Polymer Models

Abstract

If an ideal elastic solid is subjected to a step increase in stress, the strain increases suddenly and then remains constant. However, if a polymer is subjected to a step increase in stress, there will be a time-dependent continuous increase in strain after the initial elastic response; this behaviour is called creep. The time constant associated with this process is called the retardation time. Alternatively, if a step increase in strain is applied, then the stress decreases with time; this is stress relaxation. The time constant in this case is called the relaxation time. These time constants can be related on a microscopic level to the fundamental molecular structure through various activation processes. However, many features of time-dependent polymer behaviour can be described by using simple phenomenological models (see Viscoelasticity).