Spontaneous deformation of main-chain liquid-crystalline elastomers composed of smectic polyesters

Abstract

We observe the spontaneous shape change of a uniaxially deformed liquid-crystalline elastomer composed of smectic main-chain liquid-crystalline polyesters in a cyclic heating–cooling process. Although the elastomer contracts by about 115% on heating up to the isotropic phase, the sample length recovers by 55% on cooling to room temperature in the first heating–cooling process, and the elastomer exhibits an almost complete reversible deformation in the second heating–cooling process. By a comparison of the results of sample observation with those of X-ray analysis, we recognise that the strain λ was linearly coupled with the orientational order parameter S. In addition, the results of the X-ray analysis imply that a cybotactic nematic state, in which smectic clusters lie scattered in a nematic-like matrix, emerges after exposure to the isotropic phase.

Keywords:

• cybotactic nematics
• elastomers
• liquid-crystalline elastomers
• liquid-crystalline polymers
• polymer networks
• shape memory
• smectic clusters
• smectic liquid crystals

Acknowledgements

KH wishes to acknowledge valuable discussions with Dr Anke Hoffmann and Professor Dr Heino Finkelmann at ISMASM held at Awaji Island. We thank Dr Kensuke Osada for his advice about the synthesis of BB-n networks. We also thank Yasufumi Oka, Yuta Kato, Takehiro Nakamura and Ayumu Sagano for their experimental assistance. This work was supported by a Grant-in-Aid for Scientific Research (C) (#20550167) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), and also partially supported by the ‘Academic Frontier Project’ for private universities (2006–2008): matching fund subsidy from MEXT.