Retardation of Polymer Fluid Flow Under Great Elastic Strains

7 Retardation of Polymer Fluid Flow under Great Elastic Strains 

Fig 7a-d. Tensile force F, total (lne) and irreversible (In P) strains versus time t at different strain velocities [23, 24] (see text for explanation) 

At low values of x, normally (see Fig. 7), one maximum in dependency F(t) was observed, as it was in case of polyisobutylene at high values of x there were already two maxima. In this case (see Fig. 7c, d) four regions of strain were observed (see also Sect. 1 of this review). 

In Region IIthe flow of polymer medium develops (the velocity of irreversible strain ep increases). In this region the force F(t) passes the maximum and starts to decrease. 

Region ///begins at the point of inflection bf dependency F(t) in its decreasing section. This point corresponds to the point of inflection of the dependency ln(3(t) which increases. In this region the velocity of irreversible strain ep starts to decrease with increase in t and approaches zero (In P = const), i.e., the irreversible flow in this section is suppressed and the medium starts to strain similarly to the cross-linked rubber. In this case the force in section ep as 0 grows again which is also characteristic of the deformation of solid bodes under conditions of x = const. 

---