Development of Self-Healing d-Gluconic Acetal-Based Supramolecular Ionogels for Potential Use as Smart Quasisolid Electrochemical Materials

Harnessing Glycolipids for Supramolecular Gelation: A Contemporary Review

Within the scope of this review, our exploration spans diverse facets of amphiphilic glycolipid-based low-molecular-weight gelators (LMWGs). This journey explores glycolipid synthesis, self-assembly, and gelation with tailorable properties. It begins by examining the design of glycolipids and their influence on gel formation. Following this, a brief exploration of several gel characterization techniques adds another layer to the understanding of these materials. The final section is dedicated to unraveling the various applications of these glycolipid-based supramolecular gels. A meticulous analysis of available glycolipid gelators and their correlations with desired properties for distinct applications is a pivotal aspect of their investigation. As of the present moment, there exists a notable absence of a review dedicated exclusively to glycolipid gelators. This study aims to bridge this critical gap by presenting an overview that provides novel insights into their unique properties and versatile applications. This holistic examination seeks to contribute to a deeper understanding of molecular design, structural characteristics, and functional applications of glycolipid gelators by offering insights that can propel advancements in these converging scientific disciplines. Overall, this review highlights the diverse classifications of glycolipid-derived gelators and particularly emphasizes their capacity to form gels.

Stretchable and recyclable gelatin Ionogel based ionic skin with extensive temperature tolerant, self-healing, UV-shielding, and sensing capabilities

Fabricating sustainable ionic skin with multi-functional outstanding performances using biocompatible natural polymer-based ionogel is highly desired but remains a great challenge up to now. Herein, a green and recyclable ionogel has been fabricated by in-situ cross-linking of gelatin with a green bio-based multifunctional cross-linker of Triglycidyl Naringenin in ionic liquid. Benefiting from the unique multifunctional chemical crosslinking networks along with multiple reversible non-covalent interactions, the as-prepared ionogels exhibit high stretchability (>1000 %), excellent elasticity, fast room-temperature self-healability (>98 % healing efficiency at 6 min), and good recyclability. These ionogels are also highly conductive (up to 30.7 mS/cm at 150 °C), and exhibit extensive temperature tolerance (-23 to 252 °C) and outstanding UV-shielding ability. As a result, the as-prepared ionogel can easily be applied as stretchable ionic skin for wearable sensors, which exhibits high sensitivity, fast response time (102 ms), excellent temperature tolerance, and stability over 5000 stretching-relaxing cycles. More importantly, the gelatin-based sensor can be used in signal monitor system for various human motion real-time detection. This sustainable and multifunctional ionogel provides a new idea for easy and green preparation of advanced ionic skins.

Mechanically Robust and Room Temperature Self-Healing Ionogel Based on Ionic Liquid Inhibited Reversible Reaction of Disulfide Bonds

Although highly desired, it is difficult to develop mechanically robust and room temperature self-healing ionic liquid-based gels (ionogels), which are very promising for next-generation stretchable electronic devices. Herein, it is discovered that the ionic liquid significantly reduces the reversible reaction rate of disulfide bonds without altering its thermodynamic equilibrium constant via small molecule model reaction and activation energy evolution of the dissociation of the dynamic network. This inhibitory effect would reduce the dissociated units in the dynamic polymeric network, beneficial for the strength of the ionogel. Furthermore, aromatic disulfide bonds with high reversibility are embedded in the polyurethane to endow the ionogel with superior room temperature self-healing performance. Isocyanates with an asymmetric alicyclic structure are chosen to provide optimal exchange efficiencies for the embedded disulfide bonds relative to aromatic and linear aliphatic. Carbonyl-rich poly(ethylene-glycol-adipate) diols are selected as soft segments to provide sufficient interaction sites for ionic liquids to endow the ionogel with high transparency, stretchability, and elasticity. Finally, a self-healing ionogel with a tensile strength of 1.65 ± 0.08 MPa is successfully developed, which is significantly higher than all the reported transparent room temperature self-healing ionogel and its application in a 3D printed stretchable numeric keyboard is exemplified.

Synthesis of d-Gluconic Acetal Surfactants and Their Foaming Behaviors

Sugars are natural and environmentally benign substances, which can offer various hydroxyl groups. The understanding of details of the hydroxyl interactions in the hydrophilic groups of sugar-based surfactants, as well as the related properties, is still indistinct. Here, novel d-gluconic acetal surfactants with bicyclic and monocyclic structures in the head group were designed and synthesized. The obtained surfactant with a bicyclic architecture exhibited excellent foamability and a multistimulus-responsive behavior toward foam stabilization. In addition, the control of foamability from defoaming and foaming could be achieved by changing pH values or bubbling gas of CO₂/N₂. To explore the structural effects such as hydroxyl groups and rigidity of the head group on the properties of sugar-based surfactants, another kind of amphiphilic molecule with various OH- groups and a monocycle in the head group was designed for comparison. These two series of amphiphilic molecules both exhibited good surface activity. However, only the d-gluconic acetal surfactant with a bicyclic structure and a smaller number of OH- groups exhibited excellent foamability. Further studies showed that the foam behaviors were attributed to the conformation and arrangement of the surfactant molecule at the surface layer with the assistance of hydrogen bonds formed by hydroxyl groups and H₂O molecules. In addition, the surfactant could provide an environmentally friendly foamer in many potential applications.

Dual Thermo-Responsive and Strain-Responsive Ionogels for Smart Windows and Temperature/Motion Monitoring

In this work, a stretchable, dual thermo-responsive and strain-responsive ionogel has been synthesized by one-step photopolymerization. The obtained ionogel shows an ultrahigh stretchability (∼3000%), a high ionic conductivity (up to 3.1 mS/cm), and a good temperature tolerance (-40 to 300 °C). Importantly, these ionogels show an upper critical solution temperature-type phase transition with a wide tunable phase-transition temperature (17.5-42.5 °C) and reversible color/transparency switching. In particular, the as-prepared ionogel-based flexible/wearable temperature monitors and smart windows show an excellent designability and programmability, temperature modulation ability, and thermal responsiveness. Moreover, the ionogels-based strain sensors have temperature- and strain-dual responsibility and a broad strain-sensing range (1-700%), which can effectively monitor various motions. This strategy of fabricating dual thermo- and strain-responsive ionogels by using a one-step method and only one polymer holds great promise for the next generation of multifunctional stimuli-responsive materials.

Supramolecular Thixotropic Ionogel Electrolyte for Sodium Batteries

Owing to the potential of sodium as an alternative to lithium as charge carrier, increasing attention has been focused on the development of high-performance electrolytes for Na batteries in recent years. In this regard, gel-type electrolytes, which combine the outstanding ionic conductivity of liquid electrolytes and the safety of solid electrolytes, demonstrate immense application prospects. However, most gel electrolytes not only need a number of specific techniques for molding, but also typically suffer from breakage, leading to a short service life and severe safety issues. In this study, a supramolecular thixotropic ionogel electrolyte is proposed to address these problems. This thixotropic electrolyte is formed by the supramolecular self-assembly of D-gluconic acetal-based gelator (B8) in an ionic liquid solution of a Na salt, which exhibits moldability, a high ionic conductivity, and a rapid self-healing property. The ionogel electrolyte is chemically stable to Na and exhibits a good Na⁺ transference number. In addition, the self-assembly mechanism of B8 and thixotropic mechanism of ionogel are investigated. The safe, low-cost and multifunctional ionogel electrolyte developed herein supports the development of future high-performance Na batteries.

Wearable Sensors Adapted to Extreme Environments Based on the Robust Ionogel Electrolytes with Dual Hydrogen Networks

Nonvolatile ionogels are promising soft electrolyte materials for flexible electronics, but it is challenging to fabricate stable electrolytes with mechanical robustness. Here, through rationally optimizing the chemical structure of polymer matrix and ionic liquids, the high-performance ionogel electrolytes with mechanical robustness and stability were fabricated. There are double hydrogen bonding networks in the as-prepared ionogel electrolytes, one of which exists between the polymer chains while the other one existing between the polymer chains and ionic liquid molecules. By adjusting the content of the ionic liquid and the ratio of the two hydrogen bonding networks, the prepared ionogel electrolytes exhibit tunable properties with an elasticity of 1.3-30 kPa, a stretchability of more than 1800%, a fracture energy of 125.8-548.3 KJ m^-3, and a coordinated self-healing efficiency of 6.2-37.9% to satisfy the needs of different application scenarios. The assembled wearable sensors based on the high-performance ionogel electrolytes can be attached to a part of the human body, detecting various motions and body temperature. Benefiting from the nonvolatile and hydrophobic properties of the ionogel electrolytes, the wearable sensors can be operated under extreme environments including high/low temperature (-15^-100 °C) and high humidity (100% relative humidity). It is believed that this work provides prospects for the application of wearable electronic devices.

Highly transparent, self-healing and adhesive wearable ionogel as strain and temperature sensor

A stable ionogel with good self-healing capability and adhesion, excellent stretchability (2017%), high durability (1000 cycles) and high transparency (92%) is fabricated and assembled into a strain and temperature sensor with high sensitivity.

Tailoring intermolecular interactions in ion gels with rationally designed phosphonic acid polymers

Design strategies of phosphonic acid polymers established advanced ion gels with high ionic conductivity, mechanical strength, and self-healing ability via a configurable balance of ionic and hydrogen bonding interactions at the molecular level.

Elastic and Thermoreversible Iongels by Supramolecular PVA/Phenol Interactions

Iongels have attracted much attention over the years as ion-conducting soft materials for applications in several technologies including stimuli-responsive drug release and flexible (bio)electronics. Nowadays, iongels with additional functionalities such as electronic conductivity, self-healing, thermo-responsiveness, or biocompatibility are actively being searched for high demanding applications. In this work, a simple and rapid synthetic pathway to prepare elastic and thermoreversible iongels is presented. These iongels are prepared by supramolecular crosslinking between polyphenols biomolecules with a hydroxyl-rich biocompatible polymer such as poly(vinyl alcohol) (PVA) in the presence of ionic liquids. Using this strategy, a variety of iongels are obtained by combining different plant-derived polyphenol compounds (PhC) such as gallic acid, pyrogallol, and tannic acid with imidazolium-based ionic liquids, namely 1-ethyl-3-methylimidazolium dicyanamide and 1-ethyl-3-methylimidazolium bromide. A suite of characterization tools is used to study the structural, morphological, mechanical, rheological, and thermal properties of the supramolecular iongels. These iongels can withstand large deformations (40% under compression) with full recovery, revealing reversible transitions from solid to liquid state between 87 and 125 °C. Finally, the polyphenol-based thermoreversible iongels show appropriated properties for their potential application as printable electrolytes for bioelectronics.

Recent progress in self-healable ion gels

Ion gels, soft materials that contain ionic liquids (ILs), are promising gel electrolytes for use in electrochemical devices. Due to the recent surge in demand for flexible and wearable devices, highly durable ion gels have attracted significant amounts of attention. In this review, we address recent advances in the development of ion gels that can heal themselves when mechanically damaged. Light- and thermally induced healing of ion gels are discussed as stimuli-responsive healing strategies, after which self-healable ion gels based on supramolecular and dynamic covalent chemistry are addressed. Tough, highly stretchable, and self-healable ion gels have recently been fabricated through the judicious design of polymer nanostructures in ILs in which polymer chains and IL cations and anions interact. The applications of self-healable ion gels to electrochemical devices are also briefly discussed.

Supramolecular ionogels prepared with bis(amino alcohol)oxamides as gelators: ionic transport and mechanical properties

Supramolecular ionogels composed of an ionic liquid (IL) immobilized in a network of self-assembled low-molecular weight molecules have been attracting considerable interest due to their applicability as smart electrolytes for various electrochemical applications. Despite considerable scientific effort in this field, the design of a mechanically and thermally stable yet highly conductive supramolecular ionogels still remains a challenge. In this article, we report on a series of novel ionogels of three ILs containing different cations (imidazolium/pyrrolidinium) and anions (tetrafluoroborate/bis(trifluoromethylsulfonyl)imide) prepared using (S,S)-bis(amino alcohol)oxamides as gelators. The gelation behaviour of the oxamide compound depends strongly on the structural features of amino alcohol substituents. Among them, (S,S)-bis(valinol)oxamide (capable of gelling all three ILs) and (S,S)-bis(phenylalaninol)oxamide (capable of gelling ILs based on bis(trifluoromethylsulfonyl)imide with a concentration as low as ≈0.2 wt%) are highly efficient. All investigated supramolecular ionogels retain the high ionic conductivity and ion diffusion coefficients of their parent IL, even for high gelator concentrations. Further, at low temperatures we observe an enhancement of the ionic conductivity in ionogels of (i) 1-butyl-3-methylimidazolium tetrafluoroborate which can be attributed to specific interactions between ionic species and gelator molecules and (ii) 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide due to inhibited crystallization. In contrast to ionic transport, mechanical strength of the ionogels shows a wider variation depending on the type and concentration of the oxamide gelator. Among all the ionogels, that of 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide prepared with 1 wt% (S,S)-bis(phenylalaninol)oxamide exhibits the best performance: optical transparency, stability over a wide temperature range, high conductivity and high mechanical strength. The results presented here reveal the versatile nature of bis(amino alcohol)oxamides as gelators and their high potential for preparing functionalized IL-based materials.

Porous amorphous powder form phase-selective organogelator for rapid recovery of leaked aromatics and spilled oils

Phase-selective organogelators (PSOGs) have drawn wide attention due to their potential applications in recovery of leaked aromatics and spilled oils. However, powder form PSOGs with fast gelling abilities and broad applicabilities are still limited. Herein, we developed three D-gluconic acetal-based gelators with different alkyl chains, all of which show excellent gel properties for hydrocarbon solvents. The spectroscopic and X-ray results revealed that the gel formation was the synergy of hydrogen bonding, π-π stacking and van der Waals forces. Surprisingly, the powder form gelator A with a cis double bond in the alkyl chain could instantly and selectively gel aromatic hydrocarbons, and also rapidly solidify crude oils with widely ranging viscosities from seawater at room temperature within minutes. Further research revealed that A powder exhibited porous amorphous morphology because the cis double bonds broke the crystalline chain-chain interdigitation between the assemblies. Therefore, the fast dispersion and recombination of fibers under the action of oil molecules lead to the fast room temperature gel process. Overall, a non-toxic and low-cost powder form PSOG with rapid room temperature phase selective gelation ability for a wide range of oils makes it promising for the emergency treatment of oil spill and aromatics leakage.

Facile Fabrication of a Self-Healing Temperature-Sensitive Sensor Based on Ionogels and Its Application in Detection Human Breath

The biocompatible strechable ionogels were prepared by a facile solution-processed method. The ionogels showed outstanding stretchable and self-healing properties. The electrical property could revert to its original state after 4 s. The repaired ionogels could still bear stretching about 150%. Moreover, the ionogels exhibited high sensitivity and wide-detection range to temperature. The temperature-sensitive sensor could detect the human breath frequency and intensity, showing potential application in detecting disease.

A chitosan-based fluorescent hydrogel for selective detection of Fe2+ ions in gel-to-sol mode and turn-off fluorescence mode

A novel chitosan-based fluorescent hydrogel has been synthesized by chemically bonding terpyridine-bearing aldehydes onto chitosan via an acid condensation reaction.

Multifunctional Self-Healing Ionogels from Supramolecular Assembly: Smart Conductive and Remarkable Lubricating Materials

Self-healing ionogel is a promising smart material because of its high conductivity and reliable stimuli responsiveness upon mechanical damage. However, self-healing ionogels possessing rapid, complete recovery properties and multifunctionality are still limited. Herein, we designed a new d-gluconic acetal-based gelator (PB8) bearing a urea group in the alkyl side chain. Interestingly, the balance between hydrophilicity and hydrophobicity of the molecule is achieved. Thus, PB8 could form transparent ionogels because of its excellent affinity to ionic liquids (ILs), which exhibited appropriate mechanical strength, high viscoelasticity, and efficient self-healing properties. The presence of synergistic effects from hydrogen bonding, π-π stacking, and interactions between the urea-containing side chains was responsible for the self-assembly of gelators in ILs and the self-healing property mainly related to the side chains of PB8. Interestingly, the transparent PB8-IL4 ionogel possessed high conductivity and mechanical strength, moldable and injectable properties, and rapid and complete self-healing characteristics (complete recovery within 14 min), which showed excellent performance as a smart ionic conductor. Furthermore, the self-healing PB8-based ionogels with anticorrosion properties are a remarkable lubricating material in the steel-steel contact and exhibited excellent lubricating performances. Overall, an efficient PB8-based ionogel with self-healing properties has been developed for potential use both as a smart electrical conductor and as a high-performance lubricating material. The unique structure of PB8 bearing a urea group in the side chain is found to be responsible for the multifunctional ionogel formation.