Transparent, eco-friendly, super-tough “living” supramolecular polymers with fast room-temperature self-healability and reprocessability under visible light

A Visible Light-Responsive, Fast Room-Temperature Self- Healing, Mechanically Robust, Antibacterial Waterborne Polyurethane Based on Triple Dynamic Bonds

Despite the recent rapid advancements in room-temperature self-healing waterborne polyurethanes, imparting fast self-healing ability while concurrently maintaining robust mechanical performance of waterborne polyurethanes remains a formidable challenge. Herein, we propose a molecular structure design strategy for developing visible light-responsive, room-temperature self-healing, and antibacterial waterborne polyurethane (DMZWPU) containing triple dynamic bonds of diselenide bonds, multiple hydrogen bonds, and Zn(II)-carboxylate coordination bonds. This innovative approach effectively balances the tensile stress, fracture toughness, and self-healing ability of the material. Thanks to the synergy of the three dynamic bonds, the resulting DMZWPU film demonstrates a tensile stress of 40.32 MPa and a fracture toughness of 119.29 MJ/m3, respectively. Furthermore, based on the dynamic characteristics of three dynamic bonds and the dual induction of trace ethanol and visible light, the damaged DMZWPU film can recover more than 85% of the tensile stress at room temperature within 2 h. These performances outperform those of most of the currently reported room-temperature self-healable polymers (healing efficiency >80%). Due to the combined action of selenium and zinc ions, the DWZWPU film exhibits excellent antibacterial properties (sterilization rate of 100% in 24 h). Finally, the DMZWPU emulsion is effectively applied for leather finishing processes, and the results show that the DMZWPU coating exhibits excellent folding resistance, wear resistance, and room-temperature self-healing function, as well as enhanced water resistance and dry friction resistance. In summary, this study provides a novel perspective for the development of waterborne polyurethane with high mechanical performances and rapid self-healable ability at room temperature.

Visible Light-Triggered Self-Welding Perovskite Solar Cells and Modules

Flexible perovskite solar cells (F-PSCs) are highly promising for both stationary and mobile applications because of their advantageous features, including mechanical flexibility, their lightweight and thin nature, and cost-effectiveness. However, a number of drawbacks, such as mechanical instability, make their practical application difficult. Here, self-welding dynamic diselenide that is triggered by visible light into the structure of F-PSCs to improve their long-term stability by repairing cracks and defects in the absorber layer is incorporated. The diselenide confers the flexibility and self-welding properties to the Cs0.05MA0.05FA0.9PbI3 perovskite layer, enabling optimized F-PSC devices to achieve a power conversion efficiency of 24.85% while retaining ca. 92% of their initial efficiency after undergoing 15 000 bending cycles at a curvature radius of 3 mm. The corresponding flexible large-scale module with an active area of 15.82 cm2 achieved a record PCE of 21.65%.

Study on the Effect of Core-Shell Abaca Vascular Carriers on the Self-Healing and Mechanical Properties of Thermoset Panels

Self-healing panels were prepared using vinyl ester (VE) and vascular abaca fibers (unidirectional) through the hand lay-up process. Initially, two sets of abaca fibers (AF) were prepared by filling the healing resin VE and hardener and stacking both core-filled unidirectional fibers in a 90° direction to obtain sufficient healing. The experimental results demonstrated that the healing efficiency increased by approximately 3%. SEM-EDX analysis further confirmed the healing process by exhibiting spill-out resin and the respective fibers' major chemical elements at the damaged site after self-healing. The tensile, flexural, and Izod impact strengths of self-healing panels indicated improved strengths of 7.85%, 49.43%, and 53.84%, respectively, compared with fibers with empty lumen-reinforced VE panels due to the presence of a core and interfacial bonding between the reinforcement and matrix. Overall, the study proved that abaca lumens could effectively serve as healing carriers for thermoset resin panels.

Autonomous Healable Elastomers with High Elongation, Stiffness, and Fatigue Resistance

Although self-healing elastomers have been developed in a great breakthrough, it is still a challenge to develop one kind of material that can respond to the fracture instantly even though this characteristic plays an essential role in emergency circumstances. Herein, we adopt free radical polymerization to construct one polymer network equipped with two weak interactions (dipole-dipole interaction and hydrogen bonding). The elastomer we synthesized has a high self-healing efficiency (100%) and a very short healing time (3 min) in an air atmosphere, and it can also self-heal in seawater, showing an ideal healing efficiency of >80%. Additionally, on account of its high elongation (>1000%) and antifatigue capacity (no rupture after loading-unloading 2000 times), the elastomer can be utilized in a wide range of applications, including e-skin and soft robot fields.

Sunlight Stimulated Photochemical Self-Healing Polymers Capable of Re-Bonding Damages up to a Centimeter Below the Surface Even Out of the Reach of the Illumination

The development of photochemical self-healing polymers faces the the following bottlenecks: i) only the surface cracks can be restored and ii) materials' mechanical properties are lower. To break these bottlenecks, cross-linked poly(urethane-dithiocarbamate)s carrying photo-reversible dithiocarbamate bonds covalently linked to indole chromophores and benzyl groups are designed. The conjugated structure of the chromophore and benzyl enhances the addition reactivity of thiocarbonyl moiety and facilitates photo-cleavage of CS bond, so that transfer of the created radicals among dithiocarbamate linkages is promoted. Accordingly, reshuffling of the reversibly cross-linked networks via dynamic exchange between the activated dithiocarbamates is enabled in both surface layer and the interior upon exposure to the low-intensity ultraviolet (UV) light from the sun. It is found that the damages up to a centimeter below the surface can be effectively recovered in the sunshine, which greatly exceeds the maximum penetration distance of UV light (hundreds of microns). Besides, tensile strength and failure strain of the poly(urethane-dithiocarbamate) are superior to the reported photo-reversible polymers, achieving the record-high 33.8 MPa and 782.0% owing to the wide selectivity of soft/hard blocks, multiple interactions, and appropriate cross-linking architecture. The present work provides a novel paradigm of photo self-healing polymers capable of re-bonding cracks even out of the reach of the illumination.

Flame-Retardant and Self-Healing Waterborne Polyurethane Based on Organic Selenium

Waterborne polyurethane has drawn extensive attention due to its environmental friendliness and is widely used in many areas. However, it is still a great challenge to synthesize waterborne polyurethanes with flame retardancy and fast room-temperature self-healing ability, along with excellent mechanical performance and emulsion stability due to the mutually contradictory nature of these properties. Herein, waterborne polyurethanes containing organic selenium (SWPU-x) from 0.67 to 3.28 wt % were synthesized, which could simultaneously realize flame retardancy and self-healing ability based on the ability to scavenge active free radicals at high temperature and the dynamic switch of diselenide. All these SWPU-x films self-extinguished within 1 s after the ignition in the vertical combustion tests. The limiting oxygen index of SWPU-4 was improved to 28.5% with excellent UL-94 level (V-0) and self-healing efficiency (91.25%, after being healed in the photoreactor for 30 min at room temperature), together with high mechanical properties (tensile strength was 18.5 MPa and elongation at break was 869.63%), and the total heat release (THR) for SWPU-4 (49.28 MJ/m²) could decrease to 23.80% of the THR for the original waterborne polyurethane WPU (64.67 MJ/m²). This work discovered a new flame-retardant element (organic selenium) and studied its flame-retardant behaviors and self-healing function simultaneously, which would extremely extend the application of waterborne polyurethanes.

Dynamic Covalent Structure for the Design of Recyclable Polyurethane Based on the Diketone Chemistry

Herein, the rational design of an enaminone compound is reported which can be easily and conveniently designed and obtained via the reaction of amine and diketone. The dynamic enaminoneamide structure is formed via the reaction between isocyanate and enaminone in fabricating a novel dynamic crosslinked polyurethane. The new kind of polyurethane can be efficiently recycled via the shifting between crosslinked structure and oligomer for the reversible dissociation of the enaminoneamide structure. Besides remolding itself via the thermal treatment, oligomers liberated from recycled-polyurethane can directly take part in constructing a new polyurethane without further purification. Therefore, the recyclability of this polyurethane shows high-value characteristics. The ease with which polyurethane can be produced, used, recycled, and reused without losing value offers a new green solution in designing sustainable polymer materials with a high economic value and a minimal environmental burden.

A review on room-temperature self-healing polyurethane: synthesis, self-healing mechanism and application

Polyurethanes have been widely used in many fields due to their remarkable features such as excellent mechanical strength, good abrasion resistance, toughness, low temperature flexibility, etc. In recent years, room-temperature self-healing polyurethanes have been attracting broad and growing interest because under mild conditions, room-temperature self-healing polyurethanes can repair damages, thereby extending their lifetimes and reducing maintenance costs. In this paper, the recent advances of room-temperature self-healing polyurethanes based on dynamic covalent bonds, noncovalent bonds and combined dual or triple dynamic bonds are reviewed, focusing on their synthesis methods and self-healing mechanisms, and their mechanical properties, healing efficiency and healing time are also described in detial. In addition, the latest applications of room-temperature self-healing polyurethanes in the fields of leather coatings, photoluminescence materials, flexible electronics and biomaterials are summarized. Finally, the current challenges and future development directions of the room-temprature self-healing polyurethanes are highlighted. Overall, this review is expected to provide a valuable reference for the prosperous development of room-temperature self-healing polyurethanes.

Graphical abstract

Healable Strain Sensor Based on Tough and Eco-Friendly Biomimetic Supramolecular Waterborne Polyurethane

Stretchable sensors are essential for flexible electronics, which can be made with polymer elastomers as the matrix. The main challenge in producing practical devices is to obtain polymers with mechanical stability, eco-friendliness, and self-healing properties. Herein, we introduce urea bonds and 2-ureido-4[1H]-pyrimidinone (UPy) to synthesize tailored waterborne polyurethanes (WPU-UPy-x) with a hierarchical hydrogen bond (H-bond). Accordingly, sound tensile performance (strength: 53.33 MPa, toughness: 128.97 MJ m^-3), satisfying deformation recovery, and good self-healing capability of the WPU-UPy-x film are demonstrated. With atomic force microscope characterization, we find that UPy groups contribute to the highly improved microphase separation of WPU-UPy-x, responsible for good mechanical properties. As a proof of concept, a strain sensor is successfully configured, thanks to the good interfacial interactions between the polyurethane matrix and the Ti₃C₂T_x MXene conductive filler, which features sensitive and stable performance for monitoring diverse human and mechanical motions. Intriguingly, this sensor is capable of self-healing after cutting and displays well-retained sensitivity to detect the stretched signal. The as-proposed design concept for healable and sensitive strain sensors can shed light on future wearable electronics.

Dynamic Covalent Polyurethane Network Materials: Synthesis and Self-Healability

Polyurethane (PU) has not only been widely used in the daily lives, but also extensively explored as an important class of the essential polymers for various applications. In recent years, significant efforts have been made on the development of self-healable PU materials that possess high performance, extended lifetime, great reliability, and recyclability. A promising approach is the incorporation of covalent dynamic bonds into the design of PU covalently crosslinked polymers and thermoplastic elastomers that can dissociate and reform indefinitely in response to external stimuli or autonomously. This review summarizes various strategies to synthesize self-healable, reprocessable, and recyclable PU materials integrated with dynamic (reversible) Diels-Alder cycloadduct, disulfide, diselenide, imine, boronic ester, and hindered urea bond. Furthermore, various approaches utilizing the combination of dynamic covalent chemistries with nanofiller surface chemistries are described for the fabrication of dynamic heterogeneous PU composites.

Basic Approaches to the Design of Intrinsic Self-Healing Polymers for Triboelectric Nanogenerators

Triboelectric nanogenerators (TENGs) as a revolutionary system for harvesting mechanical energy have demonstrated high vitality and great advantage, which open up great prospects for their application in various areas of the society of the future. The past few years have seen exponential growth in many new classes of self-healing polymers (SHPs) for TENGs. This review presents and evaluates the SHP range for TENGs, and also attempts to assess the impact of modern polymer chemistry on the development of advanced materials for TENGs. Among the most widely used SHPs for TENGs, the analysis of non-covalent (hydrogen bond, metal-ligand bond), covalent (imine bond, disulfide bond, borate bond) and multiple bond-based SHPs in TENGs has been performed. Particular attention is paid to the use of SHPs with shape memory as components of TENGs. Finally, the problems and prospects for the development of SHPs for TENGs are outlined.

Mechanically robust and tough waterborne polyurethane films based on diselenide bonds and dual H-bonding interactions with fast visible-light-triggered room-temperature self-healability

A dynamic but mechanically robust and tough polymer network was proposed, in which the fast room-temperature self-healing of our target polymer with mechanically robust and tough features is achieved under visible light.