Review of Thermoresponsive Electroactive and Magnetoactive Shape Memory Polymer Nanocomposites

Abstract

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.

Figure 1

Illustration of the stress vs strain curve of a SMM during two conventional consecutive shape memory cycles performed under uniaxial tension. The marked strain levels ε₀, ε_p, ε_f, and are used to calculate the shape fixity and shape recovery ratios.

Figure 2

Illustration of the most common shape memory behaviors of SMMs: (a) one-way shape memory effect; (b) two-way shape memory effect; (c) multiple shape memory effect.

Figure 3

Main existing conductive and magnetic nanofillers reported in the literature to conform electro- and magnetoactive shape memory polymer composites.

Figure 4

Relationship between the shape recovery ratio and the shape fixity ratio of a SMC with different concentrations (in phr) of CBs or CNTs (reproduced with permission from ref (87); published by MDPI, 2022.)

Figure 5

Stripe of a shape memory nanocomposite of polyurethane with different numbers of printed carbon nanotube layers along its length and the resulting temperature distribution due to resistive heating (reprinted from ref (99) with permission of Elsevier.)

Figure 6

Evolution of the Green–Lagrange strain in the loading direction (ε_yy in red) and of the instantaneous electrical resistivity (ρ_e in black) with temperature of an SMP of polycaprolactone with 3 wt % MWCNTs. The test was performed at a constant stress of 600 kPa in order to study the 2W-SM cycle.

Figure 7

Sequential shape recovery due to selective resistive heating of a shape memory composite stripe. Three electrodes are painted on the surface of the SMC and are located on the right and left tips and another in between. The regions that heat up depend on which electrodes are used for injecting the electric current. During the first 10 min the current is injected between the central and left electrodes and during the last 10 min between the central and right electrodes (reprinted from ref (102), with permission of Elsevier.)

Figure 8

Illustration of the five shape recovery routes that can be followed from temporary Shape #1 to the permanent flat shape of a SMC with three different regions: CNT-SMP that can be activated with inductive heating at 13.56 MHz, neat SMP that can be activated with conventional heating, and Fe₃O₄-SMP that can be activated with inductive heating at 256 kHz. (Reproduced from ref (137) with permission of John Wiley and Sons. Copyright 2011 Wiley-VCH.)

Figure 9

Principle of operation of a multishape magnetosensitive SMC with embedded NdFeB and Fe₃O₄ particles. (a) Illustration of magnetization and composition. (b) The SMC is heated by the application of a high-frequency AC magnetic field B_h above the glass transition of the SMP. Deformation and actuation can be achieved by a DC (or low-frequency AC) magnetic field B_a. (c) Shape fixity can be achieved by removing B_h while keeping the desired B_a. (Reproduced from ref (141), with permission of John Wiley and Sons. Copyright 2019 Wiley-VCH.)

Figure 10

4D printed poly(lactic acid) SMP with embedded Fe₃O₄ composites actuated by a magnetic field for the conception of (a) tracheal scaffolds (reprinted from ref (156), with permission from Elsevier) and (b) porous bone tissue scaffolds (reprinted from ref (158). with permission from Elsevier.)

Figure 11

Illustration of the treatment of aneurysms by filling them with a SMC. (a) Compressed SMC foam being placed in a saccular aneurysm via a catheter. (b) Recovered expanded shape of the SMC filling the aneurysm space. Demonstration of the prototype for the treatment of aneurysms of a SMC with 1 wt % CNTs at (c) 0 s, (d) 30 s, and (e) 60 s after the injection of an electric current (1 A). (Reproduced from ref (162) with permission of John Wiley and Sons. Copyright 2021 Wiley-VCH).

Figure 12

(a) Wing of an unmanned aerial vehicle with a morphing flap at the trailing edge capable of changing the deformation angle between (b) 39° and (c) 32°. The actuation mechanism is through resistive heating of both the SMA wires and the SMP–nichrome composite. (Reprinted from ref (165), with permission from Elsevier.)

Figure 13

(a) Photographs and (b) IR thermal images of the SMC electroactive gripper. (Adapted with permission from ref (48). Copyright 2019 American Chemical Society.)