Supramolecular Elastomers Research Articles

Rheology, Sticky Chain, and Sticker Dynamics of Supramolecular Elastomers Based on Cluster-Forming Telechelic Linear and Star Polymers

We elucidate the properties of unentangled telechelic poly(isobutylene) (PIB) chains in bulk forming dynamic micellar networks mediated by endgroups capable of hydrogen-bonding and π–π interactions. The effects of the molecular architecture and type of endgroup on the properties of networks are studied by a combination of small-angle X-ray scattering (SAXS), rheology, low-resolution NMR, and dielectric spectroscopy (DS). It is found that star-shaped molecules form more time-stable networks with larger and somewhat more distantly arranged aggregates compared to their linear counterparts. Using stickers providing less hydrogen bonds speeds up terminal flow significantly, yet surprisingly, the nanoscale morphology, apparent activation energies, and the timescale of endgroup fluctuations probed by DS are very similar across the two sample series. The correlation of results from the three dynamic methods (rheology, NMR, and DS) thus fortifies previous findings for linear chains: (i) even for star molecules, terminal stress relaxation is governed by single-chain relaxation rather than the reorganization of whole micelles, and (ii) the cluster-related relaxation time accessed by DS has no trivial relation to the actual sticky bond lifetime, the determination of which is concluded to be an open problem.

A supramolecular polymer with ultra-stretchable, notch-insensitive, rapid self-healing and adhesive properties

Supramolecular elastomers, possessing excellent mechanical, reusable adhesivity, and rapid self-healing properties, are essential for use in various applications.

Toward Robust, Tough, Self-Healable Supramolecular Elastomers for Potential Application in Flexible Substrates.

A robust, tough, and self-healable elastomer is a promising candidate for substrate in flexible electronic devices, but there is often a trade-off between mechanical properties (robustness and toughness) and self-healing. Here, a poly(dimethylsiloxane) (PDMS) supramolecular elastomer is developed based on metal-coordinated bonds with relatively high activation energy. The strong metal-coordination complexes and their corresponding ionic clusters acting as the cross-linking points strengthen the resultant supramolecular networks, which achieves superior mechanical robustness (2.81 MPa), and their consecutive dynamic rupture and reconstruction efficiently dissipate strain energy during the stretching process, which leads to an impressive fracture toughness (32 MJ/m3). Additionally, the reversible intermolecular interactions (weak hydrogen bonds and strong sacrificial coordination complexes/clusters) can break and re-form upon heating; thus, the elastomer self-heals at a moderate temperature with the highest healing efficiency of 95%. As such, the potential of the as-prepared supramolecular elastomer for a substrate material of flexible electronic devices is discovered.

In Situ Remodeling Overrules Bioinspired Scaffold Architecture of Supramolecular Elastomeric Tissue-Engineered Heart Valves

In situ tissue engineering that uses resorbable synthetic heart valve scaffolds is an affordable and practical approach for heart valve replacement; therefore, it is attractive for clinical use. This study showed no consistent collagen organization in the predefined direction of electrospun scaffolds made from a resorbable supramolecular elastomer with random or circumferentially aligned fibers, after 12months of implantation in sheep. These unexpected findings and the observed intervalvular variability highlight the need for a mechanistic understanding of the long-term in situ remodeling processes in large animal models to improve predictability of outcome toward robust and safe clinical application.

Tough Double Metal-ion Cross-linked Elastomers with Temperature-adaptable Self-healing and Luminescence Properties

Smart materials with a combination of tough solid-like properties, fast self-healing and optical responsiveness are of interests for the development of new soft machines and wearable electronics. In this work, tough physically cross-linked elastomers that show high mechanical strength, intriguing temperature-adaptable self-healing and fluorochromic response properties are designed using aluminum (Al) and fluorescent europium (Eu) ions as cross-linkers. The ionic Al-COOH binding is incorporated to construct the strong polymer network which mainly contributes to the mechanical robustness of the elastomer consisting of two interpenetrated networks. The Eu-iminodiacetate (IDA) coordination is mainly used to build the weaker but more dynamic network which dominate the elasticity, self-healing and luminescence of the elastomer. Moderate Eu3+ and Al3+ contents give these supramolecular elastomers high toughness. The temperature-sensitive Eu-IDA coordination enables tunable self-healing rate and efficiency along with fast Eu-centered “ON/OFF” switchable red emission. The mechanical, self-healing and luminescence properties of these elastomers can be adjusted by tuning the ratio of the two types of metal ions. This elastomer is potentially applicable for biosensors, wearable optoelectronics and anticounterfeiting materials.

Supramolecular thermoplastic elastomers via self‐complementary quadruple hydrogen bonding between polybutadiene‐based triblock copolymers

AbstractTwo series of triblock copolymers, polycaprolactone‐b‐polybutadiene‐b‐polycaprolactone (PCL‐b‐PB‐b‐PCL, CBC) and polylactide‐b‐polybutadiene‐b‐polylactide (PLA‐b‐PB‐b‐PLA, LBL), have been synthesized through the ring‐opening polymerization (ROP) of ε‐caprolactone (ε‐CL)/D,L‐lactide (D,L‐LA) catalyzed by Sn(Oct)2 with hydroxyl‐terminated polybutadiene (HTPB) as a macroinitiator. Then, these triblock copolymers are end‐functionalized with 2‐ureido‐4[1H]‐pyrimidinone (UPy) groups to obtain the supramolecular multiblock copolymers UCBC and ULBL as supramolecular thermoplastic elastomers (TPEs). The thermal properties of UCBC and ULBL samples are measured by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical analysis (DMA). The tensile tests of all the samples prepared are carried out to investigate the influence of the content of hard segments and the microstructure of PB soft segments on the mechanical properties of supramolecular TPEs.

Self-Healing and Reconfigurable Actuators Based on Synergistically Cross-Linked Supramolecular Elastomer.

Stimulus-responsive soft actuators show great potential in intelligent robot systems for their various virtues, such as arbitrary shape morphing, outstanding adaptability to environment, and multidegrees of freedom. However, it is extremely challenging to achieve a combination of excellent actuating performance and robust mechanical strength as well as self-healing property. Herein we report a near-infrared light-responsive soft actuator based on the synergistic effects of a crystalline physical cross-linked network and a hydrogen bonding supramolecular network. The actuator exhibits outstanding comprehensive performance including fast and reliable light-responsive behavior (bending angle over 90° within 1.6 s), robust mechanical strength (12.52 MPa), superfast self-healing speed (2 s), and satisfactory self-healing efficiency in both mechanical (87.68%) and actuating (99.50%) performance. In addition, it is convenient to fabricate and reconfigure the actuators by a mild-temperature molding strategy to acquire various three-dimensional structures, thus achieving diverse actuating locomotion. This work provides a powerful and facile strategy to prepare soft actuators with intriguing performance, allowing significant progress in broadening their practical application.

Stress-Softening in Particle-Filled Polyurethanes under Cyclic Compressive Loading.

Elastomer compositions containing various particulate fillers can be formulated according to the specific functions required of them. Stress softening—which is also known as the Mullins effect—occurs during high loading and unloading paths in certain supramolecular elastomer materials. Previous experiments have revealed that the load–displacement response differs according to the filler used, demonstrating an unusual model of correspondence between the constitutive materials. Using a spherical indentation method and numerical simulation, we investigated the Mullins effect on polyurethane (PU) compositions subjected to cyclic uniaxial compressive load. The PU compositions comprised rigid particulate fillers (i.e., nano-silica and carbon black). The neo-Hooke model and the Ogden–Roxburgh Mullins model were used to describe the nonlinear deformation behavior of the soft materials. Based on finite element methods and parameter optimization, the load–displacement curves of various filled PUs were analyzed and fitted, enabling constitutive parameter prediction and inverse modeling. Hence, correspondence relationships between material components and constitutive parameters were established. Such relationships are instructive for the preparation of materials with specific properties. The method described herein is a more quantitative approach to the formulation of elastomer compositions comprising particulate fillers.

Quadruple Hydrogen Bonding Supramolecular Elastomers for Melt Extrusion Additive Manufacturing.

This manuscript describes the versatility of highly directional, noncovalent interactions, i.e., quadruple hydrogen bonding (QHB), to afford novel polyurea segmented supramolecular polymers for melt extrusion three-dimensional (3D) printing processes. The molecular design of the polyurea elastomers features (1) flexible polyether segments and relatively weak urea hydrogen-bonding sites in the soft segments to provide elasticity and toughness, and (2) strong ureido-cytosine (UCyt) QHB in the hard segments to impart enhanced mechanical integrity. The resulting polyureas were readily compression-molded into mechanically-robust, transparent, and creasable films. Optimization of polyurea composition offered a rare combination of high tensile strength (95 MPa), tensile elongation (788% strain), and toughness (94 MJ/m3), which are superior to a commercially available Ninjaflex elastomer. The incorporation of QHB facilitated melt processability, where hydrogen bonding dissociation provided low viscosities at printing temperatures. During cooling, directional self-assembly of UCyt QHB facilitated the solidification process and contributed to part fidelity with the formation of a robust physical network. The printed objects displayed high layer fidelity, smooth surfaces, minimal warpage, and complex geometries. The presence of highly directional QHB effectively diminished mechanical anisotropy, and the printed samples exhibited comparable Young's moduli along (x-y direction, 0°) and perpendicular to (z-direction, 90°) the layer direction. Remarkably, the printed samples exhibited ultimate tensile strains approaching 500% in the z-direction prior to failure, which was indicative of improved interlayer adhesion. Thus, this design paradigm, which is demonstrated for novel polyurea copolymers, suggests the potential of supramolecular polymers with enhanced mechanical performance, melt processability, recyclability, and improved interlayer adhesion for melt extrusion additive manufacturing processes.

Human In Vitro Model Mimicking Material-Driven Vascular Regeneration Reveals How Cyclic Stretch and Shear Stress Differentially Modulate Inflammation and Matrix Deposition.

Resorbable synthetic scaffolds designed to regenerate living tissues and organs inside the body have emerged as a clinically attractive technology to replace diseased blood vessels. However, mismatches between scaffold design and in vivo hemodynamic loading (i.e., cyclic stretch and shear stress) can result in aberrant inflammation and adverse tissue remodeling, leading to premature graft failure. Yet, the underlying mechanisms remain elusive. Here, a human in vitro model is presented that mimics the transient local inflammatory and biomechanical environments that drive scaffold-guided tissue regeneration. The model is based on the coculture of human (myo)fibroblasts and macrophages in a bioreactor platform that decouples cyclic stretch and shear stress. Using a resorbable supramolecular elastomer as the scaffold material, it is revealed that cyclic stretch initially reduces proinflammatory cytokine secretion and, especially when combined with shear stress, stimulates IL-10 secretion. Moreover, cyclic stretch stimulates downstream (myo)fibroblast proliferation and matrix deposition. In turn, shear stress attenuates cyclic-stretch-induced matrix growth by enhancing MMP-1/TIMP-1-mediated collagen remodeling, and synergistically alters (myo)fibroblast phenotype when combined with cyclic stretch. The findings suggest that shear stress acts as a stabilizing factor in cyclic stretch-induced tissue formation and highlight the distinct roles of hemodynamic loads in the design of resorbable vascular grafts.

Universally autonomous self-healing elastomer with high stretchability

Developing autonomous self-healing materials for applications in harsh conditions is challenging because the reconstruction of interaction in material for self-healing will experience significant resistance and fail. Herein, a universally self-healing and highly stretchable supramolecular elastomer is designed by synergistically incorporating multi-strength H-bonds and disulfide metathesis in polydimethylsiloxane polymers. The resultant elastomer exhibits high stretchability for both unnotched (14000%) and notched (1300%) samples. It achieves fast autonomous self-healing under universal conditions, including at room temperature (10 min for healing), ultralow temperature (−40 °C), underwater (93% healing efficiency), supercooled high-concentrated saltwater (30% NaCl solution at −10 °C, 89% efficiency), and strong acid/alkali environment (pH = 0 or 14, 88% or 84% efficiency). These properties are attributable to synergistic interaction of the dynamic strong and weak H-bonds and stronger disulfide bonds. A self-healing and stretchable conducting device built with the developed elastomer is demonstrated, thereby providing a direction for future e-skin applications.

A photoresponsive azopyridine-based supramolecular elastomer for self-healing strain sensors

Optical-stimuli materials have been applied in many fields since it can be activated from external system and localized in time and space. Although, optically healable polymers have been well developed in recent years, to be healed under mild conditions remains a big challenge for these materials. Herein, we report the design and synthesis of a metallo-supramolecular polymer containing azopyridine ligands to address this conundrum. The resulting photo-healable polymer is highly stretchable (up to 735%) with a high toughness (16.33 MJ/m3) and excellent light-healing efficiency of ~90% after three cutting/healing cycles at mild temperature (40 °C) in various harsh conditions (e.g. underwater, subzero temperature). Furthermore, a novel bioinspired microcrack nanostructure design is presented to endow the resulted supramolecular elastomer with outstanding sensitivity to strain, which makes it very suitable for human motion monitoring applications. We believe this work will provide afflatus on future design, fabrication and application of photo-stimuli smart materials.

Protein-Inspired Self-Healable Ti3C2 MXenes/Rubber-Based Supramolecular Elastomer for Intelligent Sensing.

Progress toward the integration of electronic sensors with a signal processing system is important for artificial intelligent and smart robotics. It demands mechanically robust, highly sensitive, and self-healable sensing materials which could generate discernible electric variations responding to external stimuli. Here, inspired by the supramolecular interactions of amino acid residues in proteins, we report a self-healable nanostructured Ti3C2MXenes/rubber-based supramolecular elastomer (NMSE) for intelligent sensing. MXene nanoflakes modified with serine through an esterification reaction assemble with an elastomer matrix, constructing delicate dynamic supramolecular hydrogen bonding interfaces. NMSE features desirable recovered toughness (12.34 MJ/m3) and excellent self-healing performance (∼100%) at room temperature. The NMSE-based sensor with high gauge factor (107.43), low strain detection limit (0.1%), and fast responding time (50 ms) can precisely detect subtle human motions (including speech, facial expression, pulse, and heartbeat) and moisture variations even after cut/healing processes. Moreover, NMSE-based sensors integrated with a complete signal process system show great feasibility for speech-controlled motions, which demonstrates promising potential in future wearable electronics and soft intelligent robotics.

Self-recovery, fatigue and anti-fatigue of supramolecular elastomers

Supramolecular elastomers (SMEs) with chains bridged by covalent and non-covalent bonds demonstrate self-healing and self-recovery at room temperature. A model is developed for the kinetics of self-recovery in SME subjected to cyclic deformation. Good agreement is shown between results of simulation and observations on SMEs with metal-ligand coordination bonds, hydrogen bonds, ionic hydrogen bonds, and temporary junctions formed via inter-polymer complexation. Analysis of multi-cycle tests on SMEs reveals their anti-fatigue property (the ability to eliminate cyclic softening by introducing short intervals of recovery between subsequent cycles of deformation). Two scenarios for anti-fatigue are discussed. For SMEs with the exponential kinetics of recovery, the optimal duration of rest between cycles is close to the time needed for total self-recovery. When the recovery process involves two stages, less than 1 min of rest between cycles suffices to eliminate cyclic softening.

Synthesis and Characterization of Linear Polyisoprene Supramolecular Elastomers Based on Quadruple Hydrogen Bonding.

Supramolecular elastomers based on quaternary hydrogen bonding of ureido-pyrimidinone (UPy) groups own special properties such as reversibility, self-healing, and good processability, which can be used in many special fields. In this paper, a novel type of linear polyisoprene supramolecular elastomer (LPSE) was prepared via anionic polymerization by deliberately introducing hydroxyl, isocyanate, and UPy groups into the ends. The formation of supramolecular structure showed significant effects on the microphase structures of LPSE, which was characterized by Fourier-transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), hydrogen nuclear magnetic resonance (1H-NMR), and dynamic mechanical analysis (DMA). Results showed that the introduction of UPy groups played a certain role in the improvement of the thermal stability, toughness, and tensile strength of the elastomer. Moreover, from self-healing tests, the hydrogen bonds of UPy showed dynamic characteristics which were different from covalent sacrificial bonds and exhibited the reassociation phenomenon. This study can not only extend our understanding of the toughening effect of strong hydrogen bonds, but also help us to rationally design new and tough elastomers.

Facile preparation and properties of fluorescent thermoplastic elastomer comprised of ZnS-capped CdSe metallo-supramolecular block copolymer

Taking advantage of metal-ligand complex between Zn(II) and terpyridine (Tpy) proved by UV–vis and fluorescence test, the supramolecular thermoplastic elastomer was prepared by simple blends of quantum dots (QDs) and Tpy-terminal polystyrene-b-polyisoprene (SI-Tpy). TEM images show that QDs are stable and evenly dispersed in polyisoprene (PI) phase. The interfacial interaction between QD surface and PI phase of SI-Tpy which has phase separation between PS phase and PI phase has impact on the solubility of QD, conformation of PI soft chain and enhance the mechanical property of the material. The obtained thermoplastic elastomers have excellent fluorescence and mechanical property, which make them have potential applications in optical fields.

Imine-functionalized polysiloxanes for supramolecular elastomers with tunable mechanical properties

A series of imine-functionalized polysiloxanes were reported for the first time and used to build supramolecular coordination elastomers.

Metal-organic polyhedra crosslinked supramolecular polymeric elastomers.

Herein, supramolecular polymeric elastomers crosslinked by metal-organic polyhedra (ElastoMOPs) were designed and developed as a novel hybrid system featuring not only tunable mechanical properties but also dynamic actuation behaviors in response to dichloromethane vapor.

A supramolecular silicone dielectric elastomer with a high dielectric constant and fast and highly efficient self-healing under mild conditions

A silicone dielectric elastomer with simultaneous high dielectric constant, fast and efficient self-healing ability at mild conditions was prepared by constructing supramolecular network assembled by coordination bonds and hydrogen bonds.

Facile construction of a double network cross-linked luminescent supramolecular elastomer by hydrosilylation and pillar[5]arene host-guest recognition.

Reticulated copolymer host pillar[5]arene cross-linked with poly(dimethylsiloxane) (PDMS) was synthesized for the facile construction of a double network cross-linked elastomer upon noncovalently cross-linking with tetraphenyethylene (TPE)-based tetratopic guests through host-guest interactions. The obtained sample strips had better mechanical properties and luminescence capabilities.