Glass transition temperature contributing factors

The effects of these different factors can be seen in the Tg values of some typical polymers. A number of these values are shown in Table 3.1, together with a brief note about what feature particularly contributes to the relative level of the glass transition temperature. 

Here, Cv h(T) and Svlh(T) are the vibrational contributions to the heat capacity and the entropy, respectively. Note that the slope of the replica symmetry-breaking parameter with respect to temperature is not unity as predicted by one-step replica symmetry breaking. Rather, the slope is governed by three factors the Narayanaswamy-Moynihan nonlinearity parameter x, the Kauzmann temperature, and the ratio of the Kauzmann temperature to the glass transition temperature. 

The same factors listed in the preceding paragraph can contribute to the thermal behavior of the polymer. Two key thermal parameters are the melting point of the polymer and the glass transition temperature (Tg). For polymeric biomaterials, if the polymer Tg is below 37 °C, the polymer will be soft or mbbery when at human body temperature (37 °C). If the Tg is above 37 ° C, the polymer will be stiff. 

It can be observed that the term of (1 -x) describes the contribution of Tf. Here, Tg is the glass transition temperature. denotes the Vogel temperature, defined as (Tg - 50) (°C), tq corresponds to the reference relaxation time at Tg, and B is the loeal slope at Tg of the trace of the time-temperature superposition shift factor in the global WiUiam-Landel-Ferry (WLF) equation [53]. 

Studies by Becker et al. reveal that the glass transition temperature (T of the nanocomposites decreases gradually with the rise in clay concentration for all the epoxy systems irrespective of the functionality of the epoxy resin [32]. A lot of factors may contribute to such a decrease in glass transition temperature. Certain studies show significant improvement in T on the incorporation of clay platelets [85-86]. Interestingly some studies s ow a decrease in values on clay incorporation [87-88]. The following factors maybe responsible for the decrease in glass transition temperature [32] ... 

Figure 1.27 In general, molecular factors which contribute to a higher melting point in a polymer capable of crystallization will also contribute to a higher glass transition temperature, as shown schematically in this figure where upper line is T, eit and the lower is...

Concentration Shift Factor (ac) from Dynamic and Creep Rheological Measurements, Glass Transition Temperature (Tg), WLF Coefficients (C, and C2 [reference temperature Tq = 50 C]), and the Expected Contribution of Tg Change with Concentration to the Concentration Shift Factor... 

Whilst we accoimted for a concentration dependence of the glass transition temperature, we did not include the additional contributions to the gradient of the stress which arise from gradients in the monomeric friction factor. Once we have determined the temperatme dependence of the relaxation times using the appropriate blend Tg, we assiune the relaxation times to be fixed and not a function of concentration. Hence, our theory is strictly only applicable to blends in which each component has a similar glass transition temperature. Despite attempts to imderstand and explain the consequences that such behaviom will have on blend rheology, a clear pictme has yet to emerge. 

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