Supramolecular Adhesion at Extremely Low Temperatures: A Combined Experimental and Theoretical Investigation

A solvent-free processed low-temperature tolerant adhesive

Ultra-low temperature resistant adhesive is highly desired yet scarce for material adhesion for the potential usage in Arctic/Antarctic or outer space exploration. Here we develop a solvent-free processed low-temperature tolerant adhesive with excellent adhesion strength and organic solvent stability, wide tolerable temperature range (i.e. -196 to 55 °C), long-lasting adhesion effect ( > 60 days, -196 °C) that exceeds the classic commercial hot melt adhesives. Furthermore, combine experimental results with theoretical calculations, the strong interaction energy between polyoxometalate and polymer is the main factor for the low-temperature tolerant adhesive, possessing enhanced cohesion strength, suppressed polymer crystallization and volumetric contraction. Notably, manufacturing at scale can be easily achieved by the facile scale-up solvent-free processing, showing much potential towards practical application in Arctic/Antarctic or planetary exploration.

Biocompatible Tough Ionogels with Reversible Supramolecular Adhesion

Cohesive and interfacial adhesion energies are difficult to balance to obtain reversible adhesives with both high mechanical strength and high adhesion strength, although various methods have been extensively investigated. Here, a biocompatible citric acid/L-(-)-carnitine (CAC)-based ionic liquid was developed as a solvent to prepare tough and high adhesion strength ionogels for reversible engineered and biological adhesives. The prepared ionogels exhibited good mechanical properties, including tensile strength (14.4 MPa), Young's modulus (48.1 MPa), toughness (115.2 MJ m-3), and high adhesion strength on the glass substrate (24.4 MPa). Furthermore, the ionogels can form mechanically matched tough adhesion at the interface of wet biological tissues (interfacial toughness about 191 J m-2) and can be detached by saline solution on demand, thus extending potential applications in various clinical scenarios such as wound adhesion and nondestructive transfer of organs.

Bulk transparent supramolecular glass enabled by host-guest molecular recognition

Supramolecular glass is a non-covalently cross-linked amorphous material that exhibits excellent optical properties and unique intrinsic structural features. Compared with artificial inorganic/organic glass, which has been extensively developed, supramolecular glass is still in the infancy stage, and itself is rarely recognized and studied thus far. Herein, we present the development of the host-guest molecular recognition motifs between methyl-β-cyclodextrin and para-hydroxybenzoic acid as the building blocks of supramolecular glass. Non-covalent polymerization resulting from the host-guest complexation and hydrogen bonding formation enables high transparency and bulk state to supramolecular glass. Various advantages, including recyclability, compatibility, and thermal processability, are associated with dynamic assembly pattern. Short-range order (host-guest complexation) and long-range disorder (three dimensional polymeric network) structures are identified simultaneously, thus demonstrating the typical structural characteristics of glass. This work provides a supramolecular strategy for constructing transparent materials from organic components.

Chemical Design of Supramolecular Reversible Adhesives for Promising Applications

Supramolecular reversible adhesives have garnered significant attention due to their potential applications in various fields. These adhesives exhibit remarkable properties such as reversible adhesion, self-healing, and high flexibility. This concept aims to present a comprehensive overview of the current research progress in developing supramolecular reversible adhesives. Firstly, the fundamentals of supramolecular chemistry and the principles underlying the design and synthesis of reversible adhesive systems are discussed. Next, the concept focuses on characterizing the reversible adhesion strength of supramolecular adhesive systems that have been developed. The adhesion performance of supramolecular reversible adhesives is summarized, highlighting their unique characteristics and promising applications. Finally, the challenges and future perspectives in the field of supramolecular reversible adhesives are discussed. The comprehensive overview provided in this concept aims to inspire further research and innovation in this exciting field.

High-Toughness CO2-Sourced Ionic Polyurea Adhesives

Polyurea (PUa) adhesives are renowned for their exceptional adhesion to diverse substrates even in harsh environments. However, the presence of quadruple bidentate intermolecular hydrogen bonds in the polymer chains creates a trade-off between cohesive energy and interfacial adhesive energy. To overcome this challenge, a series of CO2-sourced ionic PUa adhesives with ultratough adhesion to various substrates are developed. The incorporated ionic segments within the adhesive serve to partially mitigate the intermolecular hydrogen bonding interactions while conferring unique electrostatic interactions, leading to both high cohesive energy and interfacial adhesive energy. The maximum adhesive strength of 10.9 MPa can be attained by ionizing the CO2-sourced PUa using bromopropane and subsequently exchanging the anion with lithium bis(trifluoromethylsulfonyl)imide. Additionally, these ionic PUa adhesives demonstrate several desirable properties such as low-temperature stability (-80 °C), resistance to organic solvents and water, high flame retardancy, antibacterial activity, and UV-fluorescence, thereby expanding their potential applications. This study presents a general and effective approach for designing high-strength adhesives suitable for a wide array of uses.

Solvent-Resistant Adhesive Gel with Thermal Post-Tunability

Adhesives have received extensive attention in flexible bioelectronics, wearable electronic medical devices, and biofuel cells. However, it is a challenge to achieve late regulation of performance once polymer-based gels are formed. Here, a double-network organogel composed of a hydrophilic and hydrophobic polymer network and a polyamide acid network was successfully prepared. In diverse liquid environments (including isopropyl alcohol, glycerol, epichlorohydrin, n-propanol, dichloromethane, triethanolamine, ethanol absolute, hydrogen peroxide, and ethyl acetate), the organogel adhesive demonstrated remarkable properties. It exhibits a strong tensile strength of 200 kPa, a high fracture strain reaching 560%, and an impressive adhesion strength of 38 kPa. In addition, the organogel demonstrates exceptional adhesive properties toward polytetrafluoroethylene, plastics, metals, rubber, and glass. Note that the organogel could also regulate adhesive and tough performance by thermally triggering a cyclization reaction even after the organogel has been formed. The strategy provides a new idea for designing soft materials with post-tunability.

Multiple hydrogen bonding driven supramolecular architectures and their biomedical applications

Supramolecular chemistry combines the strength of molecular assembly via various molecular interactions. Hydrogen bonding facilitated self-assembly with the advantages of directionality, specificity, reversibility, and strength is a promising approach for constructing advanced supramolecules. There are still some challenges in hydrogen bonding based supramolecular polymers, such as complexity originating from tautomerism of the molecular building modules, the assembly process, and structure versatility of building blocks. In this review, examples are selected to give insights into multiple hydrogen bonding driven emerging supramolecular architectures. We focus on chiral supramolecular assemblies, multiple hydrogen bonding modules as stimuli responsive sources, interpenetrating polymer networks, multiple hydrogen bonding assisted organic frameworks, supramolecular adhesives, energy dissipators, and quantitative analysis of nano-adhesion. The applications in biomedical materials are focused with detailed examples including drug design evolution for myotonic dystrophy, molecular assembly for advanced drug delivery, an indicator displacement strategy for DNA detection, tissue engineering, and self-assembly complexes as gene delivery vectors for gene transfection. In addition, insights into the current challenges and future perspectives of this field to propel the development of multiple hydrogen bonding facilitated supramolecular materials are proposed.

Upcycling Waste Thermosetting Polyimide Resins into High-Performance and Sustainable Low-Temperature-Resistance Adhesives

Thermosetting polyimide (PI) has attracted extensive attention for its excellent properties, but the approaches to its end-of-life management are not sustainable, posing great threat to the ecosystem. Herein, this work proposes a mild, sustainable, and full recovery path for recycling waste carbon fiber reinforced phenylethynyl end-capped PI resin composites. In addition to recycling reaction reagent and woven carbon fiber, degraded products (DPETI) can be fully and directly used as high-performance and sustainable adhesives. DPETI exhibits strong adhesion to various surfaces, with a maximum adhesion strength of 1.84 MPa. Due to the strong supramolecular polymerization behavior without solvent dependence, DPETI demonstrates higher adhesive strength of 2.22 MPa in the extreme environment (-196 °C), which is maintained even after 10 cycles. This work sparks a new thinking for plastic wastes recycling that is to convert unrecyclable wastes into new and sustainable materials, which has the potential to establish new links within circular economies and influence the development of materials science.

Strong Protein Adhesives through Lanthanide-enhanced Structure Folding and Stack Density

Generating strong adhesion by engineered proteins has the potential for high technical applications. Current studies of adhesive proteins are primarily limited to marine organisms, e.g., mussel adhesive proteins. Here, we present a modular engineering strategy to generate a type of exotic protein adhesives with super strong adhesion behaviors. In the protein complexes, the lanmodulin (LanM) underwent α-helical conformational transition induced by lanthanides, thereby enhancing the stacking density and molecular interactions of adhesive protein. The resulting adhesives exhibited outstanding lap-shear strength of ≈31.7 MPa, surpassing many supramolecular and polymer adhesives. The extreme temperature (-196 to 200 °C) resistance capacity and underwater adhesion performance can significantly broaden their practical application scenarios. Ex vivo and in vivo experiments further demonstrated the persistent adhesion performance for surgical sealing and healing applications.

Tough Structural Adhesives with Ultra-Resistance to Both High and Cryogenic Temperature

Structural adhesion at high temperature has been a challenge for organic adhesives, and the commercially available adhesives that can work at a temperature above 150 °C is rather limited. Herein, two novel polymers were designed and synthesized via facile strategy, which involves polymerization between melamine (M) and M-Xylylenediamine (X), as well as copolymerization of MX and urea (U). With well-balanced rigid-flexible structures, the obtained MX and MXU resins were proved to be outstanding structural adhesives at a wide range temperature of -196~200 °C. They provided room-temperature bonding strength of 13~27 MPa for various substrates, steel bonding strength of 17~18 MPa at cryogenic temperature (-196 °C), and 15~17 MPa at 150 °C. Remarkably, high bonding strength of 10~11 MPa was retained even at 200 °C. Such superior performances were attributed to a high content of aromatic units, which leads to high glass transition temperature (T_g) up to ~179 °C, as well as the structural flexibility endowed by the dispersed rotatable methylene linkages.

The aqueous supramolecular chemistry of crown ethers

This mini-review summarizes the seminal exploration of aqueous supramolecular chemistry of crown ether macrocycles. In history, most research of crown ethers were focusing on their supramolecular chemistry in organic phase or in gas phase. In sharp contrast, the recent research evidently reveal that crown ethers are very suitable for studying abroad range of the properties and applications of water interactions, from: high water-solubility, control of Hofmeister series, "structural water", and supramolecular adhesives. Key studies revealing more details about the properties of water and aqueous solutions are highlighted.

Fully recyclable multifunctional adhesive with high durability, transparency, flame retardancy, and harsh-environment resistance

Recyclable/reversible adhesives have attracted growing attention for sustainability and intelligence but suffer from low adhesion strength and poor durability in complex conditions. Here, we demonstrate an aromatic siloxane adhesive that exploits stimuli-responsive reversible assembly driven by π-π stacking, allowing for elimination and activation of interfacial interactions via infiltration-volatilization of ethanol. The robust cohesive energy from water-insensitive siloxane assembly enables durable strong adhesion (3.5 MPa shear strength on glasses) on diverse surfaces. Long-term adhesion performances are realized in underwater, salt, and acid/alkali solutions (pH 1-14) and at low/high temperatures (-10-90°C). With reversible assembly/disassembly, the adhesive is closed-loop recycled (~100%) and reused over 100 times without adhesion loss. Furthermore, the adhesive has unique combinations of high transparency (~98% in the visible light region of 400-800 nm) and flame retardancy. The experiments and theoretical calculations reveal the corresponding mechanism at the molecular level. This π-π stacking-driven siloxane assembly strategy opens up an avenue for high-performance adhesives with circular life and multifunctional integration.

A Bio-Based Supramolecular Adhesive: Ultra-High Adhesion Strengths at both Ambient and Cryogenic Temperatures and Excellent Multi-Reusability

Developing high-performance and reusable adhesives from renewable feedstocks is of significance to sustainable development, yet it still remains a formidable task. Herein, castor oil, melevodopa, and iron ions are used as building blocks to construct a novel bio-based supramolecular adhesive (BSA) with outstanding adhesion performances. It is prepared through partial coordination between melevodopa functionalized castor oil and Fe3+ ions. Noncovalent interactions between adherends and the catechol unit from melevodopa contribute to reinforcing adhesion, and the metal-ligand coordination between catechol and Fe3+ ions is utilized to strengthen cohesion. By combining strong adhesion and tough cohesion, the prepared BSA achieves an adhesion strength of 14.6 MPa at ambient temperature, a record-high value among reported bio-based adhesives as well as supramolecular adhesives to the best of knowledge. It also outperforms those adhesives at cryogenic temperature, realizing another record-high adhesion strength of 9.5 MPa at -196 °C. In addition, the BSA displays excellent multi-reusability with more than 87% of the original adhesion strength remaining even after reuse for ten times. It is highly anticipated that this line of research will provide a new insight into designing bio-based adhesives with outstanding adhesion performances and excellent multi-reusability.

Bioinspired Freeze-Tolerant Soft Materials: Design, Properties, and Applications

In nature, many biological organisms have developed the exceptional antifreezing ability to survive in extremely cold environments. Inspired by the freeze resistance of these organisms, researchers have devoted extensive efforts to develop advanced freeze-tolerant soft materials and explore their potential applications in diverse areas such as electronic skin, soft robotics, flexible energy, and biological science. Herein, a comprehensive overview on the recent advancement of freeze-tolerant soft materials and their emerging applications from the perspective of bioinspiration and advanced material engineering is provided. First, the mechanisms underlying the freeze tolerance of cold-enduring biological organisms are introduced. Then, engineering strategies for developing antifreezing soft materials are summarized. Thereafter, recent advances in freeze-tolerant soft materials for different technological applications such as smart sensors and actuators, energy harvesting and storage, and cryogenic medical applications are presented. Finally, future challenges and opportunities for the rapid development of bioinspired freeze-tolerant soft materials are discussed.

Dually-Thermoresponsive Hydrogel with Shape Adaptability and Synergetic Bacterial Elimination in the Full Course of Wound Healing

Incomplete contact between a pre-formed hydrogel and irregular wound limits the therapeutic effect of the dressing and increases the risk of infection; while great concerns have remained regarding the potential toxicity of the residual additives of chemical crosslinking for in situ forming hydrogels. Therefore, it is desirable to develop a self-adaptive hydrogel in response to skin temperature with shape adaptability and efficient antibacterial properties to prevent microbial invasion. Herein, a dually-thermoresponsive hydrogel composed of poly(N-isopropylacrylamide) (PNIPAm) and methacrylated κ-carrageenan (MA-κ-CA) is designed with compliance at physiological temperature to realize shape adaptability for completely covering irregular wounds. Furthermore, the hydrogel with near-infrared (NIR)-responsive polypyrrole-polydopamine nanoparticles (PPy-PDA NPs) and Zn²⁺ -derived zeolitic imidazolate framework (ZIF-8) can generate localized heat and gradually release Zn²⁺ to realize safe, effective synergetic photothermal-chemical bactericidal capability. In addition, the release rate of Zn²⁺ can be accelerated by NIR-induced heating, and thus a more efficient sterilization can be provided to severely infected wounds. Therefore, the proposed hydrogel would serve as a promising wound dressing for the full course of wound healing, with the abilities of perfectly covering the wound and adapting to regenerating tissue, and controllable photothermal-chemical antibacterial capability to reach high bactericidal efficiency and long-term release of antibacterial agents.

Low-molecular-weight supramolecular adhesives based on non-covalent self-assembly of a small molecular gelator

Currently developed adhesives are overwhelmingly polymeric in nature. Herein, we highlight for the first time the potential of supramolecular eutectogels assembled from small molecules as robust low-molecular-weight (LMW) supramolecular adhesives in air, water and organic solvents, and under low temperatures. These supramolecular eutectogels were produced from commercial alkyl trimethyl ammonium bromide (C_nTAB) in emerging deep eutectic solvents (DESs), which demonstrated rapid (∼2 min), robust, and tunable adhesion to both hydrophilic and hydrophobic surfaces at room temperature in air. Moreover, high adhesion performance was maintained even in liquid nitrogen (-196 °C), underwater, and in organic solvents. A study of the structure-property relationship of these adhesives and molecular dynamics (MD) simulations further clarified the assembly and adhesion mechanism of the C₁₂TAB molecules in DESs. Compared with traditional polymer adhesives and several existing examples of LMW supramolecular adhesives with solvent-free dry network structures, the spontaneous self-assembly of LMW gelators in versatile DESs provides a new strategy for the facile construction of high-strength supramolecular adhesives with gel network structures for a diverse range of harsh environments.

Supramolecular Polymeric Pressure-Sensitive Adhesive That Can Be Directly Operated at Low Temperatures

Low-temperature adhesion is ubiquitous in daily life and industry. However, most supramolecular adhesives are thermoplastic materials that require heating during the adhesion. Herein, a supramolecular approach is used to construct unique pressure-sensitive adhesives (PSAs) that can be directly operated at low temperatures (-60 °C). Supramolecular polymerization between phytic acid (PA) and water (H) endows poly(PA-H)s with excellent mechanical properties and low temperature adhesion capacity. Poly(PA-H)s can easily be processed into PSA tapes, pastes, and particles. Poly(PA-H)s were directly adhered to various surfaces by pressing at low temperatures (0 to -60 °C). No heating or high-temperature-induced solid-liquid transition was required for the low-temperature adhesion of poly(PA-H)s. With the help of structural water units in supramolecular polymers, poly(PA-H)s showed strong, stable, and organic solvent resistant adhesion performances at low temperatures, with adhesion strength of up to 3.61 MPa at -60 °C.

Dynamic reversible adhesives based on crosslinking network via Schiff base and Michael addition

It is of practical interest to obtain polymers with complex material properties in a simplified synthetic manner for a broader range of practical applications. In this work, we constructed a dynamic reversible adhesive based on branched polyamine (PA) and p-formylphenyl acrylate (FPA) by simultaneously performing Michael addition reaction and Schiff base reaction. Branched polyamines provide a large number of amino groups as reaction sites that can react with both carbon–carbon double bonds and aldehyde groups. This enables the branched polymeric adhesive system to have a large number of Schiff base bonds within it, an important property of Schiff base bonds is that they are dynamically reversible. This allows us to prepare adhesives with hyperbranched crosslinking networks and recycling properties, and we have verified that FPA–PA adhesives do not exhibit significant fatigue after multiple recycling through the gluing-destruction-gluing process. The resulting FPA–PA adhesives produce tough bonding on multi-substrates such as steel, aluminum, glass, PVC, PTFE, birch and moso bamboo, which exhibited by lap shear strength of 2.4 MPa, 1.7 MPa, 1.4 MPa, 1.3 MPa, 0.4 MPa, 1.6 MPa, and 1.8 MPa, respectively. The feasibility of the synthesis idea of simultaneous Michael addition reaction and Schiff base reaction was demonstrated, as well as the excellent performance and great application potential of FPA–PA adhesives to be recyclable on multi-substrates.

Schematic diagram of synthetic FPA–PA polymer adhesives, schematic diagram of adhesion strength on different substrates, and adhesion strength with multiple damage cycles for reuse.

Strong Dynamic Interfacial Adhesion by Polymeric Ionic Liquids under Extreme Conditions

Interfacial adhesion under extreme conditions has attracted increasing attention owing to its potential application of stopping leakages of oil or natural gas. However, interfacial adhesion is rarely stable at ultralow temperatures and in organic solvents, necessitating the elucidation of the molecular-level processes. Herein, we used the intermolecular force-control strategy to prepare four linear polymers by tuning the proportion of hydrogen bonding and the number of electrostatic sites. The obtained polymeric ion liquids displayed strong dynamic adhesion at various interfaces. They also efficiently tolerated organic solvents and ultracold temperatures. Highly reversible rheological behaviors are observed within a thermal cycle between high and ultracold temperatures. Temperature-dependent infrared spectra and theoretical calculation reveal thermal reversibility and interfacial adhesion/debonding processes at the molecular level, respectively. This intermolecular force-control strategy may be applied to produce environmentally adaptive functional materials for real applications.

Metal-ligand Interactions and Oligo(p-Phenylene Vinylene) Derivatives Based Supramolecular Polymer Possessing Variable Fluorescence Colors

Fluorescent supramolecular polymers combine the benefits of supramolecular polymers in terms of dynamic nature with the optoelectronic features of incorporated fluorophores. However, the majority of fluorescent supramolecular polymers can only exhibit a single fluorescent state, restricting their applications. Incorporating J-type dyes into supramolecular monomers is expected to impart supramolecular polymers with variable fluorescence colors, because the aggregation mode of J-type dyes is closely related to the formation of supramolecular polymers. Herein, we report a supramolecular polymer [M1·Zn(OTf)₂ ]_n , in which the monomer M1 contains a J-type dye, oligo(p-phenylene vinylene) (OPV) derivative, and two terpyridine ends. The M1 + Zn(OTf)₂ solutions exhibit fluorescence color changes varying from cyan to yellow-green in the monomer concentration ranging from 0.04 to 1.00 mM. Moreover, based on the outputs from laser scanning confocal microscopy (LSCM), the fluorescence color transition during the formation of supramolecular polymers is intuitively proven. Additionally, considering the close relationship between the supramolecular polymer structure and the fluorescence color, the fluorescence color can be regulated by introducing tetraethylammonium hydroxide (TBAOH) that can bind with Zn²⁺ competitively to break up the structure of the supramolecular polymer. This article is protected by copyright. All rights reserved.

Organic Single-Crystal Actuators and Waveguides that Operate at Low Temperatures

Applications in extreme conditions, such as those encountered in space exploration, require lightweight materials that can retain their elasticity in extremely cold environments. However, cryogenic treatment of most soft polymeric and elastomeric materials results in complete loss of their ability for elastic flow, whereby such materials that are normally ductile become stiff, brittle, and prone to cracking. Here, a facile method for preparation of hybrid organic crystalline materials that are not only cryogenically robust but are also capable of large, recoverable, and reversible deformation at low temperatures is reported. To that end, flexible organic crystals are first mechanically reinforced by a polymer coating and combined with a thermally responsive polymer. The resulting hybrid materials respond linearly and reversibly to temperatures from -15 to -120 °C without fatigue in air as well as in cold vacuum. The approach proposed here not only circumvents one of the main drawbacks that are inherent to the amorphous nature and has thus far limited the applications of polymeric materials at low temperatures, but it also provides a cost-effective access to a myriad of lightweight sensing, electronic, optical or actuating devices that can operate in low-temperature environmental settings.

Self-Evolution of High Mechanical Strength Dry-Network Polythiourethane Thermosets into Neat Macroscopic Hollow Structures

Organism-inspired hollow structures are attracting increasing interest for the construction of various bionic functional hollow materials. Next-generation self-evolution hollow materials tend to combine simple synthesis, high mechanical strength, and regular shape. In this study, we designed and synthesized a novel dry-network polythiourethane thermoset with excellent mechanical performance. The polymer film could evolve into a neat and well-organized object with a macroscopic hollow interior structure after being immersed in an aqueous NaOH solution. The self-evolution hollow structure originated from a hydrogen-bonded polymer network, which was later transformed into a network bearing both hydrogen bonds and ionic bonds. The swelling and thickness growth of this material could be controlled by the NaOH concentration and the immersion time. This unique self-evolution behavior was further utilized to produce a series of macroscopic 3D hollow-containing molds, which could be potentially applied in the production of smart materials.

Molecular Engineering Super-Robust Dry/Wet Adhesive with Strong Interface Bonding and Excellent Mechanical Tolerance

Despite the fact that synthetic adhesives have achieved great progress, achieving robust dry/wet adhesion under harsh operating environments is still challenging. Herein, inspired from the extraordinary adhesion mechanism of nature mussel protein adhesive, the balanced design concept of co-adhesion and interfacial adhesion is proposed to prepare one kind of novel copolymer adhesive of [poly(dopamine methacrylamide-co-methoxethyl acrylate-co-adamantane-1-carboxylic acid 2-(2-methyl-acryloyloxy)-ethyl ester)] [p(DMA-co-MEA-co-AD)], named as super-robust adhesive (SRAD). The SRAD exhibits ultra-high interface bonding strengths in air (∼7.66 MPa) and underwater (∼2.78 MPa) against an iron substrate. Especially, a greatly tough and stable adhesion strength (∼2.11 MPa) can be achieved after immersing the bonded sample in water for half a year. Furthermore, the SRAD demonstrates surprising wet bonding robustness/tolerance even encountering harsh conditions such as fluid shearing, dynamic loading, and cyclic mechanical fretting. The great advantages of SRAD, such as strong interface bonding, stable wet adhesion underwater, and good mechanical tolerance, makes it demonstrate huge application potential in engineering sealants and underwater adhesion.

Disulfide-Mediated Reversible Polymerization toward Intrinsically Dynamic Smart Materials

The development of a dynamic chemistry toolbox to endow materials dynamic behavior has been key to the rational design of future smart materials. The rise of supramolecular and dynamic covalent chemistry offers many approaches to the construction of dynamic polymers and materials that can adapt, respond, repair, and recycle. Within this toolbox, the building blocks based on 1,2-dithiolanes have become an important scaffold, featuring their reversible polymerization mediated by dynamic covalent disulfide bonds, which enables a unique class of dynamic materials at the intersection of supramolecular polymers and adaptable covalent networks. This Perspective aims to explore the dynamic chemistry of 1,2-dithiolanes as a versatile structural unit for the design of smart materials by summarizing the state of the art as well as providing an overview of the fundamental challenges involved in this research area and its potential future directions.

Hot Melt Super Glue: Multi-Recyclable Polyphenol-Based Supramolecular Adhesives

We report the rapid and facile synthesis of hot melt super glue (HMSG) via the formation of adhesive supramolecular networks between catechol or pyrogallol hydroxyl groups (-OH) of polyphenols and repeat units (-CH₂ CH₂ O-) of poly(ethylene glycol) (PEG) based on hydrogen bonds. The adhesion strength of HMSG, processed by heating-cooling of polyphenols and PEG without additional solvents, can be tuned up to 8.8 MPa via changing the molecular weight of PEG and the ratio of hydrogen bonding donors and receptors. The advantages of the reported HMSG lie in the ease and scalability of the assembly process, rapid adhesion on various substrates with excellent processability, resistance of low temperature and organic solvents, and recyclable adhesion strength. The solvent-free HMSG represents a promising adhesive supramolecular network to expand the versatility and application of polyphenol-based materials. This article is protected by copyright. All rights reserved.

Self-Healing, Self-Adhesive and Stable Organohydrogel-Based Stretchable Oxygen Sensor with High Performance at Room Temperature

With the advent of the 5G era and the rise of the Internet of Things, various sensors have received unprecedented attention, especially wearable and stretchable sensors in the healthcare field. Here, a stretchable, self-healable, self-adhesive, and room-temperature oxygen sensor with excellent repeatability, a full concentration detection range (0-100%), low theoretical limit of detection (5.7 ppm), high sensitivity (0.2%/ppm), good linearity, excellent temperature, and humidity tolerances is fabricated by using polyacrylamide-chitosan (PAM-CS) double network (DN) organohydrogel as a novel transducing material. The PAM-CS DN organohydrogel is transformed from the PAM-CS composite hydrogel using a facile soaking and solvent replacement strategy. Compared with the pristine hydrogel, the DN organohydrogel displays greatly enhanced mechanical strength, moisture retention, freezing resistance, and sensitivity to oxygen. Notably, applying the tensile strain improves both the sensitivity and response speed of the organohydrogel-based oxygen sensor. Furthermore, the response to the same concentration of oxygen before and after self-healing is basically the same. Importantly, we propose an electrochemical reaction mechanism to explain the positive current shift of the oxygen sensor and corroborate this sensing mechanism through rationally designed experiments. The organohydrogel oxygen sensor is used to monitor human respiration in real-time, verifying the feasibility of its practical application. This work provides ideas for fabricating more stretchable, self-healable, self-adhesive, and high-performance gas sensors using ion-conducting organohydrogels.

Adhesion behaviour of bulk supramolecular polymers via pillar[5]arene-based molecular recognition

Pillar[n]arenes were rarely used as the building blocks for supramolecular adhesives. Herein, pillar[5]arene-based supramolecular polymer materials with tough adhesion behaviours on different substrates were prepared, with adhesion strengths up to 4.75 MPa. Strong and long-term dichloromethane-resistant adhesion performances were successfully obtained.

Codes in Code: AIE Supramolecular Adhesive Hydrogels Store Huge Amounts of Information

With the continuous advancement of information technology, the requirements for the information storage capacity of materials are getting higher and higher. However, information code materials usually only store a single piece of information. In order to improve their storage capacity, aggregation-induced emission (AIE) supramolecular adhesive hydrogels with different fluorescent colors are prepared, and a "Codes in Code" method is used to demonstrate the storage capacity for large amounts of information. Four kinds of poly(vinyl alcohol) (PVA) supramolecular hydrogels with different fluorescent colors are prepared; based on the hydrogen bonds on the hydrogel surface, these hydrogels can be assembled into a hydrogel, G5, which shows multiple fluorescent colors under the irradiation of UV light. When many 1D barcode patterns or/and 2D code patterns are incorporated into G5, not only a kind of 3D information but also plenty of 1D or/and 2D information can be stored. Therefore, the information codes prepared by the "Codes in Code" method can store a large amount of information.

Poly(ionic liquid)s Containing Alkoxy Chains and Bis(trifluoromethanesulfonyl)imide Anions as Highly Adhesive Materials

Adhesive materials have wide applications in diverse fields, but the development of a novel and multipurpose adhesive is a great challenge. This study demonstrates that conventional poly(ionic liquid)s (PILs) can be designed as highly efficient adhesives by simply introducing alkoxy moieties into the cationic backbone of PILs containing bis(trifluoromethanesulfonimide) (TFSI^- ) anions. The incorporated flexible alkoxy chain not only reduces the glass transition temperature of PILs but also endows these materials with strong hydrogen bonding interactions, which, together with the unique electrostatic interaction of the PILs, simultaneously contributes to a high cohesive energy and interfacial adhesive energy. Consequently, these alkoxy PILs are highly adhesive on various substrates such as glass, ceramic, stainless steel, aluminum, and polymers, in contrast to the nonadhesive behavior of conventional PILs. Photosensitive or electronically conductive composite adhesives are fabricated by virtue of the compatibility between ionic liquids and carbon nanotubes or silver nanofibers. Interestingly, the PIL-2-TFSI adhesive possesses a unique and reversible response to electric fields and achieves up to 35% improvement in adhesive strength.

A Superstrong and Reversible Ionic Crystal-Based Adhesive Inspired by Ice Adhesion

In this study, we developed a superstrong and reversible adhesive, which can possess a high bonding strength in the "adhesive" state and detach with the application of heating. An ionic crystal (IC) gel, in which an IC was immobilized within a soft-polymer matrix, were synthesized via in situ photo-crosslinking of a precursor solution composed of N, N-dimethyl acrylamide (DMAA) and a melted IC. The obtained IC gel is homogenous and transparent at melt point. When cooled to the phase transition temperature of the IC, the gel turns into the adhesive with the adhesion strength of 5.82 MPa (on glasses), due to the excellent wetting of melted gel and a thin layer of crystalline IC with high cohesive strength formed on the substrates. The synergistic effects between IC, polymer networks and substrates were investigated by solid state ¹ H NMR and molecular dynamics simulation. Such an adhesive layer is reversable and can be detached by heating and subsequent re-adhesion via cooling. This study proposed the new design of removable adhesives, which can be used in dynamic and complex environments.

A Spider-Silk-Inspired Wet Adhesive with Supercold Tolerance

Conventional adhesives often encounter interfacial failure in humid conditions due to small droplets of water condensed on surface, but spider silks can capture prey in such environment. Here a robust spider-silk-inspired wet adhesive (SA) composed of core-sheath nanostructured fibers with hygroscopic adhesive nanosheath (poly(vinylpyrrolidone)) and supporting nanocore (polyurethane) is reported. The wet adhesion of the SA is achieved by a unique dissolving-wetting-adhering process of core-sheath nanostructured fibers, revealed by in situ observations at macro- and microscales. Further, the SA maintains reliable adhesion on wet and cold substrates from 4 to -196 °C and even tolerates splashing, violent shaking, and weight loading in liquid nitrogen (-196 °C), showing promising applicability in cryogenic environments. This study will provide an innovative route to design functional wet adhesives.