The data were calculated using input data characteristic of sucrose except for the strength parameter, D. ( ) Strong glass (D = 23). ( ) Fragile gla.ss (D = 7).

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