Responsive Shape Memory Effect Research Articles

Novel 4D-printing pellets with infrared-light responsive shape memory effect

Four-dimensional (4D)-printing technology is attractive to researchers since it combines 3D printing with smart materials to produce 3D structures with various shapes and change shapes under specific external stimuli. Herein, novel shape memory polymer (SMP) pellets with infrared-light responsive shape memory effect were developed for 4D printing applications. The structures, properties, and infrared-light responsive shape memory performances of the resulting (SMP) pellets were thoroughly investigated. The results showed PDA/SMP pellets prepared by direct loading of polydopamine (PDA) particles on SMP pellets displayed less influence on the basic properties of SMP while fluidity was enhanced. The obtained PDA/SMP pellets employed as feed materials for particle 3D printers revealed good thermal-induced shape memory performance and photo-responsive shape memory performance in printed 3D structures. Under infrared-light irradiation, the curled shape recovered to straight splines within 60 s due to the strong absorption and good photo-thermal conversion of the loaded PDA nanoparticles under infrared light. Overall, the as-prepared PDA/SMP pellets look promising for use in biomedical fields and smart devices, as well as remote control deformation with 4D printing technology.

Synthesis of Self-healing and Light-, Thermal-, and Humidity-induced Deformative Polyurethane Actuator.

Intelligent actuating materials have drawn enormous attention because of their potential applications in soft robots, smart sensors, bionics, etc. Aiming to integrate light, thermal, and humidity stimuli deformations and self-healing function into a single polymer, a smart actuating polyurethane material CPPU-50 is designed and successfully synthesized through co-polymerization of azobenzene-containing Azo-C12 , polyethylene glycol 200 (PEG200), and 4,4'-diphenylmethane diisocyanate (MDI) at a ratio of 1:1:2. The obtained polyurethane CPPU-50 exhibits good photoinduced bending, thermal responsive shape memory effect, humidity triggered deflections and self-healing properties. Furthermore, an actuator combining light and thermal stimuli is created and the self-healing CPPU-50 film can withstand the object of 1800 times without tearing. This work can pave a way for further development of long-lived multi-stimuli-responsive actuating devices and intelligent materials.

Digital light processing 4D printing multilayer polymers with tunable mechanical properties and shape memory behavior

Four-dimensional (4D) printing has currently been renowned as a world-changing technology which has recently gained significant attention amongst researchers. It enables 3D printed objects to alter its shape, properties and functions through the application of external stimuli. However, the development of 4D printing has been impeded by the overexposure effect, which has made it difficult for photocuring to print gradient structures. In this paper, we propose a novel photocuring 4D printing strategy of gradient structures with tunable properties. Multi-walled carbon nanotubes (MWCNTs) are added to the intermediate layer (Fast Layer, FL) of multilayer shape memory polymers (SMPs) to reduce curing degree and absorb overexposure. The mechanical properties and shape memory behavior of multilayer SMPs can be tuned by adjusting the layer ratio of FL with low curing degree. Outcome of microscopic images, interlayer bonding force, and shore hardness originating from this study indicates that the printed multilayer SMPs possessed excellent interlayer bonding properties as well as obvious modulus differences between each layer. The average shape recovery speed (Sa) of multilayer SMPs was almost linearly related to the slice layer number of FL. The strategy was successfully demonstrated in the fabrication of multilayer SMPs with sequential recovery and multiple deformation behavior. An electrically responsive shape memory effect was also achieved by using embedded graphite electrothermal layer to exhibit its application in time-delay devices. The proposed strategy enables the application of multilayer SMPs gradient structures in soft robotics and flexible electronics.

Actuation of shape memory poly(vinyl alcohol) and graphene oxide film in water

The PVA/GO film prepared by vacuum-assisted self-assembly exhibits quick thermo-/water- responsive shape memory effect. The anisotropic lamellar structure of GO sheets and plenty of chemical groups containing oxygen in the PVA/GO film facilitate rapid recovery in water. The lamellar structure of GO sheets improves the recovery stress of composite and results in a 16-fold increase in Young’s modulus. PVA molecular chain slides along the direction of the laminated GO sheets, consistent with the extension direction, ensuring that the composite film maintains a large fracture strain. The straight film is programmed into a spiral shape by the plasticization of water on PVA instead of ordinary heating and the spiral film can drive a weight 160 times its own weight to rotate in water at room temperature (about 25[Formula: see text]C).

Cyclic Thermomechanical Analysis of Polyethylene Glycol Based Shape Memory Polymers

Shape memory polymers (SMP’s) are a type of smart material that possess the ability to remember its original shape. Shape memory polymer quickly recovers to its original or permanent shape. As a result of these properties, SMPs can be used as sensors, actuators, and transplants, as well as auxiliary materials in a variety of applications. It has been used in a variety of domains over the previous two decades because to its shape memory capability, and its applications are growing at a quicker rate. Due to its biocompatibility, wide range of tunable stiffness, large deformation, large recovery, high elastic property, water vapour permeability, and multi responsive shape memory effect, memory polymers, polyurethanes are the most adaptable polymeric material. They offer several advantages over other types of shape memory materials, such as shape memory alloys, such as easier manufacturing, lighter weight, lower cost, larger recoverable strain, and lesser toxicity. When compared to shape memory alloys (SMA’s), SMPs have a few disadvantages, such as lower moduli, which results in lower recovery stresses, and longer response times. In some applications, a proper recovery stress derived from the elastic recovery stress created during the deformation process is crucial. There is no literature on how to synthesize SMP’s in an efficient manner. SMP’s and its classification in terms of their distinct qualities. This work focuses on the analysis of cyclic thermomechanical tests of linear SMP’s in order to address some of these problems. Form memory polymers were made using a two-step polymerization process in this study, with the composition of PEG 6000-IPDI-PEG600-BDO as 58wt%-42wt%-1ml-1ml respectively and the shape memory effect was assessed using a bend test. Cyclic thermomechanical analysis method involves tensile test procedure in thermal chamber with intermediate temperatures. Mechanical properties such as cyclic thermomechanical test, dynamic mechanical analysis, and tensile test are used in the validation process. In the primary cycle can be determined as for the sample 10 when we applied the load of 0.8 Mpa the strain was found as 200% the shape fixity and shape recovery values are 98.95 and 97.0 respectively.

Synthesis and Properties of Multistimuli Responsive Shape Memory Polyurethane Bioinspired from α‐Keratin Hair

AbstractHerein, a multistimuli responsive shape memory polyurethane (multiresponsive SMPU) containing disulfide bonds (–S–S–), bioinspired from α‐keratin hair component, was synthesized using a two‐step reaction and activated via four‐varied stimuli, including water, heat, redox agent, and UV‐light. First, the prepolymer was prepared by the reaction between the comonomers of hexamethylene diisocyanate and polycaprolactone‐2000, and once ended, 1,4‐butylene glycol and 3‐mercapto‐1,2‐propanediol (C3H8O2S) have been appended to the prepolymer to initiate the chain‐extension reaction. The chemical structure and properties of the multi‐responsive SMPU were decoded by FT‐IR, XRD, DSC, and Raman spectra. The correlation between microstructure, dynamic‐mechanical‐analysis, and shape‐memory properties of the multi‐responsive SMPU were systemically discussed. As a primary clue, the opening/closing of H‐bonds and disulfide bonds approved that they dictated the shape memory performance. The clear‐cut results clarified that the multiresponsive SMPU endowed composition‐dependent stress relaxation, and its reversible variation of storage modulus was examined by changing temperature. Owing to such molecular switches, the strip pieces were able to represent a multistimuli responsive shape memory effect —induced by water, heat, redox agent (NaHSO3‐H2O2 solutions), and UV‐light. This research paves a feasible road to prepare a novel multistimuli responsive shape memory actuator with high potential features in flexible sensor and robotic applications.

Interpenetrating polymer network/functionalized‐reduced graphene oxide nanocomposite: As an advanced functional material

AbstractIn this report, smart polyurethane‐polystyrene interpenetrating polymer network (IPN)‐based nanocomposites were fabricated using simultaneous polymerization technique with different doses of functionalized reduced graphene oxide (f‐RGO). RGO was functionalized with monoglyceride of sunflower oil in the presence of toluene diisocyanate. Successful functionalization of RGO was supported by Fourier‐transform infrared spectroscopy, X‐Ray diffraction, and transmission electron microscopy analyses. Most interestingly, the fabricated IPN‐based nanocomposites showed significant enhancements in mechanical (tensile strength: 165%; elongation at break: 198%; toughness: 340%) and thermal (thermally stable up to 262°C) properties upon incorporation of 1 weight% of f‐RGO. Moreover, the fabricated nanocomposites exhibited outstanding chemical resistance, self‐cleaning behavior through surface hydrophobicity (static contact angle: 125.6–136.5°), multi‐stimuli responsive shape memory effect (100% recovery within 33–44 s by microwave and 265–308 s by sunlight) and thermally actuated artificial muscle‐like behavior. Therefore, the studied smart nanocomposites with the aforementioned properties hold significant potential for possible advanced applications.

Smart Sponge for Fast Liquid Absorption and Thermal Responsive Self-Squeezing.

Liquid absorption and recycling play a crucial role in many industrial and environmental applications, such as oil spill cleanup and recovery, hemostasis, astronauts' urine recycling, and so on. Although many liquid absorbing materials have been developed, it still remains a grand challenge to achieve both fast absorption and efficient recycling in a cost-effective and energy-saving manner, especially for viscous liquids such as crude oil. A smart polyurethane-based porous sponge with aligned channel structure is prepared by directional freezing. Compared to common sponges with random porous structure, the as-prepared smart sponge has larger liquid absorption speed due to its lower tortuosity and stronger capillary ("tortuosity effect"). More importantly, the absorbed liquid can be remotely squeezed out due to a thermally responsive shape memory effect when the sponge is heated up. Such smart sponges with well-defined porous structure and thermal responsive self-squeezing capability have great potential in efficient liquid absorption and recycling.

A ‘cross-relaxation effects’ model for dynamic exchange of water in amorphous polymer with thermochemical shape memory effect

Dynamic exchange of water has been shown to effectively trigger thermally responsive shape memory effect (SME) in shape memory polymer (SMP) at room temperature. However, the working mechanism of cross-relaxation effects which are generated simultaneously from two stimulus fields of water and temperature, has not been understood. In this study, a ‘cross-relaxation effects’ model was formulated for describing water-induced relaxation, thermomechanical behavior and strain recovery of amorphous SMPs. Based on Maxwell’s principle, the ‘cross-relaxation effects’ model was firstly proposed to quantitatively separate the effect of dynamic exchange of water on the thermochemical SME in SMP. Then the water-induced relaxation and strain recovery have been simulated and predicted using this model. Finally, experimental data were used to verify the proposed model, and the numerical results were found to fit well with the experimental ones. This ‘cross-relaxation effects’ model is expected to provide an effective tool for precise design and control of water-induced SME and shape memory behaviors by means of the dynamic exchange of water.

A Facile Fabrication of PCL/OBC/MWCNTs Nanocomposite with Selective Dispersion of MWCNTs to Access Electrically Responsive Shape Memory Effect

poly(ε‐caprolactone) (PCL)/ethylene‐α‐octene block copolymer (OBC)/multiwalled carbon nanotubes (MWCNTs) nanocomposite was prepared in this work. After achieving the co‐continuous phase morphology of PCL/OBC binary blend by varying the composition, MWCNTs were selectively dispersed in OBC as conductive filler to investigate the electrically responsive shape memory effect. The results indicated that the shape memory effect (SME) of PCL/OBC was sensitive to the composition of component. The optimal SME could be observed when the volume fraction of PCL and OBC was 50:50, which was applied for the further exploration of electrically responsive SME. Additionally, the MWCNTs selectively located in OBC formed percolated structure when the component of MWCNTs was 1.5 vol%, and the shape recovery ratio (Rr) increased with MWCNTs content and applied voltage. Typically, the sample exhibited the excellent electrically actuated shape memory effect when the MWCNTs loading was 5 vol%. Ultimately, it only took 30 s for the sample to achieve the 100% recoverability under 30 V. POLYM. COMPOS., 40:E1353–E1363, 2019. © 2018 Society of Plastics Engineers

Triple-stimuli responsive shape memory effect of novel polyolefin elastomer/lauric acid/carbon black nanocomposites

In this study, novel shape memory composite of polyolefin elastomer (POE)/lauric acid (LA)/carbon black (CB) nanoparticles with triple-stimuli responsive shape memory effect (SME) is investigated. Crystalline small molecule LA, replacing the commonly used semi-crystalline polymers, is utilized to cooperate with POE and acts as the fixing phase. CB nanoparticles are specifically dispersed in the POE phase, resulting in the formation of intensive conductive pathways and an improvement in the recovery force. The composites can be deformed into arbitrary temporary shapes, and exhibit high shape recovery and fast response to thermo-, electro-, and solvent-stimuli. In our hands, 10 V is capable of triggering shape recovery of the POE/LA/CB (50/50/20) composite, which is undoubtedly safe for a wide range of applications. Excitingly, the electroactive SME of the composites can be conveniently regulated by the CB content and the applied voltage.

Shape memory polymer composite coatings with enhanced mechanical and antimicrobial properties

PurposeThis paper aims to exploit shape memory polymer (SMP) composite as multifunctional coatings for protecting substrates from surface wear and bacterial. The efficiency of added nano or micro-sized particles in enhancing the properties of SMP was investigated. This study also attempts to use a low-cost and effective spraying approach to fabricate the coatings. The coatings are expected to have good conformability with the substrate and deliver multi-functional performance, such as wrinkle free, wear resistance, thermal stability and antimicrobial property.Design/methodology/approachHigh-performance SMP composite coatings or thin films were fabricated by a home-made continuous spray-deposition system. The morphologies of the coatings were studied using the scanning electron microscope and the transmission electron microscope. The abrasion properties were evaluated by Taber Abraser test, and thermo-gravimetric analysis was carried out to investigate the thermal properties of prepared composites. The antimicrobial property was determined by the inhibition zone method using E. coli. The thermally responsive shape memory effect of the resulting composites was also characterized.FindingsThe morphology analysis indicated that the nanoclay was distributed on the surface of the coating which resulted in a significant improvement of the wear property. The wear resistance of the coatings with nanoclay was improved as much as 40 per cent compared with that of the control sample. The thermo-gravimetric analysis revealed that the weight loss rate of composites with nanoclay was dropped over 40 per cent. The SMP coating with zinc oxide (ZnO) showed excellent antimicrobial effect. The shape recovery effect of SMP/nanoclay and SMP/ZnO composites can be triggered by external heating and the composites can reach a full shape recovery within 60 s.Research limitations/implicationsThis study proposed a continuous spray-deposition fabrication of SMP composite coatings, which provides a new avenue to prepare novel multi-functional coatings with low cost.Originality/valueMost studies have emphasized on the sole property of SMP composites. Herein, a novel SMP composite coating which could deliver multi-functionality such as wrinkle free, wear resistance, thermal stability and antimicrobial property was proposed.

Water-Responsive Shape Recovery Induced Buckling in Biodegradable Photo-Cross-Linked Poly(ethylene glycol) (PEG) Hydrogel.

The phenomenon of recovering the permanent shape from a severely deformed temporary shape, but only in the presence of the right stimulus, is known as the shape memory effect (SME). Materials with such an interesting effect are known as shape memory materials (SMMs). Typical stimuli to trigger shape recovery include temperature (heating or cooling), chemical (including water/moisture and pH value), and light. As a SMM is able not only to maintain the temporary shape but also to respond to the right stimulus when it is applied, via shape-shifting, a seamless integration of sensing and actuation functions is achieved within one single piece of material. Hydrogels are defined by their ability to absorb a large amount of water (from 10-20% up to thousands of times their dry weight), which results in significant swelling. On the other hand, dry hydrogels indeed belong to polymers, so they exhibit heat- and chemoresponsive SMEs as most polymers do. While heat-responsive SMEs have been spotted in a handful of wet hydrogels, so far, most dry hydrogels evince the heat and water (moisture)-responsive SMEs. Since water is one of the major components in living biological systems, water-responsive SMMs hold great potential for various implantable applications, including wound healing, intravascular devices, soft tissue reconstruction, and controlled drug delivery. This provides motivation to combine water-activated SMEs and swelling in hydrogels together to enhance the performance. In many applications, such as vascular occlusion via minimally invasive surgery for liver cancer treatment, the operation time (for both start and finish) is required to be well controlled. Due to the gradual and slow manner of water absorption for water-activated SMEs and swelling in hydrogels, even a combination of both effects encounters many difficulties to meet the timerequirements in real procedures of vascular occlusion. Recently, we have reported a bioabsorbable radiopaque water-responsive shape memory embolization plug for temporary vascular occlusion. The plug consists of a composite with a poly(dl-lactide-co-glycolide) (PLGA) core (loaded with radiopaque filler) and cross-linked poly(ethylene glycol) (PEG) hydrogel outer layer. The device can be activated by body fluid (or water) after about 2 min of immersion in water. The whole occlusion process is completed within a few dozens of seconds. The underlying mechanism is water-responsive shape recovery induced buckling, which occurs in an expeditious manner within a short time period and does not require complete hydration of the whole hydrogel. In this paper, we experimentally and analytically investigate the water-activated shape recovery induced buckling in this biodegradable PEG hydrogel to understand the fundamentals in precisely controlling the buckling time. The molecular mechanism responsible for the water-induced SME in PEG hydrogel is also elucidated. The original diameter and amount of prestretching are identified as two influential parameters to tailor the buckling time between 1 and 4 min as confirmed by both experiments and simulation. The phenomenon reported here, chemically induced buckling via a combination of the SME and swelling, is generic, and the study reported here should be applicable to other water- and non-water-responsive gels.

Shape Memory Polymer Composites of Poly(styrene-b-butadiene-b-styrene) Copolymer/Liner Low Density Polyethylene/Fe3O4 Nanoparticles for Remote Activation

Magnetically sensitive shape memory poly(styrene-b-butadiene-b-styrene) copolymer (SBS)/liner low density polyethylene (LLDPE) composites filled with various contents of Fe3O4 nanoparticles were prepared. The influence of the Fe3O4 nanoparticles content on the thermal properties, mechanical properties, fracture morphology, magnetic behavior, and shape memory effect of SBS/LLDPE/Fe3O4 composites was systematically studied in this paper. The results indicated that homogeneously dispersed Fe3O4 nanoparticles ensured the uniform heat generation and transfer in the alternating magnetic field, and endowed the SBS/LLDPE/Fe3O4 composites with an excellent magnetically responsive shape memory effect. When the shape memory composites were in the alternating magnetic field (f = 60 kHz, H = 21.21 kA·m−1), the best shape recovery ratio reached 99%, the shape retention ratio reached 99.4%, and the shape recovery speed increased significantly with the increment of Fe3O4 nanoparticles. It is anticipated that tagging products with this novel shape memory composite is helpful for the purpose of an intravascular delivery system in Micro-Electro-Mechanical System (MEMS) devices.

Temperature sensing and actuating capabilities of polymeric shape memory composite containing thermochromic particles

Purpose – This paper aims to create and to study multifunctional shape memory polymer (SMP) composites having temperature-sensing and actuating capabilities by embedding thermochromic particles within the polymer matrix. Design/methodology/approach – The multifunctional materials were fabricated following a process consisting of blending (of the thermochromic particles and the SMP at various ratios), mixing, degasing, moulding and thermal curing, prepared by incorporating thermochromic particles within the polymer. The effect of the thermochromic particles on the thermomechanical properties and thermally responsive shape memory effect of the resulting multifunction SMP composites were characterised and interpreted. Findings – It was found that exposure of the composites to temperatures above 70°C led to a pronounced change of their colour that was recorded by the thermal and electrical actuation approaches and was reproducibly reversible. It was also found that the colour of the composites was independent of the mechanical state of the SMP. Such effects enabled monitoring of the onset of the set/release temperature of the SMP matrix. Furthermore, the combination of thermochromic additive and the SMP resulted in significantly improved thermomechanical strength, absorption of infrared radiation and the temperature distribution of the SMP composites. Research limitations/implications – The temperature-sensing and actuating capabilities of the polymeric shape memory composites developed through this study will help to extend the field of potential applications of such composites to fields including sensors, actuators, security labels and information dissemination, where colour indication is an advantageous feature. Originality/value – The SMP composites capable of temperature sensing and actuating are novel.

Fabrication of free-standing octagon-shaped carbon nanofibre assembly for electrical actuation of shape memory polymer nanocomposites

Purpose – The purpose of this paper is a study aimed at overcoming the interface issue between nanopaper and polymer matrix in shape-memory polymer (SMP) composite laminates caused by their large dissimilarity in electrical/thermal conductive properties. The study attempted to develop an effective approach to fabricate free-standing carbon nanofibre (CNF) assembly in octagon shape formation. The structure design and thermal conductive performance of the resulting octagon-shaped CNF assembly were optimised and simulated. Design/methodology/approach – The CNF nanopaper was prepared based on a filtration method. The SMP nanocomposites were fabricated by incorporating these CNF assemblies with epoxy-based SMP resin by a resin-transfer modelling technique. Thermal conductivity of the octagon-shaped CNF assembly was simulated using the ANSYS FLUENT software for structure design and optimisation. The effect of the octagon-shaped CNF on the thermomechanical properties and thermally responsive shape-memory effect of the resulting SMP nanocomposites were characterised and interpreted. Findings – The CNF template incorporated with SMP to achieve Joule heating triggered shape recovery at a low electric voltage of 3-10 V, due to which the electrical resistivity of SMP nanocomposites was significantly improved and lowered to 0.20 O·cm by the CNF template. It was found that the octagon CNF template with 2 mm width of skeleton presented a highest thermally conductive performance to transfer resistive heat to the SMP matrix. Research limitations/implications – A simple way for fabricating electro-activated SMP nanocomposites has been developed by using an octagon CNF template. Low electrical voltage actuation in SMP has been achieved. Originality/value – The fabricated CNF template, the structure design and analysis of dynamic thermomechanical properties of SMP are novel.