Recent Advance in Liquid Crystalline Elastomers

Abstract

This short review describes the most recent advances in the study on liquid crystalline elastomers (LCE). Concise description on liquid cryatals and liquid crystalline polymers is also given. LCE exhibits liquid crystalline state that resembles to its precursor in the uncrosslinked state. Within the mesophase range of temperature, elastic properties of LCE are different from conventional elastomers in the sense that they are energetic in nature. This is due to the partially ordered alignment of the mesogens. It was noted, however, that the optical anisotropy remained even far above clearing temperature (Ta), up to T~ + 30°C, if the specimen was under stress. Volume change of LCE with applied field is also interesting. This phenomenon leads to a high tendency of using cholestric or smectic C* LCE as a piezoelectric sensor because of the flexibility and the shape stability. Recently, mesogenic units were introduced both in the main chain and at the side groups, and the polymer was named combined main chain/side group liquid crystalline polymer6) .The main objective of this paper is to review the studies on liquid crystalline elastomers which have been conducted so far. Elastomers in this article mean crosslinked polymers which show elastomeric properties at certain conditions. Only thermotropic class of liquid crystalline materials will be considered here, because the authors assume they have higher possibility in technological applications. Uncrosslinked polysiloxanes which are quite often considered as elastomers with some reasons7~ 9) and crosslinked lyotropic liquid crystalline polymers1o~11) will not be main concerns in this review. (44)

Physically crosslinked elastomers prepared from oligomeric polyolefins with mesogenic units

“…LC polymer with threedimensional network structure is an alternative type of LC polymers. 8,9 For polymeric materials with high modulus and high strength at break, the main chain type LC polymer of linear architecture has been focused. Namely, a variety of thermoplastic main chain polymers such as polyesters, polycarbonates, polyesteramides, and polyurethanes have been studied extensively.…”