Advanced Materials Based on Polymers and Ionic Liquids

Review of ionic liquid and ionogel-based biomaterials for advanced drug delivery

Ionic liquids (ILs) play a crucial role in the design of novel materials. The ionic nature of ILs provides numerous advantages in drug delivery, acting as a green solvent or active ingredient to enhance the solubility, permeability, and binding efficiency of drugs. They could also function as a structuring agent in the development of nano/micro particles for drug delivery, including micelles, vesicles, gels, emulsion, and more. This review summarize the ILs and IL-based gel structures with their advanced drug delivery applications. The first part of review focuses on the role of ILs in drug formulation and the applications of ILs in drug delivery. The second part of review offers a comprehensive overview of recent drug delivery applications of IL-based gel. It aims to offer new perspectives and attract more attention to open up new avenues in the biomedical applications of ILs and IL-based gels.

Bioactive injectable mucoadhesive thermosensitive natural polymeric hydrogels for oral bone and periodontal regeneration

Periodontitis is an inflammation-related condition, caused by an infectious microbiome and host defense that causes damage to periodontium. The natural processes of the mouth, like saliva production and eating, significantly diminish therapeutic medication residency in the region of periodontal disease. Furthermore, the complexity and diversity of pathological mechanisms make successful periodontitis treatment challenging. As a result, developing enhanced local drug delivery technologies and logical therapy procedures provides the foundation for effective periodontitis treatment. Being biocompatible, biodegradable, and easily administered to the periodontal tissues, hydrogels have sparked substantial an intense curiosity in the discipline of periodontal therapy. The primary objective of hydrogel research has changed in recent years to intelligent thermosensitive hydrogels, that involve local adjustable sol-gel transformations and regulate medication release in reaction to temperature, we present a thorough introduction to the creation and efficient construction of new intelligent thermosensitive hydrogels for periodontal regeneration. We also address cutting-edge smart hydrogel treatment options based on periodontitis pathophysiology. Furthermore, the problems and prospective study objectives are reviewed, with a focus on establishing effective hydrogel delivery methods and prospective clinical applications.

Polymerized and Colloidal Ionic Liquids─Syntheses and Applications

The breadth and importance of polymerized ionic liquids (PILs) are steadily expanding, and this review updates advances and trends in syntheses, properties, and applications over the past five to six years. We begin with an historical overview of the genesis and growth of the PIL field as a subset of materials science. The genesis of ionic liquids (ILs) over nano to meso length-scales exhibiting 0D, 1D, 2D, and 3D topologies defines colloidal ionic liquids, CILs, which compose a subclass of PILs and provide a synthetic bridge between IL monomers (ILMs) and micro to macro-scale PIL materials. The second focus of this review addresses design and syntheses of ILMs and their polymerization reactions to yield PILs and PIL-based materials. A burgeoning diversity of ILMs reflects increasing use of nonimidazolium nuclei and an expanding use of step-growth chemistries in synthesizing PIL materials. Radical chain polymerization remains a primary method of making PILs and reflects an increasing use of controlled polymerization methods. Step-growth chemistries used in creating some CILs utilize extensive cross-linking. This cross-linking is enabled by incorporating reactive functionalities in CILs and PILs, and some of these CILs and PILs may be viewed as exotic cross-linking agents. The third part of this update focuses upon some advances in key properties, including molecular weight, thermal properties, rheology, ion transport, self-healing, and stimuli-responsiveness. Glass transitions, critical solution temperatures, and liquidity are key thermal properties that tie to PIL rheology and viscoelasticity. These properties in turn modulate mechanical properties and ion transport, which are foundational in increasing applications of PILs. Cross-linking in gelation and ionogels and reversible step-growth chemistries are essential for self-healing PILs. Stimuli-responsiveness distinguishes PILs from many other classes of polymers, and it emphasizes the importance of segmentally controlling and tuning solvation in CILs and PILs. The fourth part of this review addresses development of applications, and the diverse scope of such applications supports the increasing importance of PILs in materials science. Adhesion applications are supported by ionogel properties, especially cross-linking and solvation tunable interactions with adjacent phases. Antimicrobial and antifouling applications are consequences of the cationic nature of PILs. Similarly, emulsion and dispersion applications rely on tunable solvation of functional groups and on how such groups interact with continuous phases and substrates. Catalysis is another significant application, and this is an historical tie between ILs and PILs. This component also provides a connection to diverse and porous carbon phases templated by PILs that are catalysts or serve as supports for catalysts. Devices, including sensors and actuators, also rely on solvation tuning and stimuli-responsiveness that include photo and electrochemical stimuli. We conclude our view of applications with 3D printing. The largest components of these applications are energy related and include developments for supercapacitors, batteries, fuel cells, and solar cells. We conclude with our vision of how PIL development will evolve over the next decade.

Energy Applications of Ionic Liquids: Recent Developments and Future Prospects

Ionic liquids (ILs) consisting entirely of ions exhibit many fascinating and tunable properties, making them promising functional materials for a large number of energy-related applications. For example, ILs have been employed as electrolytes for electrochemical energy storage and conversion, as heat transfer fluids and phase-change materials for thermal energy transfer and storage, as solvents and/or catalysts for CO2 capture, CO2 conversion, biomass treatment and biofuel extraction, and as high-energy propellants for aerospace applications. This paper provides an extensive overview on the various energy applications of ILs and offers some thinking and viewpoints on the current challenges and emerging opportunities in each area. The basic fundamentals (structures and properties) of ILs are first introduced. Then, motivations and successful applications of ILs in the energy field are concisely outlined. Later, a detailed review of recent representative works in each area is provided. For each application, the role of ILs and their associated benefits are elaborated. Research trends and insights into the selection of ILs to achieve improved performance are analyzed as well. Challenges and future opportunities are pointed out before the paper is concluded.

Fenton and photo-assisted advanced oxidative degradation of ionic liquids: a review

Ionic liquids (ILs) are the class of materials which are purely ionic in nature and liquid at room temperature. Their remarkable properties like very low vapour pressure, non-inflammable and high heat resistance are responsible for their use as a very appealing solvent in a variety of industrial applications in place of regular organic solvents. Because ILs are water soluble to a certain extent, the industrial wastewater effluents are found to contaminate with their traces. The non-biodegradability of ILs attracts the attention of the researchers for their removal or degradation from wastewater. Numbers of methods are available for the treatment of wastewater. However, it is very crucial to use the most efficient method for the degradation of ILs. Advanced oxidation process (AOP) is one of the most important techniques for the treatment of ILs in wastewater which have been investigated during last decades. This review paper covers the cost-effective Fenton, photochemical and photocatalytic AOPs and their combination that could be applied for the degradation of ILs from the wastewater. Theoretical explanations of these AOPs along with experimental conditions and kinetics of degradation or removal of ILs from water and wastewater have been reported and compared. Finally, future perspectives of IL degradation are presented.

Adaptive Ion-Gel: Stimuli-Responsive, and Self-Healing Ion Gels

Ion gels are an emerging class of polymer gels in which a three-dimensional polymer network swells with an ionic liquid. Ion gels have drawn considerable attention in various fields such as energy and biotechnology owing to their excellent properties including nonvolatility, nonflammability, high ionic conductivity, and high thermal and electrochemical stability. Since the first report on ion gels (published ∼30 years ago), diverse functional ion gels exhibiting impressive physicochemical properties have been reported. In this review, recent developments in functional ion gels that can modulate their physical properties in response to environmental conditions are outlined. Stimuli-responsive ion gels that can adaptively undergo phase transitions in response to thermal and light stimuli are initially discussed, followed by an evaluation of diverse self-healing ion gels that can spontaneously mend mechanical damage through judiciously designed ion-gel networks.

Advances of Imidazolium Ionic Liquids for the Extraction of Phytochemicals from Plants

In this review, we present the research from 2013 to 2022 about the character of ionic liquids, the categories of phytochemicals, and the reasons for selecting imidazolium ionic liquids for phytochemical extraction. Then we introduce the structural formulae of the imidazolium ionic liquids commonly used in the extraction of phytochemicals, the methods used to prepare imidazolium ionic liquids, and a comprehensive introduction of how imidazolium ionic liquids are applied to extract phytochemicals from plants. Importantly, we discuss the strategies for studying the extraction mechanisms of imidazolium ionic liquids to extract phytochemicals, and the recovery methods regarding imidazolium ionic liquids and their recyclability are analyzed. Then the toxicity in imidazolium ionic liquids is pointed out. Finally, the challenges and prospects of extracting phytochemicals by imidazolium ionic liquids are summarized, and they are expected to provide some references for researchers.

Self- and Cross-Fusing of Furan-Based Polyurea Gels Dynamically Cross-Linked with Maleimides

Bio-based polyureas (PUs) with main-chain furan rings were synthesized by the polyaddition of 2,5-bis(aminomethyl)furan with various diisocyanates, such as methylene diphenyl diisocyanate. Several PU's were soluble in polar organic solvents, and were cast to form thermomechanically stable films with softening temperatures of over 100 °C. The furan rings of the PU main chains underwent a dynamic Diels-Alder (DA) reaction with bismaleimide (BMI) cross-linkers. While the mixed solution of PU and BMI did not show any apparent signs of reaction at room temperature, the DA reaction proceeded to form gels upon heating to 60 °C, which became a solution again by further heating to 80 °C (retro-DA reaction). The solution phase was maintained by rapid quenching from 80 °C to room temperature, while the gel was reformed upon slow cooling. The recovered gels exhibited self-healing properties. A scratch made by a hot knife at temperatures above 80 °C disappeared spontaneously. When two different gels were cut using a knife at room temperature, placed in contact with each other, and heated to 60 °C, they fused. The ability to control the DA/retro-DA reaction allowed gels of varying composition to heal.

Ionogel-Based Membranes for Safe Lithium/Sodium Batteries

Alkali (lithium, sodium)-based second batteries are considered one of the brightest candidates for energy-storage applications in order to utilize the random and intermittent renewable energy to achieve carbon neutrality. Conventional lithium/sodium batteries containing liquid organic electrolytes are vulnerable to electrolytes leakage and even combustion, which hinders their large-scale and reliable application. All-solid-state electrolytes which are considered to have better safety have been developed in recent years. However, most of them suffer from low ionic conductivity and large interfacial resistance with the electrode. Ionogel-electrolyte membranes composed of ionic liquids and solid matrices, have attracted much attention because of their nonvolatility, nonflammability, and superior chemical and electrochemical properties. This review focuses on the most recent advances of ionogel electrolytes that sprang up with the emerging demand and progress of safe lithium/sodium batteries. The ionogel-electrolyte membranes are discussed based on the framework components and preparation methods. Their structure and properties, including ionic conductivity, mechanical strength, electrochemical stabilities, and so on, are demonstrated in combination with their applications. The current challenges and insights on the future development of ionogel electrolytes for advanced safe lithium/sodium batteries are also proposed.

Controlling mechanical properties of ultrahigh molecular weight ion gels by chemical structure of ionic liquids and monomers

A new class of ion gels, termed ultrahigh molecular weight (UHMW) gels, formed by physical entanglement of ultrahigh molecular weight polymers in ionic liquids, are synthesised using facile one step radical polymerisation with significantly low initiator conditions, and exhibit superior mechanical characteristics such as stretchability, recyclability, and room temperature self-healing ability. In this study, UHMW gels are synthesised using various combinations of monomer and IL structures, and the effect of their chemical structures on the physicochemical properties of UHMW gels are thoroughly investigated. UHMW polymers are prepared in situ for all combinations of ILs and monomers used in this study, indicating the wide applicability of this fabrication strategy. The structure-property relationships between chemical structures and mechanical properties of UHMW gels are investigated in detail. Furthermore, the differences in self-healing efficiency of UHMW gels depending on the chemical structure is discussed in terms of individual polymer conformation and polymer-polymer interaction based on molecular dynamics simulations.

Highly stretchable and self-healable polymer gels from physical entanglements of ultrahigh-molecular weight polymers

Highly stretchable and self-healing polymer gels formed solely by physical entanglements of ultrahigh-molecular weight (UHMW) polymers were fabricated through a facile one-step process. Radical polymerization of vinyl monomers in ionic liquids under very low initiator concentration conditions produced UHMW polymers of more than 10⁶ g/mol with nearly 100% yield, resulting in the formation of physically entangled transparent polymer gels. The UHMW gels showed excellent properties, such as high stretchability, high ionic conductivity, and recyclability. Furthermore, the UHMW gel exhibited room temperature self-healing ability without any external stimuli. The tensile experiments and molecular dynamics simulations indicate that the nonequilibrium state of the fractured surfaces and microscopic interactions between the polymer chains and solvents play a vital role in the self-healing ability. This study provides a physical approach for fabricating stretchable and self-healing polymer gels based on UHMW polymers.

In situ formed thermogelable hydrogel photonic crystals assembled by thermosensitive IPNs

In this paper, soft thermosensitive photonic crystals are immobilized via a reversible temperature-triggered in situ sol-gel transition above their phase transition temperature (T_p), which may be a significant advance in the field. Specifically, a library of thermosensitive poly(N-isopropylacrylamide)/poly(acrylic acid) (PNIPAm/PAA) interpenetrating nanogels (IPNs) is synthesized, which can achieve a reversible temperature-induced sol-gel transition at a low concentration (1.1 wt%). More interestingly, as the temperature is increased above T_p, the photonic crystals assembled by these IPNs do not disappear but are "immobilized" in the in situ formed hydrogel matrix. Moreover, these colorful IPN dispersions exhibit outstanding syringe-injectability, immediately turning from an aqueous solution into an insoluble hydrogel as they are injected into PBS at 37 °C. Plus, a protein-release study showed that these injectable hydrogels show extended release times and slower release rates in comparison with dilute nanogel dispersions. In brief, these in situ formed hydrogels with brilliant structural colors have potential in optical applications, e.g., color displays, crystal immobilization, and biological applications, e.g., 3D cell culture and drug delivery.

Structural Reorganization of Imidazolium Ionic Liquids Induced by Pressure-Enhanced Ionic Liquid-Polyethylene Oxide Interactions

Mixtures of polyethylene oxide (PEO, M.W.~900,000) and imidazolium ionic liquids (ILs) are studied using high-pressure Fourier-transform infrared spectroscopy. At ambient pressure, the spectral features in the C-H stretching region reveal that PEO can disturb the local structures of the imidazolium rings of [BMIM]+ and [HMIM]+. The pressure-induced phase transition of pure 1-butyl-3-methylimidazolium bromide ([BMIM]Br) is observed at a pressure of 0.4 GPa. Pressure-enhanced [BMIM]Br-PEO interactions may assist PEO in dividing [BMIM]Br clusters to hinder the aggregation of [BMIM]Br under high pressures. The C-H absorptions of pure 1-hexyl-3-methylimidazolium bromide [HMIM]Br do not show band narrowing under high pressures, as observed for pure [BMIM]Br. The band narrowing of C-H peaks is observed at 1.5 GPa for the [HMIM]Br-PEO mixture containing 80 wt% of [HMIM]Br. The presence of PEO may reorganize [HMIM]Br clusters into a semi-crystalline network under high pressures. The differences in aggregation states for ambient-pressure phase and high-pressure phase may suggest the potential of [HMIM]Br-PEO (M.W.~900,000) for serving as optical or electronic switches.

Lithium-ion coordination-induced conformational change of PEG chains in ionic-liquid-based electrolytes

We report the structure of poly(ethylene glycol) (PEG) in a imidazolium-based ionic liquid (IL) electrolyte containing lithium bis(trifluoromethanesulfonyl)amide (LiTFSA) salt, as determined using Raman spectroscopy, high-energy X-ray total scattering (HEXTS), and molecular dynamics (MD) simulations. The Raman spectral study indicated that the TFSA anions bound to Li ions are desolvated when PEG is added to the LiTFSA/IL solution to form stable Li+-PEG complexes. Via quantitative analysis of the obtained Raman spectra, the desolvation number of the TFSA [nd, per one oxygen atom of the ethylene glycol unit (Opeg)] was determined to be ∼0.4, irrespective of the shape (star or linear) and molecular weight of the polymer. On the basis of radial distribution functions obtained from the HEXTS experiments and MD simulations, we demonstrated that the Li+-PEG complexation induces a conformational change of the PEG chain from gauche/anti-conformers to a syn conformer. This Li+-coordination-induced conformation resulted in a decrease in the radius of gyration (Rg) of the PEG chain, implying a folding behavior of polymer chains through multiple OpegLi+Opeg interactions.

Mesoporous Ionically Tagged Cross-Linked Poly(vinyl imidazole)s as Novel and Reusable Catalysts for the Preparation of N-Heterocycle Spiropyrans

Herein, two novel mesoporous cross-linked poly(vinyl imidazole)s with sulfonic acid tags, [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2), were prepared and characterized by a variety of techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, elemental mapping, energy dispersive X-ray analysis, transmission electron microscopy, thermal gravimetry, derivative thermal gravimetry, and N2 adsorption-desorption isotherms (Brunauer-Emmett-Teller). In addition, magnetic properties of poly(vinyl imidazole) sulfonic acid iron(IV) chloride [PVI-SO3H]FeCl4 (2) as an ionically tagged magnetic polymer were investigated using a vibrating sample magnetometer. The presented polymers, [PVI-SO3H]Cl (1) and [PVI-SO3H]FeCl4 (2), were successfully applied as reusable and efficient catalysts for the preparation of N-heterocycle spiropyrans. The described catalysts were recycled and reused with a marginal decrease in their catalytic activities. The desired products were prepared under mild and green conditions. The structures of the obtained products were confirmed by various analysis techniques.

Amphiphilic Cyclodextrin-Based Liquid Crystals for Proton Conduction

Novel cyclodextrin (CD)-based amphiphilic poly(carboxylic acid)s that self-assemble into highly ordered smectic liquid crystalline mesophases were investigated as a novel class of protonic conductors. These structurally well-defined materials are synthesized from nontoxic and environment-friendly CDs, which possess a unique face-to-face pseudosymmetry. By taking advantage of such geometry, a series of flexible tetraethylene glycol groups terminated with a carboxylic acid functionality were introduced to the CD's secondary face, resulting in the formation of long-range 2D hydrogen-bond networks in the smectic mesophases over a wide temperature window. This new material was found to exhibit impressive proton conductivities in solid states, up to 1.4 × 10^-2 S cm^-1 at 70 °C and 95% humidity. This constitutes the first report of amphiphilic CD-based liquid crystals applied as proton conductive materials.

New Insights on the Fast Response of Poly(Ionic Liquid)s to Humidity: The Effect of Free-Ion Concentration

The swelling mechanism is widely used to explain the response of ionic liquids (ILs) or poly(ionic liquid)s (PILs) to moisture. While a fairly broad consensus has been attained, there are still some phenomena that are not well explained. As a complement to the swelling mechanism, we systematically studied the free volume theory in the rapid response and recovery of PIL humidity performance. We chose poly(1-ethyl-3-vinylimidazolium bromide) (PIL-Br), poly(1-ethyl-3-vinylimidazolium tetrafluoroborate) (PIL-BF₄) and poly(1-ethyl-3-vinylimidazolium bis(trifluoromethane sulfonimide)) (PIL-TFSI) as model materials and investigated the impact of PIL structure including anion type, film thickness and affinity to moisture on performance to obtain the humidity sensing mechanism for PILs based on free volume theory. Hence, we can combine free volume theory with the designed PIL structures and their affinity with moisture to obtain a high concentration of free ions in PIL sensing films. Furthermore, the PIL humidity sensors also show fast, substantial impedance changes with changing humidity for real-time monitoring of the human respiratory rate due to a fast response and recovery performance. Therefore, our findings develop a new perspective to understand the humidity performance of PILs based on free volume theory, resulting in fast response and recovery properties realized by the rational design of PIL sensing films.

Cluster–Micelle Transition of a Thermo- and Photoresponsive ABC Triblock Copolymer in an Ionic Liquid

We report the photocontrollable micelle–cluster transition of an ABC-type triblock copolymer in an ionic liquid (IL). Polystyrene-b-poly(ethylene oxide)-b-poly(4-phenylazobenzyl acrylamide-r-N-isopropylacrylamide) (PSt-b-PEO-b-P(AzoBnAm-r-NIPAm)) was synthesised, where PSt is IL-phobic, PEO is IL-philic, and P(AzoBnAm-r-NIPAm) is photo- and thermoresponsive in the IL. At high temperatures, the triblock copolymer forms micelles with PSt cores; furthermore, at low temperatures, micelles self-assemble into clusters induced by the aggregation of P(AzoBnAm-r-NIPAm). Under UV irradiation, the micelles form clusters at lower temperatures than that in the dark because of the change in the solubility of P(AzoBnAm-r-NIPAm) induced by photoisomerisation of the azobenzene groups, indicating that this triblock copolymer has a photocontrollable micelle–cluster transition temperature.

Dimension control of ionic liquids

Ionic liquids have established themselves as promising soft compounds for bringing innovation to materials science. For further developing functions and abilities of ionic liquids, one of the most important challenges is to organize ionic liquids into dimensionally ordered states. In this feature article, we will present the organization of ionic liquids by endowing them with liquid-crystalline properties. In particular, focusing on the specific abilities and properties of functional ionic liquids, a variety of nanostructured ionic materials have been developed and their unique and enhanced functions have been revealed. Some potential uses of organized ionic liquids have also been mentioned.

Ion Gel Network Formation in an Ionic Liquid Studied by Time-Resolved Small-Angle Neutron Scattering

We report the time-resolved small-angle neutron scattering (SANS) study of tetra-arm poly(ethylene glycol) (TetraPEG) polymer network formation in a typical ionic liquid (IL), 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C₂mim][TFSA]). To observe time-dependent SANS profiles, the reaction rate for the AB-type cross-end coupling reaction of TetraPEG macromers was controlled by adding an analogous protic IL, 1-ethylimidazolium TFSA ([C₂imH][TFSA]). At polymer concentrations higher than the overlap concentration ( c*), the SANS profile remained unchanged during the gelation reaction, indicating that the network structure was independent of macromer connectivity in a semidiluted solution. On the other hand, at low polymer concentrations, an increase in the SANS profile intensity was clearly observed. The correlation length (ξ), estimated by a fitting analysis based on the Ornstein-Zernike function, increased as the reaction proceeded. This result indicated that the sparsely dispersed macromers formed clusters during the cross-linking process and polymer size growth followed thereafter. We found that the network formation process and homogeneity of the network structure were strongly dependent on the polymer concentration in IL solutions.

Charge Transport and Phase Behavior of Imidazolium-Based Ionic Liquid Crystals from Fully Atomistic Simulations

Ionic liquid crystals occupy an intriguing middle ground between room-temperature ionic liquids and mesostructured liquid crystals. Here, we examine a non-polarizable, fully atomistic model of the 1-alkyl-3-methylimidazolium nitrate family using molecular dynamics in the constant pressure-constant temperature ensemble. These materials exhibit a distinct "smectic" liquid phase, characterized by layers formed by the molecules, which separate the ionic and aliphatic moieties. In particular, we discuss the implications this layering may have for electrolyte applications.