Shape-memory effect controlled by the crosslinking topology in uniaxially-deformed smectic C* elastomers

摘要

We have investigated the shape-memory effects of uniaxially-deformed, chiral, smectic C (SmC*) elastomers for two different types of crosslinker, namely, a hydroquinone-type crosslinker and a rod-like crosslinker. Mesogens tilt with decreasing temperature from the SmA phase to the SmC* phase in SmC* elastomers synthesized with the hydroquinone-type crosslinker. As for SmC* elastomers with the rod-like crosslinker, however, not mesogens but smectic layers are tilted in the smectic phases, because the crosslinker is sufficiently rigid to hinder mesogens from tilting. Because the shape change of such elastomers is coupled to the transformation of molecular alignment, SmC* elastomers synthesized with the hydroquinone-type crosslinker elongate with increasing temperature in SmC* because of the decrease in molecular-tilt angle, whereas those with the rod-like crosslinker have an almost constant sample length in the temperature range of the SmC* phase, despite the rearrangement of the layer structure. Both types of elastomer exhibit a reversible shape change that corresponds to the reversible change in molecular alignment during a heating and cooling process, within successive phase transitions between the isotropic phase and the smectic C* phase. GRAPHICS