Very long linear macromolecules can occur as fluid polymers at temperatures above their point of crystallization. These are commonly referred to as polymer melts and are key ingredients in many modern materials, not least because they demonstrate a broad range of viscoelastic behaviors.
In polymer melts, the long macromolecule chains are heavily overlapping and their elastic properties were initially attributed to a temporary entanglement of the chains and transient cross-linking or friction between chains. However, it is now believed that physics of entanglements is more complicated and typically understood through the tube model.
According to Edwards’ tube model of entangled polymer networks, transverse motion of a polymer is restricted by the surrounding chains with the result that each polymer chain is effectively confined within a tube-like region1. Furthermore, the unique viscoelastic properties of polymer melts can be modified by changing the tube length, which removes the dependence on molecular weight.
It is now widely accepted that the dynamics of entangled polymers, which span a wide range of coupled time and length scales, govern the unusual properties of polymer melts. However, the majority of studies probing the dynamics of polymer melts have used computer simulation or macroscopic evaluation. It has proved extremely difficult to obtain evidence within a microscopic framework.
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