Crosslinking Topology and Chain Anisotropy of Smectic Liquid-Crystalline Elastomers

We have investigated the molecular mechanism of the spontaneous and reversible deformation of smectic elastomers during the isotropic-to-smectic phase transformation, by observing the shape change as well as an X-ray image of the elastomers for two different types of crosslinker, namely, a rod-like crosslinker and a hydroquinone-type crosslinker. The elastomer crosslinked by the rod-like crosslinker exhibits elongation corresponding to the change in the order parameter S during the isotropic-to-smectic phase transformation. As for another elastomer crosslinked by the hydroquinone-type crosslinker, which is too flexible to work as mesogen, the shape change is weakly coupled with the orientational order of mesogens. We conclude that the crosslinking topology attributed to the chemical constitution of the crosslinker predominantly controls the chain anisotropy of polymer network as well as the deformation behavior of smectic elastomers during the isotropic-to-smectic phase transformation. (C) 2009 The Japan Society of Applied Physics