Entanglements at Polymer Surfaces and Interfaces

A fundamental consequence of the long chain nature of polymers is that one chain is entangled with itself and many other chains in the bulk. These entanglements are central to many of the mechanical and dynamic properties of polymers. However, the packing of polymer chains is perturbed near an impenetrable interface. Here, it is shown that the reduction in the average volume pervaded by the polymer chain at an interface gives rise to a reduction in the number of entanglements per unit volume in comparison to that in the bulk. Consequently, the mechanical and dynamic properties of polymers near an interface are markedly different from those in the bulk. Ramifications of this reduced entanglement density are seen in experimental results dealing with adhesion, interdiffusion and surface alignment of polymers.