Thermo-responsive Shape Memory Research Articles

Two-Level 3D Column-like Nanofilms with Hexagonally-Packed Tantalum Fabricated via Anodizing of Al/Nb and Al/Ta Layers-A Potential Nano-Optical Biosensor.

Reanodizing metal underlayers through porous anodic alumina has already been used extensively to fabricate ordered columns of different metal oxides. Here, we present similar 3D multilayered nanostructures with unprecedented complexity. Two-level 3D column-like nanofilms have been synthesized by anodizing an Al/Nb metal layer in aqueous oxalic acid for forming the first level, and an Al/Ta layer in aqueous tartaric acid for forming the second level of the structure. Both levels were then reanodized in aqueous boric acid. The Ta layer deposited on partially dissolved porous anodic alumina of the first level, with protruding tops of niobia columns, acquired a unique hexagonally-packed structure. The morphology of the first and second levels was determined using scanning electron microscopy. Prolonged etching for 24 h in a 50%wt aqueous phosphoric acid was used to remove the porous anodic alumina. The formation mechanism of aluminum phosphates on the second-level columns in the process of long-time cold etching is considered. The model for the growth of columns on a Ta hexagonally-packed structure of the second level is proposed and described. The described approach can be applied to create 3D two- or three-level column-like systems from various valve metals (Ta, Nb, W, Hf, V, Ti), their combinations and alloys, with adjustable column sizes and scaling. The results of optical simulation show a high sensitivity of two-level column-like 3D nanofilms to biomedical objects and liquids. Among potential applications of these two-level column-like 3D nanofilms are photonic crystals for full-color displays, chemical sensors and biosensor, solar cells and thermoresponsive shape memory polymers.

Carbon nanofiber-reinforced shape memory polyurethanes based on HTPB/PTMG blend as anticorrosive coatings

ABSTRACT Aiming at an easy-processing shape memory polymer, we report different thermo-responsive shape memory polyurethane (SMPU) nanocomposites derived from Hydroxyl Terminated Poly-Butadiene (HTPB) and the Poly Tetra Methylene Glycol (PTMG) encapsulated with different concentrations of carbon nanofiber (CNF) in a cross-linked shape memory polyurethane (PU) matrix. By introducing the optimum concentration of the nanofiller with the PU matrix, we can improve essential properties of PU composites such as morphology, mechanical flexibility, as well as shape memory properties, which are considered the crucial requirement for the effective design of PU composites for a precise application. Two compositions of PU composites were prepared by encapsulating CNF, viz. PU-0.1CNF and PU-0.5CNF, the content of CNF being 1 wt.% and 5 wt.%, respectively. Morphological, thermal, and mechanical studies of these two PU composites show that CNF is homogeneously blended within the PU matrix and well dispersed. The thermal stability of prepared polymer films was evaluated with the help of Thermo-Gravimetry, indicating increased stability with the addition of CNF nanofillers. DSC analysis helps to determine the glass transition temperature (Tg ) as well as the shape transition temperature (Ttrans ). The tensile study confirmed that PU-0.5CNF possesses a greater Young’s modulus value and is not constant in elastic loads. The anti-corrosion property of the prepared SMPU nanocomposite coatings coated over the SS plate was evaluated using a 3.0 wt% NaCl (simulated seawater) solution. Extrapolation of Tafel plots and electrochemical impedance spectroscopy (EIS) provided a higher value of positive corrosion potential (Ecorr ) and a lower value of corrosion current (Icorr ). The electrochemical experiment results demonstrated that PU-0.1CNF nanocomposite coating on SS has better anti-corrosive properties and protection efficiency (PEF% = 98.43%) and behaves like a physical barrier to resist corrosion. These HTPB/PTMG PU nanocomposites exhibit excellent shape memory properties and have a unique composition having both the properties of anti-corrosion and shape memory effects. The results show that by properly selecting the composition we can tailor-make a PU having both anticorrosion and shape memory properties.

Shape Memory Polymer Foam for Autonomous Climate-Adaptive Building Envelopes

Reducing the continuously growing cooling energy demand of buildings is an important part of achieving global emission targets. Here, we present an innovative scenario of how the integration of a programmable material into a climate-adaptive building envelope (CABE) can create an energy-efficient thermal management system inherent to the material. This novel concept is based on a thermoresponsive shape memory polymer foam (SMP) and is designed to regulate the flow of ambient air through the building envelope in order to enable natural cooling of the structure. Hygrothermal simulation data obtained by the software WUFI® Plus indicate that significant cooling energy saving potential may be accessible with this type of concept. As a possible material basis for a corresponding adaptive element, a reactive foamed polyurethane-based SMP foam is proposed, which is capable of executing a thermoreversible shape change of more than 20% while having a suitable switching temperature range. Finally, the ecological impact of such a functional foam element is evaluated in detail as well as its influence on the overall balance of a façade construction by means of a life cycle assessment (LCA).

Halogen-bonded shape memory polymers

Halogen bonding (XB), a non-covalent interaction between an electron-deficient halogen atom and a Lewis base, is widely adopted in organic synthesis and supramolecular crystal engineering. However, the roadmap towards materials applications is hindered by the challenges in harnessing this relatively weak intermolecular interaction to devise human-commanded stimuli-responsive soft materials. Here, we report a liquid crystalline network comprising permanent covalent crosslinks and dynamic halogen bond crosslinks, which possess reversible thermo-responsive shape memory behaviour. Our findings suggest that I···N halogen bond, a paradigmatic motif in crystal engineering studies, enables temporary shape fixation at room temperature and subsequent shape recovery in response to human body temperature. We demonstrate versatile shape programming of the halogen-bonded polymer networks through human-hand operation and propose a micro-robotic injection model for complex 1D to 3D shape morphing in aqueous media at 37 °C. Through systematic structure-property-performance studies, we show the necessity of the I···N crosslinks in driving the shape memory effect. The halogen-bonded shape memory polymers expand the toolbox for the preparation of smart supramolecular constructs with tailored mechanical properties and thermoresponsive behaviour, for the needs of, e.g., future medical devices.

4D printing light-/thermo-responsive shape memory composites based on thermoplastic polyurethane/polylactic acid/polyaniline blends

In this work, a series of polylactic acid/thermoplastic polyurethane/polyaniline (PLA/TPU/PANI) blends with different weight ratios were prepared by Fused deposition molding First, six groups of PLA/TPU (U9A1/U8A2/U7A3/U6A4/U5A5/U4A6) and three groups of PLA/TPU/PANI (821/823/825) with different ratios were fabricated by melt blending. Then, the effects of different filament forming and printing process parameters on print resolution and quality were investigated. Next, printed samples were characterized by Fourier transform infrared (FTIR), Thermogravimetric analysis (TGA), Scanning electron microscopy (SEM) and mechanical experiments. The results of FTIR and TGA showed no chemical reaction between different components, and uniform distribution of the material was observed in the SEM. The tensile and compressive curves of the samples showed an inverted U-shape. Finally, the shape-memory property was evaluated by differential scanning calorimetry. For PLA/TPU blends, U8A2 had the best shape memory capability ([Formula: see text] = 80.8% and [Formula: see text] = 100%). Based on the excellent shape memory performance of PLA/TPU, the addition of PANI can introduce a light-actuated mechanism to form a binary-driven shape memory material. The composite materials prepared in this work can be applied to tissue engineering scaffolds, medical devices, soft robots and so on.

Review of Thermoresponsive Electroactive and Magnetoactive Shape Memory Polymer Nanocomposites.

Electroactive and magnetoactive shape memory polymer nanocomposites (SMCs) are multistimuli-responsive smart materials that are of great interest in many research and industrial fields. In addition to thermoresponsive shape memory polymers, SMCs include nanofillers with suitable electric and/or magnetic properties that allow for alternative and remote methods of shape memory activation. This review discusses the state of the art on these electro- and magnetoactive SMCs and summarizes recently published investigations, together with relevant applications in several fields. Special attention is paid to the shape memory characteristics (shape fixity and shape recovery or recovery force) of these materials, as well as to the magnitude of the electric and magnetic fields required to trigger the shape memory characteristics.

Thermo-responsive programmable shape memory polymer based on amidation cured natural rubber grafted with poly(methyl methacrylate)

This work proposes a facile and new approach that uses graft copolymerization and amidation reaction to prepare shape memory polymer (SMP) based on natural rubber (NR). The poly(methyl methacrylate) modified NR (MGNR) is cross-linked with diamine through an amidation reaction. In this kind of approach, a novel type of cross-linked MGNR with a three-dimensional network of amide linkage was prepared. The solvent resistance, mechanical properties, and phase morphology of MGNRs were significantly improved after being cross-linked by a diamine cross-linker. Additionally, the cross-linked MGNR40 also exhibited excellent shape fixation and shape recovery. This is a direct result of the vitrification of the grafted PMMA domains at low temperatures, preventing elastic recovery. Meanwhile, a cross-linked network from amide linkage facilitates recovery force upon heating. Hence, the shape memory performance of MGNRs can be tuned with both grafted PMMA content and the degree of diamine cross-link. The strategy in this research work offered an effective and convenient method to obtain cross-linked MGNR with unique molecular architecture. Consequently, this cross-linked MGNR delivered excellent mechanical strength and shape memory performance.

Rheological and thermoresponsive shape memory properties of polylactic acid (PLA) and styrene-butadiene-styrene (SBS) copolymer blends

Rheological and thermoresponsive shape memory properties of polylactic acid (PLA) and styrene-butadiene-styrene (SBS) copolymer blends

Two-way thermo-responsive thermoset shape memory polymer based on benzoxazine/urethane alloys using as self-folding structures

A novel two-way shape memory polymers derived from benzoxazine/urethane alloys (poly(BA-a/PU)) are developed in this research. The effect of urethane contents acted as spring elastomer on dynamic mechanical properties and two-way shape memory performance of the alloys was investigated. The experimental test and numerical simulation were also used to study and predict the ability of the developed 2WSMPs. The results showed that shape fixity at room temperature (RT) of poly(BA-a/PU) was enhanced in the range of 80–97% with the addition of PU contents. Shape recovery values to first temporary shape at Tg+20 °C of the specimen were 79–93%, whereas, those to second temporary shape at RT were 82–95%. Furthermore, 2WSMP based on poly(BA-a/PU) was reversely recovered between both temporary shapes more than 7 cycles. The experimental and numerical results revealed that poly(BA-a/PU) exhibited high 2WSMP performance for using as smart materials in self-folding structures application.

Thermo-Responsive Shape Memory Vanillin-Based Photopolymers for Microtransfer Molding.

Novel thermo-responsive shape-memory vanillin-based photopolymers have been developed for microtransfer molding. Different mixtures of vanillin dimethacrylate with tridecyl methacrylate and 1,3-benzenedithiol have been tested as photocurable resins. The combination of the different reaction mechanisms, thiol-acrylate photopolymerization, and acrylate homopolymerization, that were tuned by changing the ratio of monomers, resulted in a wide range of the thermal and mechanical properties of the photopolymers obtained. All polymers demonstrated great shape-memory properties and were able to return to their primary shape after the temperature programming and maintain their temporary shape. The selected compositions weretested by the microtransfer molding technique and showed promising results. The developed thermo-responsive shape-memory bio-based photopolymers have great potential for forming microtransfered structures and devices applicable on non-flat surfaces.

3D printing thermo-responsive shape memory polymer composite based on PCL/TPU blends

3D printing thermo-responsive shape memory polymer composite based on PCL/TPU blends

Influence of humidity on the rheology of thermoresponsive shape memory polymers

Shape Memory Polymers (SMPs) have the inherent ability to maintain a reversible temporary shape and restore a permanent shape under an external trigger. The class of materials has great potential to contribute to smart applications in soft robotics, aerospace, actuation and biomedicine. In these potential application domains, materials are often exposed to large fluctuations due to humidity influences. Therefore, a novel approach is developed to characterize the stronlgy coupled thermal, humidity and time-dependent behavior of polyurethane-based SMP. Weight gain measurements with disk samples of dimension 35,times 35 times 1.5 text {mm}^text {3} and linear expansion tests with rectangular samples of dimension 10 times 40 times 1.0 text {mm}^text {3} at different relative humidity are carried out to perform the isothermal and isohumid dynamic measurements in thermodynamic equilibrium. The time-temperature superposition is used to characterize and compare the viscoelastic properties at different relative humidity. Concerning effective material properties, a major finding of this investigation is the horizontal shift of the material parameter in the temperature space due to the presence of humidity. Thus, the humidity-dependent material behavior is fully described by a humidity-dependent glass transition temperature. The measured experiments provide a full description of the thermal, humidity and mechanical behavior of SMPs.Graphical abstract

β-Cyclodextrin-Based Ultrahigh Stretchable, Flexible, Electro- and Pressure-Responsive, Adhesive, Transparent Hydrogel as Motion Sensor.

In the present work, a multiple-stimuli-responsive hydrogel has been synthesized via polymerization of acrylamide (AAm) and N-hydroxy methyl acrylamide (HMAm) on β-cyclodextrin (β-CD). The synthesized hydrogel β-CD-g-(pAAm/pHMAm) exhibited various striking features like ultrahigh stretchability (>6000%), flexibility, stab resistivity, self-recoverability, electroresponsiveness, pressure-responsiveness, adhesiveness, and high transparency (>90%). Besides, the hydrogel has demonstrated enhanced biocompatibility, UV resistance, and thermoresponsive shape memory behaviors. On the basis of these attractive characteristics of the hydrogel, a flexible pressure sensor for the real-time monitoring of human motion with superior biocompatibility and transparency was fabricated. Moreover, due to the nanofibrillar surface morphology of the β-CD-g-(pAAm/pHMAm) hydrogel, the sensor based on the gel exhibited high sensitivity (0.053 kPa-1 for 0-3.3 kPa). The flexible sensor demonstrates very fast response time (130 ms-210 ms) with adequate stability (5000 cycles). Interestingly, the sensor can rapidly sense both robust (index finger and wrist) motions as well as tiny (swallowing and phonation) physiological actions. In addition, this adhesive hydrogel patch also acts as a potential carrier for the sustained topical release of (∼80.8% in 48 h) the antibiotic drug gentamicin sulfate.

Cold-induced shape memory hydrogels for strong and programmable artificial muscles

Thermo-responsive shape memory hydrogels generally achieve shape fixation at low temperatures, and shape recovery at high temperatures. However, these hydro-gels usually suffer from poor mechanical properties. Herein, we present a unique poly(acrylic acid)/calcium acetate shape memory hydrogel with cold-induced shape recovery performances as ultrastrong artificial muscles. Since the acetate groups could form aggregate at high temperatures and thus induce the association of the hydrogel network, the hydrogel can be fixed into a temporary shape upon heating and recover to its original shape in a cold environment. Moreover, a programmable shape recovery process is realized by adjusting the shape fixing time. In addition, the unique shape memory process enables the application demonstration as bio-inspired artificial muscles with an ultrahigh work density of 45.2 kJ m−3, higher than that of biological muscles (∼8 kJ m−3).

On the material characteristics of Ni modified Cu32Zn10Sn shape memory alloys: Mechanical and damping behaviour in consideration

The results from preliminary investigations on the mechanical properties and damping behaviour of Cu-32Zn-10Sn-xNi alloys (where x = 0.2 and 0.4) for potential application as thermo-responsive shape memory material is presented. The Cu-Zn-Sn alloys were produced through conventional liquid metallurgy route, subjected to homogenization treatment at 600 °C, and characterized using scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), hardness testing, tensile testing, and damping analysis. The results indicate that microstructures of the alloys were characterized with globular shaped grains, with marginal difference in the grain sizes and grain morphology. The alloys had in common Cu3Zn, Cu6Sn5, and CuSn intermetallic phases, while Ni3Sn2 intermetallic phase was the only distinct phase present in the Ni modified CuZnSn alloy that was absent in the unmodified CuZnSn alloy composition. In contrast to the hardness trend, the strength of the alloys was slightly invariant to the Ni addition (maximum of 3.77% improvement), and exhibited towering improvement in % elongation (44.2% and 86.5% for 0.2 wt% and 0.4 wt% Ni additions, respectively). The damping capacities of the 0.4 wt% Ni modified CuZnSn alloy (0.016 – 0.031) for the range of test temperatures, was significantly higher compared to the range recorded for the unmodified and 0.2 wt% Ni modified CuZnSn alloys (0.004–0.017 for both). The study showed that micro-alloying CuZnSn alloy with maximum of 0.4 wt% Ni, resulted in the best balance of mechanical and damping properties.

Vanillin acrylate-based thermo-responsive shape memory antimicrobial photopolymers

Vanillin acrylate-based thermo-responsive shape memory antimicrobial photopolymers

Deformable Thermo-Responsive Smart Windows Based on a Shape Memory Polymer for Adaptive Solar Modulations.

Thermo-responsive smart windows that control solar transmission are expected to be the promising solution to excessive building energy consumption and overheating of solar cell devices. The two performance indices, namely, the luminous transmission (Tlum) and the solar modulation (ΔTsol), are often intrinsically limited by conventional thermo-responsive materials, which restrict their applications in smart windows. Alternatively, constructing a deformable surface morphology of smart windows can be an effective strategy to modulate the solar transmission. Here, we report a new category of thermo-responsive smart windows with a deformable surface morphology, which can be custom designed to achieve both desirable ΔTsol and Tlum according to the sunlight incident angles of actual applications. This design is based on a thermo-responsive shape memory polymer and an optical coating, which is termed the butterfly-wing-like smart window (BSW). The BSW reversibly transforms from a temporary shape of flat topography to a predefined original shape of tilted configuration upon heating. It is demonstrated that the BSW has a high ΔTsol of 32.6% and an excellent Tlum(average) of 64.5%. This work provides a new design strategy and mechanism for thermo-responsive smart windows.

Self-sensing shape memory polymer composites reinforced with functional textiles

In this work, thermally reduced graphene oxide coated glass fabric (TRGO-GF) was used as a sensing element and reinforcement to manufacture thermo-responsive polyurethane-based self-sensing shape memory polymer composite (SSMPC). It was demonstrated that the proposed novel functional SSMPC was able to detect changes in temperature and shape recovery at the same time, providing its utility in a number of applications. The temperature sensing capability and the relationship between temperature and electrical resistance of manufactured SSMPC was demonstrated by inducing heating and cooling cycles using a heating film attached to the sample. It was shown that the proposed SSMPC was able to detect any changes in temperature taking place within the composite. The SSMPC showed a negative temperature coefficient (NTC) of resistance of −14.80 × 10−3 (°C)−1 and −7.25 × 10−3 (°C)−1 for testing regime I (30–40 °C) and testing regime II (40–50 °C) respectively. It was demonstrated through experiments that the SSMPC was able to detect the recovery ratio and rate of recovery during the thermally induced shape recovery process. It was also revealed that the extent and rate of shape recovery can be manipulated via controlling the thermal stimulus.

Dual-functional polymer blends with rapid thermo-responsive shape memory and repeatable self-healing properties

Although dynamic chemical interaction plays a crucial role for designing sustainable materials with extended lifespans and functionality, the preparation complexity and lack of acceptable mechanical strength limit their practical application. Herein, tunable thermo-responsive shape memory and self-healing bifunctional blends are fabricated by melt blending of poly(ethylene-co-methacrylic acid sodium salt) (EMNa) and poly(ethylene-co-methyl acrylate) (EMA) copolymers. To realize the complementary advantages, the ionic interactions in the EMNa ensure the structural integrity and self-healing repeatability of the blends, meanwhile the highly elastic EMA as the dispersed phase is capable to provide the main driving force during the shape recovery process. The shape recovery behavior can be well controlled by varying the EMA content. The shape recovery time shortens with increasing EMA content, and a U-shaped EMNa with 30 wt% of EMA (EMNa/EMA-30) specimen could recover to a plate shape within 8 s. Interestingly, the EMNa/EMA-30 exhibits repeatable self-healing capability, and its tensile strength can reach 19.4 and 15.9 MPa after one and three healing cycles, respectively. The self-healed EMNa/EMA-30 still exhibits excellent reusability and endurance, and the shape fixity and shape recovery ratios are both above 95% after 15 shape memory cycles. The rapid thermo-responsive shape memory effect, superior self-healing property, and prominent programmability make the EMNa/EMA blends promising in various cutting-edge applications, such as self-deployable structures, artificial muscles, and wearable devices.

Thermo-responsive and electro-active shape memory poly(styrene-b-isoprene-b-styrene)/poly(ethylene-co-1-octene)/graphene composites: Effect of size of graphene nanoplatelets

Thermally and electrically triggered poly(styrene-b-isoprene-b-styrene) (SIS) and poly(ethylene-co-1-octene) (PEO) thermoplastic elastomer blend composites having a SIS/PEO weight ratio of 40/60 were prepared by melt blending method. Two different graphene nanoplatelets (GnPs) with different sizes (small size (SG) and big size (BG)) were used as conductive fillers at different amounts. The thermo-responsive and electro-active shape memory performances of the composites as well as their morphological, mechanical and thermal properties were investigated by paying attention to the effect of size and loading degree of the graphene nano-fillers. Both the BG and the SG improved elastic modulus with increase in amount of the fillers. The modulus values increased by 553 % and 507 % for the 50BG and 50SG composites having 50 phr GnPs respectively, as compared to the blend. Heat-triggered thermo-mechanical shape memory tests showed that the BG filler is more advantageous for shape fixing whereas the SG filler is favorable to shape recovery ability. The electrical percolation threshold was achieved at relatively lower content for the BG filler. The 50BG composite exhibited electro-active shape recovery under 25 V, while the SG composite recovered its shape under 65 V. The thermal stability of the blend significantly improved by the use of the both fillers. The degradation onset temperatures of the 50SG and the 50BG composites increased by 25 °C and 10 °C, respectively, compared to the blend.