Quadruple H-Bonding Cross-Linked Supramolecular Polymeric Materials as Substrates for Stretchable, Antitearing, and Self-Healable Thin Film Electrodes

Anthracene dimer crosslinked polyurethanes as mechanoluminescent polymeric materials

The force-induced cleavage of anthracene dimer results in fluorescence and shows good sensitivity to mechano-stimuli such as pressure.

Biomimetic folding of small organic molecules driven by multiple non-covalent interactions

The supramolecular self-folding of UPy-based monomers with low molecular weight driven by multiple non-covalent interactions has been developed.

Proactively modulating mechanical behaviors of materials at multiscale for mechano-adaptable devices

How materials behave when subjected to mechanical stresses is studied by mechanics of materials. However, the application of flexible and stretchable devices exposes materials to dynamic mechanical environments. Therefore, mechano-adaptable materials and devices that can respond as pre-designed have been explored. There are two main ways to proactively modulate mechanical behaviors for materials, which involve molecular design and structural design. Molecular design has effectively integrated mechanically sensitive groups into synthetic materials for anticipated mechano-response. Structural design has broadened the boundary of conventional materials, generating mechanical metamaterials at multiscale with unique mechanical properties. Furthermore, molecular, structural plus systematic design for the application of mechano-adaptable devices have realized better electrical performance, human interaction, long-term sustainability, and even higher efficiency. Various devices based on design ideas are summarized and future challenges for proactively modulating mechanical behaviors of mechano-adaptable devices are discussed.

A dual-responsive hyperbranched supramolecular polymer constructed by cooperative host-guest recognition and hydrogen-bond interactions

A homotritopic pillar[5]arene (H3) containing adenine units was synthesized and employed to interact with a uracil derivative (6-(2,4-dioxo-3,4-dihydropyrimidin-1(2H)-yl)hexanenitrile, G) to form a hyperbranched supramolecular polymer. The hyperbranched supramolecular polymer showed a dual stimulus response both to heat and acid/base. The cooperative host-guest binding and hydrogen-bond interactions play a key role in the supramolecular polymerization.

Fabrication of Poly(acrylic acid)/Boron Nitride Composite Hydrogels with Excellent Mechanical Properties and Rapid Self-Healing Through Hierarchically Physical Interactions

Many living tissues possess excellent mechanical properties and self-healing ability. To mimic these living tissues, a series of novel composite hydrogels, poly(acrylic acid)/surface-modified boron nitride nanosheets (PAA/BNNS-NH2) were fabricated simply through hierarchically physical interactions: molecular-scale metal coordination interaction between -COOH of PAA and Fe3+ and nanoscale H-bond between -COOH of PAA and -NH2 of BNNS-NH2. The composite hydrogels exhibit both excellent mechanical properties (including enhanced fracture stress, elongation, toughness, Young's modulus, and dissipated energy) and rapid healing ability without any external stimulus. Especially, the B0.5P70 (the hydrogel with BNNS concentration of 0.5 mg mL- 1, the water content of 70 wt%) exhibits a fracture stress of ~ 1311 kPa and toughness of ~ 4.7 MJ m- 3, almost ~ 3 times and ~ 8 times to B0P70, respectively. The excellent properties, combined with the simple preparation method, endow these composite hydrogels with potential applications.

A self-healing conductive and stretchable aligned carbon nanotube/hydrogel composite with a sandwich structure

Self-healing conductive elastomers have emerged as a class of novel materials that are important for fabricating human-motion sensors, soft robots and healthcare monitoring systems. Herein, we report on a hydrogel of modified poly(γ-glutamic) acid polymer chains crosslinked by coordination complexes, which exhibits good stretchability (1375%), long-term stability (more than 40 days), and self-healing ability (99.0 ± 1.5% in 3 h). Furthermore, a "sandwich" structure composite was fabricated, which is composed of self-healing hydrogels and Au nanograin-decorated aligned multiwall carbon nanotube sheets. It possesses fast self-healing ability, a low stable electronic resistance of 10 ± 1 Ω sq^-1, in the temperature range of -40-90 °C, the humidity range of 10-90%, and a stretching range up to 200%.

Preparation of cross-linked supramolecular polymers based on benzo-21-crown-7/secondary ammonium salt host-guest interactions

We found that TC7 not only self-assembles into one-dimensional supramolecular aggregates in chloroform, but also forms cross-linked supramolecular polymers via host-guest complexation between benzo-21-crown-7 and secondary ammonium salts. Compared with one-dimensional linear supramolecular polymers, soft and long viscous fibers were pulled out from a concentrated solution of cross-linked supramolecular polymers as a result of higher viscosity and lower diffusion coefficients.

Stretchable and Self-Healing Integrated All-Gel-State Supercapacitors Enabled by a Notch-Insensitive Supramolecular Hydrogel Electrolyte

Next-generation wearable electronics are expected to endure significant deformations and mechanical damage. Therefore, self-healing stretchable electrolytes with high ionic conductivity and robust mechanical strength, which have high tolerance of deformations and spontaneously recover electrochemical properties after external damage, are necessary conditions for the realization of flexible supercapacitors. Here, a new type of zwitterionic supramolecular hydrogel cross-linked through rationally designed ionic associations and hydrogen bonds is reported (PAD/H₂SO₄). The resultant supramolecular network realizes a high ionic conductivity of 57 mS cm^-1 and unprecedented mechanical properties such as a high toughness of 35 000 J m^-2, a notch-insensitive of up to 2200% strain, and efficient instantaneous self-healing within 5 min. Acting as an electrolyte, a novel flexible supercapacitor design strategy is proposed by integrating capacitive materials directly onto the PAD/H₂SO₄ hydrogel to achieve exceptional electrochemical performance, which can be repeatable for at least 50 cutting/healing cycles. The facile and versatile strategy for the construction of the integrated all-gel-state supercapacitors with self-healing stretchable electrolytes will provide new directions for future long-life flexible devices.

Efficient Graphene/Cyclodextrin-Based Nanocontainer: Synthesis and Host-Guest Inclusion for Self-Healing Anticorrosion Application

Cyclodextrin, with a hydrophobic inner cavity and a hydrophilic exterior, is often used to encapsulate a widest range of guest molecules based on host-guest inclusion interactions. Graphene, an emerging nanobuilding material, exhibits great potential for numerous applications because of its superior characteristics. Herein, we synthesized a novel graphene/β-cyclodextrin-based supramolecular nanocontainer with excellent inhibitor encapsulating capacity and high impermeable properties. The benzotriazole (BTA)-loaded nanocontainers were then used to endow coating system with excellent passive and active anticorrosion performance. Local electrochemical impedance spectroscopy (LEIS) was performed to characterize the self-healing behavior of composite coatings. Results indicated that the protective capability of the scratched coatings can be recovered through BTA release from containers. Furthermore, the long-term corrosion resistance of container-based coating was largely improved as observed from EIS. The effective healing process involves two conditions: (1) the release of BTA from containers and formation of adsorption layers on exposed metal surfaces and (2) the impermeable graphene nanosheets greatly impeded the electrolyte penetration and corrosion extension around the scratch. This novel graphene/β-cyclodextrin-based nanocontainer endows polymer coating with efficient self-healing functionality and durable anticorrosion property.

Highly Stretchable, Self-Healable Elastomers from Hydrogen-Bonded Interpolymer Complex (HIPC) and Their Use as Sensitive, Stable Electric Skin

There is a growing interest in developing stretchable strain sensors to quantify the large mechanical deformation and strain associated with the activities for a wide range of species. Herein, we constructed elastomeric, healable hydrogen-bonded interpolymer complex (HIPC) rubberlike film by complexation of hydrogen-bond (H-bond)-donating poly(acrylic acid) (PAA) and H-bond-accepting poly(ethylene oxide) (PEO) (or poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) (F108)). All HIPC elastomers prepared from varied PAA/PEO (or PAA/F108) ratios are healable elastomers with high extensibility (with the highest strain of 1400%). Recovery of all films can automatically occur or be accelerated by externally added water droplet. The stress- and strain healing efficiencies (ησ and ηε) of the water-assisting healed PAA/F108 blends are as high as 99%. Furthermore, stretchable and healable conductor films were fabricated from silver nanowire-printed (Ag-p) and the single-walled carbon nanotube-blended (SW-b) conductor films, respectively. The healable Ag-p conductor film is an ultrasensitive strain sensor, exhibiting large electric resistance variation when stretched. In contrast, the healable SW-b film is an ultrastable strain sensor with reversible resistance strain response over 200 stretching release cycles within a high strain range of 500%. Therefore, this study provides a new and flexible HIPC strategy for the fabrication of stretchable, ultrasensitive, and stable self-healing electrode materials.

Exploring a naturally tailored small molecule for stretchable, self-healing, and adhesive supramolecular polymers

Polymeric materials with integrated functionalities are required to match their ever-expanding practical applications, but there is always a trade-off between complex material performances and synthetic simplification. A simple and effective synthesis route is reported to transform a small molecule of biological origin, thioctic acid, into a high-performance supramolecular polymeric material, which combines processability, ultrahigh stretchability, rapid self-healing ability, and reusable adhesivity to surfaces. The proposed one-step preparation process of this material involves the mixing of three commercially available feedstocks at mild temperature without any external solvent and a subsequent cooling process that resulted in a dynamic, high-density, and dry supramolecular polymeric network cross-linked by three different types of dynamic chemical bonds, whose cooperative effects in the network enable high performance of this supramolecular polymeric material.

Construction of [2]rotaxane-based supramolecular polymers driven by wheel-stopper π⋯π interactions

A new strategy for supramolecular polymerization is designed and presented, which is based on the wheel-stopper charge-transfer interactions of [2]rotaxanes.

Wearable and flexible sensors for user-interactive health-monitoring devices

The development of flexible and wearable healthcare devices facilitates a real-time monitoring of body activities as well as detecting various biosignals, which provided useful information to manage one's health condition for personal health monitoring.