Nematic Rubber Elasticity

Abstract

Abstract Nematic networks can be highly rubbery, that is capable of large extensions and com-posed of molecules with liquid-like mobility. The difference between nematic and clas-sical elastomers is principally only that of molecular shape anisotropy induced by the liquid crystalline order. The simplest description of nematic rubber elasticity is essen-tially an extension of classical molecular rubber elasticity, reviewed in Chapter 3. We shall accordingly call it a 'neo-classical' theory of rubber elasticity, referring to the identity of approach. It will be introduced in this chapter and its richness explored in subsequent chapters of this book. This chapter will conclude with simple illustrations of the neo-classical free energy not involving rotations of the director and complex strains. Already remarkable phenomena arise, for instance we describe spontaneous thermal distortion, optical distortions, complex thermal history and relaxation, the Landau the-ory of transitions and the influence of mechanical stress on thermal effects. The nematic rubber elastic free energy is simple, even if the thermo-mechanical history has been complex. Readers unconcerned about the details of how this is so should omit Sect. 6.3, marked :j:, only reading its main conclusion which is stated in its opening paragraph.