Multi-shape Memory Research Articles

Spatially Heterogeneous Dynamics in Multi-Shape Memory Polymers Undergoing Broad Glass Transitions

Spatially Heterogeneous Dynamics in Multi-Shape Memory Polymers Undergoing Broad Glass Transitions

Hygroscopic Tunable Multishape Memory Effect in Cellulosic Macromolecular Networks with a Supramolecular Mesophase

Tunable multishape memory polymers offer intriguing opportunities for memorizing multiple temporary shapes with tunable transition temperatures from one material composition. However, such multishape memory effects have been exclusively correlated with the thermomechanical behaviors of polymers, significantly limiting their applications in heat-sensitive scenarios. Here we report a nonthermal tunable multishape memory effect in covalently cross-linked cellulosic macromolecular networks, which spontaneously organize into supramolecular mesophases by water evaporation induced self-assembly. The supramolecular mesophase endows the network with a broad, reversible hygromechanical response combined with a unique moisture memory effect at ambient temperature, enabling diverse multishape memory behaviors (dual-, triple-, and quadruple-shape memory) under highly tunable and independent control of relative humidity (RH) alone. Significantly, such a hygroscopic tunable multishape memory effect readily extends the implications of shape memory polymers beyond the conventional thermomechanical regimes with potential advantages for biomedical applications.

A novel viscoelastic constitutive model of multi-shape memory polymer

In this paper, a novel viscoelastic constitutive model which can reflect the phase transformation mechanism of multi-shape memory polymer (M-SMP) is established. In this model, M-SMP is regarded as an inhomogeneous body composed of different phases, and the rheological representations of each phase are established based on the viscoelastic mechanics theory. Combined with the level set method, the conversion relationships of each adjacent two phases of M-SMP are established, and then the relationships between each phase are obtained. The constitutive model is used to simulate the thermodynamic behavior of dual-shape memory polymer (D-SMP) and triple-shape memory polymer (T-SMP), and the simulation results are compared with the experimental results and models of relevant literature. Meanwhile, the shape memory behaviors under different correlation rates are studied and analyzed considering the influence of rate correlation. The results show that the model can describe the thermodynamic behavior of M-SMP more accurately and effectively, and in shape memory process of M-SMP, there is a strong rate correlation here. The model can provide a theoretical basis for the engineering application of M-SMP.

Interfaces generation via severe plastic deformation – A new way to multiple shape memory polymer composites

Shape memory materials are classically described as a combination of switching and permanent domains for shape switching and shape recording, respectively. It is assumed that the interfaces between immiscible polymers could play a dual role - switching and permanent structural elements. In this work, we use severe plastic deformation as a method providing the formation of the interphases during the integration of thermodynamically immiscible polymers. By severe plastic deformation a composite gets much richer in interfaces than that obtained by melt blending. It can be used to produce effective multi-shape memory composites. A pair of immiscible polymers - acrylonitrile-butadiene-styrene copolymer (ABS) and poly(ethylene terephthalate) (PET) subjected to severe plastic deformation resulted in ABS/PET composite rich in interfaces with a broad glass transition. Strong plastic deformation by equal channel multi-angle extrusion resulted in the formation of large amount of intimate contact layers of ABS and PET and in strain-induced PET crystallization. Thermomechanical programming of such material rich in interfaces enabled a dual and triple shape memory with exceptional parameters.

Self-Healing, Thermadapt Triple-Shape Memory Ionomer Vitrimer for Shape Memory Triboelectric Nanogenerator.

Benefiting from the associative exchange reaction, vitrimers could be deformed to various shapes while maintaining the integrity of the network, thus being regarded as promising candidates for shape memory polymers. However, it is still a challenge to design the highly desired smart electronic devices with triple and multishape memory performances through a facile method. Here, a novel dual-cross-linked poly(acrylonitrile-co-butyl acrylate-co-hydroxyethyl methacrylate-co-zinc methacrylate) (Zn-PABHM) copolymer was developed via a facile and one-pot free radical polymerization strategy. Ionic cross-linking, the transcarbamoylation reaction, and glass transition were used to fix the permanent shape and two temporary shapes of the obtained ionomer vitrimer, respectively. The thermomechanical and stress relaxation performances of Zn-PABHM vitrimer can be customized by tuning the proportion of the chemical cross-linking and physical cross-linking knots. Furthermore, the Zn-PABHM was employed to construct a shape memory triboelectric nanogenerator, which demonstrates distinctive performance and tunable electrical outputs (37.4-96.0 V) due to variable contact areas enabled by triple shape memory effects. Consequently, the triple-shape memory ionomer vitrimer obtained via a facile and one-pot synthetic strategy has great potential in smart multifunctional electronic devices.

Luminescent composite organohydrogels with Fe3+, pH, and glucose-dependent shape memory behavior accompanied with diverse fluorescence variation

It is quite urgent to develop a smart and high through-put confidential information storage, protection, and display platform based on the fluorescent hydrogels that could exhibit diverse fluorescent variation behavior during each stimulus-based shape memory and recovery process. Herein, it proposed an effective approach to develop a novel fluorescent composite gel with Fe3+, pH, and glucose-dependent diversity fluorescence variation and shape memory behavior. For this composite gel system, based on the reversible coordination interactions between Fe3+ and carboxylic acid groups of carboxymethyl cellulose (CMC), boric acid groups of carbon dots (CDs), and hydroxyl groups of PVA, it can stabilize and memorize the temporary shapes under the stimulus of Fe3+ and pH, respectively. Meanwhile, the fluorescence of the CDs within the gels can also exhibit diversity variation behaviors during each shape recovery process. Furthermore, the compositions of the composite gel were optimized to realize relatively high efficiency of shape recovery and fluorescence variation under each type of stimulus. In summary, this study presented a universal strategy for multi-shape memory hydrogels with diverse fluorescence variation properties which exhibited prominent prospective in the field of information encryption with high-level security.

Thermo- and near infrared light-induced reversible multi-shape memory materials for actuators and sensors

Smart materials with reversible shape transformation have drawn enormous interest for their potential applications in various fields.

Catalyst-Free Vitrimer Cross-Linked by Biomass-Derived Compounds with Mechanical Robustness, Reprocessability, and Multishape Memory Effects.

Vitrimerization of thermoset polymers plays an important role in addressing resource recovery and reuse. Vitrimer elastomers with good mechanical properties often require well-designed crosslinking agents or fillers, but this increases processing complexity or reduces vitrimer dynamic properties. In this report, a simple green strategy to build a strong vitrimer elastomer is designed. Commercially available epoxidized natural rubber (ENR) is cross-linked with biomass-derived D-Fructose 1,6-bisphosphoric acid to get a vitrimer elastomer cross-linked by β-hydroxy phosphate ester bonds and has abundant hydrogen bonds. Hydrogen bonds can preferentially break and dissipate energy under external forces, which makes the sample robust. The topological network can be reformed at high temperatures through the dynamic exchange of β-hydroxy phosphate ester bonds, which gives the material malleability and recyclability. In addition, through the strategy of combining reprocessing and welding, multiple shape memory effects can be achieved in one postprocessing step. Considering that a variety of commercially available epoxy polymers are easily available, it is believed that this strategy can be a simple and versatile way to enable commercial epoxy polymers to achieve green crosslinking through biomass crosslink agents, which results in robust and recyclable vitrimers based on β-hydroxy phosphate bonds.

Negatively thermodynamic toughening in double network hydrogel towards cooling-triggered multi-shape memory effect

This paper explores fundamental mechanisms of negatively thermodynamic toughening during microphase separations of double network (DN) hydrogels, which have dynamically coordinating components with adjustable swelling behavior and designable multi-shape memory effect (multi-SME). Based on the Flory–Huggins theory and Fick’s second law, a thermodynamic model is formulated to study the diffusive dynamics, cooling-triggered multi-SME and mechanical toughness of the DN hydrogels. The negatively thermodynamic toughening effect of the DN hydrogels is strongly dependent on their water concentration, hydrophobic transition and microphase separation. Finally, effectiveness of this new model is demonstrated by applying it to predict dual-SME, quadruple-SME and cooling-triggered shape memory behaviors of DN hydrogels. This study provides a methodology for the design of shape memory DN hydrogels with tunable, giant and programmable cooling-triggered multi-SME.

A level-set viscoelastic constitutive model for multi-shape memory polymers and composites

A level-set viscoelastic constitutive model for multi-shape memory polymers and composites

Shape Memory Polymer Fibers: Materials, Structures, and Applications

Shape memory polymer (SMP) is a kind of material that can sense and respond to the changes of the external environment, and its behavior is similar to the intelligent reflection of life. Electrospinning, as a versatile and feasible technique, has been used to prepare shape memory polymer fibers (SMPFs) and expand their structures. SMPFs show some advanced features and functions in many fields. In this review, we give a comprehensive overview of SMPFs, including materials, fabrication methods, structures, multifunction, and applications. Firstly, the mechanism and characteristics of SMP are introduced. We then discuss the electrospinning method to form various microstructures, like non-woven fibers, core/shell fibers, hollow fibers and oriented fibers. Afterward, the multiple functions of SMPFs are discussed, such as multi-shape memory effect, reversible shape memory effect and remote actuation of composites. We also focus on some typical applications of SMPFs, including biomedical scaffolds, drug carriers, self-healing, smart textiles and sensors, as well as energy harvesting devices. At the end, the challenges and future development directions of SMPFs are proposed.

Multi-modal commutative dynamics in semi-crystalline polymers undergoing multiple shape memory behavior

Semi-crystalline polymers offer great opportunities for design and tuning of multi-shape memory effect (multi-SME) through their programmable melting transitions. However, coexistence of amorphous and crystalline components as well as their multiple interfaces results in complex cooperative dynamics. In this study, we propose a one-dimensional multi-modal dynamic model to describe the commutative and cooperative dynamics in semi-crystalline shape memory polymers undergoing multi-SME. A three-phase model and Takayanagi principle are firstly applied to study the cooperative dynamics of amorphous/crystalline components and their interfaces. Phase transition theory and modified Avrami theory are used to model the cooperative dynamics of glass and melting transitions, respectively. Commutative dynamics and glass/melting transitions are further investigated to achieve on-demand multi-SME and shape recovery behaviors. Finally, effectiveness of the newly established model was demonstrated to predict triple-SMEs and quadruple-SMEs in semi-crystalline polymers reported in literature, and the theoretically obtained results show good agreements with the experimental ones.

Fe3+, NIR light and thermal responsive triple network composite hydrogel with multi-shape memory effect

Recently, artificial intelligence has driven the development of shape memory hydrogels (SMHs) with complicated environmental sensitive abilities. However, current SMHs possess fundamental limitations in terms of their responsive performance and mechanical properties, which severely limits their practical applications. Herein, a triple-network composite hydrogel with Fe3+, NIR light, and thermal responsive abilities is fabricated and developed as multi-SMHs, named as PDA/CMC-Fe3+/PVA hydrogel. In this hydrogel system, the interpenetrating triple network are formed by chemically-physically co-crosslinked polyvinyl alcohol (PVA) networks, and physically crosslinked carboxymethyl cellulose (CMC)-Fe3+ network. In addition, polydopamine (PDA), which is introduced into the hydrogel system by in-situ polymerization way, could not only serve as an energy converter to endow the hydrogel with NIR-based responsive ability, but also enhance its mechanical strength. Remarkably, the as-prepared PDA/CMC-Fe3+/PVA hydrogels with the optimized compositions exhibit relatively excellent mechanical properties (tensile strength = 163.48 ± 10.42 kPa, elastic modulus = 45.42 ± 3.96 kPa, toughness = 165.02 ± 7.01 kJ/m3) due to the synergistic effect of the triple-network and PDA doping. Moreover, the composition of the hydrogel is optimized to realize a stable temporary shape and rapid recovery to the permanent shape, which is controlled by Fe3+, NIR irradiation, and thermal stimulus. The resultant hydrogels exhibit not only multi-stimulus responsive abilities, but also programmable multi-shape memory properties. The versatile shape memory properties endow potential for the materials to be used in the field of artificial intelligence.

A Triple Crosslinking Design toward Epoxy Vitrimers and Carbon Fiber Composites of High Performance and Multi-shape Memory

It remains a challenge to use a simple approach to fabricate a multi-shape memory material with high mechanical performances. Here, we report a triple crosslinking design to construct a multi-shape memory epoxy vitrimer (MSMEV), which exhibits high mechanical properties, multi-shape memory property and malleability. The triple crosslinking network is formed by reacting diglycidyl ether of bisphenol F (DGEBF) with 4-aminophenyl disulfide, γ-aminopropyltriethoxysilane (APTS) and poly(propylene glycol) bis(2-aminopropyl ether) (D2000). The triple crosslinking manifests triple functions: the disulfide bonds and the silyl ether linkages enable malleability of the epoxy network; the silyl ether linkages impart the network with high heterogeneity and broaden the glass transition region, leading to multi-shape memory property; a small amount of D2000 increases the modulus difference between the glassy and rubbery states, thereby improving the shape fixity ratio. Meanwhile, the high crosslinking density and rigid structure provide the MSMEV with high tensile strength and Young’s modulus. Moreover, integrating carbon fibers and MSMEV results in shape memory composites. The superior mechanical properties of the composites and the recyclability of carbon fiber derived from the dissolvability of MSMEV make the composites hold great promise as structural materials in varied applications.

A study on sisal-based polyurethane foam with multi-shape memory properties

SMPU-PSF exhibited a high compression rate, high controllability, and good shape recovery rate.

Renewable Castor-Oil-based Waterborne Polyurethane Networks: Simultaneously Showing High Strength, Self-Healing, Processability and Tunable Multishape Memory.

Materials with multifunctionality or multiresponsiveness, especially polymers derived from green, renewable precursors, have recently attracted significant attention resulting from their technological impact. Nowadays, vegetable-oil-based waterborne polyurethanes (WPUs) are widely used in various fields, while strategies for simultaneous realization of their self-healing, reprocessing, shape memory as well as high mechanical properties are still highly anticipated. We report development of a multifunctional castor-oil-based waterborne polyurethane with high strength using controlled amounts of dithiodiphenylamine. The polymer networks possessed high tensile strength up to 38 MPa as well as excellent self-healing efficiency. Moreover, the WPU film exhibited a maximum recovery of 100 % of the original mechanical properties after reprocessing four times. The broad glass-transition temperature of the samples endowed the films with a versatile shape-memory effect, including a dual-to-quadruple shape-memory effect.

Renewable Castor‐Oil‐based Waterborne Polyurethane Networks: Simultaneously Showing High Strength, Self‐Healing, Processability and Tunable Multishape Memory

AbstractMaterials with multifunctionality or multiresponsiveness, especially polymers derived from green, renewable precursors, have recently attracted significant attention resulting from their technological impact. Nowadays, vegetable‐oil‐based waterborne polyurethanes (WPUs) are widely used in various fields, while strategies for simultaneous realization of their self‐healing, reprocessing, shape memory as well as high mechanical properties are still highly anticipated. We report development of a multifunctional castor‐oil‐based waterborne polyurethane with high strength using controlled amounts of dithiodiphenylamine. The polymer networks possessed high tensile strength up to 38 MPa as well as excellent self‐healing efficiency. Moreover, the WPU film exhibited a maximum recovery of 100 % of the original mechanical properties after reprocessing four times. The broad glass‐transition temperature of the samples endowed the films with a versatile shape‐memory effect, including a dual‐to‐quadruple shape‐memory effect.

An Interfacial Dynamic Crosslinking Approach toward Catalyst-free and Mechanically Robust Elastomeric Vitrimer with a Segregated Structure

Elastomeric vitrimers with covalent adaptable networks are promising candidates to overcome the intrinsic drawbacks of conventional covalently-crosslinked elastomers; however, most elastomeric vitrimers show poor mechanical properties and require the addition of exogenous catalysts. Herein, we fabricate a catalyst-free and mechanically robust elastomeric vitrimer by constructing a segregated structure of sodium alginate (SA) in the continuous matrix of epoxidized natural rubber (ENR), and further crosslinking the composite by exchangeable hydroxyl ester bonds at the ENR-SA interfaces. The manufacturing process of the elastomeric vitrimer is facile and environmentally friendly without hazardous solvents or exogenous catalysts, as the abundant hydroxyl groups of the segregated SA phase can act as catalyst to activate the crosslinking reaction and promote the dynamic transesterification reaction. Interestingly, the segregated SA structure bears most of the load owing to its high modulus and small deformability, and thus ruptures preferentially upon deformation, leading to efficient energy dissipation. Moreover, the periodic stiffness fluctuation between rigid segregated SA phase and soft ENR matrix is beneficial to the crack-resisting. As a result, the elastomeric vitrimer manifests exceptional combination of catalyst-free, defect-tolerance, high tensile strength and toughness. In addition, the elastomeric vitrimer also exhibits multi-shape memory behavior which may further broaden its applications.

On demand shape memory polymer via light regulated topological defects in a dynamic covalent network

The ability to undergo bond exchange in a dynamic covalent polymer network has brought many benefits not offered by classical thermoplastic and thermoset polymers. Despite the bond exchangeability, the overall network topologies for existing dynamic networks typically cannot be altered, limiting their potential expansion into unexplored territories. By harnessing topological defects inherent in any real polymer network, we show herein a general design that allows a dynamic network to undergo rearrangement to distinctive topologies. The use of a light triggered catalyst further allows spatio-temporal regulation of the network topology, leading to an unusual opportunity to program polymer properties. Applying this strategy to functional shape memory networks yields custom designable multi-shape and reversible shape memory characteristics. This molecular principle expands the design versatility for network polymers, with broad implications in many other areas including soft robotics, flexible electronics, and medical devices.

A comprehensive review on thermomechanical constitutive models for shape memory polymers

Shape memory polymers are a class of smart materials, which are capable of fixing their deformed shapes, and can return to their original shape in reaction to external stimulus such as heat. Also due to their exceptional properties, they are mostly used in four-dimensional printing applications. To model and investigate thermomechanical response of shape memory polymers mathematically, several constitutive equations have been developed over the past two decades. The purpose of this research is to provide an up-to-date review on structures, classifications, applications of shape memory polymers, and constitutive equations of thermally responsive shape memory polymers and their composites. First, a comprehensive review on the properties, structure, and classifications of shape memory polymers is conducted. Then, the proposed models in the literature are presented and discussed, which, particularly, are focused on the phase transition and thermo-viscoelastic approaches for conventional, two-way as well as multi-shape memory polymers. Then, a statistical analysis on constitutive relations of thermally activated shape memory polymers is carried out. Finally, we present a summary and give some concluding remarks, which could be helpful in selection of a suitable shape memory polymer constitutive model under a typical application.