Shape-memory polymers (SMPs) are synthesized with adjustable glass transition temperature (T g ) ranging from 299 to 322 °C, higher than those reported previously. The polyimide containing thermal stable but flexible linkages within the backbone act as reversible phase, and high molecular weight (M n ) is necessary to form physical cross-links as fixed phase of thermoplastic shape-memory polyimide. The critical M n is 21.3 kg/mol, and the relationship between M n and T g is explored. Thermoset polyimides show higher storage modulus and better shape-memory effects than thermoplastic counterparts due to covalent cross-linking, and the effective cross-link density with the influence on their physical properties is studied. The mechanism of high-temperature shape-memory effect of polyimide on the basis of chain flexibility, molecular weight, and cross-link density is proposed, which will benefit further research on high-temperature SMPs.
Auxetic mechanical metamaterials, which expand transversally when axially stretched, are widely used in flexible electronics and aerospace. However, these chiral metamaterials suffer from three severe limitations as a typical auxetic metamaterials: narrow strain range, non-tunable mechanical behaviors, and fixed properties after fabrication. In this work, 4D printing chiral metamaterials with tunable, programmable, and reconfigurable properties are developed. The deformation mode transforms from bending dominated to stretching dominated under large deformation, leading to the stress-deformation (σ-λ) behavior of the auxetic metamaterials similar to those of the biomaterials ("J"shaped), such as tissues or organs. The programmability and reconfigurability of the developed chiral metamaterials allow mechanical behavior to change between different biomaterials with high precision. Furthermore, scaffolds with personalized mechanical properties as well as configurations and metamaterials-based light-emitting diode integrated devices demonstrate potential applications in tissue engineering and programmable flexible electronics.
As novel smart materials, shape memory polymer (SMP) and its composite (SMPC) have the ability to regain its original shape after undergoing significant deformation upon heating or other external stimuli such as light, chemic condition and so on. Their special behaviors much depends on the glass transitions due to the increasing of material temperature. Dynamic Mechanical Analysis (DMA) tests are performed on the styrene-based SMP and its carbon fiber fabric reinforced SMPC to investigate their glass transition behaviors. Three glass transition critical temperatures of SMP or SMPC are defined and a method to determine their values from DMA tests is supposed. A glass transition model is developed to describe the glass transition behaviors of SMP or SMPC based on the results of DMA tests. Numerical calculations illustrate the method determining the glass transition critical temperature is reasonable and the model can well predict the glass transition behaviors of SMP or SMPC.
We here propose a new method to analyze the thermo-electro-mechanical instability of dielectric elastomers. The equilibrium equations in this thermodynamic system at different temperatures are initially established. We then obtained the critical nominal electric field and the critical stretch under various mechanical and thermal loads, involving the effects of different stretch regimes on the system stability, i.e. the equal-biaxial stretch, the unequal-biaxial stretch and the thickness elongation. Finally, numerical results showed that as the temperature increases, the critical nominal electric field and the stretch of the dielectric elastomer are strengthened, which consequently stabilize the system. The results provide guidance to the design and synthesis of dielectric elastomer-based devices, especially for those operating at various temperatures.
Aiming at an easy-processing metallo-supramolecular polymer which possesses the shape memory property and large deformation ability, we designed a simple metal coordination complex: the blends of zinc-neutralized carboxyl-terminated polybutadiene and poly(styrene-co-4-vinylpyridine) (PSVP). The two polymers are tightly bound due to the metal coordination interactions between Zn 2+ ions from carboxyl-terminated polybutadiene and the pyridine group of the PSVP. The elastomer had reasonably good mechanical properties and was thermoplastic. Improvements in mechanical properties of the blends were realized in the rheology analysis compared with a blend without the introduction of the zinc salt. Small-angle X-ray scattering characterization showed that the microstructure of the elastomeric blend consisted of microphase-separated glassy nanodomains of principally PSVP, which served as cross-link junctions that were connected with polybutadiene chains. The elastomer exhibited good shape memory properties for large deformations, and its shape recovery efficiency could reach 81% in the first cycle and could reach 97% ± 1% in the following seven cycles.
Shape memory polymers with high glass transition temperature (HSMPs) and HSMP-based deployable structures and devices, which can bear harsh operation conditions for durable applications, have attracted more and more interest in recent years. In this article, colorless and transparent shape memory polyimide (SMCTPI) films were subjected to simulated vacuum thermal cycling, atomic oxygen (AO) and ultraviolet (UV) irradiation environments up to 600 h, 556 h and 600 h for accelerated irradiation. The glass transition temperature (Tg) determined by differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) had no obvious changes after being irradiated by varying amounts of thermal cycling, AO and UV irradiation dose. After being irradiated by 50 thermal cycles, 10 × 1021 atoms cm–2 AO irradiation and 3000 ESH UV irradiation, shape recovery behaviors of SMCTPI films also had no obvious damage even if they experienced 30 shape memory cycles, while the surface morphologies and optical properties were seriously destroyed by AO irradiation, as compared with thermal cycling and UV irradiation. The tensile strength could separately maintain 122 MPa, 120 MPa and 70 MPa after 50 thermal cycles, 10 × 1021 atoms cm–2 AO irradiation and 3000 ESH UV irradiation, which shows great potential for use in aerospace structures and devices.
Shape memory polymers (SMPs) are fascinating materials, with promising potential in a range of applications as actively moving polymers, which can undergo significant macroscopic deformation in a predefined manner between/among shapes in the presence of an appropriate stimulus. This work aims to present a systematic and up‐to‐date account of a carbon nanopaper enabled SMP composite from electrical actuation to multifunctionalization. Studies exploring nanopaper enabled SMP composites in various design principles in manufacturing, characterization, improvement, and development were included, especially for those induced by electricity and rendered multifunctional; making the article a comprehensive account of and systemic progress in SMP composite incorporated with carbon nanopaper. magnified image
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