Glass transition involved

The glass transition involves additional phenomena which strongly affect the rheology (1) Short-time and long-time relaxation modes were found to shift with different temperature shift factors [93]. (2) The thermally introduced glass transition leads to a non-equilibrium state of the polymer [10]. Because of these, the gelation framework might be too simple to describe the transition behavior. 

Relaxation processes in amorphous polymers below the glass transition involve local... 

Glass transitions involve mainly the onset or freezing of cooperative, large-amplitude motion and can be studied using thermal analysis. Temperature-modulated calorimetry, TMC, is a new technique that permits to measure the apparent, fiequency-dependent heat capacity. The method is described and a quasi-isodiermal measurement method is used to derive kinetic parameters of the glass transitions of poly(ethylene terephthalate) and polystyrene. A first-order kinetics expression can describe the approach to equilibrium and points to the limits caused by asymmetry and cooperativity of the kinetics. Activation energies vary from 75 to 350 kJ/mol, dependent on thermal pretreatment. The preexponential factor is, however, correlated with the activation energy. 

On the other hand, when an amorphous solid such as an amorphous polymer is heated its temperature increases as before. However, when the Tg is reached there is no break in the temperature increase. After Tg the rate of increase of temperature with respect to the heat supplied varies in comparison to the situation below the Tg. This means that the glass transition involves a change in heat capacity but does not involve a latent heat change. In contrast, the involves a change in latent heat as well as heat capacity. The former (Tg) is defined as a second-order transition, while the latter (T ) a first-order transition. 

The tilt angle and lattice contribution to the vibrational anisotropy in an H-phase of a mesogen was studied via the anisotropy of the recoil free fraction [23]. Other Mossbauer studies examined anisotropic diffusion at a glass transition involving an H phase to supercooled H phase transition temperature [24],... 

---