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In this study, vapor-grown carbon nanofiber (VGCNF)-filled and shape-memory epoxy (EP)-fixed melamine sponge (VGCNF@EP-MS) was fabricated for adjustable microwave shielding by dip-coating a melamine sponge with a mixture solution of VGCNF and EP. Increased EP addition to the dipping solution resulted in a decrease in the weight loading ratio (m VGCNF / m sponge) of VGCNF into the sponge from 66.2 to 15.7 wt%. For the shape memory effect, increased EP filling resulted in an improved compression fixity ratio of more than 99% but a decreased compression recovery ratio of less than 90%. By introducing ethanol (EtOH), adjustable EP filling into the sponge was achieved. Thus, moderate addition of EP into EtOH, such as 20:1 (v/v , EtOH/EP), could achieve good shape memory effects (compression fixing and recovery ratios of approximately 95% and 94%, respectively) and a high VGCNF loading ratio of approximately 58.4 wt%. For microwave shielding, 20:1 VGCNF@EP-MS showed an adjustable shielding effectiveness (SE) from 18 to 38 dB in the frequency range of 8.2 – 12.4 GHz, which was achieved using the shape memory effect for different thickness compressions and fixing. This VGCNF@EP-MS could be used for different extents of targeted electromagnetic signal adjustment in smart electromagnetic shielding. [Display omitted] • Ethanol was introduced into the dipping solution for fine filling adjustment of epoxy into the sponge matrix. • Dip-coating of shape memory epoxy was demonstrated effective to achieve a fixing for a desired compression thickness. • Deep compression of VGCNF@EP-MS is required for effective adjustment in shielding effectiveness. • ●20:1 VGCNF@EP-MS showed an adjustable microwave shielding in a large range from 18 dB to 38 dB. [ABSTRACT FROM AUTHOR]

Two‐way (reversible) chemically crosslinked semicrystalline shape memory polymers are synthesized using poly(ethylene‐co‐vinyl acetate) (PEVA) with benzoyl peroxide (BPO). The two‐way shape memory effect (2W‐SME) is achieved under both constant stress and stress‐free conditions. It is found that the stress‐free 2W‐SME can be achieved by the relationship between the initial prestretching strain (Rprestretch) and recovery strain (Rrec). Under the same prestretching stress, the stress‐free two‐way shape memory behavior can be controlled by variation of Rrec using a different setting temperature (Tset) in the recovery process. More importantly, the driving force and recovery force, as one of the key indicators for two‐way shape memory materials, are investigated, and they significantly change depending on the BPO content. The sample with high BPO content shows excellent high‐temperature creep resistant performance. A highly crosslinked structure can suppress viscous flow and provides sufficient force to allow the sample to recover its initial shape after crystal melting. Therefore, the PEVA/BPO samples are able to contract during heating. The presence of an oriented crystal structure with high applied stress that causes sample elongation during cooling is also investigated. These findings for PEVA/BPO two‐way shape memory polymers will contribute to their applications as soft actuators in various fields. [ABSTRACT FROM AUTHOR]

It is known that scaffold is a key factor in bone tissue engineering. The aim of this study was to improve the design of scaffold in order to achieve an effect of precisely matching the irregular boundaries of bone defects as well as facilitate clinical application. In this study, controllable three-dimensional porous shape memory polyurethane/nano-hydroxyapatite composite scaffolds were successfully fabricated. Detailed studies were performed to evaluate its structure, porosities, and mechanical properties, emphasizing the effect of different apertures of scaffolds on shape recovery behaviors and biological performance in vitro. Results showed its compression recovery ratios and shape recovery ratios of all scaffolds could reach more than 99 and 90%, respectively, which could let it more accurately match the irregular boundaries of bone defects. And also its cell proliferation ability was improved with the increase in the apertures. Thus, these scaffolds have potential applications for the bone tissue engineering. [ABSTRACT FROM AUTHOR]

ABSTRACT Shape memory (SM) silica/epoxy composite foams were successfully synthesized via latex technology and prepared without blowing agent addition. Silica was synthesized via tetraethoxysilane (TEOS) hydrolysis. Silica/epoxy foams were obtained from the TEOS solution and water-borne epoxy mixtures after freeze-drying and foaming in the presence of residual moisture as the blowing agent under a vacuum at 110°C. The morphologies of the resulting foams were evaluated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Compression and thermo-mechanical cycle tests were performed to measure the mechanical and SM properties of the foams. Experimental results indicated that the micrographs and mechanical properties of the foams were closely related to freeze-drying time. The final composite foams exhibited high shape recovery and fixity ratios and could maintain both properties at more than 90% even after five thermo-mechanical cycles. The properties obtained in the epoxy foams may offer new opportunities for their use in future structural applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42599. [ABSTRACT FROM AUTHOR]

• Their glass transition temperature was controlled and shifted lowered from 60 °C to 37 °C. • The SMP tube compression and expansion demonstrated fast tube recovery on the diameter direction. • The cell proliferation of mouse cells demonstrates these tube actuators can use with the human body with non-toxicity. [Display omitted] In this study, a tube actuator was successfully fabricated by incorporating shape memory polyurethane (SMPU) with dibutyl adipate (DBA) plasticizer, which distinctly produces softness and glass transition temperature switching close to human body temperature. The plasticized SMPU tube was activated at 37 °C, which is faster than the pure SMPU tube. The effect of thermal triggering on tensile and viscoelastic properties was investigated. Adding DBA plasticizers to SMPU demonstrated a quicker recovery rate than pure SMPU during tube compression and expansion. In addition, according to thermomechanical analysis results, the shape recovery ratio of the DBA plasticizer-doped tube is up to 83%, and its shape recovery ratio during tensile deformation is up to 99%. Particularly, mouse cell adhesions and proliferation on SMPU-DBA gel provide biocompatibility and nontoxicity. The bio-based mechanical properties of the tube make sensing under human temperature control an appealing possibility. The developed tube actuators can be used as artificial blood vessels and in other clinical applications. [ABSTRACT FROM AUTHOR]

• Actuation of the plasticized SMP was accomplished by heating and electric. • The SMP gels could be stretched up to a high strain and then rapidly recover back to their original form. • The two-way shape deformation of contraction and expansion were investigated over 6 electric on-off cycles. The largest contraction reached 6.76 % with an electric field of 34.24 V/μm. In this work, shape memory materials were developed for use as soft actuators. Shape memory polymers (SMPs) generally demonstrate good actuation on direct thermal heating. Here, we also demonstrate SMPs with good electric actuation via the incorporation of dibutyl adipate (DBA) plasticizers with shape memory polyurethane to form an SMP gel, which is a soft dielectric material. The effect of the plasticizer on the shape memory behavior under thermal stimulus was investigated. The SMP gel had faster shape recovery than the pure SMP and almost fully recovery. A dielectric SMP actuator was prepared and its two-way shape deformation of contraction and expansion, were investigated over 6 electric on-off cycles. The largest contraction reached 6.76 % with an electric field of 34.24 V/μm. The developed dielectric elastomer actuator displayed a multifunctional response to thermal and electric stimuli. This material has potential for alternative actuation applications including biomaterials. [ABSTRACT FROM AUTHOR]

[Display omitted] • Epoxy/PEG nanofibers have been successfully developed by improving the spinnability of epoxy resin. • The mechanical and thermal properties of epoxy/PEG nanofiber membranes were regulated by PEG. • The shape memory function of epoxy/PEG nanofiber membranes were achieved. • Epoxy/PEG shape memory nanofiber yarn was successfully developed. To improve the spinnability of thermoplastic epoxy resin and develop epoxy resin-based shape memory nanofiber materials, polyethylene glycol (PEG) was utilized to regulate the properties of thermoplastic epoxy. The process involved the preparation of thermoplastic epoxy/PEG nanofibers using melt-dispersion and electrospinning techniques. The addition of PEG has enabled the electrospinning of the thermoplastic epoxy, with EPP-5 having the smallest average diameter (227 nm) and EPP-10 showing the most uniform morphology. FTIR analysis confirmed sufficient polymerization of epoxy resin. The water contact angle analysis revealed that an appropriate amount of PEG reduced the hydrophilicity of the nanofiber membranes, with the EPP-10 showing a 14.9 ° increase in water contact angle compared to the EPP-5. The mechanical analysis demonstrated that an appropriate amount of PEG improved the nanofibers' yield stress, breaking strain, and maximum tensile stress. The EPP-10 exhibited a 3.27 MPa increase in yield stress, a 19.54 % increase in breaking strain, and a 1.17 MPa increase in maximum tensile stress compared to the EPP-5. Thermal analysis showed that epoxy/PEG nanofibers decomposed mainly between 400 ℃ and 500 ℃. Thermomechanical analysis revealed a reduction in the T g of epoxy/PEG films with the addition of PEG, among which the T g of EPP-25 was 55.1 ℃ lower than that of EPP-0. The epoxy/PEG nanofiber membrane exhibits excellent shape memory performance, among which the EPP-10 exhibits the best shape recovery effect. In addition, the EPP-10 yarn stretched to 160 % of original length recovered within 25 s, and EPP-10 yarn tied in a temporary shape recovered to original shape within 15 s. In conclusion, by modulating the properties of thermoplastic epoxy through PEG, the spinnability of thermoplastic epoxy was achieved, and shape memory epoxy/PEG nanofibers with potential applications in the field of smart textiles were developed. [ABSTRACT FROM AUTHOR]

Abstract Multi-layer graphene oxide (MLGO) coated shape memory polyurethane (MLGO@SMPU) with different layers was fabricated by multiple dipping for adjustable shape memory switching devices. The MLGO, which stacked together in parallel, evenly covered the surface of the SMPU. Stress strain testing indicated that the coating of GO improved the mechanical strength of these MLGO@SMPU composites in the stretching stage below the strain of approximately 6%. Adhesive force testing suggested that the first GO layer could adhere well to the SMPU surface, but the interaction force between GO layers was weak. The angle recovery ratio and time, bending recovery force, and angle fixity ratio of these MLGO@SMPU composites were evaluated using homemade evaluation apparatus. Results indicated that with the increase of GO layers from one to five layers, the MLGO@SMPU gave an angle recovery ratio reduced to 83.2%, recovery time decreased to 7.6 s, bending recovery force increased to 18.3 mN, and angle fixity ratio decreased to 83.3%. This novel and straightforward approach of dipping graphene oxide onto shape memory substrates for adjustable recovery ratio, time and force has the potential to be applied to smart switching devices including sensors and actuators. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

To combine the piezoelectric effect and shape memory effect, various kinds of smart composites are developed through compounding lead zirconate titanate (PZT) particles with average diameters of 400 nm and shape memory polyurethane (SMPU) matrices. Compared with pristine SMPU, the resulting composites are enhanced by more than 133% in the maximum recovery stresses. Additionally, the film actuators made from these composites can generate 1 nm resolution displacements without any control method in a common laboratory environment when the step voltage signals are applied to them. This feature partly profits from the softness of SMPU matrices which, to some extent, protects PZT particles from ambient noise. Moreover, taking the advantage of shape memory effect easily deforms the film actuators into a variety of designed shapes. As a consequence, the shaped actuators are able to produce many more displacements while the positioning errors remain the same. The displacements of the “U” type actuator and the “Z” type actuator are respectively 18 nm (about 4.7 times displacement of the corresponding film actuator) at 840 V and 75 nm (about 13.3 times displacement of the corresponding film actuator) at 600 V. The proposed smart composites strongly show the potential to lower the requirements of nanopositioning and reduce costs. [ABSTRACT FROM AUTHOR]

Shape memory polymers (SMPs) have received great attention and scientific interest in widespread technological development during last few decades. Besides the development of novel SMPs, various techniques have been practiced for characterization of shape memory effect (SME) of SMPs. In this study, the shape memory effect and recovery stress property of the carbon nanotube (CNT)/waterborne epoxy (WEP) nanocomposites below and above the glass transition temperature ( T g ) of the nanocomposites and under isostrain and isostress were systematically investigated via thermal mechanical analysis (TMA), respectively. The experimental results showed that the nanocomposites exhibit excellent shape memory effect. The shape memory fixity and recovery ratios were approximately 100% even below glass transition temperature ( T g ). A remarkable point is that the strain of the nanocomposites suddenly increased with the temperature decreasing in a certain period of the heating-cooling cycles under isostress condition and the strain increment increased with temperature in general. Especially at low temperature, the recovery stress was very sensitive to temperature under isostrain condition of ±0.25 °C temperature with differential of 25.5 °C developed pressure difference of 0.20 MPa. Moreover, TMA is a practical method for quantifying the SME and recovery stress properties of SMPs and their composites. [ABSTRACT FROM AUTHOR]

This study developed a multi-stimuli temperature shape-memory epoxy–polyethylene glycol (PEG) film with skin-responsive and self-healing properties. The epoxy–PEG films can be regulated between rigid and flexible by the dispersion of PEG with different contents. All have excellent shape-memory properties at the respective stimuli temperatures with recovery rates between 92.6 % and 99.0 %. The epoxy–PEG films can perform shape-memory response and healing at room and human body temperatures based on the PEG regulation. The completely cut films with a PEG content of 30 wt% can maintain an average tensile strength of 63.1 % after healing at room temperature. Films with a PEG content of 40 wt% after healing at room and human body temperatures can maintain average tensile strengths of 70.0 % and 93.3 %, respectively. The films healed at human body temperature still maintained an average recovery rate of 85.0 % in the shape-memory cycling test. The environmentally developed shape-memory epoxy–PEG film with controllable thermal and mechanical properties can meet the needs of various stimuli temperatures and execution modes, switching between multiple shapes, self-healing, reuse, reprocessing, and recycling, significantly expanding the application potential for thermoplastic epoxy, especially in the fields of flexible smart materials. [Display omitted] • The mechanical and thermal properties of the epoxy film are regulated. • The stimuli temperature controllability of shape memory epoxy film is realized. • The response of shape memory epoxy film to human skin is realized. • The healing and reuse functions of shape memory epoxy film are realized. [ABSTRACT FROM AUTHOR]

This study prepared shape-memory thermoplastic epoxy (TEP)-polyethylene glycol (PEG) filaments for the first time, and the heat-stimuli controllability of shape memory function was innovatively endowed by adding PEG in an environmentally friendly way. PEG regulates the glass transition temperature of PEG-modified thermoplastic epoxy (TEP–PEG) without interfering with the polymerization reaction of epoxy. The melt spinning temperature of TEP–PEG is also reduced from 300 °C to 220 °C, and the spinning effect is improved. After PEG modification, Young's modulus of TEP–PEG filaments drawn from TEP–PEG pellets was higher at room temperature. The developed TEP–PEG filaments have excellent shape memory effect with high shape recovery rates of 93.1%–99.0%, and shape fixation rates ranging from 95.8% to 99.1% are also improved after PEG modification. Furthermore, TEP–PEG filaments have controllable stimuli temperatures of shape memory ranging from 69 °C to 105 °C. Additionally, the recovery stress of TEP–PEG filaments after PEG modification was increased to 1.77 MPa, and the recovery temperature of the maximum recovery stress is reduced from 97 °C to 58 °C as PEG content increases to 15 wt%. The problems of difficult melt processing and uncontrollable stimuli temperature for TEP were solved in this study. The developed TEP-PEG filaments with heat-stimuli controllability of the shape memory function demonstrated excellent thermal actuation capabilities and have shown greater application potential in thermal actuation, smart textiles, and artificial muscles. [Display omitted] • The spinning temperature of epoxy was regulated more environmentally friendly. • Epoxy filaments with different T g were obtained without reducing mechanical property. • The heat-stimuli controllability of shape memory function for epoxy filaments was realized by adding PEG. • Epoxy filaments showed greater thermal actuation ability by adding PEG. [ABSTRACT FROM AUTHOR]

In this paper, an epoxy resin mixture composed of epoxy and phenol monomers is used to prepare thermoplastic epoxy polymer (EP-TP) through a polymerization reaction and shape memory thermoplastic epoxy filament (SMEF-TP) was successfully developed for the first time through a melt-drawing process. Tensile tests showed that the yield stress of the developed SMEF-TP reached 63 MPa, which is an increase of 54% compared with EP-TP films. Shape memory experiments showed that the developed SMEF-TP has excellent shape memory performance, with a shape fixation rate of 97%, a shape recovery rate of over 97%, and good stability in cycling. Based on the shape memory performance analysis, the shape recovery stress of the SMEF-TP was characterized. Shape recovery stress responded to temperature stability and increased with the increase of strain, reaching 1.45 MPa at a strain of 35%. The SMEF-TP can reach an energy density of 0.066 J/cm3 during thermal actuation and shows greater application potential when processed into textiles. In addition, the chemical structure, thermal performance, and dynamic mechanical performance of SMEF-TPs are analyzed. The developed SMEF-TP shows excellent shape memory performance, and the output shape recovery stress is more than 5 times that of EP-TP film, which provides huge application potential in the fields of artificial muscles and smart textiles. • Successfully developed shape memory thermoplastic epoxy filament. • Epoxy filament has excellent tensile strength. • Epoxy filament shows excellent shape memory performance. • Epoxy filament can output considerable shape recovery stress. [ABSTRACT FROM AUTHOR]

In recent years, shape memory polyurethane (SMPU) as a smart material has been used in various applications owing to its desirable shape memory effect and biocompatibility. In this study, unidirectional SMPU nanofibers are innovated by electrospinning to clarify the mechanical and shape memory properties with nanofiber directions. The results showed that when the nanofiber alignment degree is 0° (parallel to the tensile direction), the aligned SMPU nanofibers achieved the obvious improvement of tensile strength (increased to 135%) and elastic modulus (increased to 313%), compared with the random SMPU nanofiber. Moreover, the developed aligned nanofibers exhibited good ability against stress relaxation and creep under constant strain or constant stress conditions in cyclic loading. The aligned SMPU nanofibers with a 0° alignment degree exhibited excellent shape memory properties with shape recovery rates larger than 93% and shape fixity rates larger than 90%, and a dramatic increase of shape recovery stress. • The aligned shape memory polyurethane (SMPU) nanofibers are developed with different alignment degrees. • High performance of shape memory and recovery property is obtained by the aligned SMPU nanofibers. • The relationships between shape fixity, shape recovery ratio and nanofiber alignment are investigated systemically. • Obvious improvement of mechanical properties with 0° nanofibers is identified. • The mechanism of shape memory effect with aligned nanofibers are clarified. [ABSTRACT FROM AUTHOR]

The popularity of flexible energy harvesters has grown rapidly in recent decades because of their high flexibility for application in wearable and implantable devices. Flexibility and functionality are key issues for their use in wider engineering applications. In this study, we present a multifunctional flexible energy harvester based on aligned lead zirconate titanate (PZT)/shape memory polyurethane (SMPU) nanofibers and applying its shape memory properties for use with surfaces with curved and/or complex structures. Mechanical and thermomechanical analyses and energy harvesting tests were performed on random and aligned nanofibers to investigate the influence of nanofiber orientation and its shape memory properties. Our results showed that, compared with random nanofibers, 0° aligned PZT/SMPU nanofibers (the nanofibers' direction is parallel to the tensile direction) demonstrated higher mechanical, shape memory and energy harvesting properties. In particular, the energy harvesting properties (output voltages) were increased by 5.4 times. In addition, taking advantage of the shape memory effect, the PZT/SMPU energy harvester can be deformed into various curved shapes to match complex structures while maintaining its original piezoelectric characteristics, which resulted in enhanced energy harvesting from curved surfaces. The developed energy harvester realized better piezoelectricity as a result of its nanofiber arrangement, and offers a flexible ability to match various surfaces with complex structures to achieve more effective energy harvesting. [ABSTRACT FROM AUTHOR]

• The two-way shape memory PEVA/BPO foams were successfully innovated. • The thermo-crosslinking method was used in the foaming process. • The pore sizes related to the two-way shape memory properties were clarified. Two-way reversible shape memory polymer foams with porous three-dimensional structures were prepared using salt-leaching technology based on benzoyl peroxide (BPO) thermo-crosslinked poly(ethylene-co-vinyl acetate) (PEVA). Various pore sizes of PEVA/BPO porous foam were obtained using different NaCl particle sizes. The PEVA/BPO foams with various pore sizes exhibited reversible shape changes that allowed contraction during cooling and expansion during heating. The ideal two-way shape memory performance can be clearly observed in the large pore size sample PEVA/BPO-450. The morphology was characterized by scanning electron micron microscopy (SEM) and X-ray microcomputed tomography scanning (μCT) analysis. The compression behavior of PEVA/BPO foam was also investigated. These properties of two-way reversible shape memory PEVA/BPO foams could qualify their use as lightweight porous actuators in artificial intelligence and aerospace applications. [ABSTRACT FROM AUTHOR]

• Each PEVA-B10 sample had optimal actuation performance and an excellent recovery ratio of over 99%. • The samples (PEVA/BPO soft materials) with high crosslinking densities had significantly improved recovery ratio. • The developed PEVA/BPO materials were adequately soft and had good mechanical properties, even at large deformation. We synthesized two-way (reversible) chemically crosslinked semi-crystalline shape memory polymers with various crosslinking densities from poly(ethylene-co-vinyl acetate) (PEVA) with various contents of benzoyl peroxide (BPO). The developed materials were capable of reversible shape change, and we ensured that the "switch on" temperature, which triggers shape change, was within a reasonable range. Each PEVA-B10 (PEVA with 10 wt% BPO) sample had optimal actuation performance and an excellent recovery ratio of over 99%. The BPO crosslinker played an important role in allowing the samples to return to their original shape, and the samples (PEVA/BPO soft materials) with high crosslinking densities had significantly improved recovery ratios. As a result, the developed PEVA/BPO materials were adequately soft and had good mechanical properties, even at large deformation. Therefore, the materials are potentially useful as soft material actuators, or for other applications. [ABSTRACT FROM AUTHOR]