Creep activation parameters, relaxation transitions

Temperature Dependencies of Creep Activation Parameters and Their Connection with Relaxation Transitions... 

In this Section, the process of deformation, relaxation, and fracture are examined only within a restricted temperature range between the main 0 and a) relaxational transitions, Tp < T < T. The kinetics of creep, relaxation of stress and Young s modulus, and fracture are investigated experimentally as a function of the external stress applied to a sample and/or the increase in temperature. It is shown that the kinetics of the processes considered are described by Arrhenius-type equations. Then, the activation parameters (the energy and the volume) of the kinetic equations are calculated and compared with each other. This procedure demonstrates the identical physical nature of these processes. 

Below we consider the results of our systematic research of deformation kinetics for glassy polymers over the wide ranges of temperatures and deformations, using the laser-interferometric technique under consideration [11,278,280-287], This research allowed us (1) to study the dependencies of kinetic parameters of creep on these factors, (2) to reveal the regular relations between the activation parameters of polymer creep, (3) to demonstrate their intimate connection with the parameters of relaxation transitions, and (4) to confirm directly the intermolecular physical nature of potential barriers of polymer plasticity. ... 

Table 9 shows the satisfactory agreement between the activation parameters of deformation and relaxation transitions. Thus, the activation volumes of both processes coincide in the temperature region of P-relaxation with Kuhn segment volume m = mp = Ak. For PMMA, the main contribution to creep kinetics below -100°C is provided by small-scale kinetic units (w = 1 and Qo = 10-15kJmoD ) that corresponds to low-temperature 8-relaxation, namely, liberation of a monomer unit in PMMA [23,99]. AtT > Tp, approaching Tg, the kinetic parameters of deformation increase by a factor of 3. Curves 4 and 6 in Fig. 69 show that an w vs T plot practically repeats the plot of the activation volumes of the relaxation processes over the entire temperature range studied. 

---