Remotely actuated polymer nanocomposites—stress-recovery of carbon-nanotube-filled thermoplastic elastomers

Abstract

Stimuli-responsive (active) materials undergo large-scale shape or property changes in response to an external stimulus such as stress, temperature, light or pH. Technological uses range from durable, shape-recovery eye-glass frames, to temperature-sensitive switches, to the generation of stress to induce mechanical motion. Here, we demonstrate that the uniform dispersion of 1-5 vol.% of carbon nanotubes in a thermoplastic elastomer yields nanocomposites that can store and subsequently release, through remote means, up to 50% more recovery stress than the pristine resin. The anisotropic nanotubes increase the rubbery modulus by a factor of 2 to 5 (for 1-5 vol.%) and improve shape fixity by enhancing strain-induced crystallization. Non-radiative decay of infrared photons absorbed by the nanotubes raises the internal temperature, melting strain-induced polymer crystallites (which act as physical crosslinks that secure the deformed shape) and remotely trigger the release of the stored strain energy. Comparable effects occur for electrically induced actuation associated with Joule heating of the matrix when a current is passed through the conductive percolative network of the nanotubes within the resin. This unique combination of properties, directly arising from the nanocomposite morphology, demonstrates new opportunities for the design and fabrication of stimuli-responsive polymers, which are otherwise not available in one material system.

Development of stiff, strong, yet tough composites by the addition of solvent exfoliated graphene to polyurethane

“…In the PU films, we observed a single peak at ~25 o C. A number of researchers have associated this peak with melting of soft segment crystallites. [32][33][34][35][36][37][38] For both solvents, we see the reduction in intensity of this peak as graphene content is increased until by 30wt% no SS crystallites are observable. This strongly suggests that the presence of graphene somehow impedes the formation of soft segment crystallites.…”

Polymer nanocomposites

“…19 Additionally, using weakly interacting rod-like nanoparticles in an elastomeric or thermosetting matrix leads to the possibility of forming interpenetrating polymeric network with highly disparate mechanical properties that are hitherto unanticipated based on traditional polymeric interpenetrating networks. 25 While significant challenges still remain in predicting the dispersion of nanoparticles in single component polymeric matrices, 26 the ability to disperse nanoparticles in multicomponent polymeric matrices, especially to direct them to specific phases or to the interface between phaseseparated structures, promises even greater opportunities. Experimental and theoretical efforts are only just beginning.…”

Initiation of shape-memory effect by inductive heating of magnetic nanoparticles in thermoplastic polymers

“…Another example for shape-memory polymers with T trans being a T m are block copolymers from poly(ethylene terephthalate) and poly(ethylene oxide) (5). Compounds from shape-memory polymers and inorganic particles, including SiC particles (6, 7), carbon black (8,9), and nanotubes (10,11), were prepared. The incorporation of particles leads to enhanced mechanical properties (6,8) or electric conductivity (7,9).…”