Nematic elastomers - A new state of matter?

Recent experimental and theoretical work shows that nematic elastomers have a highly mobile director, despite being nominally solid liquid crystals. We review this work and show that such a system represents an essentially new state of matter with non-symmetric elasticity, new nematic transitions, discontinuous stress-strain relations and an ability to behave like liquids for some special class of deformations. These phenomena have been seen in large monodomain samples made in nematic fields or by multistage crosslinking under stresses. Modelling of monodomain elastomers is straightforward and successfully explains the unusual mechanical behaviour observed. The theory is a direct extension of the classical theory of conventional rubbers; we call it the neo-classical theory of elastomers. Being a molecular theory, it describes the very large extensions at which the new transitions occur. We outline problems for the future, principally those of polydomains. Copyright (C) 1996 Elsevier Science Ltd.