A multiresponsive, shape-persistent, and elastic supramolecular polymer network gel constructed by orthogonal self-assembly

Supramolecular strategy for smart windows

Supramolecular strategy-based materials are outlined and their applications for fabricating smart windows are summarized for future exploration of ideal smart windows.

Controllable supramolecular assembly and architecture transformation by the combination of orthogonal self-assembly and competitive self-sorting assembly

New supramolecular polymers were prepared by the combination of orthogonal self-assembly and competitive self-sorting assembly methods.

LCST behavior controlled by size-matching selectivity from low molecular weight monomer systems

LCST behavior was controlled by crown ether–cation recognition motifs via size-matching selectivity.

Controlling interfacial interactions of supramolecular assemblies by light-responsive overcrowded alkenes

A light-responsive supramolecular polymer was constructed by an AB-type monomer containing a light-responsive overcrowded alkene. The primary assemblies of the supramolecular polymer can further undertake secondary self-assembly by interfacial host-guest connections, which can be manipulated by light stimuli to convert into discrete primary assemblies.

Self-healing and shape-memory properties of polymeric materials cross-linked by hydrogen bonding and metal–ligand interactions

Polymeric materials were prepared by cross-linking them with two independent non-covalent interactions, namely hydrogen bonding and metal–ligand interactions.

Desymmetrization of disubstituted aromatic crown ethersviaintramolecular Cannizzaro reactions

Ba⁺⁺templated Cannizzaro reactions convert symmetrical aromatic crown ether dialdehydes of various types [dibenzo and bis(meta-phenylene)] and sizes (20–32 atom rings) to acid–alcohol functionalized crown ethers in 70–98% yields.

Discrete and Polymeric Self-Assembled Palladium(II) Complexes as Supramolecular Gelators

Supramolecular gels prepared from low-molecular-weight gelators have been extensively explored. However, the exploitation of discrete or polymeric metal complexes as gelators is a relatively recent trend. The synthesis of self-assembled coordination complexes from palladium(II) and selected ligands is well established, but the potential of these complexes as gelators is a less explored treasure. Herein we focus on the gelation abilities of some self-assembled palladium(II) complexes and the resulting unique properties. First, discrete complexes with PdL, PdL₂ , Pd₂ L, Pd₂ L₂ , Pd₂ L₄ , and Pd₃ L₆ compositions are discussed. Second, gelation behavior promoted by coordination-polymer-like gelators formed in situ is explored. These gel samples have been employed in catalysis and the uptake of organic and dye molecules from the solution and gas phases. It is concluded that untapped unique properties can be realized by further exploration of designer palladium(II) complexes.

Chirality-Enabled Liquid Crystalline Physical Gels with High Modulus but Low Driving Voltage

Self-supporting liquid crystalline physical gels with facile electro-optic response are highly desirable, but their development is challenging because both the storage modulus and driving voltage increase simultaneously with gelator loading. Herein, we report liquid crystalline physical gels with high modulus but low driving voltage. This behavior is enabled by chirality transfer from the molecular level to three-dimensional fibrous networks during the self-assembly of 1,4-benzenedicarboxamide phenylalanine derivatives. Interestingly, the critical gel concentration is as low as 0.1 wt %. Our findings open doors to understanding and exploiting the role of chirality in organic gels.

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.

Construction of Metallacage-Cored Supramolecular Gel by Hierarchical Self-Assembly of Metal Coordination and Pillar[5]arene-Based Host-Guest Recognition

In this work, a Pd₂ L₄ metallacage 2•([BF₄ ]^- )₄ with four pillar[5]arene units is first prepared and characterized by 1D multinuclear NMR (¹ H, ¹¹ B, and ¹⁹ F NMR), 2D ¹ H-¹ H correlation spectra, ¹ H-¹³ C heteronuclear single quantum coherence, and diffusion-ordered NMR spectroscopy, and electrospray ionization time-of-flight mass spectrometry. By the introduction of a ditopic guest molecule 3 into a chloroform solution of 2•([BF₄ ]^- )₄ , a supramolecular polymer network gel is successfully constructed based on the metal coordination interactions and host-guest recognition between the pillar[5]arene units of 2•([BF₄ ]^- )₄ and neutral ditopic guest molecule 3. The temperature and pH responsivenesses of the supramolecular gel are studied, which are further employed for the controlled release of different cargos. As a demonstration, emodin and methylene blue are trapped in the cavities of the metallacage and in the pores of the supramolecular gel, respectively. Methylene blue is first released along with the gel-sol transition while emodin is then released by the further addition of acid to destroy the metallacage. This study explores the use of metallacage-cored supramolecular network gels for sequential controlled release and contributes to the development of smart and adaptive materials.

Reversing Redox Responsiveness of Hydrogels due to Supramolecular Interactions by Utilizing Double-Network Structures

Stimuli-responsive hydrogels have been actively researched, and some of them have been put into practical use. When we create and use stimuli-responsive hydrogel materials, controlling stimuli responsiveness of hydrogels is a very important issue. In this research, we prepared hydrogels having single-network (SN) or double-network (DN) gel structures with the host-guest interaction groups cyclodextrin and methyl viologen and evaluated their stimuli responsiveness. The results of the tensile and compression tests showed that the hydrogels with SN and DN structures exhibited opposite stimuli responsiveness in response to the redox reaction of methyl viologen through the association and dissociation of the host molecule, β-cyclodextrin, and the guest molecule, methyl viologen. Spectroscopic measurements and rheological studies all indicated that this difference in stimuli responsiveness originated from the polymer-network structures. In addition, a chemically cross-linked DN gel was prepared and its redox responsiveness was evaluated.

A simple strategy for robust preparation and characterisation of hydrogels derived from chitosan and amino functional monomers for biomedical applications

Molecular interactions of amino functional (AF) monomers with chitosan (CS) lead to the formation of external stimuli responsive hydrogels (HGs). These have the potential to produce biomaterials with novel properties by a simple blending approach. Six independent AF monomers such as diethylenetriamine (DETA), bis(3-aminopropyl)amine (BAPA), 3,3'-diamino-N-methyldipropyleamine (DAMPA), hexamethylenediamine (HMDA), N,N-dimethylethylamine (DMEA) and diethylamine (DEA) with distinct functional groups and chain lengths were designed to form stable HGs at physiological pH. Such AF monomers are able to form HGs within a short time (in the range from 10 to 19 seconds) by physically interacting with CS. This is an alternative to the covalently crosslinking reaction process, providing cost effective HG biomaterials. HG complexes were characterized by rheometry, differential scanning calorimetry (DSC), and Fourier transform infrared (FTIR) spectroscopy. The interaction between AF monomers and the CS polymer has been discussed and the results have been confirmed by FTIR analysis. The storage modulus (G'), loss modulus (G'') and complex viscosity (η*) were evaluated for all HGs using a rheometer, and the ratios of CS and the particular AF monomer were optimized for stable HG formation. The swelling ratio was evaluated using a simple method and was found to be directly related to the structure of the AF monomer, pH and temperature. These HGs were utilised for encapsulation, and the release of active molecules (e.g., reactive red 120 (RR120) as a model compound) was measured at low pH 5.5, physiological pH 7.4 and high pH 9.5. The cell viability and cellular compatibility of the HGs were evaluated in vitro cell culture, demonstrating that all the five different types of HGs support cellular compatibility, attachment and growth. The physical mixing of AF monomers with CS is expedited for the development of new bespoke economically viable biomaterials.

Mechanically Robust Atomic Oxygen-Resistant Coatings Capable of Autonomously Healing Damage in Low Earth Orbit Space Environment

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-4[1H]-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.

Ionic Gels and Their Applications in Stretchable Electronics

Ionic gels represent a novel class of stretchable materials where ionic conducting liquid is immobilized in a polymer matrix. This review focuses on the design of ionic gel materials and device fabrication of ionic-gel-based stretchable electronics. In particular, recent progress in ionic-gel-based electronic skin (pressure/strain sensors, electric double-layer transistors, etc.), flexible displays, energy storage devices, and soft actuators are summarized, followed by a discussion of challenges in developing ionic-gel-based electronics and suggestions for future research directions that might overcome those challenges.

Fluorescent Metallacage-Core Supramolecular Polymer Gel Formed by Orthogonal Metal Coordination and Host-Guest Interactions

Herein, we report the preparation of a multifunctional metallacage-core supramolecular gel by orthogonal metal coordination and host-guest interactions. A tetragonal prismatic cage with four appended 21-crown-7 (21C7) moieties in its pillar parts was first prepared via the metal-coordination-driven self-assembly of cis-Pt(PEt3)2(OTf)2, tetraphenylethene (TPE)-based sodium benzoate ligands and linear dipyridyl ligands. Further addition of a bisammonium linker to the cage delivered a supramolecular polymer network via the host-guest interactions between the 21C7 moieties and ammonium salts, which formed a supramolecular gel at relatively higher concentrations. Due to the incorporation of a TPE derivative as the fluorophore, the gel shows emission properties. Multiple stimuli responsiveness and good self-healing properties were also observed because of the dynamic metal coordination and host-guest interactions used to stabilize the whole network structure. Moreover, the storage and loss moduli of the gel are 10-fold those of the gel without the metallacage cores, indicating that the rigid metallacage plays a significant role in enhancing the stiffness of the gel. The studies described herein not only enrich the functionalization of fluorescent metallacages via elegant ligand design but also provide a way to prepare stimuli-responsive and self-healing supramolecular gels as robust and smart materials.

Fabrication of Self-Healing Hydrogels with On-Demand Antimicrobial Activity and Sustained Biomolecule Release for Infected Skin Regeneration

Microbial infection has been considered as one of the most critical challenges in bioengineering applications especially in tissue regeneration, which engenders severe threat to public health. Herein, a hydrogel performing properties of rapid self-healing, on-demand antibiosis and controlled cargo release was fabricated by a simple assembly of Fe complex as the cross-linker and hyaluronic acid as the gel network. This hydrogel is able to locally degrade and release Fe³⁺ to kill bacteria as needed because of hyaluronidase excreted by surrounding bacteria, resulting in efficient antibacterial activity against different types of bacteria. The sustained release property of certain types of growth factors was also observed from this hydrogel owing to its dense network. Moreover, this hydrogel could repeatedly heal itself in minutes because of the coordination interaction between Fe³⁺ and COOH, exhibiting good potential in bioengineering applications on the exposed tissue, where the materials are easily damaged during daily life. When topically applied onto damaged mouse skin with infection of Staphylococcus aureus, the hydrogel is able to inhibit microbial infections, meanwhile promoting cutaneous regeneration, which formed new skin with no inflammation within a 10 day treatment. These results demonstrate the potential application of this self-healing hydrogel for the integrated therapy of antibiosis and tissue regeneration.

Effective combination therapy of percutaneous ethanol injection and chemotherapy based on injectable low molecular weight gels

Percutaneous ethanol injection (PEI) therapy was used in liver cancer treatment, however, the therapeutic ethanol in PEI easily flew away from injected solid tumours and hinder the treatment effect. In this paper, injectable supramolecular gels formed by self-assembly of low molecular weight gelators (LMWGs) based on glycylglycine modified phenylboronic acid were prepared to localize ethanol and load chemotherapeutic drug for in situ synergistic therapy. The mechanism, morphology and rheological property of supramolecular gels were characterized by NMR, UV, SEM, etc. The rheological study revealed that the gels were formed in situ rapidly and recovered promptly once damaged. The gels were non-toxicity to both normal 3T3 fibroblasts cells and 4T1 breast cancer cells. Doxorubicin (DOX) hydrochloride and ethanol were encapsulated in the gels for the combination of chemotherapy and PEI therapy. The in vivo anticancer activity of the DOX-loaded gels was carried out in tumour bearing mice. The injected gels were coated around tumour tissues to lock ethanol, and DOX was released sustainingly from the gels to maintain effective concentration to induce the apoptosis of tumour cells. DOX-loaded gels and the ethanol exhibited excellent therapeutic efficacy and low side effects in local cancer therapy.

Organogel-Derived Covalent-Noncovalent Hybrid Polymers as Alkali Metal-Ion Scavengers for Partial Deionization of Water

We show that crown ethers (CEs) 1-5 congeal both polar and nonpolar solvents via their self-assembly through weak noncovalent interactions (NCIs) such as CH···O and CH···π interactions. Diisopropylidene-mannitol (6) is a known gelator that self-assembles through stronger OH···O H bonding. These two gelators together also congeal nonpolar solvents via their individual self-assembly. Gelator 6 self-assembles swiftly to fibers, which act as templates and attract CE to their surface through H bonding and thereby facilitate their self-assembly through weak NCI. Polymerization of styrene gels made from CE and 6, followed by the washing off of the sacrificial gelator 6, yields robust porous polystyrene-crown ether hybrid matrices (PCH), having pore-exposed CEs. These PCHs not only were efficient in sequestering alkali metal ions from aqueous solutions but also can be recycled. This novel use of organogels for making solid sorbents for metal-ion scavenging might be of great interest.

Warm/cool-tone switchable thermochromic material for smart windows by orthogonally integrating properties of pillar[6]arene and ferrocene

Functional materials play a vital role in the fabrication of smart windows, which can provide a more comfortable indoor environment for humans to enjoy a better lifestyle. Traditional materials for smart windows tend to possess only a single functionality with the purpose of regulating the input of solar energy. However, different color tones also have great influences on human emotions. Herein, a strategy for orthogonal integration of different properties is proposed, namely the thermo-responsiveness of ethylene glycol-modified pillar[6]arene (EGP6) and the redox-induced reversible color switching of ferrocene/ferrocenium groups are orthogonally integrated into one system. This gives rise to a material with cooperative and non-interfering dual functions, featuring both thermochromism and warm/cool tone-switchability. Consequently, the obtained bifunctional material for fabricating smart windows can not only regulate the input of solar energy but also can provide a more comfortable color tone to improve the feelings and emotions of people in indoor environments.

Materials for smart windows usually possess single functionality, thus developing materials that regulate solar energy whilst changing color to affect human emotion is desirable. Here the authors combine pillar[6]arenes and ferrocene/ferrocenium groups to produce warm/cool tone-switchable thermochromic materials.

Photoregulating of Stretchability and Toughness of a Self-Healable Polymer Hydrogel

Supramolecular hydrogels that are assembled through dynamic host-guest interactions have presented apparent potential in the construction of materials with promising performance. Herein, a photoregulated hydrogel cross-linked by host-guest interactions with multifunctions of high stretchability, strong toughness, and rapid self-healing property is reported. The hydrogel exhibits unique light-responsive property due to the introduction of two photoisomerized groups. For example, the stress-strain curve of the original hydrogel indicates 1020% rupture strain with the maximum tensile strain value of 214 kPa. Upon 365 nm light irradiation for an hour, its tensile strain increases to 15 times with lower tensile stress indicating a better stretchability. Moreover, the hydrogel is photochromic and surface patternable, where it can reversibly switch color between luminous yellow and brown while exposed to 365 and 440 nm light irradiation. It holds great promise for applying in self-recovering optically controlled and labeled elastic mechanical materials.

Multi-mode supermolecular polymerization driven by host-guest interactions

A novel supermolecular self-assembly based on ternary host-guest interaction between cucurbit[8]uril (CB[8]), 1,1'-dimethyl-4,4'-bipyridinium dication (MV) and coumarin derivative was applied for the construction of linear supramolecular polymer with high degree of polymerization in aqueous solution. Accompanied by the introduction of azobenzene on linear ABBA type monomer the supermolecular polymerization is different and the morphology changes from linear to dendritic polymer. The successful supramolecular polymerization of linear and dendritic supramolecular polymers by non-covalent host-guest molecular recognition was confirmed by various characterization methods, such as 1H NMR spectroscopy, ROESY, transmission electron microscopy (TEM) and dynamic light scattering (DLS) measurements. Meanwhile, the supramolecular polymerization could promote the conversion of the azobenzene from cis to trans, which ultimately results in no isomerism upon UV irradiation.

Cucurbit[8]uril-Regulated Colloidal Dispersions Exhibiting Photocontrolled Rheological Behavior

In situ photocontrol over shear-thickening of condensed colloidal dispersions is of paramount importance in a wide range of applications including process technology and photorheological fluids. Its development and practicability, however, are hampered by the lack of well-designed photoresponsive systems. Here, a colloidal suspension whose rheological behavior is readily switchable between shear-thinning and shear-thickening using an external light stimulus is reported. This smart colloidal solution contains hybrid raspberry-like colloids prepared by employing cucurbit[8]uril as a supramolecular linker to assemble functional Fe₃ O₄ nanoparticles onto a silica core. The formed raspberry colloids are photoresponsive and can be reversibly disassembled under UV irradiation.

Divalent Pseudorotaxane with Polarized Plug-Socket and Padlock Functions

A dual-pore structured host composed of one 24-crown-8 and one 34-crown-10, and a "U"-shaped guest consisting of two different recognition units, one dibenzylammonium and one viologen, were synthesized and bound 1:1 into a divalent pseudorotaxane P1. P1 can mimic the inserting and pulling out functions of a polarized plug-socket system under solvent driven stimulus and can also realize the locking and unlocking actions of a padlock under pH stimulus.

Integrative Self-Sorting: One-Pot Synthesis of a Hetero[4]rotaxane from a Daisy-Chain-Containing Hetero[4]pseudorotaxane

The structural complexity of mechanically interlocked molecules are very attractive to chemists owing to the challenges they present. In this article, novel mechanically interlocked molecules with a daisy-chain-containing hetero[4]rotaxane motif were efficiently synthesized. In addition, a novel integrative self-sorting strategy is demonstrated, involving an ABB-type (A for host, dibenzo-24-crown-8 (DB24C8), and B for guest, ammonium salt sites) monomer and a macrocycle host, benzo-21-crown-7 (B21C7), in which the assembled species in hydrogen-bonding-supported solvent only includes a novel daisy-chain-containing hetero[4]pseudorotaxane. The found self-sorting process involves the integrative recognition between B21C7 macrocycles and carefully designed components simultaneously containing two types of secondary ammonium ions and a host molecule, DB24C8 crown ether. The self-sorting strategy is integrative to undertake self-recognition behavior to form one single species of pseudorotaxane compared with the previous report. This self-sorting system can be used for the efficient one-pot synthesis of a daisy-chain-containing hetero[4]rotaxane in a good yield. The structure of hetero[4]rotaxane was confirmed by ¹ H NMR spectroscopy and high-resolution electrospray ionization (HR-ESI) mass spectrometry.

Triple Noncovalent-Interaction-Containing Supramolecular Polymer Vesicle Chemosensors with Dynamically Tunable Detection Ranges

Chemosensors (CSs) with dynamically tunable detection ranges have important significance for their expansion in practical applications; however, most CSs possess an unchangeable detection limit. In this work, we report the first example of a supramolecular polymer vesicle (SPV) chemosensor with a dynamically tunable detection range. SPVs containing porphyrin (PP) moieties and β-cyclodextrin (β-CD)/azobenzene (Azo) host-guest interactions were first constructed. The obtained SPVs were used to detect Zn²⁺ with a high selectivity and sensitivity over a wide detection limit range of 8.67×10^-9 to 1.99×10^-11 under UV light irradiation. The corresponding sensing mechanism was attributed to the synergistic effects of the triple noncovalent interactions, including the metal-ligand coordination of PP/Zn²⁺ and the double host-guest interactions of β-CD/Azo and β-CD/PP.

Enantiopure Tertiary Urea and Thiourea Derivatives of Trianglamine Macrocycle: Structural Studies and Metallogeling Properties

Synthesis and detailed experimental and theoretical study on new urea and thiourea derivatives of chiral trianglamine are presented. In solution, the urea derivative of the trianglamine adopts cone conformation, whereas a respective thiourea derivative exists in solution predominantly as a partial cone conformer. In the crystalline phase, the thiourea trianglamine derivative adapts partial cone conformation. In the solid state, the two symmetry independent molecules of thiourea trianglamine create bilayers, containing molecules arranged in a zipper motif. The bilayers are separated by channels filled with disordered solvent molecules. The thiourea derivative of trianglimine appeared to be a simple, low molecular weight supergelator that formed stable chiral metallogels in N,N-dimethylformamide with Ag(I), Cu(I). and Cu(II) salts. The enantiomeric enrichment of the macrocycle is a necessary condition for effective gelling because neither racemic nor enantiomerically enriched samples (up to 50% ee) form metallogels. The metallogels formed from silver cations and thiourea trianglamine show reversible thixotropic property rarely observed in metallogels.

Multi-responsive coordination polymers utilising metal-stabilised, dynamic covalent imine bonds

We report how the combination of dynamic covalent imine bonds and coordination bonds in a single polymer material not only imparts enhanced stability to the final polymer, but also allows the material to be sensitive to a range of stimuli, offering more fine-grained control over its properties.

Recent Achievements of Self-Healing Graphene/Polymer Composites

Self-healing materials have attracted much attention because that they possess the ability to increase the lifetime of materials and reduce the total cost of systems during the process of long-term use; incorporation of functional material enlarges their applications. Graphene, as a promising additive, has received great attention due to its large specific surface area, ultrahigh conductivity, strong antioxidant characteristics, thermal stability, high thermal conductivity, and good mechanical properties. In this brief review, graphene-containing polymer composites with self-healing properties are summarized including their preparations, self-healing conditions, properties, and applications. In addition, future perspectives of graphene/polymer composites are briefly discussed.

Stimuli responsive ion gels based on polysaccharides and other polymers prepared using ionic liquids and deep eutectic solvents

Ion gels and self-healing gels prepared using ionic liquids (ILs) and deep eutectic solvents (DESs) have been largely investigated in the past years due to their remarkable applications in different research areas. Herewith we provide an overview on the ILs and DESs used for the preparation of ion gels, highlight the preparation and physicochemical characteristics of stimuli responsive gel materials based on co-polymers and biopolymers, with special emphasis on polysaccharides and discuss their applications. Overall, this review summarizes the fundamentals and advances in ion gels with switchable properties prepared using ILs or DESs, as well as their potential applications in electrochemistry, in sensing devices and as drug delivery vehicles.

Modulating Pt⋯Pt metal–metal interactions through conformationally switchable molecular tweezer/guest complexation

Pt(ii)⋯Pt(ii) metal–metal interactions can be modulated for molecular tweezer/guest complexation systems in response to pH variation.

Bistable [2]rotaxane encoding an orthogonally tunable fluorescent molecular system including white-light emission

By combining a rotaxane-type molecular switch and traditional fluorescent switch, an orthogonally tunable fluorescent molecular system was constructed, which can generate multicolor fluorescence including white light.

A H2S and I− dual-responsive supramolecular polymer constructed via pillar[5]arene-based host–guest interactions and metal coordination

A supramolecular polymer was designed and prepared by self-assembly of a pillar[5]arene dimer (AA-type), constructed from Ag-coordination, and a homoditopic (BB-type) guest (G). The supramolecular polymer displayed H₂S and I⁻ dual responsiveness due to the sensitivity of Ag⁺ to H₂S and I⁻.

Cyclodextrin-based host–guest supramolecular hydrogel and its application in biomedical fields

CD-based host–guest supramolecular hydrogels and their potential biomedical application.

Strong, tough and mechanically self-recoverable poly(vinyl alcohol)/alginate dual-physical double-network hydrogels with large cross-link density contrast

Strong and tough poly(vinyl alcohol) (PVA)/alginate hydrogen-bonded-ionic dual-physical double-network (DN) hydrogels have been successfully prepared by a facile route of a freeze–thaw (25–25–25 °C) cycle followed by concentrated (1.0 mol L⁻¹ of) aqueous-Ca²⁺ immersion of PVA/Na alginate (SA) mixed aqueous solutions. It was found that, at mole ratios of the PVA- to SA repeat units of 20/1 to 80/1, the DN gels likely evolved a semi-interpenetrating polymer network (IPN) morphology of rigid alginate networks dispersed in while interlocking with ductile PVA network to accomplish DN synergy that gave their high strength and toughness, where the high alginate rigidity originated probably from its dense cross-link induced syneresis and dispersion along crosslink-defective voids to result in little internal stress concentration. Tentatively mechanistically, as the 20/1–80/1 DN gels were stretched steadily, their mechanical response was gradually differentiated into distinct synergistic states: the sparsely hydrogen-bonded PVA served as a ductile matrix to bear small fractions of the established stresses at its large elongations; whereas the densely ionically (i.e. Ca²⁺) cross-linked alginate functioned as a rigid skeleton to sustain the remaining larger stresses upon its smaller local strains. Promisingly, this ductile-rigid matrix-skeleton synergistic mechanism of semi-IPN morphology may be universally extended to all A/B DN hydrogels of large A–B rigidity (or cross-link density) contrast, whether the cross-link nature of network(s) A or B is covalent, ionic, hydrogen bonded or van der Waals interacted. The strong and tough DN gels also displayed satisfactory self-recovery of viscoelastic behaviour, in that their Young's modulus and dissipated energy in the uniaxial tensile mode and dynamic storage and loss moduli in the oscillatory shear mode all recovered significantly from non-linear viscoelastic regimes despite different degrees of failure to revert to (quasi)linear viscoelasticity.

Intermediate compositions enable synergised, strong-and-tough dual-physical double-network hydrogels of dispersion-induced rigid, ionic alginate-networks interlocking with global ductile, hydrogen-bonded poly(vinyl alcohol)-network.

Chirality control of multi-stimuli responsive and self-healing supramolecular metallo-hydrogels

The spontaneous formation of supramolecular metallo-hydrogels showing multi stimuli-responsiveness and intrinsic self-healing properties upon the interaction of chiral-histidine with Zn²⁺ ions.

A crown-ether-based moldable supramolecular gel with unusual mechanical properties and controllable electrical conductivity prepared by cation-mediated cross-linking

Supramolecular gels that possess high mechanical properties and unusual electrical conductivity were prepared by incorporating Cs⁺.