Relaxation transitions glass transition

Roudaut, G., Maglione, M., and Le Meste, M. 1999b. Relaxations below glass transition temperature in bread and its components. Cereal Chem. 76, 78-81. 

Asymptotic Laws and Preasymptotic Correction Formulas for the Relaxation Near Glass-Transition Singularities. 

Fig. 4. Pulsed NMR data for poly(vinyl acetate), as a typical example for polymer relaxation. The glass transition corresponds to the abrupt change in T2 and the high temperature minima in T, and T( curves. Lower temperature minima in T, and Tj curves are attributed to a side group relaxation (reprinted from Ref.11 with permission)...

An attempt has been made to describe the particular stress-optical behaviour observed close to Tg. The idea was to associate the entropic part of the stress with relaxation times corresponding roughly to the rubbery plateau and the terminal zone (see Fig. 12), whereas the non-entropic part is assumed to be related to shorter time relaxation phenomena (glass transition and glassy state). This approach is similar to that proposed by Inoue et al. [34] who considered two contributions to the stress with different associated stress-optical coefficients. 

Relaxation phenomena can be detected somewhere in the middle between these two extremes. For polymers, it is important to be aware of their relaxation behavior. We mention two typical relaxation phenomena, glass transition and high elasticity. 

Branched polyethylene shows a different behaviour (Fig. 7.47). At low temperatures, below the P relaxation (the glass transition of polyethylene), the behaviour is similar to that of linear polyethylene. At higher temperatures, above Tp, the modulus of the amorphous component is crystallinity-dependent. 

For relaxations below glass transition temperature (sub-Tg transitions), almost linear relationship between log v and reverse temperature, 1/T, is always observed (Fig. 14b). The extrapolation of these dependences to 1/T = 0, gives the value of V 10 Hz with the accuracy within one to two orders of magnitude. This means that these relaxations relate to quasi-independent motional events and obey the Arrhenius expression for frequency of jumps of the kinetic units... 

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

---