Shape Memory Function Research Articles

Magnetic coercivity control by heat treatment in Heusler Ni–Mn–Ga(–B) single crystals

The combination of enlarged magnetic coercivity and magnetic shape memory (MSM) functionality is essential for novel magnetomechanical effects in MSM alloys. We found that increasing the density of thermal antiphase boundaries (APBs) provides a method to increase the magnetic coercivity without deteriorating the MSM functionality. APB density was controlled by different heat treatments in Ni–Mn–Ga (–B) MSM single crystals with five-layered modulated martensite structure. Slow cooling ∼1 K/min of Ni–Mn–Ga through the B2′–L21 transition resulted in a low density (<1/micrometer) of APBs observed by magnetic force microscopy and low coercivity <2 mT. Water quenching resulted in fine magnetic and APB patterns and enlarged the coercivity to 24 mT at room temperature, and this further increased with decreasing temperature up to 41 mT at 10 K. The analysis of magnetization approach to saturation indicated the antiferromagnetic character of APBs on which the magnetic domain walls were pinned. Despite the one to two order increase of coercivity, the twinning stress remained low, between 0.7 and 1.4 MPa, and about 6% MSM effect was observed. The best ratio between coercivity and twinning stress (17 mT/0.7 MPa) was obtained for the sample quenched in air. Contrary to previous reports, 100 ppm B doping of Ni–Mn–Ga had no or weak effect on the magnetic coercivity. Instead, the major effect originated from the high density of antiphase boundaries.

Thermally and Near-Infrared Light-Induced Shape Memory Polymers Capable of Healing Mechanical Damage and Fatigued Shape Memory Function.

The fabrication of shape memory polymers that are mechanically robust and capable of being induced by near-infrared (NIR) light and healing mechanical damage and the fatigued shape memory function remains a challenge. In this study, thermally and NIR-light-induced shape memory polymers with self-healing ability and satisfactory mechanical robustness are fabricated by dispersing poly(acrylic acid) (PAA)-grafted graphene oxide (GO) (PAA-GO) into poly(vinyl alcohol) (PVA) matrix. The PVA/PAA-GO3% films with a PAA-GO content of 3.0 wt % have a fracture stress of ∼70.4 MPa and a Young's modulus of ∼2.8 GPa. The PVA/PAA-GO3% films exhibit an excellent shape memory performance because PVA and PAA-GO form a stable network through hydrogen-bonding interaction between them. Meanwhile, the PVA/PAA-GO3% films are capable of recovering from temporary shape to permanent shape under NIR light irradiation because of excellent photothermal conversion property of the GO nanosheets. More importantly, benefiting from the reversibility of hydrogen-bonding interactions between PVA and PAA-GO nanosheets, the shape memory PVA/PAA-GO3% films are capable of healing physical damage and the fatigued shape memory function with the assistance of water, which greatly enhance their reliability as shape memory materials and prolong their service life.

Beyond the strain recoverability of martensitic transformation in NiTi

Tensile deformation of a medical grade NiTi wire was investigated in a wide temperature range from −100 °C to 450 °C. Supplemental in-situ electrical resistance, synchrotron x-ray diffraction, digital image correlation and ex-situ TEM methods were employed to characterize deformation/transformation processes acting at high temperatures and stresses. Conventional superelastic deformation due to stress induced martensitic transformation taking place around room temperature becomes gradually accompanied by dislocation slip in the temperature range 30–80 °C. With further increasing temperature, stress induced martensitic transformation still proceeds in localized manner but the length of the forward stress plateau increases, volume fraction of the martensite phase at the end of forward stress plateau decreases, unrecovered strain increases and {114} austenite twins appeared in the microstructure of deformed wires. These observations were explained by the activity of a new deformation mechanism - stress induced B2=>B19´=>B2T martensitic transformation into twinned austenite coupled with dislocation slip. Thermodynamic and crystallographic aspects of this B2=>B19´=>B2T martensitic transformation breaking the strain recoverability limit of cubic to monoclinic martensitic transformation were outlined. To rationalize the observed thermomechanical responses of the wire at elevated temperatures, a TRIP like deformation mechanism based on this transformation was incorporated into an existing constitutive model of thermomechanical behaviors of NiTi. The model was numerically implemented into finite element code, simulations were performed and compared with the experimentally observed behaviors. It was found that the B2=>B19´=>B2T martensitic transformation destroys the shape memory functionality of NiTi but renders it excellent ductility in thermomechanical loads, introduces nanoscale heterogeneity into its austenitic microstructure and allows for its low temperature processing and shape setting.

Reprogrammable recovery and actuation behaviour of shape-memory polymers

Shape memory is the capability of a material to be deformed and fixed into a temporary shape. Recovery of the original shape can then be triggered only by an external stimulus. Shape-memory polymers are highly deformable materials that can be programmed to recover a memorized shape in response to a variety of environmental and spatially localized stimuli as a one-way effect. The shape-memory function can also be generated as a reversible effect enabling actuation behaviour through macroscale deformation and processing, specifically by dictating the macromolecular orientation of actuation units and of the skeleton structure of geometry-determining units in the polymers. Shape-memory polymers can be programmed and reprogrammed into arbitrary shapes. Both recovery and actuation behaviour are reprogrammable. In this Review, we outline the common basis and key differences between the two shape-memory behaviours of polymers in terms of mechanism, fabrication schemes and characterization methods. We discuss which combination of macromolecular architecture and macroscale processing is necessary for coordinated, decentralized and responsive physical behaviour. The extraction of relevant thermomechanical information is described, and design criteria are shown for microscale and macroscale morphologies to gain high levels of recovered or actuation strains as well as on-demand 2D-to-3D shape transformations. Finally, real-world applications and key future challenges are highlighted. Shape-memory materials can generate programmable movements triggered by an external stimulus, such as an environmental change. In this Review, the authors discuss mechanisms, fabrication schemes, characterization methods and applications of the one-way shape-memory effect enabling shape recovery and of reversible shape-memory effects exhibiting actuation behaviour.

Processability of 4D printable modified polycaprolactone with self-healing abilities

Shape memory polymers (SMPs) with their responsive nature are good candidates for the field of sensors and actuators, in particular for soft robotics. To enhance their durability and mimic natural tissues, self-repairing properties are required. The 4D printing of shape memory polymers has already been demonstrated but the coupling with the self-healing behavior was recently presented. The aim of this work was to study the processability of a SMP with thermally induced healing abilities by digital light projection (DLP) technology to obtain 4D printed smart objects. Polycaprolactone (PCL) was co-crosslinked with 2-ureido-4[1H]-pyrimidinone (UPy) units in this newly prepared material showing shape memory and self-healing functionalities, both thermally triggered. To verify the possibility to 4D print the reactive mixture, a rheological characterization was carried out. Printed PCL/UPy-based objects showed a stiffness similar to pure PCL-based ones, and healing properties comparable to cast specimens. Tensile characterization was performed to confirm the suitability of this material for the soft robotic field. This potential application was also supported by the printing and damaging of an opposing thumb: shape memory functionalities were still preserved after healing, making these printed actuators suitable for the production of components for human-machine interactions

Magnetic Coercivity Control by Heat Treatment in Heusler Ni-Mn-Ga(-B) Single Crystals

The combination of enlarged magnetic coercivity and magnetic shape memory (MSM) functionality is essential for novel magnetomechanical effects in MSM alloys. We found that increasing the density of thermal antiphase boundaries (APBs) provides a method to increase the magnetic coercivity without deteriorating the MSM functionality. APB density was controlled by different heat treatments in Ni-Mn-Ga(-B) MSM single crystals with five-layered modulated martensite structure. Slow cooling ~1 K/min of Ni-Mn-Ga through the B2'-L21 transition resulted in a low density (<1/micrometer) of APBs observed by magnetic force microscopy and low coercivity <2 mT. Water quenching resulted in fine magnetic and APB patterns and enlarged the coercivity to 24 mT at room temperature, and this further increased with decreasing temperature up to 41 mT at 10 K. The analysis of magnetization approach to saturation indicated the antiferromagnetic character of APBs on which the magnetic domain walls were pinned. Despite the one to two order increase of coercivity, the twinning stress remained low, between 0.7 to 1.4 MPa, and about 6% MSM effect was observed. The best ratio between coercivity and twinning stress (17 mT / 0.7 MPa) was obtained for the sample quenched in air. Contrary to previous reports, 100 ppm B doping of Ni-Mn-Ga had no or weak effect on the magnetic coercivity. Instead, the major effect originated from the high density of antiphase boundaries.

High‐Strain Shape Memory Behavior of PLA–PEG Multiblock Copolymers and Its Microstructural Origin

ABSTRACTShape memory properties of two thermoplastic multiblock copolymers composed of poly(lactic acid) (PLA) and poly(ethylene glycol) (PEG) having different PEG‐segment lengths of 6 and 11 kDa were studied. The performance as a shape memory polymer at high strain level (600%) and its interrelations with shape‐programming conditions, molecular orientation, and microstructural changes are elucidated. A significant contribution of strain‐induced crystallization of PLA segments to the improvement of temporary shape fixation was evidenced upon increasing draw ratio and/or shape‐holding duration as well as programming temperature (within certain range) without largely sacrificing the shape recoverability. Series of microstructural characterizations reveal the occurrence of fibrillar‐to‐lamellar transformation upon shape recovery (at 60 °C) of the samples programmed at 40 °C, generating shish–kebab crystalline morphology. Such phenomenon is responsible for the high‐strain shape memory effect of these materials. The unprecedented formation of shish–kebab structure at such relatively low temperature (instead of the melting temperature range) in solid state observed in these copolymers as well as their high‐strain shape memory functionality would bestow the promising future for their practicability in diverse areas. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 241–256

Multi-triggered Supramolecular DNA/Bipyridinium Dithienylethene Hydrogels Driven by Light, Redox, and Chemical Stimuli for Shape-Memory and Self-Healing Applications.

Multi-triggered DNA/bipyridinium dithienylethene (DTE) hybrid carboxymethyl cellulose (CMC)-based hydrogels are introduced. DTE exhibits cyclic and reversible photoisomerization properties, switching between the closed state (DTEc), the electron acceptor, and the open isomer (DTEo) that lacks electron acceptor properties. Onesystem introduces a dual stimuli-responsive hydrogel containing CMC chains modified with electron donor dopamine sites and self-complementary nucleic acids. In the presence of DTEc and the CMC scaffold, a stiff hydrogel is formed, cooperatively stabilized by dopamine/DTEc donor-acceptor interactions and by duplex nucleic acids. The cyclic and reversible formation and dissociation of the supramolecular donor-acceptor interactions, through light-induced photoisomerization of DTE, or via oxidation and subsequent reduction of the dopamine sites, leads to hydrogels of switchable stiffness. Another system introduces a stimuli-responsive hydrogel triggered by one of three alternative signals. The stiff, multi-triggered hydrogel consists of CMC chains cross-linked bydopamine/DTEc donor-acceptor interactions, and by supramolecular K+-stabilized G-quadruplexes. The G-quadruplexes are reversibly separatedin the presence of 18-crown-6 ether and reformed upon the addition of K+. The stiff hydrogel undergoes reversible transitions between high-stiffness and low-stiffness states triggered by light, redox agents, or K+/crown ether. The hybrid donor-acceptor/G-quadruplex cross-linked hydrogel shows shape-memory and self-healing features. By using three different triggers and two alternative memory-codes, e.g., the dopamine/DTEc or the K+-stabilized G-quadruplexes, the guided shape-memoryfunctionof the hydrogel matrices is demonstrated.

Near-infrared light triggered shape memory and self-healable polyurethane/functionalized graphene oxide composites containing diselenide bonds

In this work, polyurethane/functionalized graphene oxide composites containing diselenide bonds were fabricated by covalently incorporating functionalized graphene oxide (FGO) into hydroxyl-terminated polyurethane prepolymers via in-situ polymerization. It was found that the isocyanate terminated molecules were covalently attached onto the graphene oxide surface, and the FGO could act as a multifunctional reinforcer in mechanical and photo-thermal properties of polyurethane composites. Significant enhancements of mechanical, thermal transport, and crystallization performances of composites were observed with the incorporation of 2 wt% of FGO. Due to the photo-thermal and crystallization-induced effects of FGO as well as the exchangeable characteristic of diselenide bonds, the PID-FGO2 composite exhibited both shape memory and repeatable self-healing functions upon exposure to near infrared (NIR) irradiation. In particular, the introduction of diselenide bonds could greatly improve the healing efficiency from ∼45% to ∼90%, and the healing efficiencies were maintained above 75% even after five healing cycles. Such favorable healing is acquired by the photo-thermal response, shape memory effect, and diselenide exchange reaction simultaneously, and the shape memory effect is of great importance for assisting the healing process. We expect that this work could provide a viable avenue for multifunctional composite materials.

Rapid floating zone growth of Ni2MnGa single crystals exhibiting magnetic shape memory functionality

To obtain a material exhibiting magnetically induced reorientation (MIR), one of the magnetic shape memory effects, a well-developed method for single crystal growth is crucial. A [100] oriented Ni2MnGa single crystal exhibiting MIR was successfully prepared using the floating-zone technique with a high speed of 80 mm/h. The comparison with a sample grown by Bridgman method and a reference sample grown in AdaptaMat Ltd. by directional solidification is provided based on elemental homogeneity, crystallographic quality by x-ray diffraction, transformation behaviour and magnetic properties. All these methods indicated that the single crystal grown by floating zone with high speed is comparable or superior to the samples prepared by other methods. Importantly, the magnetization measurement revealed that the single crystal prepared this way exhibits MIR down to 10 K.

A novel low colored and transparent shape memory copolyimide and its durability in space thermal cycling environments

Recently, shape memory polymers (SMPs) with high optical transmittance have been paid great attentions to endow the flexible optoelectronics with shape memory functions. Herein, a low colored and transparent shape memory copolyimide (SMcoPI) is obtained by suppressing the charge transfer complex interactions. The optical transmittance of the synthesized SMcoPI film could reach at ∼86% at the wavelength of 450 nm, far higher than the nearly zero optical transmittance of yellow and brown Kapton H. The better optical transparency could be attributed to the loose molecular chain arrangements induced by the meta-substituted groups and flexible ether linkages. The glass transition temperature (Tg) range of the synthesized SMcoPI films is from 179 °C to 220 °C, which is higher than that of reported optically transparent SMPs. The effective decomposition temperature at the weight loss of 5 wt% is 517 °C, showing excellent thermal stability. The SMcoPI also demonstrated good shape memory behaviors with high shape recovery ratio (Rr, >96%) and shape fixity ratio (Rf, >97%). In addition, the SMcoPI could maintain high optical transmittance, good thermostability and excellent shape memory behaviors after the ground-stimulated space thermal cycling test for 250 h. The synthesized SMcoPI has application potentials in high temperature areas or optoelectronic devices.

The role of bimodal grain size distribution in nanocrystalline shape memory alloys

We report on a phase field simulation study of the effects of grain size and grain size distribution on martensitic transformations in shape memory alloys (SMAs). Recent experimental studies of polycrystalline SMAs revealed interesting grain size effects when grain sizes are reduced to tens of nanometers. While small grain sizes yield superior mechanical strength, the material loses its shape memory property if grain sizes are smaller than some critical size. To reintroduce shape memory properties, and at the same time retain strong mechanical properties, we propose to introduce several large grains (much larger than the critical transformation grain size) amid the nano-sized grains, which yields a grain microstructure with a bimodal grain size distribution. A phase field model is adopted to simulate the martensitic transformation in polycrystals, to which excess grain boundary energy is introduced that suppresses martensitic transformation in the grain boundaries. We observe that simulated as-quenched microstructures of the bimodal grain size distribution may in a special case equilibrate as a phase composite (austenite + martensite). The spatial distribution of these phases and alloy functionalities (shape memory) may be controlled by the design of the grain size distribution. Loading and unloading simulations of the equilibrium martensitic microstructures show that the large grains enable martensitic detwinning to occur, hence reintroducing shape memory functionality to the nanocrystalline SMA.

Thermo-Mechanical Properties of Glass Fiber Reinforced Shape Memory Polyurethane for Orthodontic Application.

Glass fiber reinforced shape memory polyurethane (GFRSMPU) has great potential to be an alternative kind of material for orthodontic archwires for overcoming the disadvantages of metal wires in terms of esthetic and allergy and deficiency of pure shape memory polyurethane (SMPU) wires in mechanical properties. The objective of this study was to investigate the thermo-mechanical properties and shape recovery functions of GFRSMPU and evaluate the feasibility of using this composite for orthodontic archwires. GFRSMPU were made from short cut glass fibers and SMPU by mixing extrusion. Scanning electron microscope (SEM) and differential scanning calorimetry (DSC) were performed to investigate the distribution of glass fibers in the mixture and glass transition temperature (Tg). Then the thermo-mechanical properties, including tensile modulus, flexural modulus and stress relaxation effects, were measured. Furthermore, shape recovery functions of GFRSMPU characterized by the shape recovery ratio and force were investigated through shape recovery tests, typodont models and finite element analysis (FEA). SEM images indicated that an excellent dispersity of glass fibers was obtained after double-extrusion. DSC experiments showed Tg was not enormously affected with the existence of glass fibers, but the mechanical properties of GFRSMPU were greatly improved. Shape recovery tests showed reduction of shape recovery ratio of the GFRSMPU material with the addition of glass fibers, but dentition aligning time was reduced by 50% in the simulation performed on identical typodont models with GFRSMPU archwires filled with 30 wt.% glass fibers. The FEA results illustrated that the reacting forces of GFRSMPU archwires with 30 wt.% glass fiber was increased by 96.36% compared with pure SMPU archwires. The mechanical properties of GFRSMPU can be considerably improved by adding glass fibers, and the shape memory function would be well preserved too. Enhanced SMPU owns a good application prospect in orthodontics for dentation aligning on the preliminary stage, as well as other medical fields.

A UV-curable epoxy with “soft” segments for 3D-printable shape-memory materials

Three-dimensional (3D)-printable shape-memory polymers (SMPs) are of great interest for making advanced shape-memory materials. However, it has been challenging to combine 3D-printable capability with shape-memory function into one material. Here, we report a UV-curable epoxy with excellent shape-memory performance and improved toughness as compared with traditional epoxy counterpart. The epoxy system is realized by cross-linking epoxy resin diglycidyl ether of bisphenol F (DGEBF) (“hard” segments) with toughening agent 3-ethyl-3-oxetanemethanol (TMPO) (“soft” segments), which finally creates a three-dimensional network with TMPO-co-DGEBF block structures. The fold-deploy tests show that the shape fixity ratio (Rf) and the shape recovery ratio (Rr) of the epoxy with 50 wt% TMPO soft segment are above 97 and 99% even after 20 cycles of testing, respectively. In addition to bringing shape-memory performance, the toughness of the epoxy system is notably improved by the TMPO soft segments. This study provides a very promising epoxy system for 3D-printable shape-memory materials.

4D printing of net shape parts made from Ni-Mn-Ga magnetic shape-memory alloys

This work investigates an additive manufacturing route of producing functional net shaped parts from pre-alloyed magnetic shape-memory Ni-Mn-Ga powders. Three types of Ni-Mn-Ga powders were used in this investigation: spark eroded in liquid nitrogen (LN2), spark eroded in liquid argon (LAr), and ball milled (BM). Additive manufacturing via powder bed binder jetting, also known as 3D printing (3DP), was used in this research due to both relatively easy control of part porosity and the possibility to obtain complex shaped parts from Ni-Mn-Ga alloys. The four-dimension (4D) is created by the predictable change in 3D printed part configuration over time as the result of shape-memory functionality. Binder jetting of Ni-Mn-Ga powders followed by curing and sintering proved successful in producing net shaped porous structures (spring-like, 3-D hierarchical lattice structures, etc.) with good mechanical strength. Parts with porosities between 24.08% and 73.43% have been obtained by using powders with distinct morphologies. The printed Ni-Mn-Ga parts undergo reversible martensitic transformation during heating and cooling, which is a prerequisite for the shape-memory behavior. Thermo-magneto-mechanical trained 3D printed parts obtained from ball milled Ni-Mn-Ga powders showed reversible magnetic-field-induced strains (MFISs) of up to 0.01%. The additive manufacturing is a viable technology in solving the design issues of functional parts made of Ni-Mn-Ga magnetic shape-memory alloys (MSMA).

Entanglement-Based Thermoplastic Shape Memory Polymeric Particles with Photothermal Actuation for Biomedical Applications.

Triggering shape-memory functionality under clinical hyperthermia temperatures could enable the control and actuation of shape-memory systems in clinical practice. For this purpose, we developed light-inducible shape-memory microparticles composed of a poly(d,l-lactic acid) (PDLLA) matrix encapsulating gold nanoparticles (Au@PDLLA hybrid microparticles). This shape-memory polymeric system for the first time demonstrates the capability of maintaining an anisotropic shape at body temperature with triggered shape-memory effect back to a spherical shape at a narrow temperature range above body temperature with a proper shape recovery speed (37 < T < 45 °C). We applied a modified film-stretching processing method with carefully controlled stretching temperature to enable shape memory and anisotropy in these micron-sized particles. Accordingly, we achieved purely entanglement-based shape-memory response without chemical cross-links in the miniaturized shape-memory system. Furthermore, these shape-memory microparticles exhibited light-induced spatiotemporal control of their shape recovery using a laser to trigger the photothermal heating of doped gold nanoparticles. This shape-memory system is composed of biocompatible components and exhibits spatiotemporal controllability of its properties, demonstrating a potential for various biomedical applications, such as tuning macrophage phagocytosis as demonstrated in this study.

4D printed thermally activated self-healing and shape memory polycaprolactone-based polymers

The ability to change the shape of 3D printed objects as a function of time is known as 4D printing. Shape memory polymers with their shape-changing behavior are emerging as attractive materials to produce actuators for soft robotics. They can be transformed from one shape to another by a thermo-mechanical programming process. Self-repairing capabilities are also desirable for soft actuators to enhance their durability and mimic natural tissues. The possibility to produce 4D printed polymers with shape memory effect has proven but self-healing behavior was not attained so far in 4D printed shape memory objects. The focus of the present work is to demonstrate the capability of a newly developed material and of a customized low-cost 3D printer to produce 4D printed self-repairing objects. A 4D printed shape memory polymer with thermally induced healing abilities is first presented in this work and achieved by digital light projection (DLP) technology. Shape memory and self-healing functionalities are thermally triggered and obtained respectively using polycaprolactone (PCL) chains and 2-ureido-4[1H]-pyrimidinone (UPy) units co-crosslinked in this newly prepared material. Printed PCL/UPy-based objects show a stiffness similar to PCL-based ones, a higher elongation at break and a shape memory effect better than other printed PCL samples found in literature. The printability of shape memory objects is demonstrated with the printing of an opposing thumb, capable of being moved forward to the tip of a forefinger and then backward. Shape memory functionalities are still preserved after healing, making these printed actuators suitable for the production of components for human-machine interactions and soft robotics.

Thermal induced shape‐memory and self‐healing of segmented polyurethane containing diselenide bonds

ABSTRACTHerein, we synthesized a series of polyurethane copolymers (PUs) with poly(1,4‐butylene adipate) glycol as soft segment and 2,4‐toluene diisocyanate as well as extenders including 1,4‐butanediol and di(1‐hydroxyethylene) diselenide as hard segment. The chemical structure, thermal property, crystallization behavior, shape memory, and self‐healing performances of the PUs were systematically characterized by a series of experiments. It was found that the PU2 containing a higher diselenide component (∼33 mol %) exhibited both shape memory and self‐healing behaviors under a moderate temperature (∼57 °C). Meanwhile, the PUs showed a good repeatability of shape memory function, and their fixity and recovery ratios were all above 90%. Additionally, the dynamic exchangeable feature of diselenide bonding endues the PUs chains with an acceptable reprocessability and self‐healing performances, and the PU2 sample could be healed for five times by thermal treatment with the healing efficiencies above 70%. This work provides a heuristic perspective for the development of shape memory and self‐healing materials. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46326.

Healability Demonstrates Enhanced Shape-Recovery of Graphene-Oxide-Reinforced Shape-Memory Polymeric Films.

The fabrication of shape-memory polymers or films that can simultaneously heal the mechanical damage and the fatigued shape-memory function remains challenging. In this study, mechanically robust healable shape-memory polymeric films that can heal the mechanical damage and the fatigued shape-memory function in the presence of water are fabricated by layer-by-layer assembly of branched poly(ethylenimine) (bPEI)-graphene oxide (GO) complexes with poly(acrylic acid) (PAA), followed by the release of the (PAA/bPEI-GO)*n films from the underlying substrates. The free-standing (PAA/bPEI-GO0.02)*35 films made of bPEI-GO complexes with a mass ratio of 0.02 between GO nanosheets and bPEI are mechanically robust with a Young's modulus of 19.8 ± 2.1 GPa and a hardness of 0.92 ± 0.15 GPa and exhibit excellent humidity-induced healing and shape-memory functions. Benefiting from the highly efficient healing function, the (PAA/bPEI-GO0.02)*35 films can heal cuts penetrating thorough the entire film and achieve an ∼100% shape-recovery ratio for a long-term shape-memory application. Meanwhile, the shape-memory function of the mechanically damaged (PAA/bPEI-GO0.02)*35 films can be finely restored after being healed in water. The shape-memory functions of the (PAA/bPEI-GO0.02)*35 films and their healing capacity originate from the reversibility of electrostatic and hydrogen-bonding interactions induced by water between PAA and bPEI-GO complexes.

A flexible rechargeable zinc-ion wire-shaped battery with shape memory function

A flexible wire-shaped rechargeable Zn-ion battery with shape memory function was fabricated, delivering decent performances and good recoverability to mechanical deformation.