Fabrication of poly(ε‐caprolactone) (PCL)/poly(propylene carbonate) (PPC)/ethylene‐α‐octene block copolymer (OBC) triple shape memory blends with cycling performance by constructing a co‐continuous phase morphology

In this paper, a triple shape memory material was prepared by ultra‐simple melt blending from poly(ε‐caprolactone) (PCL), poly(propylene carbonate) (PPC) and ethylene‐α‐octene block copolymer (OBC). The obtained material possessed a co‐continuous phase morphology and presented an excellent triple shape memory effect (triple‐SME). Theoretical prediction demonstrated that a special continuous phase morphology could be constructed by adjusting the proportions of the blend. Moreover, the results indicated that a close relationship existed between the phase morphology and the triple‐SME of PCL/PPC/OBC. The sample with 35 vol% PPC content contributed to the formation of a continuous phase morphology and exhibited the optimal triple‐SME. Additionally, the sample PCL/PPC/OBC (32.5/35/32.5) showed outstanding structure and performance stability during cycle loading–unloading tests, which evidenced the prominent cycling shape memory property (nearly 100% shape fixing and recovery of temporary shape). Overall, this work could provide an efficient, convenient and recyclable method to obtain high‐performance shape memory materials. © 2020 Society of Chemical Industry     

Significantly improving electro‐activated shape recovery performance of shape memory nanocomposite by self‐assembled carbon nanofiber and hexagonal boron nitride

This study presents two effective approaches to significantly improve the electro‐thermal properties and electro‐activated shape recovery performance of shape memory polymer (SMP) nanocomposites that are incorporated with carbon nanofibers (CNFs) and hexagonal boron nitrides (h‐BNs), and show Joule heating triggered shape recovery. CNFs were self‐assembled and deposited into buckypaper form to significantly improve the electrical properties of SMP and achieve the shape memory effect induced by electricity. The h‐BNs were either blended into or self‐assembled onto CNF buckypaper to significantly improve the thermally conductive properties and electro‐thermal performance of SMPs. Furthermore, the shape recovery behavior and temperature profile during the electrical actuation of the SMP nanocomposites were monitored and characterized. It was found that a unique synergistic effect of CNFs and h‐BNs was presented to facilitate the heat transfer and accelerate the electro‐activated shape recovery behavior of the SMP nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40506.     

Influence of uniaxial compression on the shape memory behavior of vitrimer composite embedded with tension-programmed unidirectional shape memory polymer fibers

Tension programmed shape memory polymer (SMP) fibers have been used as sutures for closing wide-opened cracks per the close-then-heal strategy. However, the composite may be subjected to compression loading during service. These compression loads can reduce the amount of recoverable strain in these pre-tensioned fibers, limiting their ability to close cracks. The purpose of this study is to investigate the effect of in-service compression loading on the shape memory effect (SME) of composites consisting of SMP fiber and SMP matrix. To this end, pre-stretched shape memory Polyethylene Terephthalate (PET) fibers were embedded into a shape memory vitrimer to obtain composite samples with different fiber volume fractions. The SME of both the PET fiber and the vitrimer was investigated. The effect of compression load on the SME of the composite was studied. It is found that, uniaxial compression on the composite along the fiber direction significantly reduced the shrinking ability of the embedded pre-tensioned SMP fibers. Hence, this is a factor that needs to be considered when designing such types of self-healing composites.     

Synthesis of novel ZnO/carbon xerogel composites: Effect of carbon content and calcination temperature on their structural and photocatalytic properties

This paper reports the development of new ZnO/carbon xerogel composites (XZn w) for photocatalytic applications. The use of black wattle tannin as a precursor to the carbon xerogel aimed at reducing costs and environmental impacts. The composites were characterized by diffuse reflectance spectroscopy (DRS), BET surface area, scanning electron microscopy (FEG-SEM), X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy (EDS), infrared spectroscopy (IR), and X-ray diffraction (XRD). The photocatalytic performance of the materials was evaluated in the decomposition process of methylene blue, a known toxic pollutant. The impacts of the catalyst dosage and calcination temperature on the photocatalytic process were also examined systematically. The X-ray profiles of the XZn w evidenced the existence of the hexagonal structure of the zinc oxide (wurtzite) in the composites. The XPS and XRD analyses confirmed the incorporation of carbon in the zinc oxide crystalline structure. The higher carbon content resulted in a larger surface area. All composites presented the ability to absorb radiation in less energetic wavelengths, contrary to pure zinc oxide that only absorbs radiation of wavelengths below 420?nm. The optimal dosage and calcination temperature were found to be 0.2?g?L^?1 and 300?°C. All the developed composites displayed significant photocatalytic activities in the decomposition of methylene blue under both visible and solar light. The composites had superior photocatalytic efficiency under visible light when compared to pure zinc oxide. The XZn 0.5 presented the best degradation efficiency under visible radiation. All materials presented similar photocatalytic responses under solar light, evidencing the synergy between the carbon xerogel and the zinc oxide. The photocatalytic mechanism was evaluated by trapping experiments to be mainly controlled by the electron vacancies that are generated during the photoexcitation of the composites.     

Recent progress in shape memory polymer: New behavior,enabling materials,and mechanistic understanding

Shape memory polymers (SMPs), as a class of programmable stimuli-responsive shape changing polymers, are attracting increasing attention from the standpoint of both fundamental research and technological innovations. Following a brief introduction of the conventional shape memory effect (SME), progress in new shape memory enabling mechanisms and triggering methods, variations of in shape memory forms (shape memory surfaces, hydrogels, and microparticles), new shape memory behavior (multi-SME and two-way-SME), and novel fabrication methods are reviewed. Progress in thermomechanical modeling of SMPs is also presented.     

Macroscopic carbon nanofibers for use as photocatalyst support

To reduce the drawbacks related to the use of powders or immobilized catalysts in gas- and liquid-phase applications, a new material for the use as photocatalyst support was obtained by chemical vapor decomposition at 700 °C of an ethane–hydrogen mixture over a woven glass microfiber supported nickel catalyst, consequently leading to carbon nanofibers with macroscopic shaping, consisting in woven glass microfibers supporting a dense network of entangled 40 nm diameter carbon nanofibers. This material could be directly used after synthesis without any subsequent purification treatment due to the high yield and totally selective carbon nanofiber production. This shape memory design results in the direct use of the carbon nanofiber–woven glass microfiber composite as support without any post-synthesis shaping. The presence of hydrophilic oxygenated groups located at the outer surface of the carbon nanofibers allowed the sol–gel preparation of a woven glass microfiber–carbon nanofiber supported TiO₂ (20 wt.%) catalyst, using tetraisopropoxide as precursor. This new photocatalyst was totally stable under UV irradiation.     

Near‐Infrared Light Triggered Soft Actuators in Aqueous Media Prepared from Shape‐Memory Polymer Composites

Light triggered soft actuator in aqueous media has applications in operating underwater objects, creating liquid flow, and adjusting reaction velocity, etc. Here, composites prepared from commercial materials, poly[ethylene‐ran‐(vinyl acetate)] (EVA) and aniline black (AB), are reported as one cost efficient material for preparing such actuator, where EVA and AB work respectively as shape‐memory polymer matrix and near‐infrared light triggered photothermal filler. Upon irradiation, the temperature of the composites increases greatly with light power density and AB content. Light‐induced shape‐memory effect (SME) with recovery ratio >98%, temperature‐memory effect (TME), and reversible bidirectional shape‐memory effect (rbSME) of the prepared composites in air are realized. Higher light power density is required to trigger the shape recovery in aqueous media, while good SME, TME, and rbSME are also achieved. Releasing device and gripper are used to indicate the feasibility of the composites as light triggered soft underwater actuators.

     

Influence of annealing-induced phase separation on the shape memory effect of graphene-based thermoplastic polyurethane nanocomposites

Thermoplastic polyurethane (TPU) is a multiblock copolymer that exhibits an attractive shape memory effect (SME). Its morphology consists of a soft segment (SS), which corresponds to the polyol or a long-chain diol, while the hard segment involves the intercalation of a diisocyanate and a chain extender. Due to the distinct thermodynamic parameters of each monomer, these segments are not miscible with each other, resulting in a phase-separated structure in their morphology. This structure is characterized by the formation of soft and hard domains (SD and HD), respectively. When incorporating 0.1 wt% of graphene nanoplatelets (GNP) or 0.1 wt% of multilayer graphene oxide (mGO) into the TPU matrix using solution casting process, a contribution to the phase separation of these domains is observed. This phenomenon becomes even more pronounced when graphene-based nanocomposites are subjected to annealing at 110°C for 24 hours, indicating a good interaction between the GO and GNP with the HD and SS, respectively. After annealing, the nanocomposites (TPU + GNP and TPU + mGO) exhibit improved performance in SME, as evidenced by an approximately 9% increase in the shape recovery ratio compared to the nonannealed TPU. Additionally, all nanocomposites maintained a high strain during SME programming, surpassing that of pure TPU, both before and after annealing. This suggests a direct influence of the graphene-based nanoparticles on the shape memory effect.     

Shape‐memory behaviors of sensitizing radiation‐crosslinked polycaprolactone with polyfunctional poly(ester acrylate)

The sensitizing effects of polyfunctional poly(ester acrylate) on the radiation crosslinking of polycaprolactone (PCL) were studied. The influences of the use of the polyfunctional material, the number of functional groups, and the radiation dose on the radiation crosslinking, dynamic mechanical properties, and shape‐memory behaviors of PCL, respectively, were investigated. The radiation crosslinking of PCL, under the conditions in which the polyfunctional material was applied, did not follow the classic Charlesby–Pinner equation but instead followed the Chen–Liu–Tang relation. The efficiency of the radiation crosslinking of PCL was distinctly improved with the polyfunctional material. The greater the usage and functional group number were, the greater gel content and the more distinctive the radiation‐crosslinking effects were. This also indicated that the polyfunctional material directly participated in the crosslinking reaction. Dynamic mechanical analysis indicated that enhanced radiation crosslinking better raised the heat deformation temperature of PCL and presented a higher and wider rubbery‐state plateau; it also produced greater strength at temperatures higher than the melting temperature and provided greater force for recovering the deformation than pure PCL. The shape‐memory results revealed that sensitizing crosslinked PCL presented 100% recoverable deformation and a quicker recovery rate. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 634–639, 2005     

Two‐Way Reversible Shape Memory Properties of Benzoyl Peroxide Crosslinked Poly(ethylene‐co‐vinyl acetate) under Different Stress Conditions

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 (R_prestretch) and recovery strain (R_rec). Under the same prestretching stress, the stress‐free two‐way shape memory behavior can be controlled by variation of R_rec using a different setting temperature (T_set) 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.     

奥氏体变形对形状记忆合金Fe-28Mn-6 Si-5Cr亚结构和记忆行为的影响

本文研究了奥氏体变形（高于Ｍｄ温度）对Ｆｅ－２８Ｍｎ－６Ｓｉ－５Ｃｒ（％）合金形状记忆效应和亚结构的影响,结合热机械训练结果,揭示了影响合金形状记忆效应的主要因素。实验结果表明,所研究的合金在７００℃下进行９％的拉伸变形后,合金会产生均匀分布在奥氏体中的方向一致的层错和位错等亚结构,从而改善合金的形状记忆效应。奥氏体变形和热机械训练方法提高形状记忆效应的本质是由于分别通过动态回复和静态回复改善奥氏体母相的亚结构,与奥氏体母相强度的变化没有必然的联系。     

Simultaneous growth of well-aligned diamond and graphitic carbon nanostructures through graphite etching

A hot filament chemical vapor deposition process based on hydrogen etching of graphite has been developed to synthesize diamond and graphitic carbon nanostructures. Well-aligned diamond and graphitic carbon nanostructured thin films have been synthesized simultaneously on differently pretreated silicon substrates in a pure hydrogen plasma. Graphitic nanocones, diamond nanocones and carbon nanotubes were selectively grown on uncoated, diamond and nickel pre-coated silicon substrates, respectively, in a single deposition process. The nanocones are solid cones with submicron scale roots and nanometer-size sharp tips. The nanotubes are hollow tubes with outer diameter of approximately 50 nm. The orientation of the well-aligned carbon nanostructures depends on the direction of the electric field at the samples surface. Nucleation and growth of diamond on the nanocones were further investigated under similar conditions without plasma. Diamond nanocomposite films have been obtained by depositing a nanocrystalline diamond film on the layer of diamond nanocones.     

Multiple shape memory behaviors of natural Eucommia ulmoides rubber and polybutene‐1 composites

We fabricated a series of novel shape memory composites using natural Eucommia ulmoides rubber (EUR) and polybutene‐1 (PB‐1) as basic materials for the first time. The shape memory composites were prepared via simple physical blending and chemical crosslinking methods with co‐continuous architecture and multiple shape memory behaviors. These composites and their preparation methods might be widely used in the field of heat shrinkable tubes. We studied the mechanical, thermal and shape memory properties of the composites, and proposed schemes to explain their dual and triple shape memory effects. In the EUR/PB‐1 composites, both the crosslinking network of the composites and crystalline regions of PB‐1 could function as the fixed domain, and the crystalline zones of EUR and PB‐1 could act as the reversible domain individually or jointly. The composites exhibited excellent dual shape memory properties with blending ratios of 90/10 and 80/20, and good triple shape memory properties with blending ratios of 70/30 and 60/40. © 2018 Society of Chemical Industry     

Improvement in mechanical,electrical, and shape memory properties of the polystyrene-based carbon fiber-reinforced polymer composites containing carbon nanotubes

Carbon fiber-reinforced polymers based on polystyrene matrix containing elastomer and carbon nanotubes (CNTs) were produced by compression molding. The effects of carbon fabric (CF) concentration and silane treatment on the morphology, mechanical, electrical, and shape memory properties of the multilayer composites were investigated. The SEM analyses showed that fibers of the silane-treated CFs were more homogeneously covered with the polymer layers than the untreated CFs. The tensile strength and modulus of the composites increased by 521% and 125%, respectively, with an increasing number of CF plies from one to five. Upon silane treatment, the tensile strength of the multilayer composite improved by 26%, and the tensile modulus decreased by 18.4%. Electrical conductivities of the composites were in the semiconductor region due to the presence of both CNTs and CFs. 100% shape recovery less than a minute recovery time was obtained for all the composites with electrically triggered bending test.     

Conducting Shape Memory Polyurethane‐Polypyrrole Composites for an Electroactive Actuator

Summary: Electroactive shape memory composites were prepared using polyurethane block copolymer and conducting polypyrrole by chemical oxidative polymerization. The electrical conductivity, thermal and mechanical properties, and morphology of the composites were investigated, and a voltage‐triggered shape memory effect was demonstrated. The polyurethane synthesized had a transition temperature near 46 °C. The presence of polypyrrole increased the conductivity of the composites, and a high conductivity of the order of 10^?2 S/cm was obtained at 6–20 wt.‐% polypyrrole. Such a conductivity of composites was enough to show electroactive shape recovery by heating above the transition temperature of 40–45 °C due to melting of the polycaprolactone soft segment domain. Thus a good shape recovery of 85–90% could be obtained in the shape recovery test with bending mode when an electric field of 40 V was applied.

Electroactive shape recovery behavior of PU/PPy composite.     

Modeling shape memory effect in uncrosslinked amorphous biodegradable polymer

Shape memory effect (SME) is critical for minimally invasive surgical procedures in medicine. In this paper, the shape memory behavior of amorphous biodegradable polymer, poly(d,l-lactide-co-glycolide), is experimentally investigated. Based on the experimental observations and the understanding of the underlying mechanism of SME, a one-dimensional constitutive model is derived to describe the shape memory behavior in the context of (1) the stress-strain behavior in deformation, (2) the isothermal recovery and (3) the recovery at constant heating rate, by using a set of model constants. By fine tuning the model constants, a good agreement between the experimental results and computer predictions was achievable.     

Microwave-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) interpenetrating polymer networks chemically linked to SiC nanoparticles

Microwave (MW)-induced shape-memory poly(vinyl alcohol)/poly(acrylic acid) (PVA/PAA) interpenetrating polymer networks (SMP-IPNs) were prepared through in situ polymerization. Silicon carbide (SiC) nanoparticles were modified by 3-(methacryloyloxy) propyltrimethoxysilane (KH570). 3-(Methacryloyloxy) propyltrimethoxysilane was covalently bonded on the surface of SiC through the reaction of silanol and the methoxy groups. The polymerization of acrylic acid (AA) using N,N′-methylenebis (2-propenamide) (MBA) as cross-linker in PVA solution was initiated through the double bonds of KH-570 grafted on SiC, leading to a PAA polymer network cross-linked with MBA. The PVA molecular chains run through the PAA cross-linking network and form an IPN structure. Therefore, SiC as a strong MW absorbing material could be chemically cross-linked into polymer matrix. The effect of composition on the properties of SMP-IPN was studied using dynamic mechanical analysis, dielectric properties and shape memory effect (SME) test. The results showed that the introduction of SiC in IPNs not only provided samples with excellent MW-induced shape memory effect (SME), but also caused a higher equilibrium temperature under MW irradiation. Moreover, both SiC content and applied MW power affected the shape recovery properties of PVA/PAA interpenetrating composites. MW-induced SMPs offered great advantages such as fast recovery, high recovery rate, and remote actuation. This study provides the potential applications of the fast and environmentally friendly SMPs used as MW-responsive sensors, implantable devices, etc.     

Fabrication of Shape‐Memory Aerogel Based on Chitosan/Poly(ethylene glycol) Diacrylate Semi‐Interpenetrating Networks via a Facile and Eco‐Friendly Strategy

While the field of shape memory polymers (SMPs) has developed rapidly, it is still highly challenging to obtain SMPs in the form of aerogels (SMPAs) due to the unique technique used for the fabrication of the aerogels and their high porosity. Herein, a thermally induced SMPA based on chitosan/poly(ethylene glycol) diacrylate (CS/PEGDA) semi‐interpenetrating networks is reported that are produced using an eco‐friendly strategy. The main network is responsible for the shape memory effect (SME) and can be easily tuned by varying the feed ratio of the two PEGDA precursors, which have different molecular weights. The crystalline segment in poly(ethylene glycol) diacrylate (PEGDA) with higher molecular weight acts as the molecular switch, and the PEGDA with lower molecular weight endows the network with an efficient degree of crosslinking. Meanwhile, the chitosan (CS) is interpenetrated into the main network to enhance the aerogel. The SME is realized both at the macroscale and the microscale, as is further demonstrated for three different models with various shapes.     

Effect of sodium dodecyl sulfate on shape-memory properties of side-chain crystalline hydrogel via micellar copolymerization

A chemical shape-memory hydrogel containing crystalline structure is prepared via micellar copolymerization of hydrophilic monomer acrylamide (AM) and hydrophobic monomer octadecyl acrylate (C18) in a sodium dodecyl sulfate (SDS) solution. The influence of SDS on the shape-memory behavior of hydrogel investigated by differential scanning calorimetry (DSC) and Temperature-dependent X-ray indicate that the melting and crystallization peaks derived from the thermal properties of C18 units is different from peaks corresponding to the pure SDS. In addition, the microstructure evolution information of hydrogels dose not change upon heating process, regardless of the presence or absence of SDS. Therefore, only the hydrophobic associations formed by C18 blocks play a decisive role in the shape memory function of hydrogel system. The difference between the transition process (from temporary shape to permanent shape) of hydrogel with and without SDS at different temperature is because that the hydrophobic region of side chain crystallization of SDS-free hydrogel may escape the restriction of SDS and become more sensitive to temperature, they can preferentially return to their initial shape under the same time and temperature than SDS-containing gels. Whether SDS exists only affect the speed of shape memory behavior, but not the microstructure evolution of hydrogel system.