Polymers

Abstract

Here we discuss systemsPolymer made of much larger molecules than simple liquids, in fact the macromolecules known as polymers. The peculiarity of polymers which gives them their most remarkable mechanical properties is that the conformation, that is, the geometric configuration of a given molecule, is not predetermined. Depending on the stresses it may be subject to, such a molecule can adopt a whole range of different conformations, from completely folded up into what is known as a coil to a fully stretched out configuration. The size and flexibility of polymers can lead to more complex internal structures than one finds for materials made up of small molecules, and they have consequences for the mechanical behaviour of mixtures that include them. As for simple materials, when the temperature rises, the polymer chains become more mobile relative to one another. The polymer is in a liquid state. We shall mainly be concerned here with polymers in the liquid state or else solidified by specific interactions between the chains (crosslinked polymers or polymer gels). Different concentration regimes can be identified depending on the interactions between the polymer chains. We are then in a position to discuss the mechanical behaviour of polymers in these different regimes.