INTRODUCTION

Liquid crystals have been defined as a remarkable, paradoxical state of matter intermediate between true liquids and true crystals because their molecules or regions within the molecules have a mobility similar to that of true liquids, yet show orientational and sometimes positional order similar to that of solid crystals (Collings, 1990). While most types of liquid crystal are able to flow, liquid crystal elastomers (LCEs), also described as solid liquid crystals are not. LCEs have only recently been suggested to be a novel state of matter (Warner and Terentjev, 1996), although the theoretical existence of this state was first postulated more than 25 years ago by de Gennes (1969, 1975) and the term ‘solid liquid crystal’ was originally used in a now outmoded way to describe the more heavily cross-linked nematic resins (Bouligand et al., 1974). However, it was not until the late 1980s and early 1990s that LCEs were first synthesised by Finkelman's group at Freiburg University (Barclay and Ober, 1993; Schneider et al., 2000).

Both classical rubbers and LCEs are weakly cross-linked polymers showing reversible extensibility and energy storage (Legge et al., 1991). A major difference between these two classes of materials is that the polymer chains in classical rubbers are highly disordered at rest, while those of LCEs show orientational order earning them the term ‘anisotropic elastomers’ (Texeira, 1999). LCEs can be defined as lightly cross-linked main chain or side chain (Northolt and Sikkema, 1991) liquid crystalline polymers showing elastomeric properties.