In this short review we give an overview of selected macroscopic properties of sidechain liquid crystalline elastomers (LCEs) focusing on three closely related topics (a) the influence of relative rotations between the director and the strain field on various reorientation instabilities, (b) the nonlinear stress–strain curves for the polydomain–monodomain transition and for the reorientation transition in LCE monodomains and (c) the shear mechanical response of LCEs in the linear regime. We consider only already existing real materials and do not discuss hypothetical “ideal” systems. We conclude that all observations reported to date can be accounted for without invoking the concept of soft elasticity, but instead relying on macroscopic dynamics in the linear and the nonlinear domain.

We derive the complete set of macroscopic dynamic equations for ferrogels under an external magnetic field, including the magnetization as an independent dynamic degree of freedom. The magnetoelasticity comes in the form of magnetostriction and through the magnetic part of the Maxwell stress. Various dynamic couplings of the elastic degree of freedom with the magnetization and the magnetic field are found. We discuss static elongation, shear deformations, and the modified sound spectrum in the presence of an external magnetic field.

Motivated by the experimentally observed shear-induced destabilization and reorientation of smectic-$A$-like systems, we consider an extended formulation of smectic-$A$ hydrodynamics. We include both, the smectic layering (via the layer displacement u and the layer normal $\mathrm{p̂})$ and the director $\mathrm{n̂}$ of the underlying nematic order in our macroscopic hydrodynamic description and allow both directions to differ in nonequilibrium situations. In an homeotropically aligned sample the nematic director does couple to an applied simple shear, whereas the smectic layering stays unchanged. This difference leads to a finite (but usually small) angle between $\mathrm{n̂}$ and $\mathrm{p̂},$ which we find to be equivalent to an effective dilatation of the layers. This effective dilatation leads, above a certain threshold, to an undulation instability of the layers. We generalize our earlier approach [G. K. Auernhammer, H. R. Brand, and H. Pleiner, Rheol. Acta 39, 215 (2000)] and include the cross couplings with the velocity field and the order parameters for orientational and positional order and show how the order parameters interact with the undulation instability. We explore the influence of various material parameters on the instability. Comparing our results to recent experiments and molecular dynamic simulations, we find a good qualitative agreement.

We study the influence of nonlinear effects on the electrohydrodynamics of uniaxial nematic liquid crystals. To measure a novel reversible nonlinear coupling between an electric field, distortions of the director, and the stress tensor, we suggest an experimental setup and predict the occurrence of a flow in an initially static configuration. We show that the dissipative effects proposed by R. S.Akopyan and B. Ya. Zeldovich [Sov. Phys.—JETP 60, 953 (1985)] do not exist.