This review collects recent developments in the field of liquid crystalline elastomers (LCEs) with an emphasis on their use for actuator and sensor applications. Several synthetic pathways leading to crosslinked liquid crystalline polymers are discussed and how these materials can be oriented into liquid crystalline monodomains are described. By comparing the actuating properties of different systems, general structure-property relationships for LCEs are obtained. In the final section, how these materials can be turned into usable devices using different interdisciplinary techniques are described.

Oriented liquid-crystalline (LC) elastomers (polar monodomains, concerning the direction of polarisation) have been prepared from polar monodomains of ferroelectric LC-polysiloxanes by a radical photocrosslinking process. Attempts to perform ferroelectric switching lead in these soft elastomers to an elastic stress which prohibitsfor low voltagesa complete reorientation of the polar axis (ferroelectric switching). A ferroelectric switching can, however, be observed for high voltages. The loop of hysteresis of this switching is asymmetric concerning the zero point of the driving voltage. Piezoelectric measurements show that these elastomers combine an elastic memory for one polar state with enough flexibility to allow a reorientation of the polar axis.

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A side-chain liquid crystal (LC) block copolymer with a ferroelectric smectic C* LC block has been shown to exhibit bistable switching behavior in electric fields. Ferroelectric switching was demonstrated for block copolymers with volume fractions of 0.58 and 0.52 liquid crystal block. SAXS and TEM showed that the bulk morphologies of these two materials were hexagonally packed minority amorphous polystyrene (PS) cylinders and alternating lamellar amorphous PS layers, respectively. Cross-sectional TEM of a 10 µm thick film of the 0.58 volume fraction liquid crystal material used for the optical switching studies showed the cylinders to be well aligned along the shear direction and orthogonal to the applied electric field direction. It is believed that switching is possible due to an unwinding of the pitch of the smectic C* phase due to the presence of the intermaterial dividing surface of the microphase-separated cylindrical domains of the block copolymer which spatially confine the mesophase. This interaction realizes the concept of a microphasestabilized ferroelectric liquid crystal (MSFLC) device.