Shape-memory polymer nanocomposites with a 3D conductive network for bidirectional actuation

Electrical stimulation has many advantages than thermal methods for shape-memory polymers (SMPs); the bulk polymers is essential for developing high performance electroactive systems and creating an efficient conductive path^1-3 . Here, we show that a three-dimensional (3D) porous carbon nanotube sponge can serve as a built-in integral conductive network to provide internal, homogeneous, in situ Joule heating for shape-memory polymers, thus significantly improving the mechanical and thermal behavior of SMPs. As a result, the 3D nanocomposites show a fast response and produce large exerting forces during shape recovery. We further studied the construction of a double-layer composite structure for bidirectional actuation, in which the shape change is dominated by the temperature-dependent exerting force from the top and bottom layer. Our large stroke shape-memory nanocomposites have promising applications in many areas including artificial muscles and bionic robots^4-5.