Controlled Actuation of a Carbon Nanotube/Epoxy Shape-Memory Liquid Crystalline Elastomer

Thermally induced shape-memory polymers are materials based on exploiting one or more phase transitions, such as glass, melting, or clearing transition, to trigger a shape-memory effect. Among shape-memory polymers, liquid crystalline elastomers are considered as very interesting candidates, thanks to the synergistic effect of the ordered liquid crystalline phase and the polymeric network on their programming and recovering behavior. Here, the synthesis of new shape-memory smectic epoxy-based elastomers incorporating multiwalled carbon nanotubes is reported. The realized materials show two types of shape-memory behavior that can be selectively actuated by choosing the appropriate thermal recovery conditions. The surface modification of the nanotubes enables a dramatic enhancement of the actuation extent at low nanofiller content. Moreover, the stress threshold required to trigger the reversible thermomechanical actuation is significantly decreased. The effect of nanotubes on thermomechanical properties of the materials is elucidated and correlated to the microstructure and phase behavior of the host system. Results demonstrate that the incorporation of multiwalled carbon nanotubes amplifies the soft-elastic response of the liquid crystalline phase to external stimuli. Tunable thermomechanical properties of these systems make them potentially suitable for a variety of applications ranging to robotics, sensing and actuation, and artificial muscles.