Intelligent Materials: Shape-Memory Polymers

A finite deformation thermomechanical constitutive model for triple shape polymeric composites based on dual thermal transitions

Stimuli-responsive materials are smart materials capable to adjust their properties (e.g. shape and size) in response to an external or internal stimulus including temperature, light, magnetic field, mechanical stress, and pH. Shape memory polymers (SMPs) are attractive class of stimuli-responsive, programmable smart materials with shape-memory behavior: memorize their original, permanent shape; deform and fix into a secondary, temporary shape; and recover the original, permanent shape upon applying an external stimulus. In recent years, advancing intelligent supercapacitors and batteries have attracted significant attention whereas stimuli-responsive materials were integrated to induce stimuli-responsive properties to introduce new properties or mitigate some of the existing issues such as thermal management, mitigating volume change-induced performance degradation, recovery from a mechanical deformation, self-healing, electrochromism. Indeed, integrating energy storage technologies with a variety of stimuli are a fascinating method to realize smart functions [1-3].Herein, we aim to develop a heat-responsive battery capable of mitigating the impact of incidental mechanical abuse or deformation. To achieve this, a shape-memory solid polymer electrolyte (SMSPE) is engineered and incorporated into lithium metal batteries (LMBs). In response to an external heat, the engineered SMSPEs recover their original shape and size from mechanical deformations such as bending and elongation. This study opens-up a promising approach for engineering intelligent batteries responsive to unfavorable internal or external stimuluses, with potential to have a broad impact on other energy storage technologies in different sizes and shapes. The Li|SPSPEs|LFP full cell batteries display a long-term cycle life with a discharge capacity of ~120 mAh g−1 at C/10 in ambient temperature with around 90% capacity retention after 100 cycles. Moreover, the Li|SPSPEs|Li symmetrical cells exhibit a long-term stability with a low voltage polarization at a current density of 0.05 mAh cm−2 for up to 1000 cycles.Overall, the proposed approach shows a promising design principle which can open up new possibilities for the next-generation batteries and their safe operation. With vast range of available SMPs with tunable chemistries, transition temperatures, and high shape-memory performance, and opens up new frameworks to address a variety of detrimental, unresolved issues such as thermal runaway, with potential expansion to the other energy storage technologies.

Four-dimensional design and programming of shape-memory magnetic helical micromachines

Polycaprolactone-based shape memory foams as self-fitting vaginal stents

Summary While there have been various lost circulation materials (LCMs) available in the market for treating fractures during the drilling of oil and gas wells, there is still a demand for a technology to seal large fractures. Considering limitations on the size of the particles that can be circulated through the drilling equipment, especially the bottomhole assembly, simply enlarging conventional LCM particles becomes ineffective for sealing large vugs and fractures. In this study, we use shape memory polymers (SMPs) to prepare programmed LCMs with various temporary shapes, which can transform to their permanent shapes with much larger dimensions as compared to their temporary shapes. A series of steps for thermomechanical programming of SMP is designed to trigger their expansion at the reservoir temperature. The dimensions of the programmed shapes can be an order of magnitude smaller than the ones for the original shapes, making their transport through the flowlines feasible, and bridging wide-opened fractures possible. The basic idea is that, after recovery, the SMP-based LCMs form an entangled network across a large width of fracture, and SMP particles recovered within the network, filling in the pores to form an effective sealing. We seek the capability of entangled ladders and interwoven fibers in forming a network across the fracture. A permeability plugging apparatus (PPA) is used to examine the efficiency of developed LCMs. The technique of 3D X-ray computed tomography (CT) is used to visualize the internal structure of formed plugs, enabling us to understand the mechanisms of bridging, plugging, and sealing.

Shape memory polymers (SMP) belong to the class of stimuli-responsive materials and have generated significant research interest. Their capability to retain an imposed, temporary shape and to recover the initial, permanent shape upon exposure to an external stimulus depends on the “functional determinants”, which in simplistic terms, can be divided into structural/morphological and processing/environmental factors. The primary aim of the first part of this review is to reflect the knowledge about these fundamental relationships. In a next step, recent advances in shape memory polymer composites are summarized. In contrast to earlier reviews, studies on the impairment of shape memory properties through various factors, such as aging, compression and hibernation, lubricants, UV light and thermo-mechanical cycling, are extensively reviewed. Apart from summarizing the state-of-the-art in SMP research, recent progress is commented.

Shape memory polymers (SMPs) are known as smart polymer materials which can be deformed and fixed in a temporary shape and can recover to its original shape upon an external stimulus such as temperature which is the main stimulus for general SMPs. In this research, a renewable natural resource based on vanillin-furfurylamine benzoxazine (V-fa) and eugenol-furfurylamine benzoxazine (E-fa) are developed to substitute the use of petroleum based polybenzoxazine. The as-synthesized V-fa and E-fa show the degradation temperature at 5% weight loss to be as high as 343 and 310?C and char content to be 66 and 54%, respectively. Effects of epoxidized castor oil (ECO) content at 10-50wt% filled in bio-based polybenzoxazine on thermal, mechanical and shape memory properties of bio-based polybenzoxazine/bio-based epoxy SMPs are thoroughly investigated. The results reveal that with increase in ECO content, storage modulus and glass transition temperature of V-fa/ECO and E-fa/ECO copolymer decreased providing the values of 2.27 GPa to 1.60 GPa and 158?C to 100?C, respectively for V-fa/ECO copolymer and 1.53 GPa to 1.16 GPa and 40?C to -17?C, respectively for E-fa/ECO copolymer. In shape memory properties, the V-fa/ECO SMPs show shape fixity values at a room temperature of 86-94% and the values decrease with increasing ECO content, while the temporary shape at room temperature of the E-fa/ECO SMPs cannot fixed. Additionally, the V-fa/ECO SMPs provided the shape recovery values at Tg+20?C of 81-96% and the values increase with increasing of ECO content. Furthermore, it was observed that the V-fa/ECO copolymer having 40wt% of V-fa content exhibits good balance properties between shape memory performance and thermomechanical properties and it can be greatly recovered to the original shape for 5 cycles.

Auto‐programmable shape memory polymers (AP‐SMPs) can deform automatically without external manipulation, exhibiting either a free‐standing temporary shape or a permanent shape. The unique shape memory behaviors derive mainly from control by two factors, water and temperature. However, the control mechanism is unknown. This study analyzes and demonstrates the dual‐control mechanism of water and temperature in the three shape‐changing processes of AP‐SMPs. First, the AP‐SMP is immersed in warm water (50 °C). Asymmetric swelling of bilayer films provides the driving force for the shape auto‐programming of the AP‐SMP. The solvent effect of water reduces the glass transition temperature (Tg) of the AP‐SMP, which becomes lower than the medium temperature in warm water. AP‐SMP can be programmed automatically. Then, the AP‐SMP is removed from water and placed in air at room temperature. The Tg value of the matrix film increases notably in air and exceeds the medium temperature. The temporary shape of the AP‐SMP can thus be fixed. Finally, the AP‐SMP can quickly return to its permanent shape when the medium temperature exceeds the matrix film Tg in air. The dual control shape memory mechanism provides insights into the design and development of AP‐SMPs.

The term "shape memory effect" refers to the ability of a material to be deformed and fixed into a temporary shape, and to recover its original, permanent shape upon an external stimulus (1). Shape memory polymers have attracted much interest because of their unique properties, and applied tremendously in medical area, such as biodegradable sutures, actuators, catheters and smart stents (2, 3). Shape memory usually is a thermally induced process, although it can be activated by light illumination, electrical current, magnetic, or electromagnetic field (4-6). During the process, the materials are heated directly or indirectly above their glass transition temperature (Tg) or the melting temperature (Tm) in order to recover the original shape. Non-thermally induced shape memory polymers eliminate the temperature constrains and enable the manipulation of the shape recovered under ambient temperature (7, 8). Herein, we report a novel strategy of water induced shape memory, in which the formation and dissolution of poly(ethylene glycol) (PEG) crystal is utilized for the fixation and recovery of temporary deformation of hydrophilic polymer. This water-induced shape recovery is less sensitive to temperature, of which 95% deformation is fixed in circumstance and over 75% recovery is reached even at 0 oC.

Polymers can demonstrate shape memory (SM) effects by being temporarily fixed in a nonequilibrium shape and then recover their permanent shape when exposed to heat, light, or other external stimuli. Many previously developed shape memory polymers (SMPs) use the dramatic molecular chain mobility change around the glass transition temperature Tg to realize the SM effect. In these materials, the temporary shape cannot be repeated unless it is reprogramed, and therefore the SM effect is one way. Recently, a semicrystalline SMP, which can demonstrate both one- and two-way SM effects, was developed by one of our groups (Chung, T., Rorno-Uribe, A., and Mather, P. T., 2008, “Two-Way Reversible Shape Memory in a Semicrystalline Network,” Macromolecules, 41(1), pp. 184–192). The main mechanism of the observed SM effects is due to stretch induced crystallization. This paper develops a one-dimensional constitutive model to describe the SM effect due to stretch induced crystallization. The model accurately describes the complex thermomechanical SM effect and can be used for the future development of three-dimensional constitutive models.

ABSTRACTShape memory polymers (SMP) can be deformed to a stable, temporary shape and recovered to their original shape by applying a stimulus. These networks rely on the presence of two types of net points to establish their permanent and temporary shapes. Classical strategies to stabilize temporary shapes rely on cooling below Tg/Tm where macromolecules become pinned in a stressed state. Recovery of the SMP usually involves heating to above the transition temperature where the permanent shape is remembered. Employing reversible binding groups (RBGs) in SMPs has emerged as an alternative strategy for stabilizing temporary shapes or imparting recyclability of the permanent shape. The use of dynamic chemistry often engenders additional functionality such as intrinsic self‐healing characteristics or alternative shape recovery triggering strategies. SMPs bearing both supramolecular and covalent RBGs will be reviewed with an emphasis on hydrogen bonding, ionic interactions, metal–ligand coordination, and dynamic covalent exchange and addition reactions. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1340–1364

Sequential and selective shape memory by remote electrical control

Shape memory polymers (SMPs) are stimuli‐response materials known for their ability to be actuated from temporary shape into original shape. Because of this unique functionality SMPs are promising materials for diverse applications fields, including smart biomedical devices, aviation, automobile, structures or coatings. In this article, the work has been focused on the chemical modification of an epoxy monomer Bisphenol A diglycidyl ether (DGEBA) which was carried out by using allyl amines as curing agents and a thiol. When both systems Epoxy‐Amine/Tiol‐Ene were photopolymerized, a soft phase is introduced through a thiol‐ene system and a rigid phase is given by the polymerization of the epoxy polymer when it reacts with the curing agent allyl amine. One of the main requirements in SMPs is the presence of soft and rigid phases. The study of the effect of the concentration of three different curing agents, allyl amine type, over the capacity of the conformed polymers to return to their original shape was evaluated. DMA analysis was used to determine the Tg in the polymers, once obtained, the polymers were treated on a hot water bath above 10 °C their Tg, then the evaluation of the memory shape was carried out by two tests, bending and torsion. SMPs were obtained and specimens with 20% of concentration of allyl amine as curing agent showed an improvement in their ability of memory shape with a 99% of recovery.

Biostable shape memory polymers that remain stable in physiological conditions are beneficial for user-defined shape recovery in response to a specific stimulus. For potential commercialization and biocompatibility considerations, biomaterial synthesis must be simple and scalable. Hence, a library of biostable and cytocompatible shape memory polymers with tunable thermomechanical properties based on hard segment content was synthesized using a solvent-free method. Polymer surface chemistry, thermomechanical and shape memory properties, and biostability were assessed. We also investigated the effects of processing methods on thermomechanical and shape memory properties. All polymers showed high glass transition temperatures (>50 °C), which indicates that their temporary shape could be preserved after implantation. Polymers also demonstrate high shape fixity (73-80%) and shape recovery (93-95%). Minimal mass loss (<5%) was observed in accelerated oxidative (20% H2O2) and hydrolytic (0.1 M NaOH) media. Additionally, minimal shape recovery (∼0%) occurred in programmed samples with higher hard segment content that were stored in degradation media. After 40 days of storage in media, programmed samples recovered their primary shapes upon heating to temperatures above their transition temperature. Annealing to above the polymer melting point and solvent casting of polymers improved shape memory and thermal properties. To enable their potential use as biomaterial scaffolds, fiber formation of synthesized polyurethanes was compared with those of samples synthesized using a previously reported solvent-based method. The new method provided polymers that can form fibrous scaffolds with improved mechanical and shape memory properties, which is attributed to the higher molecular weight and crystalline content of polymers synthesized using the new, solvent-free approach. These biostable segmented polyurethanes could be coupled with a range of components that respond to specific stimuli, such as enzymes, magnetic field, pH, or light, to enable a specific shape change response, which could be coupled with drug and/or bioactive material delivery in future work.

External stress-free reversible multiple shape memory polymer enabled by using broad melting range as equivalent multiple switching phases