Self-Assembled Gels Formed in Deep Eutectic Solvents: Supramolecular Eutectogels with High Ionic Conductivity

Mechanically Resilient, Self-Healing, and Environmentally Adaptable Eutectogel-Based Triboelectric Nanogenerators for All-Weather Energy Harvesting and Human-Machine Interaction

Triboelectric nanogenerators (TENGs) have garnered significant attention for mechanical energy harvesting, self-powered sensing, and human-machine interaction. However, their performance is often constrained by materials that lack sufficient mechanical robustness, self-healing capability, and adaptability to environmental extremes. Eutectogels, with their inherent ionic conductivity, thermal stability, and sustainability, offer an appealing alternative as flexible TENG electrodes, yet they typically suffer from weak damage endurance and insufficient self-healing capability. To overcome these challenges, here, we introduce an internal-external dual reinforcement strategy (IEDRS) that enhances internal bonding dynamics within the eutectogel matrix, composed of glycidyl methacrylate and deep eutectic solvent, and integrates plant-derived lignin as an external reinforcer. Notably, the resultant eutectogel, named GLCL, exhibits appealing collection merits including superior mechanical robustness (1.53 MPa tensile stress and 1.85 MJ/m3 toughness), ultrastrong adhesion (4.76 MPa), high self-healing efficiency (84.7%), and significant environmental adaptability (-40 to 100 °C). These improvements ensure that the assembled triboelectric nanogenerator (GLCL-TENG) produces stable and robust electrical outputs, maintained even under dynamic and postdamage conditions. Additionally, the GLCL-TENG exhibits significant extreme environmental tolerance and durability, maintaining high and consistent electrical outputs over a wide temperature range (-40 to 100 °C) and throughout 10,000 cycles of repeated contact-separation. Leveraging these robust performances, the GLCL-TENG excels in all-weather biomechanical energy harvesting and accurate individual motion detection and functions as a self-powered interface for wireless vehicular control. This work presents a viable material design strategy for developing tough and self-healing eutectogel electrodes, emphasizing the potential application of TENGs in all-weather smart vehicles.

A functional eutectogel based on ultrahigh-molecular weight polymers: Physical entanglements in deep eutectic solvent

Eutectogels have emerged as a promising material for wearable devices due to its superior ionic conductivity, non-volatility, and low cost. Despite numerous efforts, only a limited number of polymers and gelling mechanisms have been successfully employed in the fabrication of eutectogels. In this study, an effective three-dimensional network is developed based on the entanglements of polymer chains, facilitating the formation of an entangled eutectogel. The fabrication process involves directly dissolving ultra-high molecular weight polyvinylpyrrolidone (PVP) in deep eutectic solvent (reline) through a simple heating-cooling method. The resulting eutectogel, containing 40 wt% PVP, exhibits excellent stretchability of 1410 % strain, toughness of 544.8 kJ/m3, and ionic conductivity of 0.015 S/m. It also generates a reliable resistance signal suitable for strain-sensing applications. Furthermore, this entangled eutectogel displays self-healing capabilities, enabled by the diffusion and re-entanglement of polymer chains. This work not only demonstrates a facile fabrication approach for an entangled eutectogel but also provides the first investigation into employing long chain entanglements in the development of eutectogels.

Tough and Stretchable Zwitterionic Eutectogels via Copolymerization-Induced Phase Separation in a Targeted Deep Eutectic Solvent

Deep eutectic solvent (DES)-based eutectogels show significant promise for flexible sensors due to their high ionic conductivity, non-volatility, biocompatibility, and cost-effectiveness. However, achieving tough and stretchable eutectogels is challenging, as the highly polar DES tends to screen noncovalent bonds, such as hydrogen and ionic bonds, between polymer chains, limiting their mechanical strength. In this work, this issue is addressed by leveraging the limited solubility of zwitterionic polymers in a specific DES to induce phase separation, promoting dipole-dipole interactions between polymer chains. These interactions improve energy dissipation under mechanical stress, allowing the creation of tough and stretchable P(MAA-co-VIPS)/TBAC-EG eutectogels through a copolymerization-induced phase separation approach. Methacrylic acid (MAA) and sulfobetaine vinylimidazole (VIPS) are copolymerized within a tetrabutylammonium chloride-ethylene glycol (TBAC-EG) DES, resulting in a bicontinuous network. The bicontinuous structure consists of a PVIPS-rich phase that enhances toughness via dipole-dipole interactions, and a PMAA solvent-rich phase that enables high stretchability. The resulting eutectogel demonstrates excellent mechanical properties, including a strength of 1.76 MPa, toughness of 16.61 MJ m⁻3, and remarkable stretchability of 1293%, along with self-recovery, self-healing, and shape-memory capabilities. The zwitterionic polymer-specific DES design opens up broad application potential for these eutectogels in diverse fields.

Gelation Dynamics steering Frontiers in Technology: Unraveling Hotspots and Research Trends through Scientometric insights

The serendipitous occurrence of gels in science has been a milestone for further industrial revolutionization. The controlled formation and disassembly of gels coupled with their viscoelastic properties and their ability to undergo extensive structural modification to suit different applications have led to the widespread use of gelation technology in different domains of science such as sensing, material chemistry and physics, medicine, food and nutrition, ecology, and more. With the rising interest in gelators and gels applications, accurately depicting the current status of gelation and associated technology is of paramount importance for researchers and scholars already immersed in gel technology as well as those aiming to delve into this field. Utilizing bibliometrics offers a systematic approach to analyze trends, citation patterns, and the impact of research, providing crucial insights for advancing knowledge and innovation in gel technology. By performing a comprehensive bibliometric analysis of scientific publications, using Vosviewer, Citespace, and Biblioshiny, in terms of co-authorship and co-citations of publications, and also the co-occurrence analysis of countries, institutions, authors, and keywords Research frontiers and hotspots in gelation and associated technologies in 21st century can be assessed. The result indicated a research frontier in the discipline of ecology, earth, and marine for gelator application and current hotspots within the research field of gelation technology in; catalysis, eutectogels development as an alternative for ionic liquid gels, gelators in drug delivery for antibacterial activity, oleogels in the food industry, low molecular weight hydrogels for tissue repair and 4D printing and gelators application for oil spill remediation and dye removal. This work, although not assessing fully the qualitative aspect of a research field, gives a broad quantitative analysis and direction of research within a research field. The result of this work will provide a comprehensive overview of the evolution of research in the field of gelation technology and a global understanding of research frontiers, hotspots, and drawbacks within the field to researchers and scholars willing to work in this research area.

Green Polymer Electrolytes Prepared by a Cost-Effective Approach

The preparation of solid polymer electrolytes (SPEs) using poly(ethylene oxide) (PEO) typically involves incorporating fillers or undergoing chemical modifications to reduce crystallinity and enhance conductivity. PEO with a lower molecular weight, known as polyethylene glycol (PEG), exhibits higher conductivity, despite weaker mechanical strength. It is commonly employed as a plasticizer to improve the conductivity of SPEs or to fabricate PEG-based gel polymer electrolytes (GPEs). In this study, we use a straightforward approach to create innovative SPEs by blending liquid polymer electrolytes (LPEs), particularly low-molecular-weight polyethylene glycol (PEG), with a molecular weight of 400 g/mol, and sustainable poly(l-lactide) (PLLA). Solid PEG/PLLA forms are achieved by introducing 30 wt % of PLLA. Subsequently, the addition of lithium salts results in the development of novel PEG/PLLA SPEs. Another focal point of this study involves incorporating 1,3:2,4-dibenzylidene sorbitol (DBS) into these PEG/PLLA systems. DBS, an organic gelator derived from natural sugars, demonstrates self-assembly, leading to the formation of a nanofibrillar network structure. Leveraging DBS's ability to form organogels in liquid organic environments, we facilitate the transformation of low PLLA content LPEs into innovative solvent-free GPEs. Our prepared PEG/PLLA SPEs exhibited a maximum conductivity value of 4.39 × 10-5 S/cm, approximately five times higher than that of neat PEG (10000 g/mol) SPEs. The ionic conductivity exhibited a declining trend as the content of PLLA and DBS increased. However, there was an improvement in electrochemical stability. Furthermore, the incorporation of PLLA and DBS into electrolytes contributed to enhanced mechanical support and stability within the electrolyte layer. This, in turn, mitigated capacity decay and improved the cycling performance of assembled lithium-ion cells.

Strong and Thermo-Switchable Gel Adhesion Based on UCST-Type Phase Transition in Deep Eutectic Solvent

It remains a great challenge to achieve strong and reversible hydrogel adhesion. Hydrogel adhesives also suffer from poor environmental stability due to dehydration. To overcome these problems, here reversible adhesive gels are designed using a new switching mechanism and new solvent. For the first time, the study observes UCST (upper critical solution temperature)-type thermosensitive behaviors of poly(benzyl acrylate) (PBnA) polymer and gel in menthol:thymol deep eutectic solvents (DESs). The temperature-induced phase transition allows adjusting cohesive force, and hence adhesion strength of PBnA gels by temperature. To further improve the mechanical and adhesion properties, a peptide crosslinker is used to allow energy dissipation when deforming. The resulting eutectogel exhibits thermal reversible adhesion with a high switching ratio of 14.0. The adhesion strength at attachment state reaches 0.627 MPa, which is much higher than most reversible adhesive hydrogels reported before. The low vapor pressure of DES endows the gel excellent environmental stability. More importantly, the gel can be repeatedly switched between attachment and detachment states. The strong and reversible gel adhesive is successfully used to design soft gripper for the transport of heavy cargos and climbing robot capable of moving on vertical and inverted surface in a manner similar to gecko.

Stabilization of Non-Native Folds and Programmable Protein Gelation in Compositionally Designed Deep Eutectic Solvents

Proteins are adjustable units from which biomaterials with designed properties can be developed. However, non-native folded states with controlled topologies are hardly accessible in aqueous environments, limiting their prospects as building blocks. Here, we demonstrate the ability of a series of anhydrous deep eutectic solvents (DESs) to precisely control the conformational landscape of proteins. We reveal that systematic variations in the chemical composition of binary and ternary DESs dictate the stabilization of a wide range of conformations, that is, compact globular folds, intermediate folding states, or unfolded chains, as well as controlling their collective behavior. Besides, different conformational states can be visited by simply adjusting the composition of ternary DESs, allowing for the refolding of unfolded states and vice versa. Notably, we show that these intermediates can trigger the formation of supramolecular gels, also known as eutectogels, where their mechanical properties correlate to the folding state of the protein. Given the inherent vulnerability of proteins outside the native fold in aqueous environments, our findings highlight DESs as tailorable solvents capable of stabilizing various non-native conformations on demand through solvent design.

Short Peptide and Amino Acid-Based Supramolecular Ionogels and Eutectogels

The capability of peptide and amino acid-based molecules to act as ionogelators and eutectogelators entrapping ionic liquids (ILs) and deep eutectic solvents (DESs) forming ionogels and eutectogels has gathered attention in recent decades. The self-assembly process, primarily driven by non-covalent interactions as hydrogen bonding, remains serendipitous in nature. This review provides a comprehensive and detailed report on self-assembly of unmodified and modified amino acids and peptides in the non-conventional solvents, ILs and DESs. Understanding these processes holds great promise for the development of innovative soft-materials, and to the progress of supramolecular systems in non-conventional solvent environments.

Regioselective synthesis of 4-arylamino-1,2-naphthoquinones in eutectogel as a confined reaction medium using LED light

Predicting selectivity and conversion in a confined reaction medium under photochemical conditions is highly challenging as compared to the corresponding conventional synthesis. Herein, we report the use of a simple carbohydrate-derived eutectogel to facilitate LED-light-induced regioselective synthesis of 4-arylamino-1,2-naphthoquinones in good yield. This methodology, by including a reusable reaction medium, proved to have the potential of affording the regioselective formation of various desired products in good yields.

Tunable durian seed gum-derived eutectogel as a novel coating material: Rheological, thermal, textural and barrier properties for enhanced food preservation

As a promising green and sustainable coating material, gum was extracted from durian seed to produce eutectogel, which the properties were tunable using natural deep eutectic solvent (NADES). Ten different eutectogels were successfully synthesized using durian seed gum (DSG) and xanthan gum (XG) gelators at different composition (5, 10, 15 %) to gel choline chloride-glucose (1:1), choline chloride-fructose (1:2) and betaine-glucose-water (1:1:1) NADESs. Results revealed that eutectogel was non-Newtonian and weak gel material with excellent thermostability up to 200 °C. When the gum content increased, the resulted eutectogel showed higher viscosity, yield stress, hardness, gumminess, adhesiveness, and weight holding capacity. In overall, choline chloride-fructose (1:2) NADES and 10 % of DSG formed an excellent eutectogel which remained stable and compatible upon 12 weeks of storage. It displayed superior viscoelastic, texture, gases and moisture barrier properties which were beneficial for food coating application. This eutectogel was able to extend the shelf life of fresh-cut apples during storage with lower weight loss and higher total phenolic content (TPC). The potential future of this well-characterized tunable DSG-derived eutectogel includes, but not limited to, food and pharmaceutical industries, smart sensing, flexible wearable electronics, water purification, supercapacitors and batteries.

One-step Fabrication of Physical Eutectogel with Recyclability: Crystalline Domain Regulation Induced by Microgels

HYPOTHESIS

Despite their non-volatility, low cost, and recyclability, physical eutectogels' appeal is hindered by the intricate fabrication process and the involvement of hazardous chemicals. The network of polyvinyl alcohol (PVA) in deep eutectic solvent (choline chloride and glycerol) might be developed by the addition of microgels of polyacrylic acid (Carbopol).

EXPERIMENTS

Hydrogen-bond interactions between Carbopol and PVA are revealed through Fourier-transform infrared spectroscopy. The impact of microgels on crystalline domains and the polymer network can be observed using X-ray diffraction and scanning electron microscopy. The physical properties of the eutectogel, including mechanical strength and ionic conductivity, are investigated as well. Finally, the strain-sensing ability and remarkable recyclability of the eutectogel are demonstrated.

FINDINGS

The physical eutectogel can be obtained through a one-step fabrication process using only green and low-cost materials. It demonstrates robust strength (1.02 MPa) and remarkable stretchability (1000 % strain). This is attributed to the uniform dispersion of PVA crystalline domains within the deep eutectic solvent, facilitated by the hydrogen bonds and space restriction effects between PVA and Carbopol. Furthermore, the physical eutectogel with recyclability can consistently generate electrical resistance signals, highlighting its potential as a reliable strain sensor.

Ultra-Tough and Highly Stretchable Dual-Crosslinked Eutectogel Based on Coordinated and Non-Coordinated Two Types Deep Eutectic Solvent Mixture

Eutectogels are gaining attention in flexible device applications for their superior ionic conductivity, stability, biocompatibility, and cost-effectiveness. However, most existing eutectogels suffer from low strength and toughness. Herein, ultra-tough and highly stretchable polyacrylamide (PAM) eutectogels featuring a dual-crosslinked network comprising chemical cross-linking and physical cross-linking facilitated by metal coordination bonds and hydrogen bonds are developed. This is achieved through a controlled strategy involving polymerization of acrylamide in a coordinated metal salt-type deep eutectic solvent (DES) combined with a non-coordinated choline chloride (ChCl)-type DES mixture. By varying the molar ratio of these two types of DES, exceptional and adjustable mechanical properties of the resulting eutectogel are achieved, including a high tensile strength ranging from 2.9 to 8.2 MPa and elongation at break ranging from 1725 to 747%, at a 70 wt% DES content. Furthermore, the reversible non-covalent crosslinking in these eutectogels enables self-recovery and self-healing capabilities of eutectogels. The prepared eutectogels also exhibit outstanding ionic conductivity (3.56 mS cm-1 ), making them well-suited for use as strain sensors in human motion detection. The toughening strategy is universally effective for creating tough eutectogels using coordinated metal salt-type DES with various metal ions, as well as a diverse range of coordinatable polymers.

Supramolecular gels - a panorama of low-molecular-weight gelators from ancient origins to next-generation technologies

Supramolecular gels, self-assembled from low-molecular-weight gelators (LMWGs), have a long history and a bright future. This review provides an overview of these materials, from their use in lubrication and personal care in the ancient world, through to next-generation technologies. In academic terms, colloid scientists in the 19th and early 20th centuries first understood such gels as being physically assembled as a result of weak interactions, combining a solid-like network having a degree of crystalline order with a highly mobile liquid-like phase. During the 20th century, industrial scientists began using these materials in new applications in the polymer, oil and food industries. The advent of supramolecular chemistry in the late 20th century, with its focus on non-covalent interactions and controlled self-assembly, saw the horizons for these materials shifted significantly beyond their historic rheological applications, expanding their potential. The ability to tune the LMWG chemical structure, manipulate hierarchical assembly, develop multi-component systems, and introduce new types of responsive and interactive behaviour, has been transformative. Furthermore, the dynamics of these materials are increasingly understood, creating metastable gels and transiently-fueled systems. New approaches to shaping and patterning gels are providing a unique opportunity for more sophisticated uses. These supramolecular advances are increasingly underpinning and informing next-generation applications - from drug delivery and regenerative medicine to environmental remediation and sustainable energy. In summary, this article presents a panorama over the field of supramolecular gels, emphasising how both academic and industrial scientists are building on the past, and engaging new fundamental insights and innovative concepts to open up exciting horizons for their future use.

Photoswitchable and Reversible Fluorescent Eutectogels for Conformal Information Encryption

Smart fluorescent materials that can respond to environmental stimuli are of great importance in the fields of information encryption and anti-counterfeiting. However, traditional fluorescent materials usually face problems such as lack of tunable fluorescence and insufficient surface-adaptive adhesion, hindering their practical applications. Herein, inspired by the glowing sucker octopus, we present a novel strategy to fabricate a reversible fluorescent eutectogel with high transparency, adhesive and self-healing performance for conformal information encryption and anti-counterfeiting. Using anthracene as luminescent unit, the eutectogel exhibits photoswitchable fluorescence and can therefore be reversibly written/erased with patterns by non-contact stimulation. Additionally, different from mechanically irreversible adhesion via glue, the eutectogel can adhere to various irregular substrates over a wide temperature range (-20 to 65 °C) and conformally deform more than 1000 times without peeling off. Furthermore, by exploiting surface-adaptive adhesion, high transparency and good stretchability of the eutectogel, dual encryption can be achieved under UV and stretching conditions to further improve the security level. This study should provide a promising strategy for the future development of advanced intelligent anti-counterfeiting materials.

Degradable Supramolecular Eutectogel-Based Ionic Skin with Antibacterial, Adhesive, and Self-Healable Capabilities

The development of degradable, cost-effective, and eco-friendly ionic conductive gels is highly required to reduce electronic waste originating from flexible electronic devices. However, biocompatible, degradable, tough, and durable conductive gels are challenging to achieve. Herein, we develop a facile strategy for the design and synthesis of degradable tough eutectogels by integrating an electrostatically driven supramolecular network composed of branched polyacrylic acid (PAA) and monoethanolamine (MEA) into a green deep eutectic solvent with chitosan quaternary ammonium salt (CQS). The specially designed PAA/MEA/CQS eutectogels present multiple desired properties, including high transparency, widely adjustable mechanical properties, high resilience, reliable adhesiveness, excellent self-healing ability, good conductivity, remarkable anti-freezing performance, and antibacterial properties. The dynamic and reversible supramolecular interactions not only significantly enhance the mechanical properties of the PAA/MEA/CQS eutectogels but also enable fast degradation, addressing the dilemma between mechanical strength and degradability. More importantly, a biocompatible and degradable multifunctional ionic skin is successfully fabricated based on the PAA/MEA/CQS eutectogel, exhibiting high sensitivity, a wide sensing range, and a rapid response speed toward strain, pressure, and temperature. Thus, this study offers a promising strategy for fabricating degradable tough eutectogels, which show great potential as high-performance ionic skins for next-generation flexible wearable electronic devices.

Synthesis of a magnetic micro-eutectogel based on a deep eutectic solvent gel immobilized in calcium alginate: Application for green analysis of melamine in milk and dairy products

A new three-component magnetic eutectogel composed of a crosslinked copolymeric deep eutectic solvent (DES) and polyvinylpyrrolidone-coated Fe₃O₄ nano-powder impregnated in calcium alginate gel was synthesized and applied as a sorbent material in a green alternative micro solid-phase extraction of melamine in milk and dairy products. The analyses were performed using the HPLC-UV technique. The copolymeric DES was prepared through thermally-induced free-radical polymerization of [2-hydroxyethyl methacrylate]:[thymol] DES (1:1 mol ratio) as functional monomer, azobisisobutyronitrile (as initiator), and ethylene glycol dimethacrylate (as crosslinker). The sorbent was characterized using ATR-FTIR, ¹H & ¹³C FT-NMR, SEM, VSM, and BET techniques. The stability of the eutectogel in water and its effect on the pH of the aqueous solution was studied. A one-at-a-time approach was applied to optimize the impact of significant factors influencing sample preparation efficiency (sorbent mass, desorption conditions, adsorption time, pH, and ionic strength). The method validation was performed by evaluating matrix-matched calibration linearity (2-300 μg kg^-1, r² = 0.9902), precision, system suitability, specificity, enrichment factor, and matrix effect. The obtained limit of quantification (0.38 μg kg^-1) was lower than the established maximum level for melamine by Food and Drug Administration (FDA) (0.25 mg kg^-1), Food and Agriculture Organization (FAO) (0.5 & 2.5 mg kg^-1), and The European Union (EU) (2.5 mg kg^-1) in milk and dairy products. The optimized procedure was applied for the analysis of melamine in bovine milk, yogurt, cream, cheese, and ice cream. The obtained normalized recoveries of 77.4-105.3% (RSD% <7.0%) were acceptable regarding the practical default range set by the European Commission (70-120%, RSD≤20%). The sustainability and green aspects of the procedure were evaluated by the Analytical Greenness Metric Approach (0.6/1.0) and the Analytical Eco-Scale tool (73/100). This paper presents the first-time synthesis and application of this micro-eutectogel for the analysis of melamine in milk and milk-based dairy products.

Constituent- and Composition-Dependent Surfactant Aggregation in (Lanthanide Salt + Urea) Deep Eutectic Solvents

Due to the ease of tailoring the physicochemical properties by simply changing a constituent or composition, deep eutectic solvents (DESs) possess widely varying capabilities for surfactant self-assembly that could depend on the surfactant headgroup charge. The self-aggregation process of three surfactants, sodium dodecylsulfate (SDS), cetyltrimethylammonium bromide (CTAB), and Triton X-100 (TX-100), dissolved in DESs composed of a lanthanide salt (Ln) and urea (U) is investigated. The role of the identity of the metal salt is assessed by using [La(NO₃)₃·6H₂O] (La) and [Ce(NO₃)₃·6H₂O] (Ce) and that of the composition is deciphered by systematically changing the mole ratio of the metal salt and urea in (La/U) DESs. The response to a fluorescence probe pyrene-1-carboxaldehyde along with electrical conductance and surface tension measurements is used to obtain the critical aggregation concentration (CAC). While the CACs in 1:3.5 (Ln/U) for SDS are significantly lower than that in water, the values are marginally higher for CTAB and TX-100. The CACs for all three surfactants are similar in 1:3.5 (La/U) and (Ce/U) DESs, implying that the identity of the metal in the salt is not so important. Increasing the urea composition in (La/U) DESs results in increased CAC for SDS and CTAB; however, a minimal decrease in CAC is observed for TX-100. From the temperature dependence of CAC, thermodynamic parameters, ΔG_agg⁰, ΔH_agg⁰, and ΔS_agg⁰, of the surfactant self-aggregation process are estimated. These parameters reveal that while at a lower urea content, the SDS/CTAB self-assembly process is enthalpically driven, it becomes entropically favored at higher urea concentrations. The TX-100 self-aggregation in these DESs is found to be strongly enthalpically favored and entropically un-favored. These parameters are explained as a combination of passage of the solvophobic surfactant chain from the bulk DES to the aggregate pseudo-phase and differential orientation/organization of DES constituents around surfactant monomers and/or aggregates.

Peptide-enhanced tough, resilient and adhesive eutectogels for highly reliable strain/pressure sensing under extreme conditions

Natural gels and biomimetic hydrogel materials have been able to achieve outstanding integrated mechanical properties due to the gain of natural biological structures. However, nearly every natural biological structure relies on water as solvents or carriers, which limits the possibility in extreme conditions, such as sub-zero temperatures and long-term application. Here, peptide-enhanced eutectic gels were synthesized by introducing α-helical "molecular spring" structure into deep eutectic solvent. The gel takes full advantage of the α-helical structure, achieving high tensile/compression, good resilience, superior fracture toughness, excellent fatigue resistance and strong adhesion, while it also inherits the benefits of the deep eutectic solvent and solves the problems of solvent volatilization and freezing. This enables unprecedentedly long and stable sensing of human motion or mechanical movement. The electrical signal shows almost no drift even after 10,000 deformations for 29 hours or in the -20 °C to 80 °C temperature range.

Biocompatible Self-Assembled Hydrogen-Bonded Gels Based on Natural Deep Eutectic Solvents and Hydroxypropyl Cellulose with Strong Antimicrobial Activity

Natural deep eutectic solvents (NADES)-hydroxypropyl cellulose (HPC) self-assembled gels with potential for pharmaceutical applications are prepared. FT-IR, 1HNMR, DSC, TGA and rheology measurements revealed that hydrogen bond acceptor−hydrogen bond donor interactions, concentration of NADES and the water content influence significantly the physico-chemical characteristics of the studied gel systems. HPC-NADES gel compositions have thermal stabilities lower than HPC and higher than NADES components. Thermal transitions reveal multiple glass transitions characteristic of phase separated systems. Flow curves evidence shear thinning (pseudoplastic) behavior. The flow curve shear stress vs. shear rate were assessed by applying Bingham, Herschel−Bulkley, Vocadlo and Casson rheological models. The proposed correlations are in good agreement with experimental data. The studied gels evidence thermothickening behavior due to characteristic LCST (lower critical solution temperature) behavior of HPC in aqueous systems and a good biocompatibility with normal cells (human gingival fibroblasts). The order of antibacterial and antifungal activities (S.aureus, E.coli, P. aeruginosa and C. albicans) is as follows: citric acid >lactic acid > urea > glycerol, revealing the higher antibacterial and antifungal activities of acids.

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.

Li-N Interaction Induced Deep Eutectic Gel Polymer Electrolyte for High Performance Lithium-Metal Batteries

As emerging eutectic mixtures, deep eutectic electrolytes (DEEs) show unique properties for Li-metal batteries (LMBs). However, the limited choice and inferior electrode compatibility hinder their further development in LMBs. Herein, we report a new 1,2-dimethylimidazole (DMIm)-based deep eutectic gel polymer electrolyte induced by Li-N interaction. We demonstrate that incorporating electron-withdrawing polyvinylidene difluoride (PVDF) polymer into the DMIm-based DEE changes the coordination environment of Li⁺ ions, leading to a high transference number of Li⁺ ions (0.65) and superior interface stability between the electrolyte and Li anode. The deep eutectic gel polymer electrolyte exhibits excellent non-flammability, high ionic conductivity (1.67 mS cm^-1 at 30 °C), and high oxidation voltage (up to 4.35 V vs. Li/Li⁺ ). The Li||LFP cell based on the newly developed deep eutectic gel polymer electrolyte can achieve superior long-term cycling stability at a wide range of rates.

Eutectogels as Matrices to Manipulate Supramolecular Chirality and Circularly Polarized Luminescence

Solvent is regarded as a factor in tuning the supramolecular chirality of self-assemblies. Deep eutectic solvents (DESs) show diverse properties in contrast to other common solvents, which are emerging in fabricating functional aggregates and nanoarchitectures. Nevertheless, the emergence and manipulation of supramolecular chirality in DES still remain mysterious. Exploring supramolecular chirality in DES would produce tunable chiroptical materials considering their feasible preparation process and abundant hydrogen bonding sites. In this work, we explored the occurrence and manipulation of supramolecular chirality in DES. Transfer from inherent chiral DES to solutes in either aggregated or monomeric building units is blocked. However, the chiral assembly of π-conjugated amino acids was realized. Compared to aqueous media, self-assembly in DES hinders the spontaneous structural and chirality evolution that benefit from efficient solvation, where the π-conjugated amino acids were involved as hydrogen bonding donors. DES performs as a dye-friendly matrix to afford chiroptical eutectogels with tunable circularly polarized luminescence, whereby a large dissymmetry g-factor of up to 0.015 was realized. DES behaves as feasible and flexible solvents to fabricate and stabilize functional soft chiral self-assemblies with controllable chiroptical properties.

Gelation behavior and supramolecular chirality of a BTA derivative in a deep eutectic solvent

As novel solvents, deep eutectic solvents (DESs) are non-toxic, easily producible and biocompatible, which is attractive for eutectogel fabrication. In this work, a benzene 1,3,5-tricarboxamide (BTA) derivative (substituted by three hexanoic acid) was selected to prepare a supramolecular gel in a suitable DES composed of choline chloride and phenylacetic acid molecules. The obtained eutectogel exhibited higher stability than that produced in conventional solvents. The gel microstructure was composed of spiral fiber networks as confirmed from atomic force microscopy and scanning electron microscopy observations. Macroscopic chirality was therefore recognized by the circular dichromatic spectrum, though such a supramolecular chiral signal was random. To explore the gelation mechanism, the effect of BTA derivative molecular structure change was systematically investigated. With the help of Fourier transform infrared spectroscopy and powder X-ray diffraction, the gel formation was attributed to the π-π stacking of adjacent BTA molecules and the three-fold hydrogen bond between amide groups or the hydrogen bond between carboxylic groups. Furthermore, the directional hydrogen bonds between BTA and solvent molecules induced their aggregate to form one-dimensional fibers, which were either left- or right-handed. The obtained results not only extend the gel systems in DESs, but also help design the supramolecular chirality from non-chiral molecules.

Ionic Conductivity Enhancement in UHMW PEO Gel Electrolytes Based on Room-Temperature Ionic Liquids and Deep Eutectic Solvents

Physical gels made of poly(ethylene oxide) (PEO) and deep eutectic solvents urea-Li bis(trifluoromethanesulfonyl)imide (TFSI) and ethylene glycol/LiTFSI, or pyrrolidinium ionic liquid solutions PYR13TFSI-LiTFSI and PYR14TFSI-LiTFSI, are prepared by a fast, single-step process, which involves no auxiliary solvents or intermediates and is reproducible and scalable. The properties of these gels are studied as a function of the PEO content and its molecular weight and the nature of the liquid electrolyte. The gels prepared with a low concentration (1-5 wt %) of ultrahigh molecular weight (UHMW) PEO are tough, stretchable materials which resemble soft elastomers and are also self-healing and transparent. Their rheology shows the conventional behavior of physical polymer gels, so that the higher the molecular weight of PEO, the lower the polymer concentration needed to produce the gel. However, the ion conductivities and diffusivities of the gels are striking, in many cases being equal to or significantly higher than those of pure liquid electrolytes. This ion conductivity enhancement is the highest for the lowest PEO concentration with the highest molecular weight. This unprecedented molecular weight dependence of conductivity and diffusivity is the result of two combined effects: the liquid electrolyte chemical structure modification as a consequence of the addition of PEO and the development of elastic networks, where ion mobility and rheology are uncoupled when the PEO added is of UHMW.

Emerging iongel materials towards applications in energy and bioelectronics

In the past two decades, ionic liquids (ILs) have blossomed as versatile task-specific materials with a unique combination of properties, which can be beneficial for a plethora of different applications. The additional need of incorporating ILs into solid devices led to the development of a new class of ionic soft-solid materials, named here iongels. Nowadays, iongels cover a wide range of materials mostly composed of an IL component immobilized within different matrices such as polymers, inorganic networks, biopolymers or inorganic nanoparticles. This review aims at presenting an integrated perspective on the recent progress and advances in this emerging type of material. We provide an analysis of the main families of iongels and highlight the emerging types of these ionic soft materials offering additional properties, such as thermoresponsiveness, self-healing, mixed ionic/electronic properties, and (photo)luminescence, among others. Next, recent trends in additive manufacturing (3D printing) of iongels are presented. Finally, their new applications in the areas of energy, gas separation and (bio)electronics are detailed and discussed in terms of performance, underpinning it to the structural features and processing of iongel materials.

Bulk and interfacial nanostructure and properties in deep eutectic solvents: Current perspectives and future directions

Deep eutectic solvents (DESs) are a tailorable class of solvents that are rapidly gaining scientific and industrial interest. This is because they are distinct from conventional molecular solvents, inherently tuneable via careful selection of constituents, and possess many attractive properties for applications, including catalysis, chemical extraction, reaction media, novel lubricants, materials chemistry, and electrochemistry. DESs are a class of solvents composed solely of hydrogen bond donors and acceptors with a melting point lower than the individual components and are often fluidic at room temperature. A unique feature of DESs is that they possess distinct bulk liquid and interfacial nanostructure, which results from intra- and inter-molecular interactions, including coulomb forces, hydrogen bonding, van der Waals interactions, electrostatics, dispersion forces, and apolar-polar segregation. This nanostructure manifests as preferential spatial arrangements of the different species, and exists over several length scales, from molecular- to nano- and meso-scales. The physicochemical properties of DESs are dictated by structure-property relationships; however, there is a significant gap in our understanding of the underlying factors which govern their solvent properties. This is a major limitation of DES-based technologies, as nanostructure can significantly influence physical properties and thus potential applications. This perspective provides an overview of the current state of knowledge of DES nanostructure, both in the bulk liquid and at solid interfaces. We provide definitions which clearly distinguish DESs as a unique solvent class, rather than a subset of ILs. An appraisal of recent work provides hints towards trends in structure-property relationships, while also highlighting inconsistencies within the literature suggesting new research directions for the field. It is hoped that this review will provide insight into DES nanostructure, their potential applications, and development of a robust framework for systematic investigation moving forward.

Synthesis of Highly Ion-Conductive Lignin Eutectogels in a Ternary Deep Eutectic Solvent and Nitrogen-Doped 3D Hierarchical Porous Carbons for Supercapacitors

A new strategy has been developed to synthesize deep eutectic solvent (DES)-based lignin eutectogels by the chemical crosslinking of homogeneously dispersed lignin with poly(ethylene glycol)diglycidyl ether (PEGDE) in a ternary DES of choline chloride (ChCl)/urea/glycerol. The as-prepared lignin eutectogels have high ionic conductivity, high strength, and extreme temperature stability, which can be used as sensors for flexible electronics. N-doped hierarchical porous carbons (HPCs) are prepared when the eutectogels were solvent-replaced and sintered in the atmosphere of N₂ and CO₂, which results in the formation of porous carbon with a sufficient specific surface area and a three-dimensional framework composed of a hierarchical porous structure. They were used as electrodes with excellent capacitance performance attributed to the synergy of reasonable pore size distribution and excellent nitrogen doping efficiency. The electrode displayed a significantly enhanced specific capacitance (270 F g^-1 at a current density of 1.0 A g^-1 in a three-electrode system and 224 F g^-1 at 0.5 A g^-1 in a two-electrode system) and high-performance stability (7% capacitance loss over 10,000 cycles at 8 A g^-1) as a supercapacitor electrode. It indicates the great promise of the lignin eutectogels for both sensing and energy storage applications.

Single Amino-Acid Based Self-Assembled Biomaterials with Potent Antimicrobial Activity

The design and development of soft biomaterials based on amino acid and short-peptide have gained much attention due to their potent biomedical applications. A slight alteration in the side-chain of single amino acid in a peptide or protein sequence has a huge impact on the structure and function. Phenylalanine is one of the most studied amino acids, which contains an aromatic phenyl group connected through a flexible -CH₂ - unit. In this work, we have examined whether flexibility and aromatic functionality of phenylalanine (Phe) are important in gel formation of model gelator Fmoc-Phe-OH or not. To examine this hypothesis, we synthesized Fmoc-derivatives of three analogues unnatural amino acids including cyclohexylalanine, phenylglycine, and homophenylalanine; which are slightly varied from Phe. Interestingly, all these three new analogues formed hydrogels in phosphate buffer at pH 7.0 having different gelation efficacy and kinetics. This study suggests that the presence of aromatic side-chain and flexibility are not mandatory for the gelation of this model gelator. Newly synthesized unnatural amino acid derivatives have also exhibited promising antimicrobial activity towards gram-positive bacteria by inhibiting cellular oxygen consumption. We further determined the biocompatibility of these amino acid derivatives by using a hemolysis assay on human blood cells. Overall studies described the development of single amino acid-based new injectable biomaterials with improved antimicrobial activity by the slight alteration in the side-chain of amino acid.

Super-stretchable and extreme temperature-tolerant supramolecular-polymer double-network eutectogels with ultrafast in situ adhesion and flexible electrochromic behaviour

The current tough and stretchable gels with various integrated functions are mainly based on polymer hydrogels. By introducing a non-covalent supramolecular self-assembled network into a covalently cross-linked polymer network in the presence of eco-friendly and cost-effective deep eutectic solvents (DESs), we developed a new small molecule-based supramolecular-polymer double-network (SP-DN) eutectogel platform. This exciting material exhibits high stretchability and toughness (>18 000% areal strain), spontaneous self-healing ability, ultrafast (∼5 s) in situ underwater and low-temperature (-80 °C) adhesion, and unusual boiling water-resistance, as well as strong base-, strong acid- (even aqua regia), ultra-low-temperature- (liquid nitrogen, -196 °C), and high-temperature- (200 °C) resistance. All these outstanding properties strongly recommend the SP-DN eutectogels as a quasi-solid electrolyte for soft electrochromic devices, which exhibited exceptional flexibility and consistent electrochromic behaviours in harsh mechanical or temperature environments. The experimental and simulation results uncovered the assembly mechanism of the SP-DN eutectogels. Unlike polymer hydrogels, the obtained SP-DN eutectogels showed high molecular design freedom and structural versatility. The findings of this work offer a promising strategy for developing the next generation of mechanically robust and functionally integrated soft materials with high environmental adaptability.

Eutectics: formation, properties, and applications

Various eutectic systems have been proposed and studied over the past few decades. Most of the studies have focused on three typical types of eutectics: eutectic metals, eutectic salts, and deep eutectic solvents. On the one hand, they are all eutectic systems, and their eutectic principle is the same. On the other hand, they are representative of metals, inorganic salts, and organic substances, respectively. They have applications in almost all fields related to chemistry. Their different but overlapping applications stem from their very different properties. In addition, the proposal of new eutectic systems has greatly boosted the development of cross-field research involving chemistry, materials, engineering, and energy. The goal of this review is to provide a comprehensive overview of these typical eutectics and describe task-specific strategies to address growing demands.

Fracto-eutectogels: SDS fractal dendrites via counterion condensation in a deep eutectic solvent

Glyceline, a deep eutectic solvent comprising glycerol and choline chloride, is a green nonaqueous solvent with potential industrial applications. Molecular mechanisms of surfactant self-assembly in deep eutectic solvents are expected to differ from those in their constituent polar components and are not well understood. Here we report the observation of self-assembled SDS fractal dendrites with dimensions up to ∼mm in glyceline at SDS concentrations as low as cSDS ∼ 0.1 wt%. The prevalence of these dendritic fractal aggregates led to the formation of a gel phase at SDS concentrations above ≥1.9 wt% (the critical gelation concentration cCGC). The gel microscopic structure was visualised using polarised light microscopy (PLM); rheology measurements confirmed the formation of a colloidal gel, where the first normal stress difference was negative and the elastic modulus was dominant. Detailed nano-structural characterisation by small-angle neutron scattering (SANS) further confirmed the presence of fractal aggregates. Such SDS aggregation or gelation has not been observed in water at such low surfactant concentrations, whereas SDS has been reported to form lamellar aggregates in glycerol (a component of glyceline). We attribute the formation of the SDS fractal dendrites to the condensation of counterions (i.e. the choline ions) around the SDS aggregates - a diffusion-controlled process, leading to the aggregate morphology observed. These unprecedented results shed light on the molecular mechanisms of surfactant self-assembly in deep eutectic solvents, important to their application in industrial formulation.

Self-Adhesive, Stretchable, Biocompatible, and Conductive Nonvolatile Eutectogels as Wearable Conformal Strain and Pressure Sensors and Biopotential Electrodes for Precise Health Monitoring

Conductive stretchable hydrogels and ionogels consisting of ionic liquids can have interesting application as wearable strain and pressure sensors and bioelectrodes due to their soft nature and high conductivity. However, hydrogels have a severe stability problem because of water evaporation, whereas ionogels are not biocompatible or even toxic. Here, we demonstrate self-adhesive, stretchable, nonvolatile, and biocompatible eutectogels that can always form conformal contact to skin even during body movement along with their application as wearable strain and pressure sensors and biopotential electrodes for precise health monitoring. The eutectogels consist of a deep eutectic solvent that has high conductivity, waterborne polyurethane that is an elastomer, and tannic acid that is an adhesive. They can have an elongation at a break of 178%, ionic conductivity of 0.22 mS/cm, and adhesion force of 12.5 N/m to skin. They can be used as conformal strain sensors to accurately monitor joint movement and breath. They can be even used as pressure sensors with a piezoresistive sensitivity of 284.4 kPa^-1 to precisely detect subtle physical movements like arterial pulses, which can provide vital cardiovascular information. Moreover, the eutectogels can be used as nonvolatile conformal electrodes to monitor epidermal physiological signals, such as electrocardiogram (ECG) and electromyogram (EMG).

Non-volatile conductive gels made from deep eutectic solvents and oxidised cellulose nanofibrils

Ionogels offer huge potential for a number of applications including wearable electronics and soft sensors. However, their synthesis has been limited and often relies on non-renewable or non-biocompatible components. Here we present a novel two-component ionogel made using just deep eutectic solvents (DESs) and cellulose. DESs offer a non-volatile alternative to hydrogels with highly tuneable properties including conductivity and solvation of compounds with widely varying hydrophobicity. DESs can be easily made from cheap, biodegradable and biocompatible components. This research presents the characterisation of a series of soft conductive gels made from deep eutectic solvents (DESs), specifically choline chloride-urea and choline chloride-glycerol, with the sole addition of TEMPO-oxidised cellulose nanofibrils (OCNF). A more liquid-like rather than gel-like conductive material could be made by using the DES betaine-glycerol. OCNF are prepared from sustainable sources, and are non-toxic, and mild on the skin, forming gels without the need for surfactants or other gelling agents. These DES-OCNF gels are shear thinning with conductivities up to 1.7 mS cm^-1 at ∼26 °C. Given the thousands of possible DESs, this system offers unmatched tunability and customisation for properties such as viscosity, conductivity, and yield behaviour.

Self-assembled luminescent cholate gels induced by a europium ion in deep eutectic solvents

Deep eutectic solvents (DESs) with excellent physicochemical properties similar to ionic liquids and biocompatibility are potential solvent candidates for designing novel lanthanide luminescent soft materials. In this paper, the fabrication and characterization of such luminescent gels in three choline chloride (ChCl)-based DESs through self-assembly of the sodium cholate and europium nitrate are presented. The microstructure and gel-like nature of the obtained eutectogels were explored and confirmed by scanning electron microscopy and rheology measurements. While Fourier transform infrared spectroscopy and small-angle X-ray scattering were used to analyze the gel formation mechanism, which was considered to be synergistically driven by metal coordination, hydrogen bonding and solvophobic interactions. All three eutectogels exhibited good photophysical properties. Among these, the one formed in ChCl/urea DES was found to possess the strongest mechanical strength. While the one formed in ChCl/glycerol DES exhibited the longest luminescence lifetime and quantum efficiency. The obtained results demonstrate the possibility of using DESs to construct lanthanide luminescent soft materials or control their properties through the choice of hydrogen-bond donor molecules.

Electric-Field-Induced Gradient Ionogels for Highly Sensitive, Broad-Range-Response, and Freeze/Heat-Resistant Ionic Fingers

Human fingers exhibit both high sensitivity and wide tactile range. The finger skin structures are designed to display gradient microstructures and compressibility. Inspired by the gradient mechanical Young's modulus distribution, an electric-field-induced cationic crosslinker migration strategy is demonstrated to prepare gradient ionogels. Due to the gradient of the crosslinkers, the ionogels exhibit more than four orders of magnitude difference between the anode and the cathode side, enabling gradient ionogel-based flexible iontronic sensors having high-sensitivity and broader-range detection (from 3 × 10² to 2.5 × 10⁶  Pa) simultaneously. Moreover, owing to the remarkable properties of the gradient ionogels, the flexible iontronic sensors also show good long-time stability (even after 10 000 cycles loadings) and excellent performance over a wide temperature range (from -108 to 300 °C). The flexible iontronic sensors are further integrated on soft grips, exhibiting remarkable performance under various conditions. These attractive features demonstrate that gradient ionogels will be promising candidates for smart sensor applications in complex and extreme conditions.

Greener, Faster, Stronger: The Benefits of Deep Eutectic Solvents in Polymer and Materials Science

Deep eutectic solvents (DESs) represent an emergent class of green designer solvents that find numerous applications in different aspects of chemical synthesis. A particularly appealing aspect of DES systems is their simplicity of preparation, combined with inexpensive, readily available starting materials to yield solvents with appealing properties (negligible volatility, non-flammability and high solvation capacity). In the context of polymer science, DES systems not only offer an appealing route towards replacing hazardous volatile organic solvents (VOCs), but can serve multiple roles including those of solvent, monomer and templating agent-so called "polymerizable eutectics." In this review, we look at DES systems and polymerizable eutectics and their application in polymer materials synthesis, including various mechanisms of polymer formation, hydrogel design, porous monoliths, and molecularly imprinted polymers. We provide a comparative study of these systems alongside traditional synthetic approaches, highlighting not only the benefit of replacing VOCs from the perspective of environmental sustainability, but also the materials advantage with respect to mechanical and thermal properties of the polymers formed.

Deep eutectic solvent for curing of phthalonitrile resin: Lower the curing temperature but improve the properties of thermosetting

Long curing duration and high curing temperature are commonly known to restrict the application of the phthalonitrile resin. In this study, a deep eutectic solvent (DES) containing ZnCl2 and urea has been developed to improve the curing process of the resorcinol-based phthalonitrile resin (DPPh) without sacrificing the useful properties of the resin. For the molar ratio of ZnCl2 and urea as 1:1 (ZnCl2-urea (1–1)), the initial curing temperature and apparent activation energy of the system were recorded as 179.5°C and 90.1 kJ/mol, respectively, indicating a reduction of 31.2% and 39.0% as compared to the pristine ZnCl2 system. More importantly, with curing time of 6 h and post-curing temperature of 300°C, the temperature at 5% weight loss as well as glass transition temperature of the resin with DES as the curing agent were 523.1°C and 370.2°C, respectively, demonstrating a significant improvement as compared to the resin cured with ZnCl2. In addition, the satisfactory long-term oxidation stability of the resin could also be obtained by employing the new curing agent. The findings from this study open a functional pathway for facile preparation of the high-performance curing agent for the phthalonitrile resin.

Ultralow-Molecular-Weight Stimuli-Responsive and Multifunctional Supramolecular Gels Based on Monomers and Trimers of Hydrazides

The simpler, the better. A series of simple, neutral and ultralow-molecular-weight (MW: 140-200) hydrazide-derived supramolecular gelators have been designed and synthesized in two straightforward steps. For non-conjugated cyclohexane-derived hydrazides, their monomers can self-assemble to form gels through intermolecular hydrogen bonds and dipole-dipole interactions. Significantly, conjugated phthalhydrazide can self-aggregate into planar and circular trimers through intermolecular hydrogen bonds and then self-assemble to form gels through intermolecular π-π stacking interactions. It is interesting that these simple gelators exhibit unusual properties, such as self-healing, multi-response fluorescence, and visual and selective recognition of chiral (R)/(S)-1,1'-binaphthalene-2,2'-diamine and S^2- through much different times of gel re-formation and blue-green color change, respectively. These results underline the importance of supramolecular gels and extend the scope of supramolecular gelators.