The fabrication of highly durable skin‐mimicking sensors remains challenging because of the unavoidable fatigue and physical damage that sensors are subjected to in practical applications. In this ...study, ultra‐durable ionic skins (I‐skins) with excellent healability and high sensitivity are fabricated by impregnating ionic liquids (ILs) into a mechanically robust poly(urea‐urethane) (PU) network. The PU network is composed of crystallized poly(ε‐caprolactone) and flexible poly(ethylene glycol) that are dynamically cross‐linked with hindered urea bonds and hydrogen bonds. Such a design endows the resultant ionogels with high mechanical strength, good elasticity, Young's modulus similar to that of natural skin, and excellent healability. The ionogel‐based I‐skins exhibit a high sensitivity to a wide range of strains (0.1–300%) and pressures (0.1–20 kPa). Importantly, the I‐skins show a highly reproducible electrical response over 10 000 uninterrupted strain cycles. The sensing performance of the I‐skins stored in open air for 200 days is almost the same as that of the freshly prepared I‐skin. The fractured I‐skins can be easily healed by heating at 65 °C that restores their original ultra‐durable sensing performance. The long‐term durability of the I‐skins is attributed to the combination of non‐volatility of the ILs, excellent healability, and well‐designed mechanical properties.
Highly sensitive ultra‐durable ionic skins (I‐skins) are fabricated by impregnating ionic liquids into a mechanically robust poly(urea‐urethane) network. Even after being stored in open air for 200 days, the I‐skins exhibit a highly reproducible electrical response over 10 000 uninterrupted strain cycles. The fractured I‐skins can be easily healed to regain their original sensing performance.
The spraying method is developed for the fabrication of mechanically robust and self‐healing superhydrophobic coatings, which comprise highly porous and rough polyelectrolyte coatings preserved with ...low‐surface‐energy healing agents. These coatings can repetitively and autonomically restore superhydrophobicity in humid environments. After depletion of healing agents, superhydrophobic coatings with dual healing agents can regain their self‐healing ability by re‐spraying fluoroalkylsilane.
It remains a challenge to fabricate healable and recyclable polymeric materials with simultaneously enhanced tensile strength, stretchability, and toughness. Herein, we report a simple approach to ...fabricate high-performance polymer hydrogels that not only integrate high tensile strength, stretchability, and toughness but also possess self-healing and recycling capabilities. The polymer hydrogels are fabricated by mixing a positively charged polyelectrolyte mixture of poly(diallyldimethylammonium chloride) (PDDA)/branched poly(ethylenimine) (PEI) with a negatively charged polyelectrolyte mixture of poly(sodium 4-styrenesulfonate) (PSS)/poly(acrylic acid) (PAA) in an aqueous solution followed by molding, drying, and rehydration. The (PDDA/PEI)–(PSS/PAA) hydrogels with in situ-formed PDDA–PSS nanoparticles have a tensile strength, strain at break, and toughness of 1.26 ± 0.06 MPa, 2434.2 ± 150.3%, and 19.53 ± 0.48 MJ/m3, respectively. The toughness of the (PDDA/PEI)–(PSS/PAA) hydrogels is ∼5.2 and ∼108 times higher than that of the PEI–PAA and PDDA–PSS hydrogels, respectively. Benefiting from the high reversibility of the hydrogen-bonding and electrostatic interactions, the (PDDA/PEI)–(PSS/PAA) hydrogels can efficiently heal from physical damage to restore their original mechanical properties at room temperature in water. Moreover, the (PDDA/PEI)–(PSS/PAA) hydrogels after being dried and ground can be recycled under a pressure of ∼3 kPa at room temperature in the presence of water to reuse the damaged hydrogels.
Near‐infrared (NIR) light‐driven bilayer actuators capable of fast, highly efficient, and reversible bending/unbending motions toward periodic NIR light irradiation are fabricated by exploiting the ...photothermal conversion and humidity‐sensitive properties of polydopamine‐modified reduced graphene oxide (PDA‐RGO). The bilayer actuator comprises a PDA‐RGO layer prepared by a filtration method, and this layer is subsequently spin‐coated with a layer of UV‐cured Norland Optical Adhesive (NOA)‐63. Given the hydrophilicity of PDA, the PDA‐RGO layer can absorb water to swell and lose water to shrink. The intrinsic NIR absorbance of RGO sheets convertes NIR light into thermal energy, which transfers the humidity‐responsive PDA‐RGO layer to be NIR light‐responsive. Considering that the shape of the NOA‐63 layer remains unchanged under NIR light, periodic NIR light irradiation leads to asymmetric shrinkage/expansion of the bilayer, which enables fast and reversible bending/unbending motions of the bilayer actuator. We demonstrate that compared with a poly(ethylenimine)‐modified graphene oxide layer, the PDA‐RGO layer is unique in fabricating highly efficient bilayer actuators. A NIR light‐driven walking device capable of performing quick worm‐like motion on a ratchet substrate is built by connecting two polyethylene terephthalate plates as claws on opposite ends of the PDA‐RGO/NOA‐63 bilayer actuator.
Near‐infrared (NIR) light‐driven bilayer actuators are fabricated by exploiting the photothermal conversion and humidity‐sensitive properties of polydopamine‐modified reduced graphene oxide. The bilayer actuator is capable of fast, highly efficient, and reversible bending/unbending motions toward periodic NIR light irradiation. The bilayer actuator is also utilized to build a NIR light‐driven walking device capable of performing quick worm‐like motion.
The fabrication of mechanically robust polymeric materials capable of self-healing and recycling remains challenging because the mobility of polymer chains in such polymers is very limited. In this ...work, mechanically robust supramolecular thermosets capable of healing physical damages and recycling under mild conditions are fabricated by trimerization of bi-(ortho-aminomethyl-phenylboronic acid)- and tri-(ortho-aminomethyl-phenylboronic acid)-terminated poly(propylene glycol) oligomers (denoted as Bi-PBA-PPG and Tri-PBA-PPG, respectively). The resultant supramolecular thermosets are cross-linked by dynamic covalent bonds of nitrogen-coordinated boroxines. The mechanical properties of the supramolecular thermosets can be systematically tailored by varying the ratios between Tri-PBA-PPG and Bi-PBA-PPG, which changes the cross-linking density of nitrogen-coordinated boroxines and the topology of the supramolecular thermosets. The mechanically strongest supramolecular thermosets with a molar ratio of Tri-PBA-PPG to Bi-PBA-PPG being 1:2 have a glass transition temperature of ∼36 °C, a tensile strength of ∼31.96 MPa, and a Young’s modulus of ∼298.5 MPa. The high reversibility of nitrogen-coordinated boroxines and the flexibility of poly(propylene glycol) chains enable the supramolecular thermosets with the strongest mechanical strength to be highly efficiently healed at 55 °C and recycled under a pressure of 4 MPa at 60 °C to regain their original mechanical strength and integrity.
In this paper, nitrogen‐coordinated boroxines are exploited for the fabrication of self‐healing and recyclable polymer composites with enhanced mechanical properties. The 3D polymer networks ...cross‐linked with nitrogen‐coordinated boroxines are first synthesized through the trimerization of ortho‐aminomethyl‐phenylboronic acid groups at the terminals of poly(propylene glycol) (PPG) chains, and subsequently, the mechanically robust polymer composites are fabricated by utilizing the complexation of nitrogen‐coordinated boroxine‐containing PPG (N‐boroxine‐PPG) with poly(acrylic acid) (PAA) and hydrogen‐bonding interactions between them. The N‐boroxine‐PPG is soft with a tensile strength of 0.19 MPa, whereas the tensile strengths of N‐boroxine‐PPG/PAA composites can be tailored to range from 1.7 to 12.7 MPa by increasing the PAA contents in the polymer composites. It is revealed that the amine ligands can facilitate the formation and dissociation of nitrogen‐coordinated boroxines at room temperature. Moreover, the reversibility of nitrogen‐coordinated boroxines and hydrogen‐bonding interactions enable multiple cycles of healing and recycling of the damaged N‐boroxine‐PPG/PAA composites. The healed and recycled N‐boroxine‐PPG/PAA polymer composites regain most of their mechanical strength.
Nitrogen‐coordinated boroxines are exploited for the fabrication of mechanically robust self‐healing and recyclable polymer composites by the complexation of nitrogen‐coordinated boroxines‐crosslinked poly(propylene glycol) with poly(acrylic acid). Because of the high reversibility of nitrogen‐coordinated boroxines, the as‐prepared polymer composites exhibit excellent self‐healing and recycling capacity. The polymer composites can retain their original mechanical robustness even after multiple cycles of healing and recycling process.
It is challenging to fabricate mechanically super‐strong polymer composites with excellent healing capacity because of the significantly limited mobility of polymer chains. The fabrication of ...mechanically super‐strong polymer composites with excellent healing capacity by complexing polyacrylic acid (PAA) with polyvinylpyrrolidone (PVPON) in aqueous solution followed by molding into desired shapes is presented. The coiled PVPON can complex with PAA in water via hydrogen‐bonding interactions to produce transparent PAA–PVPON composites homogenously dispersed with nanoparticles of PAA–PVPON complexes. As healable materials, the PAA–PVPON composite materials with a glass transition temperature of ≈107.9 °C exhibit a super‐high mechanical strength, with a tensile strength of ≈81 MPa and a Young's modulus of ≈4.5 GPa. The PAA–PVPON composites are stable in water because of the hydrophobic interactions among pyrrolidone groups. The super‐high mechanical strength of the PAA–PVPON composite materials originates from the highly dense hydrogen bonds between PAA and PVPON and the reinforcement of in situ formed PAA–PVPON nanoparticles. The reversibility of the relatively weak but dense hydrogen bonds enables convenient healing of the mechanically strong PAA–PVPON composite materials from physical damage to restore their original mechanical strength.
Healable and mechanically super‐strong polymer composite materials are fabricated by complexation of poly(acrylic acid) (PAA) with poly(vinylpyrrolidone) (PVPON). The transparent PAA–PVPON composite materials exhibit a tensile strength of ≈81 MPa and a Young's modulus of ≈4.5 GPa. The fractured PAA–PVPON composite materials can heal under mild conditions to restore their original mechanical strength.
Polymeric materials used in spacecraft require to be protected with an atomic oxygen (AO)‐resistant layer because AO can degrade these polymers when spacecraft serves in low earth orbit (LEO) ...environment. However, mechanical damage on AO‐resistant coatings can expose the underlying polymers to AO erosion, shortening their service life. In this study, the fabrication of durable AO‐resistant coatings that are capable of autonomously healing mechanical damage under LEO environment is presented. The self‐healing AO‐resistant coatings are comprised of 2‐ureido‐41H‐pyrimidinone (UPy)‐functionalized polyhedral oligomeric silsesquioxane (POSS) (denoted as UPy‐POSS) that forms hydrogen‐bonded three‐dimensional supramolecular polymers. The UPy‐POSS supramolecular polymers can be conveniently deposited on polyimides by a hot pressing process. The UPy‐POSS polymeric coatings are mechanically robust, thermally stable, and transparent and have a strong adhesion toward polyimides to endure repeated bending/unbending treatments and thermal cycling. The UPy‐POSS polymeric coatings exhibit excellent AO attack resistance because of the formation of epidermal SiO2 layer after AO exposure. Due to the reversibility of the quadruple hydrogen bonds between UPy motifs, the UPy‐POSS polymeric coatings can rapidly heal mechanical damage such as cracks at 80 °C or under LEO environment to restore their original AO‐resistant function.
Self‐healing atomic oxygen (AO)‐resistant coatings are fabricated by depositing 2‐ureido‐41H‐pyrimidinone (UPy)‐functionalized polyhedral oligomeric silsesquioxane (POSS) on polyimides. The coatings composed of hydrogen‐bonded UPy‐POSS supramolecular polymers are mechanically robust, thermally stable, and transparent and exhibit excellent AO resistance. The AO‐resistant coatings can autonomously heal mechanical damage under a low‐earth‐orbit environment to restore their AO‐resistant function.
The fabrication of shape memory polymers that are mechanically robust and capable of being induced by near-infrared (NIR) light and healing mechanical damage and the fatigued shape memory function ...remains a challenge. In this study, thermally and NIR-light-induced shape memory polymers with self-healing ability and satisfactory mechanical robustness are fabricated by dispersing poly(acrylic acid) (PAA)-grafted graphene oxide (GO) (PAA-GO) into poly(vinyl alcohol) (PVA) matrix. The PVA/PAA-GO3% films with a PAA-GO content of 3.0 wt % have a fracture stress of ∼70.4 MPa and a Young’s modulus of ∼2.8 GPa. The PVA/PAA-GO3% films exhibit an excellent shape memory performance because PVA and PAA-GO form a stable network through hydrogen-bonding interaction between them. Meanwhile, the PVA/PAA-GO3% films are capable of recovering from temporary shape to permanent shape under NIR light irradiation because of excellent photothermal conversion property of the GO nanosheets. More importantly, benefiting from the reversibility of hydrogen-bonding interactions between PVA and PAA-GO nanosheets, the shape memory PVA/PAA-GO3% films are capable of healing physical damage and the fatigued shape memory function with the assistance of water, which greatly enhance their reliability as shape memory materials and prolong their service life.
