Shape Memory Process Research Articles

Shape Memory: An Efficient Method to Develop the Latent Photopatterned Morphology for Elastomer in Two/Three Dimension

Shape memory behavior was applied here as a new approach for developing the latent photopatterned morphologies in two/three dimension (2D/3D) on the modified poly(styrene-block-butadiene-block-styrene) (SBS). By attaching anthracene groups onto the SBS chains, the elastomer frozen in the deformed state was photopatterned via the photodimerization of anthracene. Upon thermal treatment, shape memory process could effectively develop the latent photopatterning induced 2D-2D and 2D-3D shape transformation. Due to the reversible dimerization of anthracene, the photoinduced patterns and the shape conformation could be erased and redeveloped for multiple times.

Highly Stretchable, Shape Memory Organohydrogels Using Phase-Transition Microinclusions.

Shape memory effect in polymer materials has attracted considerable attention due to its promising applications in a variety of fields. However, shape memory polymers prepared by conventional strategy suffer from a common problem, in which high strain capacity and excellent shape memory behavior cannot be simultaneously achieved. This study reports a general and synergistic strategy to fabricate high-strain and tough shape memory organohydrogels that feature binary cooperative phase. The phase- transition micro-organogels and elastic hydrogel framework act synergistically to provide excellent thermomechanical performance and shape memory effect. During shape memory process, the organohydrogels exhibit high strain capacity, featuring fully recoverable stretching deformation by up to 2600% and compression by up to 85% beneath a load ≈20 times the organohydrogel's weight. Furthermore, owing to the micro-organogel and hydrogel heterostructures, the interfacial tension derived from heterophases dominates the shape recovery of the organohydrogel material. Simple processing and smart surface patterning of the shape memory behavior and multiple shape memory effects can also be realized. Meanwhile, these organohydrogels are also nonswellable in water and oil, which is important for multimedia applications.

Multiple shape memory effects of trans‐1,4‐polyisoprene and low‐density polyethylene blends

AbstractA novel series of shape memory blends of trans‐1,4‐polyisoprene (TPI) and low‐density polyethylene (LDPE) were prepared using a simple physical blending method. The mechanical, thermal and shape memory properties of the blends were studied and schemes proposed to explain their dual and triple shape memory behaviors. It was found that the microstructures played an important role in the shape memory process. In TPI/LDPE blends, both the TPI crosslinking network and LDPE crystalline regions could work as fixed domains, while crystalline regions of LDPE or TPI could act as reversible domains. The shape memory behaviors were determined by the components of the fixed and reversible domains. When the blend ratio of TPI/LDPE was 50/50, the blends showed excellent dual and triple shape memory properties with both high shape fixity ratio and shape recovery ratio. © 2017 Society of Chemical Industry

Shape Memory Actuation of Janus Nanoparticles with Amphipathic Cross-Linked Network.

Preparation of nanoscale Janus particles that can respond to external stimulation and, at the same time, be prepared using an easily achievable method presents a significant challenge. Here, we have demonstrated the shape memory of Janus nanoparticles (SMJNPs) with a multifunctional combination of Janus nanostructure and a shape memory effect, composed of a well-defined amphipathic sucrose-poly(ε-caprolactone) cross-linked network. A sudden negative pressure method was first used to prepare the Janus-shaped nanoparticles (temporary shape), which can switch their shape and wettability. The Janus-shaped nanoparticle is an amphipathic structure composed of hydrophilic and hydrophobic parts. Moreover, in response to temperature, the nanoparticle can recover their nanosphere state via a shape memory process. The novel Janus nanoparticles with the shape memory property also show a great potential for application such as drug delivery.

The molecular mechanism of the thermo-responsive shape memory effect of self-assembled poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} fiber

A new molecular mechanism is proposed to explain the shape memory effect of mesogen-jacketed liquid crystalline polymer fiber—poly-{2,5-bis[(4-butoxyphenyl)oxycarbonyl]styrene} (PBPCS) fiber-designed in the molecular level. Due to the strong “coupling effect” between flexible backbone and rigid side mesogens, the molecular structure of PBPCS can be regarded as “dual chains” model that is constituted by a flexible backbone chain and a rigid side chain in parallel. The flexible backbone chains are reversible above the transition temperature and act as a switch structure, the physically cross-linked points caused by the π–π weak interactions between rigid side mesogens are responsible for memorizing a shape function and act as a fixing structure; therefore, the switch structure (flexible backbone) and the fixing structure (rigid mesogens) are found in each macromolecular chain. Furthermore, the shape memory behavior of PBPCS fibers is discussed by a viscoelastic molecular model consisting of two Maxwell models in parallel, the obtained theoretical values by “dual chains” model was in agreement with experimental results, very well. The viscoelastic molecular model described for shape memory process was correlated to the molecular mechanism explained for shape memory effect. This work provides a new idea and significant approach for design of new shape memory polymers.

High Strength Self‐Healing Magnetic Elastomers With Shape Memory Effect

Development of self‐healing and shape memory elastomers is important for artificial smart materials. Here, a novel shape memory magnetic elastomer with high mechanical strength consisting of conventional polymer and Fe3O4 nanoparticles is reported. The elastomer exhibit superparamagnetism, and superior self‐healing performance at elevated temperature. The tensile strength of the healed elastomer can be up to 12.0 MPa, and almost equal to that of virginal sample. These materials are capable of remote controlling in shape memory process and actuating behavior, and can be used in many applications, ranging from wireless‐controller to actuator or biomedical devices, and other remote shape memory systems.

Oxide Formation on NiTi Surface: Influence of the Heat Treatment Time to Achieve the Shape Memory

Several studies regarding superficial treatments of Nitinol (NiTi) shape-memory have been developed aiming to the improve corrosion resistance and to block the Ni release to adjacent tissues. The necessary heat treatment to achieve the shape memory effect normally occurs at temperatures between 500 and 600 °C. However, titanium oxide (TiO2) is formed on the NiTi surface during the shape memory process heat treatment. In this work the effects of the heat treatment time on the surface characteristics of the formed NiTi oxide, at temperatures that promote the shape-memory (530 and 570 °C), were evaluated. The TiO2 layers which were obtained were evaluated by X-ray diffraction (XRD), energy dispersive X-ray (EDX), scanning electron microscope (SEM), thermogravimetric analysis (TGA), wettability and roughness. The results show that by increasing the exposure time at the temperature of 570 °C the formation of a thicker oxide is promoted, with less superficial roughness and of a hydrophobic nature. According to the literature, these characteristics indicate that the obtained oxide layer has properties that accelerat the osseointegration process.

Dynamic Optical Gratings Accessed by Reversible Shape Memory.

Shape memory polymers (SMPs) have been shown to accurately replicate photonic structures that produce tunable optical responses, but in practice, these responses are limited by the irreversibility of conventional shape memory processes. Here, we report the intensity modulation of a diffraction grating utilizing two-way reversible shape changes. Reversible shifting of the grating height was accomplished through partial melting and recrystallization of semicrystalline poly(octylene adipate). The concurrent variations of the grating shape and diffraction intensity were monitored via atomic force microscopy and first order diffraction measurements, respectively. A maximum reversibility of the diffraction intensity of 36% was repeatable over multiple cycles. To that end, the reversible shape memory process is shown to broaden the functionality of SMP-based optical devices.

Shape memory effect during preparation of alumia ceramic tubes

Pure alumina ceramic tube and 95 alumina ceramic (the ceramic with 95.84% alumina) tube were prepared by using self-prepared alumina micrometer powder without agglomeration as raw material. The ceramic green was shaped by isostatic pressing and sintered at different temperature from 800 to 1 600 °C for 2 h. The 95 ceramic tube sintered at 1 550 °C for 2 h had mean particle size of 4 μm, bend strength of 437 MPa and volume density of 3.714 g/cm3. Shape memory effect during sintering was observed. XRD results showed that no phase transition occurred during shape memory process, which indicated that shape memory effect was not caused by phase transition. Several probable causes of the alumina ceramic shape memory effect were discussed in this paper.

Probing the structure evolution/orientation induced by interaction between polyurethane segments and SiO2 surface in shape memory process

The effects of interactions between nano-SiO2 and polyurethane segments on structure and orientation behaviors in shape memory process have been systematically investigated. Polyurethane (PU)/nano-SiO2 composites were prepared by solution mixing in tetrahydrofuran (THF). The scanning electron microscopy (SEM) observation shows that nano-SiO2 particles are well dispersed in PU matrix. Besides the shape memory performance of pure PU is superior to that of PU/nano-SiO2 composite with 3 wt% filler content. It has been proved that the nano-SiO2 has some interaction with the segments of PU, affecting the orientation behaviors of polyurethane in both drawing and recovery process. In the drawing process, the hard segments at the domain interface and soft segments of PU-3% have a perpendicular direction at the small strain, and then possess a parallel orientation at larger deformation, whereas those of PU-0% orient positively from the beginning to the end. Moreover, the mobility of both soft and hard segments is retarded mostly by the nano-SiO2. In addition, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) tests have also been done. The results indicate that crystallization is quite small influenced by the addition of nano-SiO2.

Sodium dodecyl sulfate/epoxy composite: water-induced shape memory effect and its mechanism

With the aim of integrating a family of functional composites, possessing a conspicuous water-induced shape memory effect (SME), a novel sodium dodecyl sulfate–epoxy shape memory composite was constructed. The original fabrication strategy of the composite was designed based on the chemical interaction constructed 3D microvoid on the shape memory composite surface. Compared with the pure epoxy shape memory polymer, the composites display a gratifying water-induced shape memory effect. The results indicate that the water-induced shape recovery rate of the composite is accelerated through increasing the temperature or decreasing the specimen thickness. An immersion test in water suggests that the chemical interaction and physical swelling effect have a significant influence on the water-induced shape memory process. This research advocates the design concept and presents some experimental results of the water-driven smart composite. The potential application range is expected to expand more widely, including a humidity sensor, temperature/humidity switch, underwater deployable structure and a power source transforming chemical energy into mechanical energy for an ultralow-power device.

Polymers with Dual Light-Triggered Functions of Shape Memory and Healing Using Gold Nanoparticles

Shape-memory and stimuli-healable polymers (SMP and SHP) are two types of emerging smart materials. Among the many stimuli that can be used to control SMP and SHP, light is unique because of its unparalleled remote activation and spatial control. Generally, light-triggered shape memory and optically healable polymers are different polymers and it is challenging to endow the same polymer with the two light-triggered functions because of their structural incompatibility. In this paper, we describe a general polymer design that allows a single material to exhibit both light-controlled shape memory and optical healing capabilities. We show that by chemically cross-linking a crystalline polymer and loading it with a small amount of gold nanoparticles (AuNPs), the polymer displays optically controllable shape memory and fast optical healing based on the same localized heating effect arising from the surface plasmon resonance of AuNPs. The photothermal effect controls, on the one hand, the shape memory process by tuning the temperature with respect to Tm of the crystalline phase and, on the other hand, activates the damage healing through crystal melting and recrystallization. Moreover, we show that these two features can be triggered separately in a sequential manner.

Recovery performance and characteristics in shape memory effects of aliphatic polyether urethane

The analysis on the recovery performance and characteristics in shape memory effects is helpful for the optimal design and engineering applications of shape memory polymers and their composites. To investigate the relationships among recovery performance, material parameters, and loading conditions, by taking aliphatic polyether urethane as an example, the researchers simulate the shape memory behaviors numerically using a three‐dimensional viscoelastic model. The material parameters for this model are taken from stress relaxation tests, rather than dynamic mechanical analysis tests. Both the unconstrained and the constrained recovery behaviors during strain‐controlled shape memory processes are analyzed. The results reveal that the unconstrained recovery occurs at the same temperature regardless of the applied strain values. Another interesting result is that the shape recovery temperature in unconstrained recovery situations increases and the maximum recovery stress under constrained recovery conditions decreases with the increase of heating rates. Copyright © 2013 John Wiley & Sons, Ltd.

Modeling the glass transition of amorphous networks for shape-memory behavior

In this paper, a thermomechanical constitutive model was developed for the time-dependent behaviors of the glass transition of amorphous networks. The model used multiple discrete relaxation processes to describe the distribution of relaxation times for stress relaxation, structural relaxation, and stress-activated viscous flow. A non-equilibrium thermodynamic framework based on the fictive temperature was introduced to demonstrate the thermodynamic consistency of the constitutive theory. Experimental and theoretical methods were developed to determine the parameters describing the distribution of stress and structural relaxation times and the dependence of the relaxation times on temperature, structure, and driving stress. The model was applied to study the effects of deformation temperatures and physical aging on the shape-memory behavior of amorphous networks. The model was able to reproduce important features of the partially constrained recovery response observed in experiments. Specifically, the model demonstrated a strain-recovery overshoot for cases programmed below Tg and subjected to a constant mechanical load. This phenomenon was not observed for materials programmed above Tg. Physical aging, in which the material was annealed for an extended period of time below Tg, shifted the activation of strain recovery to higher temperatures and increased significantly the initial recovery rate. For fixed-strain recovery, the model showed a larger overshoot in the stress response for cases programmed below Tg, which was consistent with previous experimental observations. Altogether, this work demonstrates how an understanding of the time-dependent behaviors of the glass transition can be used to tailor the temperature and deformation history of the shape-memory programming process to achieve more complex shape recovery pathways, faster recovery responses, and larger activation stresses.

Microscopic residual stress evolution during deformation process of an FeMnSiCr shape memory alloy investigated using white X-ray microbeam diffraction

Microscopic residual stress evolution in different austenite (γ) grains during shape memory process in an FeMnSiCr alloy was investigated using the white X-ray microbeam diffraction technique. The use of high-energy white X-ray microbeam with small beam size allowed us to measure the microscopic residual stress in coarse γ grains with specific orientation. After tensile deformation large compressive residual stress was evolved in γ grains due to the formation of stress-induced ε martensite, but upon recovery heating it almost disappeared as a result of reverse transformation of martensite. The magnitude of compressive residual stress was higher in grains with orientations close to 〈144〉 and 〈233〉 orientations than in a grain with near 〈001〉 orientation. Analysis of the microstructure of each grain using electron backscattering diffraction suggested that the difference in the magnitude of compressive residual stress could be attributed to different martensitic transformation characteristics in the grains.

Shape-memory polymers with multiple transitions: complex actively moving polymers

Shape-memory polymers (SMPs) are able to perform shape transitions in a pre-defined pathway in response to suitable external stimuli such as heat, magnetism, electricity, moisture, or light. Most of the SMPs are dual-shape materials, which enable a single shape transition from a temporary to a permanent shape. Recently, triple-shape polymers (TSPs), which are capable of accomplishing two shape transitions, as well as multi-shape polymers with shape changes have been introduced including temperature-memory polymers (TMPs) with tunable multiple shape transitions. Different concepts for obtaining multi-shape polymers are introduced and the sophisticated structural design concepts in combination with tailored shape-memory creation processes (SMCPs) are explained. Future opportunities emerge in alternative actuation methods and exploration of potential applications.

Enhanced toughness and shape memory behaviors of toughed epoxy resin

This paper reports on an approach to enhance the toughness of shape memory epoxy by using polypropylene glycol diglycidyl ether (G) as the toughening agent. The mechanical properties and shape memory behavior of the toughened resin systems with different loading level of G were studied, respectively. Results of the torsional braid analysis (TBA) test indicated that G had good compatibility with the epoxy resin matrix and induced a decrease in the glass transition temperature, Tg, of the toughened systems when compared to that of the neat resin system; and the decrease in Tg scaled with the content of G added in the system. Impact strength tests showed that the impact strength was improved significantly by adding G into the resin system and it increased by a factor of 13.7 for the system with 13 wt.% content of G. In addition, the toughened systems were found to yield during the impact strength test whereas brittle fracture occurred for the neat epoxy resin system; this behavior could be further confirmed by the results of scanning electron microscopy (SEM). In the shape memory behavior tests, strain fixity ratio reached as high as 98.9% for toughened systems with 7, 9, 11, 13, and 15 wt.% of G. Toughened systems also displayed changed shape recovery behavior that was comparable with that of the neat epoxy resin system during shape memory process.

Shape memory properties of polycaprolactone‐based polyurethanes prepared by reactive extrusion

AbstractThe shape memory properties of polycaprolactone‐based polyurethanes (PCLUs) synthesized via a novel route of reactive extrusion were investigated in terms of the deformation amplitude, temperature, and rate by differential scanning calorimetry (DSC), dynamic mechanical analyzer, and polarized optical microscopy (POM). DSC analysis shows that the crystalline melting temperature and crystallinity of PCLU increased monotonically with increasing the average polymerization degree $ ( \overline {DPn}) $ of poly(ε‐caprolactone) (PCL) block. The retract force increased with increasing the temperature and reached the maximum (6–7 MPa) within 45–55°C. Furthermore, a modified model with two recovery stages was postulated to elucidate the shape memory process, which is visually presented by POM analysis. The two stages of tensile and compressive recovery are distinguished by the inflexion temperature, within 43–48°C and 64–66°C, respectively. The shape fixity is about 60–70% and can be improved to 100% by choosing proper deformation temperature. The tensile deformation recovery ratio was 80–98% due to the water absorption, whereas the compressive deformation recovery ratio was almost 100%. Besides, recovery tests show that the lowest recovery temperature ranged from 24 to 47°C was influenced by the deformation temperature, rate and the PCL block $ ( \overline {DPn}) $. Thus, the shape memory properties can be adjusted according to different purposes. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013

A spatially and temporally controlled shape memory process for electrically conductive polymer–carbon nanotube composites

Crosslinked P(MMA-BA)–CNTs shape memory composites prepared by ultrasound assisted in situ polymerization, have both relatively high electrical conductivities and good shape memory properties. Electrical resistance heating was used as a trigger to realize the spatial and temporal control of the shape memory process and to obtain multiple shapes by selecting the place where the electrical voltage was applied or switching the power on/off.

A geometric approach to the modeling of the catheter–heart interaction for VR simulation of intra-cardiac intervention

Cardiac intervention is a minimally invasive diagnostic and therapeutic procedure used to treat cardiac diseases. The mapping of heart geometry with minimal visual assistance presents a technical challenge for interventional cardiologists attempting catheter navigation. This paper presents a geometric approach to modeling the catheter–heart interaction for VR simulations of catheter navigation within a heart chamber. Three types of modeling are used to model the interaction between the catheter and the heart wall: non-slip, pseudo-slip and slip modeling. A two-step shape memory process that minimizes the bending of and strain on the catheter is designed for catheter deformation for non-slip or pseudo-slip contact, and a progressive group linkage bending process that constrains the catheter curvature and position within the volume enclosure is designed for catheter deformation for slip contact. The proposed model is consistent with the observations made during the experiment. The model is able to deform the catheter in any free-state shape within the volume enclosure and is independent of local motion increment. Thus, it presents advantages in terms of complexity and real-time requirements.