Perspective and Scope of this Text

Polymers possess many interesting and useful properties that are quite different from those of more traditional engineering materials and these properties cannot be explained or modeled in engineering design situations by traditional approaches. As suggested by Rosen (1993), verification can be observed with three simple experiments. 

Silly Putty This material (polydimethyl siloxane) bounces when dropped but flows when laying stationary and, obviously, has some characteristics of an elastic solid and some characteristics of a viscous fluid. 

Joule Effect A rubber band will contract when heated while a weight is suspended from it. Other materials will undergo the expected thermal expansion. 

Welssenburg Effect When a rod is rotated in a molten polymer or in a concentrated polymer solution, the liquid will rise on rod. For other fluids, the lowest point in fluid will be at rod. 

One manifestation of the time dependent character of polymers is that they exhibit characteristics of both an elastic solid and that of a viscous fluid as with the example of silly putty above. For this reason, materials such as polymers that exhibit such properties are often said to be viscoelastic. Sometimes the term viscoelastic is used primarily for solid polymers 

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