Sequential and selective shape memory by remote electrical control

Development of an Electroactive and Thermo-Reversible Diels-Alder Epoxy Nanocomposite Doped with Carbon Nanotubes

The manufacturing of Diels-Alder (D-A) crosslinked epoxy nanocomposites is an emerging field with several challenges to overcome: the synthesis is complex due to side reactions, the mechanical properties are hindered by the brittleness of these bonds, and the content of carbon nanotubes (CNT) added to achieve electroactivity is much higher than the percolation thresholds of other conventional resins. In this work, we develop nanocomposites with different D-A crosslinking ratios (0, 0.6, and 1.0) and CNT contents (0.1, 0.3, 0.5, 0.7, and 0.9 wt.%), achieving a simplified route and avoiding the use of solvents and side reactions by selecting a two-step curing method (100 °C-6 h + 60 °C-12 h) that generates the thermo-reversible resins. These reversible nanocomposites show ohmic behavior and effective Joule heating, reaching the dissociation temperatures of the D-A bonds. The fully reversible nanocomposites (ratio 1.0) present more homogeneous CNT dispersion compared to the partially reversible nanocomposites (ratio 0.6), showing higher electrical conductivity, as well as higher brittleness. For this study, the nanocomposite with a partially reversible matrix (ratio 0.6) doped with 0.7 CNT wt.% was selected to allow us to study its new smart functionalities and performance due to its reversible network by analyzing self-healing and thermoforming.

A Multiple Remotely Controlled Platform from Recyclable Polyurethane Composite Network with Shape-Memory Effect and Self-Healing Ability

Stimuli-responsive materials can transform from temporary to permanent shapes by specific external triggers. However, the damage might inevitably occur to them when exposed to complex environments, causing a significant reduction in their lifetime and quality. In this study, recyclable remotely controlled shape-changing polyurethane composite with self-healing compacity is developed from polyethylene glycol, polytetrahydrofuran diol using isophorone diisocyanate as crosslinker. After the incorporation of magnetite nanoparticles (MNPs), remote heating could be generated by near-infrared irradiation and alternating magnetic fields. The results show that MNPs are uniformly distributed in the smart networks, resulting in tunable temperature changes of the polymer composite material under various direct/indirect triggering in bending experiments, presenting different shape recovery rates. Moreover, to enhance the self-healing capability, a disulfide bond is introduced into the polymer networks, and the results show that highly efficient and rapid healing could be achieved from tensile tests, scanning electron microscopy as well as optical microscopy. Additionally, the synergistic effect of transesterification and the dynamic exchange of disulfide bonds brin the networks reproducibility for recycling use. The obtained material is promising to be an alternative material for soft robots and smart sensors.

Review of Thermoresponsive Electroactive and Magnetoactive Shape Memory Polymer Nanocomposites

Electroactive and magnetoactive shape memory polymer nanocomposites (SMCs) are multistimuli-responsive smart materials that are of great interest in many research and industrial fields. In addition to thermoresponsive shape memory polymers, SMCs include nanofillers with suitable electric and/or magnetic properties that allow for alternative and remote methods of shape memory activation. This review discusses the state of the art on these electro- and magnetoactive SMCs and summarizes recently published investigations, together with relevant applications in several fields. Special attention is paid to the shape memory characteristics (shape fixity and shape recovery or recovery force) of these materials, as well as to the magnitude of the electric and magnetic fields required to trigger the shape memory characteristics.