Temporary networks rubber elasticity

The transient net work model is an adaptation of the network theory of rubber elasticity. In concentrated polymer solutions and polymer melts, the network junctions are temporary and not permanent as in chemically crosslinked rubber, so that existing junctions can be destroyed to form new junctions. It can predict many of the linear viscoelastic phenomena and to predict shear-thinning behavior, the rates of creation and loss of segments can be considered to be functions of shear rate. 

The observed plateau in the rubbery region is a consequence of high molecular mass, as the long molecules tend to entangle, with the formation of physical cross-links that restrict molecular flow through the formation of temporary networks. At long times such physical entanglements are usually labile and lead to some irreversible flow, in contrast with the situation for permanent chemical cross-links, such as those introduced when mbber is vulcanised. It follows directly from the theory of rubber elasticity (Chapter 4) that the value... 

A model based on temporary network rubber elasticity is presented Gat may explain Gis raGer unexpected behavior. 

Figures 1 and 2 reveal some surprising facts. First, the nonlinear strain measures obtained from equilibrium measurements on a large number of crossllnked rubbers lie in the same range as those obtained from transient measurements on the same types of material. This indicates that the nonlinear relation between stress and elastic strain is the same for permanent and temporary structures in the network. The fact that time and strain effects are separable over a large time scale for a number of crossllnked rubbers, which is revealed by the stretching rate independence of the strain measure calculated for these networks, is in accordance with this conclusion.

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