Supramolecular Association of a Block Copolymer via Strong Hydrogen Bonding to Form Self-Healable Ionogels

The drive to enhance the operational durability and reliability of stretchable and wearable electronic and electrochemical devices has led to the exploration of self-healing materials that can recover from both physical and functional failures. In the present study, we fabricated a self-healable solid polymer electrolyte, referred to as an ionogel, using reversible hydrogen bonding between the ureidopyrimidone units of a block copolymer (BCP) network swollen in an ionic liquid (IL). The BCP consisted of poly(styrene-b-(methyl acrylate-r-ureidopyrimidone methacrylate)) [poly(S-b-(MA-r-UPyMA)], with the IL-phobic polystyrene forming micellar cores that were interconnected via intercorona hydrogen bonding between the ureidopyrimidone units. By precisely regulating the molecular weight and the composition of the hydrogen-bondable motifs, the mechanical, electrical, and self-healing characteristics of the ionogel were systematically evaluated. The resulting ionogel samples exhibited suitable stretchability, ionic conductivity, and room-temperature self-healability due to reversible hydrogen bonding. To highlight the applicability of the self-healing ionogel as a high-capacitance gate insulator, an electrolyte-gated transistor (EGT) was fabricated using a poly(3-hexylthiophene-2,5-diyl) semiconductor, and the performance of the EGT was fully recovered from a complete cut without any external stimuli.

Glassy gels toughened by solvent

Glassy polymers are generally stiff and strong yet have limited extensibility1. By swelling with solvent, glassy polymers can become gels that are soft and weak yet have enhanced extensibility1-3. The marked changes in properties arise from the solvent increasing free volume between chains while weakening polymer-polymer interactions. Here we show that solvating polar polymers with ionic liquids (that is, ionogels4,5) at appropriate concentrations can produce a unique class of materials called glassy gels with desirable properties of both glasses and gels. The ionic liquid increases free volume and therefore extensibility despite the absence of conventional solvent (for example, water). Yet, the ionic liquid forms strong and abundant non-covalent crosslinks between polymer chains to render a stiff, tough, glassy, and homogeneous network (that is, no phase separation)6, at room temperature. Despite being more than 54 wt% liquid, the glassy gels exhibit enormous fracture strength (42 MPa), toughness (110 MJ m-3), yield strength (73 MPa) and Young's modulus (1 GPa). These values are similar to those of thermoplastics such as polyethylene, yet unlike thermoplastics, the glassy gels can be deformed up to 670% strain with full and rapid recovery on heating. These transparent materials form by a one-step polymerization and have impressive adhesive, self-healing and shape-memory properties.

Polymer solubility mechanism in ionic liquids: 1H-NMR spectra and two-parameter hydrogen bonding analysis

Understanding the polymer solubility in ionic liquids (ILs) is important for polymer processing or polymeric material preparation. Previously, two-parameter H-bonding analysis has been proposed to clarify that polymer solubility in ILs is dominated by H-bonding interactions (Y. F. Yuan et al., Phys. Chem. Chem. Phys., 2021, 23, 21893-21900). In the present work, 1H-NMR spectra are adopted to characterize the H-bonding interactions between polymers and ILs, which provide a microscopic relation between polymer solubility and two-parameter H-bonding analysis.

Ionic Liquid Interface as a Cell Scaffold

In sharp contrast to conventional solid/hydrogel platforms, water-immiscible liquids, such as perfluorocarbons and silicones, allow the adhesion of mammalian cells via protein nanolayers (PNLs) formed at the interface. However, fluorocarbons and silicones, which are typically used for liquid cell culture, possess only narrow ranges of physicochemical parameters and have not allowed for a wide variety of cell culturing environments. In this paper, it is proposed that water-immiscible ionic liquids (ILs) are a new family of liquid substrates with tunable physicochemical properties and high solvation capabilities. Tetraalkylphosphonium-based ILs are identified as non-cytotoxic ILs, whereon human mesenchymal stem cells are successfully cultured. By reducing the cation charge distribution, or ionicity, via alkyl chain elongation, the interface allows cell spreading with matured focal contacts. High-speed atomic force microscopy observations of the PNL formation process suggest that the cation charge distribution significantly altered the protein adsorption dynamics, which are associated with the degree of protein denaturation and the PNL mechanics. Moreover, by exploiting dissolution capability of ILs, an ion-gel cell scaffold is fabricated. This enables to further identify the significant contribution of bulk subphase mechanics to cellular mechanosensing in liquid-based culture scaffolds.

Ionic Liquids: An Ideal Solvent for Tuning the UCST Phase Behavior of Polymer Gels

Liquid-liquid phase separation (LLPS) is a common stimulus-responsive phenomenon widely studied and applied in constructing intelligent systems such as microfluidic valves, smart windows, and biosensors. However, LLPS in an aqueous solution has limited applicability confined to a narrow temperature range within 0-100 °C. In addition, for easy exploitation of thermoresponsive behavior, phase separation must be stable and accurately predictable under varying conditions. This study proposes a gel system exhibiting UCST phase behavior using ionic liquids (ILs) and hydrophilic polymers, whose phase transition temperature can be linearly tuned within a wide range (from subzero to over 100 °C) by varying the mixing ratio of ILs in their blends. Similar to the mixing of ILs with structurally similar cations, mixing ILs containing different anions proved to be an effective ideal random mixing method based on experimental results and molecular dynamics simulations. This mixing mechanism of ILs accounts for the linear regulation of the UCST of the ionogels when the mixing ratio of ILs in their blends varies. Moreover, the unique feature of ILs was further demonstrated using other hydrophilic polymer networks and multiple combinations of ILs, suggesting the generality of this strategy for UCST regulation in the ionogels.

Autonomous underwater adhesion driven by water-induced interfacial rearrangement

Underwater adhesives receive extensive attention due to their wide applications in marine explorations and various related industries. However, current adhesives still suffer from excessive water absorption and lack of spontaneity. Herein, we report an autonomous underwater adhesive based on poly(2-hydroxyethyl methacrylate-co-benzyl methacrylate) amphiphilic polymeric matrix swollen by hydrophobic imidazolium ionic liquid. The as-prepared adhesive is tough and flexible, showing little to none instantaneous underwater adhesion onto the PET substrate, whereas its adhesion energy on the substrate can grow more than 5 times to 458 J·m-2 after 24 hours. More importantly, this process is entirely spontaneous, without any external pressing force. Our comprehensive studies based on experimental characterizations and molecular dynamic simulations confirm that such autonomous adhesion process is driven by water-induced rearrangement of the functional groups. It is believed that such material can provide insights into the development of next-generation smart adhesives.

Ionic-Liquid-Mediated Deconstruction of Polymers for Advanced Recycling and Upcycling

Ionic liquids (ILs) are a promising medium to assist in the advanced (chemical and biological) recycling of polymers, owing to their tunable catalytic activity, tailorable chemical functionality, low vapor pressures, and thermal stability. These unique physicochemical properties, combined with ILs' capacity to solubilize plastics waste and biopolymers, offer routes to deconstruct polymers at reduced temperatures (and lower energy inputs) versus conventional bulk and solvent-based methods, while also minimizing unwanted side reactions. In this Viewpoint, we discuss the use of ILs as catalysts and mediators in advanced recycling, with an emphasis on chemical recycling, by examining the interplay between IL chemistry and deconstruction thermodynamics, deconstruction kinetics, IL recovery, and product recovery. We also consider several potential environmental benefits and concerns associated with employing ILs for advanced recycling over bulk- or solvent-mediated deconstruction techniques, such as reduced chemical escape by volatilization, decreased energy demands, toxicity, and environmental persistence. By analyzing IL-mediated polymer deconstruction across a breadth of macromolecular systems, we identify recent innovations, current challenges, and future opportunities in IL application toward circular polymer economies.

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.

Tough Ionogels: Synthesis, Toughening Mechanisms, and Mechanical Properties-A Perspective

Polymeric ionogels are polymer networks swollen with ionic liquids (i.e., salts with low melting points). Ionogels are interesting due to their unique features such as nonvolatility, high thermal and electrochemical stability, excellent ionic conductivity, and nonflammability. These properties enable applications such as unconventional electronics, energy storage devices (i.e., batteries and supercapacitors), sensors and actuators. However, the poor mechanical performance of ionogels (e.g., fracture strength < 1 MPa, modulus < 0.1 MPa, and toughness < 1000 J m^-2) have limited their use, thus motivating the need for tough ionogels. This Perspective summarizes recent advances toward tough ionogels by highlighting synthetic methods and toughening mechanisms. Opportunities and promising applications of tough ionogels are also discussed.

Tough and stretchable ionogels by in situ phase separation

Ionogels are compelling materials for technological devices due to their excellent ionic conductivity, thermal and electrochemical stability, and non-volatility. However, most existing ionogels suffer from low strength and toughness. Here, we report a simple one-step method to achieve ultra-tough and stretchable ionogels by randomly copolymerizing two common monomers with distinct solubility of the corresponding polymers in an ionic liquid. Copolymerization of acrylamide and acrylic acid in 1-ethyl-3-methylimidazolium ethyl sulfate results in a macroscopically homogeneous covalent network with in situ phase separation: a polymer-rich phase with hydrogen bonds that dissipate energy and toughen the ionogel; and an elastic solvent-rich phase that enables for large strain. These ionogels have high fracture strength (12.6 MPa), fracture energy (~24 kJ m^-2) and Young's modulus (46.5 MPa), while being highly stretchable (~600% strain) and having self-healing and shape-memory properties. This concept can be applied to other monomers and ionic liquids, offering a promising way to tune ionogel microstructure and properties in situ during one-step polymerization.

Polymer solubility in ionic liquids: dominated by hydrogen bonding

Polymer solubility in ionic liquids (ILs) cannot be predicted by the solubility parameter approach based on the "like dissolves like" principle. According to the Kamlet-Abraham-Taft (KAT) multi-parameter polarity scale, ILs can be categorized on the basis of hydrogen-bond acidity or basicity ones. The experimental observations, that acidic ILs easily dissolve basic polymers and basic ILs dissolve acidic polymers, reflect the complementary nature of hydrogen-bonding interactions. A quantitative hydrogen-bonding analysis is proposed for predicting the solubility by taking the product of ΔαΔβ as an indicator of the competition between cross-association and self-association hydrogen bonding (H-bonding), where Δα is the difference of acidity parameters between the polymer and IL, and Δβ is the difference of basicity. This solubility criterion has been validated by the solubility data of 19 polymers (11 acidic and 8 basic) in 11 ILs (7 acidic and 4 basic). These principles based on KAT parameters can be applied to other systems dominated by hydrogen bonding.

Unusual Lower Critical Solution Temperature Phase Behavior of Poly(benzyl methacrylate) in a Pyrrolidinium-Based Ionic Liquid

Polymer/ionic liquid systems are being increasingly explored, yet those exhibiting lower critical solution temperature (LCST) phase behavior remain poorly understood. Poly(benzyl methacrylate) in certain ionic liquids constitute unusual LCST systems, in that the second virial coefficient (A₂) in dilute solutions has recently been shown to be positive, indicative of good solvent behavior, even above phase separation temperatures, where A₂ < 0 is expected. In this work, we describe the LCST phase behavior of poly(benzyl methacrylate) in 1-butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)imide for three different molecular weights (32, 63, and 76 kg/mol) in concentrated solutions (5–40% by weight). Turbidimetry measurements reveal a strong concentration dependence to the phase boundaries, yet the molecular weight is shown to have no influence. The critical compositions of these systems are not accessed, and must therefore lie above 40 wt% polymer, far from the values (ca. 10%) anticipated by Flory-Huggins theory. The proximity of the experimental cloud point to the coexistence curve (binodal) and the thermo-reversibility of the phase transitions, are also confirmed at various heating and cooling rates.

Direct Observation of Photo-Induced Reversible Sol-Gel Transition in Block Copolymer Self-Assembly Containing an Azobenzene Ionic Liquid

Using atomic force microscopy, the photo-induced reversible changes in a block copolymer self-assembly containing an azobenzene ionic liquid, which undergoes sol-gel transition is directly observed. This is the first report on the sol-gel transition of an ABA-type block copolymer consisting of upper critical solution temperature (UCST)-type A blocks in a photoresponsive ionic liquid mixture. The sol-gel transition is accompanied by an order-to-disorder structural change, which subsequently induces a change in the ionic conductivity. Surprisingly, the photo-induced ionic conductivity and rheological changes occurs rapidly (≈30 s) despite the dense (≈80 wt%) polymeric system. The rapid structural change is probably attributable to the fast diffusion of the ionic liquid.

Self-Assembly of Diblock Copolymers Containing Thermo- and Photoresponsive Lower Critical Solution Temperature Phase Behavior Polymer with Tunable Assembly Temperature in an Ionic Liquid Mixture

This work prepared a type of diblock copolymer with thermo- and photosensitivity in ionic liquids (ILs). P(N,N-dimethylacrylamide) (compatible with ILs) was prepared as one segment, while butyl acrylate (BA) and 4-phenylazophenylmethacrylate (AzoMA) were copolymerized as another segment P(AzoMA-r-BA) with stimuli responsiveness. The diblock copolymer showed tunable lower critical micellization temperature (LCMT) in two mixed imidazole ionic liquids. The value of LCMT depends on not only the conformation status of the azo group in copolymers but also the azo group content in copolymers and mixed ratio of ionic liquids. Based on this tunable LCMT, photoinduced micellization/demicellization can be achieved near room temperature by alternate irradiation with visible and ultraviolet light, and it is totally reversible.

Solvation Structure of Poly(benzyl methacrylate) in a Solvate Ionic Liquid: Preferential Solvation of Li-Glyme Complex Cation

We report the solvation structure of a lower critical solution temperature (LCST)-type thermoresponsive polymer in a solvate ionic liquid (SIL, i.e., an ionic liquid comprising solvate ions) to elucidate the predominant interaction for the dissolution of the thermoresponsive polymer in SIL at low temperatures. The solvation structure of poly(benzyl methacrylate) (PBnMA) and a model compound of its monomer in a typical glyme-based SIL, [Li(G4)][TFSA] (G4: tetraglyme; TFSA: bis(trifluoromethanesulfonyl)amide), have been investigated using high-energy X-ray total scattering and all-atom molecular dynamics simulations. In the model compound/SIL system, the intermolecular components extracted from the total G( r)s revealed that the ester moiety of BnMA is preferentially solvated by Li cations through a cation-dipole interaction, which induces slight desolvation of the G4 molecules, and the aromatic ring of BnMA is secondarily solvated by the [Li(G4)] cation complex through a cation-π interaction with maintaining the complex structure. In contrast, TFSA anions are attracted only by the [Li(G4)] cation. These interactions result in the formation of a solvation layer of SILs around the aromatic ring, which plays a key role in the negative entropy and enthalpy of mixing. Meanwhile, in the polymer solution, the coordination number of the Li cation around the ester moiety significantly decreased. This could be ascribed to the steric effect of the bulky side chains, preventing the approach of the [Li(G4)] cation complex to the ester moiety located near the main chain. These solvation structures lead to small absolute values of negative entropy and enthalpy of mixing, which together are key factors to understand the LCST-type phase behavior in the IL system.

Control of Phase Separation in Polystyrene/Ionic Liquid-Blended Films by Polymer Brush-Grafted Particles

Immiscible composite materials with controlled phase-separated structures are important in areas ranging from catalysis to battery. We succeeded in controlling the phase-separated structures of immiscible blends of polystyrene (PS) and two ionic liquids (ILs), namely, N, N-diethyl- N-(2-methoxyethyl)- N-methylammonium bis(trifluoromethylsulfonyl)imide (DEME-TFSI) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, by adding precisely designed concentrated polymer brush-grafted (CPB-grafted) silica nanoparticles (CPB-SiPs) prepared by surface-initiated atom-transfer radical polymerization. We discuss relationships between chemical species and molecular weights of the CPB and phase-separated structures. When the CPB was composed of a PS homopolymer of an appropriate molecular weight, the IL phase formed a continuous structure and a quasi-solid-blended film was successfully fabricated because the CPB-SiPs were adsorbed at the PS/IL interface and prevented macroscopic phase separation. We propose that CPB-SiP adsorption and the fabrication of quasi-solid films are governed by the degree of penetration of the matrix PS chains into the CPB and deformability of the CPB-SiPs. We found that the DEME-TFSI domain size can be controlled by the CPB-SiP content and that only 1 wt % of the CPB-SiPs was needed to fabricate a quasi-solid film. In addition, we investigated the ionic properties of the quasi-solid PS/DEME-TFSI-blended film. Owing to continuous ion channels composed only of DEME-TFSI, the film exhibited an ionic conductivity of 0.1 mS/cm, which is relatively high compared to previously reported quasi-solid electrolytes. Finally, we demonstrated that an electric double-layer capacitor fabricated using this film as the electrolyte exhibited high charge/discharge cycling stability and reversibility.

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.

Tuning of volume phase transition for poly(N-isopropylacrylamide) ionogels by copolymerization with solvatophilic monomers

Ionogels are crosslinked polymer networks that swell in ionic liquids (ILs) and exhibit high conductivity and chemical stability. Combined with a representative thermally responsive polymer, poly(N-isopropylacrylamide) (PNIPAm), previously studied ionogels fulfilled the requirements for smart responsive materials, but their transition temperature in hydrophobic ILs exceeded that which could be used for practical applications. In this study, we prepared transition temperature tunable ionogels via copolymerization of NIPAm with solvatophilic N,N'-diethylacrylamide (NDEAm). The hydrophobic diethyl moiety in NDEAm promoted ionogel solvatophilicity toward the IL, resulting in a larger swelling ratio, lower volume phase transition temperature, and narrower transition range with increase in NDEAm content in the prepared ionogels. Based on these fundamental observations, ionogels that exhibit a volume phase transition near room temperature were prepared. We also studied the swelling and deswelling kinetics of the prepared ionogels, revealing that the deswelling rate is much slower than swelling due to the formation of a dense skin layer on the ionogel surface.

Self-Healing Micellar Ion Gels Based on Multiple Hydrogen Bonding

Ion gels, composed of macromolecular networks filled by ionic liquids (ILs), are promising candidate soft solid electrolytes for use in wearable/flexible electronic devices. In this context, the introduction of a self-healing function would significantly improve the long-term durability of ion gels subject to mechanical loading. Nevertheless, compared to hydrogels and organogels, the self-healing of ion gels has barely investigated been because of there being insufficient understanding of the interactions between polymers and ILs. Herein, a new class of supramolecular micellar ion gel composed of a diblock copolymer and a hydrophobic IL, which exhibits self-healing at room temperature, is presented. The diblock copolymer has an IL-phobic block and a hydrogen-bonding block with hydrogen-bond-accepting and donating units. By combining the IL and the diblock copolymer, micellar ion gels are prepared in which the IL phobic blocks form a jammed micelle core, whereas coronal chains interact with each other via multiple hydrogen bonds. These hydrogen bonds between the coronal chains in the IL endow the ion gel with a high level of mechanical strength as well as rapid self-healing at room temperature without the need for any external stimuli such as light or elevated temperatures.

A simulation method for the phase diagram of complex fluid mixtures

The phase behavior of complex fluid mixtures is of continuing interest, but obtaining the phase diagram from computer simulations can be challenging. In the Gibbs ensemble method, for example, each of the coexisting phases is simulated in a different cell, and ensuring the equality of chemical potentials of all components requires the transfer of molecules from one cell to the other. For complex fluids such as polymers, successful insertions are rare. An alternative method is to simulate both coexisting phases in a single simulation cell, with an interface between them. The challenge here is that the interface position moves during the simulation, making it difficult to determine the concentration profile and coexisting concentrations. In this work, we propose a new method for single cell simulations that uses a spatial concentration autocorrelation function to (spatially) align instantaneous concentration profiles from different snapshots. This allows one to obtain average concentration profiles and hence the coexisting concentrations. We test the method by calculating the phase diagrams of two systems: the Widom-Rowlinson model and the symmetric blends of freely jointed polymer molecules for which phase diagrams from conventional methods are available. Excellent agreement is found, except in the neighborhood of the critical point where the interface is broad and finite size effects are important. The method is easy to implement and readily applied to any mixture of complex fluids.

Steric Stabilization of γ-Fe2O3 Superparamagnetic Nanoparticles in a Hydrophobic Ionic Liquid and the Magnetorheological Behavior of the Ferrofluid

Hydrophobic ionic liquid ferrofluids (ILFFs) are studied for use in electrospray thrusters for microsatellite propulsion under nonatmospheric and in high-temperature environments. We synthesized a hydrophobic ILFF by dispersing sterically stabilized γ-Fe₂O₃ nanoparticles (NPs) in the ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. A diblock copolymer, C4-RAFT-AA₁₀-DEAm₆₀, was synthesized to facilitate multipoint bidentate anchoring to the NP through the acrylic acid block. The DEAm₆₀ layer was incorporated to generate steric repulsion between particles to protect against the aggregation of magnetized particles arising from dipole-dipole attraction. The effect of shearing and variation in the magnetic field strength on the steric repulsion was examined using the DLVO theory. The effect of varying the magnetic field strength and particle concentration on the viscoelastic properties of the ferrofluid was evaluated using rheometry. The viscosity of the ferrofluid increased with the magnetic field strength, indicating that the magnetized particles assembled into a structure. The level of straining required to break down the structure formed by the magnetized particles increased with the magnetic field strength and particle concentration. The absence of particle interlocking during shearing was indicated by the smooth viscosity versus shear rate traces. The DLVO analysis showed that increasing the magnetic attraction between the particles causes the DEAm₆₀ brush layers on the particles to overlap more, resulting in an increase in the steric repulsion. As overlapping increases, osmotic repulsion is caused before progressing to a strong elastic repulsion. The effect of the polymer solubility and particle interaction due to hydrodynamic forces on the steric repulsion was also analyzed.

Block copolymer self-assembly in ionic liquids

Recent developments in block copolymer self-assembly in ionic liquids are reviewed from both fundamental and applied aspects.

Thermosensitive Phase Separation Behavior of Poly(benzyl methacrylate)/Solvate Ionic Liquid Solutions

We report a lower critical solution temperature (LCST) behavior of binary systems consisting of poly(benzyl methacrylate) (PBnMA) and solvate ionic liquids: equimolar mixtures of triglyme (G3) or tetraglyme (G4) and lithium bis(trifluoromethanesulfonyl)amide. We evaluated the critical temperatures (T_cs) using transmittance measurements. The stability of the glyme-Li⁺ complex ([Li(G3 or G4)]⁺) in the presence of PBnMA was confirmed using Raman spectroscopy, pulsed-field gradient spin-echo NMR (PGSE-NMR), and thermogravimetric analysis to demonstrate that the complex was not disrupted. The interaction between glyme-Li⁺ complex and PBnMA was investigated via ⁷Li NMR chemical shifts. Upfield shifts originating from the ring-current effect of the aromatic ring within PBnMA were observed with the addition of PBnMA, indicating localization of the glyme-Li⁺ complex above and below the benzyl group of PBnMA, which may be a reason for negative mixing entropy, a key requirement of the LCST.

Advanced Materials Based on Polymers and Ionic Liquids

Ionic liquids (ILs) are ambient temperature molten salts, which have attracted considerable attention owing to their unique properties. In this contribution, we review advanced materials composed of ILs and polymers for the basis of a new design protocol to fabricate novel materials. As electrolytes for electrochemical devices, cross-linked polymers containing ILs (ion gels) are endowed with functional properties inherited from ILs and mechanical consistency derived from polymers. To create such materials, micro-phase separation of block copolymers and colloidal arrays in the ILs are utilized. Based on the molecular design of task-specific ILs, the resultant ion gels are applicable as electrolytes for actuator, fuel cell, and secondary battery applications. Thermo- and photo-responsive polymers in ILs are also highlighted, whereby such stimuli elicit changes in the solubility of the self-assembly of block copolymers and colloidal arrays in the ILs. Further, thermo- and photo-reversible changes in the self-assembled structure can be exploited to demonstrate sol-gel transitions and fabricate photo-healable materials.

Tunable Upper Critical Solution Temperature of Poly(N-isopropylacrylamide) in Ionic Liquids for Sequential and Reversible Self-Folding

We demonstrate sequential folding of micropatterned polymer actuators by tuning the upper critical solution temperature (UCST) of poly(N-isopropylacrylamide) (PNIPAM) copolymers in the ionic liquid (IL) 1-ethyl-3-methylimidazolium bis(trifluoro-methylsulfonyl) imide. Incorporation of comonomers having different hydrogen-bonding capacities, acrylic acid and methyl acrylate, is shown to shift the UCST of PNIPAM to higher and lower temperatures, respectively. Relying on the ability to tune the transition temperature through copolymerization along with the wide thermal range afforded by the IL as a solvent, we fabricated a photopatterned self-folding device which shows reversible and sequential bending of three sets of hinges. Such sequential and reversible bending of microactuators offers potential for the design of complex self-folding origami and soft robots.