ABSTRACT
In this chapter we extend the study of the dynamic properties of polymer liquids in two new
directions. In Chapter 9 we considered only dilute solutions, but here we will consider also very
concentrated solutions and molten polymers. In Chapter 9 we also focused on the steady-flow
viscosity, or the diffusion over long time intervals; now we will examine the time-or frequency-
dependent response of polymer liquids to an imposed deformation or force. This response can be
characterized by a variety of material functions, such as the viscosity, the modulus, and the compliance. In general, we will find that polymer liquids are viscoelastic, i.e., their behavior is intermediate between (elastic) solids and (viscous) liquids. The phenomenon of viscoelasticity is
familiar to anyone who has played with Silly Putty. If you roll some into a ball, and leave it for a
few hours, it flows to adopt the shape of its container. This behavior is that of a liquid; it just takes
a long time because the viscosity is very high. On the other hand, if you stretch a sample very
rapidly, and immediately release one end, the sample will partially recover toward its original
dimensions. This recovery is an elastic response, and is more typical of solids than liquids. The
previous chapter concerned the elasticity of polymer networks, and important results from that
discussion will be directly incorporated into our treatment of viscoelasticity.
