Stereochemistry-Dependent, Mechanoresponsive Supramolecular Host Assemblies for Fullerenes: A Guest-Induced Enhancement of Thixotropy

3D printing flexible zinc-ion microbatteries with ultrahigh areal capacity and energy density for wearable electronics

A flexible zinc ion micro-battery with ultra-high surface capacity (10.1 mA h cm^-2) and energy density (8.1 mW h cm^-2), as well as good flexibility, is fabricated based on the co-doping effect of V₂O₅ through an improved 3D printing technology, and is further integrated with flexible solar cells for self-powered wearable electronics.

Structural insights into self-assembly of a slow-evolving and mechanically robust supramolecular gel via time-resolved small-angle neutron scattering

The supramolecular assembly process is a widespread phenomenon found in both synthetically engineered and naturally occurring systems, such as colloids, liquid crystals and micelles. However, a basic understanding of the evolution of self-assembly processes over time remains elusive, primarily owing to the fast kinetics involved in these processes and the complex nature of the various non-covalent interactions operating simultaneously. With the help of a slow-evolving supramolecular gel derived from a urea-based gelator, we aim to capture the different stages of the self-assembly process commencing from nucleation. In particular, we are able to study the self-assembly in real time using time-resolved small-angle neutron scattering (SANS) at length scales ranging from approximately 30 Å to 250 Å. Systems with and without sonication are compared simultaneously, to follow the different kinetic paths involved in these two cases. Time-dependent NMR, morphological and rheological studies act complementarily to the SANS data at sub-micron and bulk length scales. A hollow columnar formation comprising of gelator monomers arranged radially along the long axis of the fiber and solvent in the core is detected at the very early stage of the self-assembly process. While sonication promotes uniform growth of fibers and fiber entanglement, the absence of such a stimulus helps extensive bundle formation at a later stage and at the microscopic domain, making the gel system mechanically robust. The results of the present work provide a thorough understanding of the self-assembly process and reveal a path for fine-tuning such growth processes for applications such as the cosmetics industry, 3D printing ink development and paint industry.

Domination of H-Bond Interactions in the Solvent-Triggering Gelation Process

Gels prepared with the solvent-triggering method are attractive for their easy and fast preparation; however, the role of solvents in this process remains unclear, which hinders the efficient and accurate control of desired gel properties. In this study, the role of solvents in the solvent-triggering gelation process is studied using 9-fluorenylmethoxycarbonyl (Fmoc)-protected diphenylalanine (Fmoc-FF) as the gelator. Density functional theory (DFT)-based calculations and corresponding wavefunction analyses are conducted to identify the H-bonding interaction sites between the molecules. The calculation results clearly annotate the activating role of DMF and the triggering role of H₂O in the gelation process. The solvation of Fmoc-FF by DMF can activate the H-bonding sites on the peptide chain, showing a conformation reversal and higher electrostatic potentials. Then, the H-bonding between Fmoc-FF and H₂O is facilitated to trigger gelation. The physical Fmoc-FF/DMF/H₂O gels show easily tuned mechanical strengths (G' of 10²-10⁵ Pa), injectable potentials (general yield strain < 100%), and stable recoverability (80-98% within 100 s). The regulation of these properties depends on not only the gelator concentration but also the H-bonding interactions with solvent molecules, which have seldom been studied in detail before. By understanding the effect of solvents, low-molecular-weight gelator-based gels can be designed, prepared, and tuned efficiently for potential applications.

Multiple Stimuli-Responsive Supramolecular Gel Formed from Modified Adenosine

Urea derivatives 1 and 2, synthesized from adenosine, were designed as low-molecular-weight gelators. Hydrophobic groups have been introduced into all or part of the hydroxy groups of the hydrophilic ribose moiety of 1 and 2 to control the solvophilicity of the molecules and their aggregates. Compound 2 selectively formed supramolecular gels in halogenated solvents such as chloroform and 1,2-dichloroethane. The supramolecular gel of 2 and chloroform was thermally stable and its gel-to-sol phase transition temperature was higher than the boiling point of chloroform. The physical properties of the supramolecular gel were investigated by determining its viscoelastic properties using a rheometer. The supramolecular gel realized multiple stimuli-responsive reversible gel-sol phase transitions. The supramolecular gel showed reversible phase transition by repeated warming-cooling cycles accompanying with the gel-sol transitions. The supramolecular gel could undergo five repeated mechano-responsive gel-sol transitions. Gel-to-sol phase transition could also be achieved by adding various anions to the supramolecular gel, such as tetrabutylammonium fluoride. Regelation was realized by adding boron trifluoride etherate to the fluoride ion containing sol. Addition of methanol to the supramolecular gel also induced gel-to-sol phase transition. Regelation was realized by adding molecular sieves 4 Å to the suspension.

Water-soluble host-guest complexes between fullerenes and a sugar-functionalized tribenzotriquinacene assembling to microspheres

A sugar-functionalized water-soluble tribenzotriquinacene derivative bearing six glucose residues, TBTQ-(OG) 6 , was synthesized and its interaction with C60 and C70-fullerene in co-organic solvents and aqueous solution was investigated by fluorescence spectroscopy and ultraviolet-visible spectroscopy. The association stoichiometry of the complexes TBTQ-(OG) 6 with C60 and TBTQ-(OG) 6 with C70 was found to be 1:1 with binding constants of K a = (1.50 ± 0.10) × 105 M-1 and K a = (2.20 ± 0.16) × 105 M-1, respectively. The binding affinity between TBTQ-(OG) 6 and C60 was further verified by Raman spectroscopy. The geometry of the complex of TBTQ-(OG) 6 with C60 deduced from DFT calculations indicates that the driving force of the complexation is mainly due to the hydrophobic effect and to host-guest π-π interactions. Hydrophobic surface simulations showed that TBTQ-(OG) 6 and C60 forms an amphiphilic supramolecular host-guest complex, which further assembles to microspheres with diameters of 0.3-3.5 μm, as determined by scanning electron microscopy.

An Li+-enriched Co2+-induced metallogel: a study on thixotropic rheological behaviour and conductance

An alkali base and counterion-selective red metallogel (1% w/v) has been synthesized by mixing the adipic acid-derived ligand H₂AL with LiOH, followed by the addition of 1 equivalent of Co(OAc)₂ in DMF. The addition of Co(OAc)₂ not only resulted in the formation of a 2 : 2 (M : L) complex, but also led to the consecutive steps of aggregation, fiber creation, entrapment of the solvent and eventually gelation. The metallogel formation and the mechanism behind gelation have been well characterized and established using various instrumental techniques such as FTIR spectroscopy, UV-vis spectroscopy, FE-SEM, TEM, PXRD, ESI-mass spectrometry, Job's plot and rheology analysis. Nyquist plots suggested a large decrease in the resistance value from 11.3 kΩ to 4.2 kΩ for the solution obtained from the ligand deprotonated by LiOH (AL^2-) and Co(OAc)₂ containing the metallogel. The Nyquist plot and resistance of the metallogel have also been studied under the influence of temperature and ultrasound stimuli. The extensive rheological measurements provide information about the strength of the gel network and the highly reversible nature and thixotropic behaviour of the metallogel.

A tetrathiafulvalene–l-glutamine conjugated derivative as a supramolecular gelator for embedded C60 and absorbed rhodamine B

An l-glutamine-containing tetrathiafulvalene gelator could form charge-transfer complex gels in the presence of C₆₀, and also the native gel exhibited excellent absorption properties for the removal of rhodamine B from aqueous solution.

Multi-stimuli-responsive hydrogels of gluconamide-tailored anthracene

In this work, two amphiphilic gluconamide-tailored anthracene gelators 1 and 2 have been synthesized, and found to form stable hydrogels with fibril structures. The stimuli-responsive behaviors of hydrogel 1 and 2 were investigated thoroughly by temperature-dependent 1H NMR, UV-Vis, rheometry, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results showed that hydrogel 1 exhibited multiple responsive behaviours upon exposure to stimuli including temperature, anions, light, electron-deficient chemicals and external stress; conversely, hydrogel 2 showed a distinct responsive phenomenon attributed to a subtle structural difference in the linker. This work demonstrates that gluconamide-tailored anthracene gelators could be a potential soft material and highlights the importance of a precisely designed structure.

Supramolecular Gel as the Template for Catalysis, Inorganic Superstructure, and Pharmaceutical Crystallization

A supramolecular gel is a fascinating combination of flexibility and orderliness. While the supramolecular nature of crosslinking contributes towards the adaptivity and the reversibility of the system, orderliness at the molecular level amplifies the functional output and induces extraordinary selectivity into the system. Therefore, use of supramolecular gels as the soft template is an emerging area of research, which includes but not limited to catalysis of a chemical or a photochemical process, transcription of gel property to a substrate, or even controlling the nucleation of drug molecules. This review aims to highlight the template effect of supramolecular gels in the above-mentioned areas relevant to novel fundamental chemistry, technology, and healthcare.

Hofmeister Anion-Induced Tunable Rheology of Self-Healing Supramolecular Hydrogels

ᅟ: Physical gelation behaviors of a series of D-gluconic acetal-based derivatives bearing fatty alkyl amine moieties have been investigated. One of these molecules exhibits excellent gelation behaviors in water, and the resultant hydrogels are found to display self-healing properties. Interestingly, the elasticity and strength of the resulting gel can be tuned by the addition of different kinds of Hofmeister salts. The gel formation mechanism was proposed based on the analysis of FT-IR,1HNMR, and XRD, indicating that the main driving force for the self-assembly was the π-π stacking of the benzene rings in the aqueous solution system. Overall, our research provides an efficient approach for facilely tuning the properties of the D-gluconic acetal-based hydrogel. ᅟ.

Gels with sense: supramolecular materials that respond to heat, light and sound

Advances in the field of supramolecular chemistry have made it possible, in many situations, to reliably engineer soft materials to address a specific technological problem. Particularly exciting are "smart" gels that undergo reversible physical changes on exposure to remote, non-invasive environmental stimuli. This review explores the development of gels which are transformed by heat, light and ultrasound, as well as other mechanical inputs, applied voltages and magnetic fields. Focusing on small-molecule gelators, but with reference to organic polymers and metal-organic systems, we examine how the structures of gelator assemblies influence the physical and chemical mechanisms leading to thermo-, photo- and mechano-switchable behaviour. In addition, we evaluate how the unique and versatile properties of smart materials may be exploited in a wide range of applications, including catalysis, crystal growth, ion sensing, drug delivery, data storage and biomaterial replacement.

New composite thixotropic hydrogel composed of a polymer hydrogelator and a nanosheet

A composite gel composed of a water-soluble aromatic polyamide hydrogelator and the nanosheet Laponite®, a synthetic layered silicate, was produced and found to exhibit thixotropic behaviour. Whereas the composite gel contains the gelator at the same concentration as the molecular gel made by the gelator only, the composite gel becomes a softer thixotropic gel compared to the molecular gel made by the gelator only. The reason for this could be that bundles of polymer gelator may be loosened and the density of the polymer network increased in the presence of Laponite.

Low Molecular Weight Supramolecular Gels Under Shear: Rheology as the Tool for Elucidating Structure-Function Correlation

Self-healing low molecular weight supramolecular gels (SMGs) represent an emerging class of smart materials, which can closely mimic the complex biological healing process, such as blood clotting, bone repair or wound healing. However, a lack of understanding of the structure-function correlation in the self-assembly process limits their molecular design and subsequent property tuning. The indispensability of a rheological study on supramolecular gels lies in direct transcription of the assembly property to the viscoelastic behavior of the material. This is similarly relevant to healable and non-healable systems. Thus, using rheology as a tool for elucidating structure-function relationships in self-assembled systems has huge potential. This review article will depict a general introduction of rheology in the field of soft matter including SMGs, followed by representative studies with interpretations, and discussion on future challenges. Altogether, this would be an effort, where an in-depth rheological study complemented with a real-time visualization with the help of microscopy, and introduction of other sophisticated real-time experiments, could be a step forward to capture the mystery of self-assembly process.

Synthesis of an electronically conductive hydrogel from a hydrogelator and a conducting polymer

A polymer hydrogelator mixed with a water-soluble electronically conductive polymer exhibits thixotropy due to the hydrogelator although each component at low concentrations does not exhibit this behaviour.

Thixotropic stiff hydrogels from a new class of oleoyl-d-glucamine-based low-molecular-weight gelators

A series of tripartite compounds comprising oleoyl, amino acid and d-glucamine moieties form stiff molecular hydrogels with strong thixotropic properties.

Salt Tunable Rheology of Thixotropic Supramolecular Organogels and Their Applications for Crystallization of Organic Semiconductors

Physical gelation behaviors of a series of novel bisurea-based derivatives bearing fatty alkyl tertiary amine moieties have been explored in water and common organic solvents. One of these amines exhibits very good thixotropic gels in apolar aromatic solvents (e.g., xylenes). The corresponding sol-gel transition is instantaneous and could be repeated for at least 50 cycles. Interestingly, the elasticity and strength of the resulting gels can be remarkably enhanced initially by the addition of a trace amount of tetrabutylammonium acetate (TBA) followed by a subsequent drop with further salt addition. Temperature-dependent ¹H NMR confirmed that hydrogen bonding is the main driving force for the physical gelation. TEM, rheology, ¹H NMR titration, and examination of critical gelation concentration (CGC) reveal that the phenomenon is due to the dominated effects, the salting out effect at lower TBA concentration, or the anion-urea hydrogen bonding at higher TBA concentration. Furthermore, the obtained transparent gels in this work can be used as good media for growing crystals of several organic semiconductors.

Nanoengineering of a Supramolecular Gel by Copolymer Incorporation: Enhancement of Gelation Rate, Mechanical Property, Fluorescence, and Conductivity

In the quest to engineer the nanofibrillar morphology of folic acid (F) gel, poly(4-vinylpyridine-co-styrene) (PVPS) is judiciously integrated as a polymeric additive because of its potential to form H-bonding and π-stacking with F. The hybrid gels are designated as F-PVPSx gels, where x denotes the amount of PVPS (mg) added in 2 mL of F gel (0.3%, w/v). The assistance of PVPS in the gelation of F is manifested from the drop in critical gelation concentration and increased fiber diameter and branching of F-PVPSx gels compared to that of F gel. PVPS induces a magnificent improvement of mechanical properties: a 500 times increase of storage modulus and ∼62 times increase of yield stress in the F-PVPS5 gel compared to the F gel. The complex modulus also increases with increasing PVPS concentration with a maximum in F-PVPS5 gel. Creep recovery experiments suggest PVPS induced elasticity in the otherwise viscous F gel. The fluorescence intensity of F-PVPSx gels at first increases with increasing PVPS concentration showing maxima at F-PVPS5 gel and then slowly decreases. Gelation is monitored by time-dependent fluorescence spectroscopy, and it is observed that F and F-PVPSx gels exhibit perfectly opposite trend; the former shows a sigmoidal decrease in fluorescence intensity during gelation, but the latter shows a sigmoidal increase. The gelation rate constants calculated from Avrami treatment on the time-dependent fluorescence data manifest that PVPS effectively enhances the gelation rate showing a maximum for F-PVPS5 gel. The hybrid gel exhibit 5 orders increase of dc conductivity than that of F-gel showing semiconducting nature in the current-voltage plot. The Nyquist plot in impedance spectra of F-PVPS5 xerogel exhibit a depressed semicircle with a spike at lower frequency region, and the equivalent circuit represents a complex combination of resistance-capacitance circuits attributed to the hybrid morphology of the gel fibers.

A novel multi-stimuli responsive gelator based on d-gluconic acetal and its potential applications

The goal of integrating multi-stimuli responsiveness and versatile applications into a single organogelator is achieved.

Thixotropic Supramolecular Gel Based on l-Lysine Derivatives

The dimer l-lysine derivatives, in which two N^α,N^ε-diacyl-l-lysines were crosslinked by calcium ion, were synthesized through a simply synthetic procedure and their gelation properties were examined. These compounds functioned as an organogelator; especially, the gelators possessing both a linear and a branched alkyl chains had the better organogelation ability and formed the thermally stable and rigid organogel. In addition, some organogels had a thixotropic property, which were responsive to a mechanical stimulus and reversibly underwent the gel–sol transition at room temperature. The thixotropic behavior was confirmed by visual contact and rheological experiments. Furthermore, it was assumed the mechanism of the thixotropic behavior.

Visual Recognition of Aliphatic and Aromatic Amines Using a Fluorescent Gel: Application of a Sonication-Triggered Organogel

A naphthalimide-based fluorescent gelator (N1) containing an alkenyl group has been designed and characterized. This material is able to gelate alcohols via a precipitate-to-gel transformation when triggered with ultrasound for less than 2 min (S-gel). The gelation process in n-propanol was studied by means of absorption, fluorescence, and IR spectra, scanning electron microscopy (SEM) images, and X-ray diffraction patterns. The fluorescence intensity of N1 decreased during the gelation process in a linear relationship with the sonication time. The S-gel of N1 could be used to sense aliphatic and aromatic amines by measuring the change in the signal output. For example, the addition of propylamine to the S-gel of N1 resulted in a dramatic enhancement of the fluorescence intensity, accompanied by a gel-to-sol transition. On the contrary, when the S-gel of N1 was treated with aromatic amines such as aniline, fluorescence was quenched and there was no gel collapse. The sensing mechanisms were studied by (1)H NMR, small-angle X-ray scattering, SEM and spectroscopic experiments. It is proposed that isomerization of the alkenyl group of N1 from the trans to cis form occurs when the S-gel is treated with propylamine, resulting in a gel-sol transition. However, the aromatic aniline molecules prefer to insert into the gel networks of N1 via hydrogen-bonding and charge-transfer interactions, maintaining the gel state. As potential applications, testing strips of N1 were prepared to detect aniline.

Mixing biomimetic heterodimers of nucleopeptides to generate biocompatible and biostable supramolecular hydrogels

As a new class of biomaterials, most supramolecular hydrogels formed by small peptides require the attachment of long alkyl chains, multiple aromatic groups, or strong electrostatic interactions. Based on the fact that the most abundant protein assemblies in nature are dimeric, we select short peptide sequences from the interface of a heterodimer of proteins with known crystal structure to conjugate with nucleobases to form nucleopeptides. Being driven mainly by hydrogen bonds, the nucleopeptides self-assemble to form nanofibers, which results in supramolecular hydrogels upon simple mixing of two distinct nucleopeptides in water. Moreover, besides being biocompatible to mammalian cells, the heterodimer of the nucleopeptides exhibit excellent proteolytic resistance against proteinase K. This work illustrates a new and rational approach to create soft biomaterials by a supramolecular hydrogelation triggered by mixing heterodimeric nucleopeptides.

Sol–gel transition accelerated by the co-assembly of two components in supramolecular hydrogels

N-Palmitoyl-Gly-His (PalGH) and glycerol monopalmitate (GMP) in water co-assembled into fibrils with twisted ribbon structures and formed a homogeneous network, resulting in gel formation. The mixture exhibits sol–gel transition while a gel made from only PalGH does not.

A novel calix[4]arene-based dimeric-cholesteryl derivative: synthesis, gelation and unusual properties

The exceptionally high thermo-stability and superior thixotropic property may make the C2N2C/benzene gel find important real-life applications.

Long-chain alkylamide-derived oil gels: mixing induced onset of thixotropy and application in sustained drug release

Oil gels composed of long-chain alkylamides exhibited thixotropic properties, although the same property was absent in each alkylamide.

Light induced E–Z isomerization in a multi-responsive organogel: elucidation from 1H NMR spectroscopy

Light induced E–Z isomerization along imine bond in a multiresponsive organogel of anthracene attached 3,4,5-tris(dodecyloxy)benzohydrazide gelator altering morphology, fluorescence and mechanical properties is elucidated from ¹H NMR spectra.

Functionality-oriented molecular gels: synthesis and properties of nitrobenzoxadiazole (NBD)-containing low-molecular mass gelators

Two nitrobenzoxadiazole (NBD)-containing cholesteryl (Chol) derivatives were prepared by introducing d/l-phenylalanine into the linkers between the NBD and Chol units. The compounds were denoted as and , respectively. The gelation behaviors of them were tested in 34 liquids. It was found that the chirality of the linkers shows a great effect on the gelation ability and the gel properties of the two compounds. SEM studies demonstrated that the gelator in the gel of /DMSO aggregated into uniform fibrous structures. FTIR, (1)H NMR and UV-Vis spectroscopy measurements revealed that intermolecular hydrogen bonding and π-π stacking are two main driving forces to promote the gel formation. Interestingly, the /DMSO gel exhibits rapid and reproducible gel-sol phase transition and fluorescence quenching upon introduction of ammonia. Furthermore, both the gel and the fluorescence emission could be fully recovered upon evaporation of the ammonia gas introduced. Spectroscopy and model system studies revealed the association of ammonia with the nitro group of the NBD unit of the compound, which is recognized as the main reason for the chemical responses of the gel system. On the basis of the discovery, an ammonia sensing film had been fabricated and made into a device. Furthermore, a device-based and conceptual "ammonia leaking" monitoring instrument was developed. A preliminary test demonstrated that the performance of the system is exceptionally good, a typical and persuasive example to show the important real-life applications of molecular gels.

N-Alkylamido-d-glucamine-based gelators for the generation of thixotropic gels

Hydrogels made from new gelators exhibit thixotropic properties, whereas hydrogels formed with structurally similar N-alkyl-d-glucamide have a tendency to crystallize.

A large dipole moment to promote gelation for 4-nitrophenylacrylonitrile derivatives with gelation-induced emission enhancement properties

4-Nitrophenylacrylonitrile derivatives were gelator, but analogues without nitro group were not, indicating that the electron-withdrawing nitro moiety was important for gel formation. Moreover, the organogels exhibited fluorescence enhancement.

Onset of mixing-induced thixotropy in hydrogels by mixing two homologues of low-molecular-weight hydrogelators

We determined the onset of thixotropy in hydrogels when two homologues of low-molecular-weight hydrogelators, N-alkyl-d-glucamides (CnNG), were mixed.

Creation of thixotropic multicomponent alkylamide organogels containing non-volatile oil as potential drug release host materials

Multicomponent alkylamide organogels containing non-volatile oils were generated as potential thixotropic host materials for medicinal applications such as ointments.

A new composite thixotropic hydrogel composed of a low-molecular-weight hydrogelator and a nanosheet

New composite comprised of low-molecular-weight hydrogelator and the nanosheet Laponite®, showed thixotropic behaviour.

Self-assembly of azobenzene-based two-component gels

Two-component gels were formed and their photophysical properties were dependent on the ratio of the two compounds.