Specific Relaxation Processes and Flow Behavior

In this section, the focus was on the difference in the characteristic times observed in measurements of compliances or moduli, respectively. In the explanation, we had to use two different symbols, the notation t for the retardation time and f for the relaxation time. In what follows we shall not persist in this differentiation and write r generally, for all kinds of characteristic times observed in experiments. 

After the introduction of the various interrelated response functions and basic concepts like the Debye process and the derived spectral representations in the second part of this chapter we now come to the description and discussion of actual polymer behavior. In fact, relaxation processes play a dominant role and result in a complex pattern of temperature-dependent and frequency-dependent properties. 

We already have a general picture suitable for considerations. As has been emphasized, dealing with fluid polymers means dealing with an ensemble of chains that can exist in a manifold of different conformational states. Thermal equilibrium is a dynamical situation where chains change between these states activated by thermal energies. The microscopic dynamics shows up in the macroscopic experiments. Relaxation rates observed in certain mechanical or dielectrical measurements equal the rates of transitions within a certain group of conformations. 

The rates of conformational transitions of a chain encompass an enormously wide range. Local rearrangements including only a few adjacent monomers are usually rapid and take place with rates similar to those in ordinary liquids. Conformational changes of more extended sequences require much longer times. In particular, relaxatory modes associated with the chain 

In the remaining part of this chapter, we discuss the properties of some major groups of relaxation processes in pol3uners as there are 

---

Specific Relaxation Processes and Flow Behavior 257 Low Frequency Properties of Polymer Melts... 

---