We demonstrate that Li + hopping conduction, which cannot be explained by conventional models i.e., Onsager's theory and Stokes' law, emerges in highly concentrated liquid electrolytes composed of LiBF 4 and sulfolane (SL). Self-diffusion coefficients of Li + (D Li ), BF 4 − (D BF 4 ), and SL (D SL ) were measured with pulsed-field gradient NMR. In the concentrated electrolytes with molar ratios of SL/LiBF 4 ≤ 3, the ratios D SL /D Li and D BF 4 /D Li become lower than 1, suggesting faster diffusion of Li + than SL and BF 4 − , and thus the evolution of Li + hopping conduction. X-ray crystallographic analysis of the LiBF 4 /SL (1:1) solvate revealed that the two oxygen atoms of the sulfone group are involved in the bridging coordination of two different Li + ions. In addition, the BF 4 − anion also participates in the bridging coordination of Li + . The Raman spectra of the highly concentrated LiBF 4 −SL solution suggested that Li + ions are bridged by SL and BF 4 − even in the liquid state. Moreover, detailed investigation along with molecular dynamics simulations suggests that Li + exchanges ligands (SL and BF 4 − ) dynamically in the highly concentrated electrolytes, and Li + hops from one coordination site to another. The spatial proximity of coordination sites, along with the possible domain structure, is assumed to enable Li + hopping conduction. Finally, we demonstrate that Li + hopping suppresses concentration polarization in Li batteries, leading to increased limiting current density and improved rate capability compared to the conventional concentration electrolyte. Identification and rationalization of Li + ion hopping in concentrated SL electrolytes is expected to trigger a new paradigm of understanding for such unconventional electrolyte systems.

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.

The tacticity effect on phase separation process of poly(N-isopropylacrylamide) (PNiPAM) aqueous solutions was investigated by dynamic light scattering (DLS) and small angle neutron scattering (SANS) measurements. SANS measurement revealed that hydrophobicity of PNiPAM consisting of meso- and racemo-isomers increased with increasing the meso-content. This result is in accordance with the result of the previous experimental and simulation study on NiPAM dimers (DNiPAM) and trimers (TNiPAM) [ Katsumoto Y Katsumoto Y J. Phys. Chem. B20101141331213318, and Autieri E. Autieri E. J. Phys. Chem. B201111558275839]; i.e., meso-diad is more hydrophobic than racemo-diad. In addition, a series of scattering experiments revealed that the ratio of meso-diad does not affect the static structure or the shrinking behavior of a single chain, but strongly affects the aggregation behavior. The PNiPAMs with low meso-content suddenly associate around the phase separation temperature, while that of the high meso-content gradually aggregate with increasing temperature. We propose that phase transition behavior of PNiPAM aqueous solutions can be controlled by changing the stereoregularity of the polymer chain.

We report a high-toughness ion gel with a nearly ideal polymer network prepared in an imidazoliumbased aprotic ionic liquid (aIL) with a controlled solution pH. We formed the ion gel from tetra-armed poly(ethylene glycol) (TetraPEG), i.e., an A−B-type cross-end coupling reaction of two different TetraPEG prepolymers. To complete this A−Btype reaction, we needed to optimize the reaction rate such that the two TetraPEGs were mixed homogeneously, which strongly depends on the pH or [H + ] in the aIL solution. To control solution pH, we established a "pH-buffering IL" by adding an imidazolium-based protic IL (as a proton source) and its conjugated base to the solvent aIL. We demonstrated that the pH-buffering IL exhibits a successful pH-buffering effect to maintain a constant pH (≈16.2, apparent value) during the gelation reaction. From a kinetic study, we found that the gelation reaction undergoes a simple second-order reaction of the two TetraPEGs in the pH-buffering IL. The gelation rate constant, k gel , in the present ion gel system was 2 orders of magnitude smaller than that in the corresponding hydrogel system, which is ascribed to the difference in the activation entropy, ΔS ‡ , of the cross-end coupling reactions. The reaction efficiency at the cross-linking point was experimentally estimated to be 92% by spectroscopic measurements. We thus conclude that a nearly ideal polymer network was formed in the pH-buffering IL system. This is reflected in the excellent mechanical property of the ion gel, even at a low polymer content (=6 wt %).

Ion gels consisting of poly(ethylene glycol) (PEG) network and ionic liquids were synthesized via Michael addition reaction using tetra-arm PEG (tetra-PEG) precursors with amino groups and maleimide groups at the chain ends. The use of the addition reaction to synthesize the tetra-PEG networks ensures that any byproducts, which may influence the electrochemical properties of the obtained gel, are not released in the reaction system. Fourier transform infrared (FT-IR) spectra, gel fraction, and rheological measurements indicated the progress of the addition reaction. A polymer network started to be formed after 2 h when the two tetra-PEG precursors were mixed in an ionic liquid at polymer concentrations above overlap concentration (= 7.2 wt %). From tensile test, the elastic modulus of the ion gel was estimated to be lower than that of conventional hydrogel, indicating some flaws in the network. Compared with the theoretical elastic modulus for tetra-PEG network, the reaction efficiency of the tetra-PEG ion gel (10 wt %) using the Michael addition reaction was ca. 80%, which was lower than that of conventional hydrogels using condensation reaction (ca. 90%). However, a Mooney−Rivlin plot of the ion gel indicates that the polymer network has few loop chains and entanglements and relatively homogeneous structure. The fracture energy of the tetra-PEG ion gels (10 wt %) was more than 30 times higher than that of a 30 wt % PMMA ion gel prepared by conventional free radical polymerization. The improved strength of the tetra-PEG ion gel was caused by relatively few structural defects. Polymer actuators were fabricated using the tetra-PEG ion gel as an electrolyte layer by sandwiching the gel between two carbon electrodes. The tetra-PEG ion gel actuators showed greater durability than a PMMA ion gel actuator.

The transport properties of ionic liquid (IL)/sulfonated polyimide (SPI) composite membranes for CO2 separation were explored in relation to their nanostructures. 1-Butyl-3-methyl­imidazolium bis­(trifluoromethane­sulfonyl)­amide ([C4mim]­[NTf2]), 1-butyl-3-methyl­imidazolium hexafluoro­phosphate ([C4mim]­PF6), and 1-butyl-1-methyl­pyrrolidinium bis­(trifluoromethane­sulfonyl)­amide ([P14]­[NTf2]) were selected as the ILs. These composite membranes enable favorable CO2 separation and superior mechanical properties. SPI is plasticized by the IL, which induces a decrease in the elastic modulus; however, due to the formation of bicontinuous nanostructures of IL-rich and SPI-rich phases, a modulus of >10 MPa is retained even with the incorporation of 75 wt % IL. [C4mim]­[NTf2] and [C4mim]­PF6 exhibit stronger plasticization effects on SPI than [P14]­[NTf2]. The diffusion coefficients of CO2 and N2, which were measured by the time-lag method, abruptly increase with increasing IL content in the [C4mim]­[NTf2]/SPI composite membranes, which coincided with a change from an isolated to a continuous IL-rich phase structure. On the other hand, the selective solubility of CO2 in the [C4mim]­[NTf2]/SPI composite membranes exhibits no relation with the IL content. Consequently, the permeation coefficient (P CO2 ) of the membranes increases with increasing IL content without decreasing the separation factor (αCO2/N2 ), showing P CO2 = 431 barrer and αCO2/N2 = 30 at 30 °C.

A high-performance CO 2 separation membrane consisting of an ion gel has been prepared. The tetra-armed poly(ethylene glycol) ion gel contains a large fraction of ionic liquid (94 wt %) and shows excellent CO 2 permselectivity over a wide temperature range, up to 100°C. We also demonstrate that the ion gel can absorb CO 2 without solvent seeping at a high pressure of 3 MPa.Room-temperature ionic liquids (ILs) have been widely applied to electrochemical, synthetic, and separation processes as green solvents due to their unique properties such as nonvolatility, nonflammability, good thermal stability, and high ionic conductivity. ILs are recognized as designable solvents, and their structural diversity enables us to control their solvent properties, for example, the miscibility with various chemicals such as metal ions, synthesized and biological polymers, and acidic gases. In the last decade, CO 2 absorption and separation technologies using ILs have attracted much attention, because CO 2 is highly soluble in ILs relative to other neutral gases like N 2 , H 2 , and CH 4 . A large number of investigations have been performed until now to improve the CO 2 absorption properties since the first report on the high solubility of CO 2 in the dialkylimidazolium-based IL.1 A membrane separation process generally requires smaller operational energy, lower running cost, and smaller equipment footprint compared with an absorption process. The supported IL membranes (SILMs), i.e., polymeric or inorganic porous materials filled with ILs, show comparable or higher permeabilities and selectivities of CO 2 than conventional polymeric membranes.2 SILMs have a higher long-term stability than supported membranes with organic solvents, because of nonvolatility and high thermal stability of ILs. However, SILMs cannot hold ILs under pressurized conditions, which is a serious disadvantage for the gas separation membrane. Polymeric ILs, i.e., self-crosslinking ILs were also applied as CO 2 separation membranes.3 However, it was pointed out that their separation performances are inferior to those of the SILMs due to the limited CO 2 diffusion in their rigid polymer matrix. Therefore, ion gels with a low polymer content and/or a high fraction of "free" IL content are more favorable materials for CO 2 separation membrane.Recently, some research groups reported the CO 2 separation performances of ion gels with relatively low polymer contents. . They also reported a high-toughness ion gel with 10 wt % triblock copolymer, which was prepared by crosslinking reactions in the IL. 5 The electrical conductivity is about 2/3 that of the neat IL because the ionic mobility is obstructed by the nonconductive part in their ion gel. Kamio et al.4d reported a CO 2 N 2 separation membrane using poly(vinylpyrrolidone)-based ion gels containing 5070 wt % amino acid IL, and the ion gel shows a compression breaking stress of 1 MPa at 70 wt % IL content. They demonstrated that both CO 2 permeability and selectivity are significantly improved with increasing IL ...

We report a new approach for investigating polymer structures in solution systems, including polymer–solvent interactions at the molecular level. The solvation structure of poly­(benzyl methacrylate) (PBnMA) in an imidazolium-based ionic liquid (IL) has been investigated at the molecular level using high-energy X-ray total scattering (HEXTS) with the aid of all-atom molecular dynamics (MD) simulations. The X-ray radial distribution functions derived from both experimental HEXTS and theoretical MD (G exp(r) and G MD(r), respectively) were in good agreement in the present PBnMA/IL system. The G(r) functions were successfully separated into two components for the inter- and intramolecular contributions. Here, the former corresponds to polymer solvation (or polymer–solvent interactions) and the latter to polymer structure, such as conformation and interactions between side chains (benzyl groups) in PBnMA. The intermolecular G MD inter(r) revealed that the side chains are preferentially solvated by imidazolium cations rather than anions. On the other hand, the intramolecular G MD intra(r) suggested that PBnMA is also stabilized by interactions among the aromatic side chains (π–π stacking). Thus, polymer (benzyl group)–cation interactions and benzyl group stacking within a PBnMA chain coexist in the PBnMA/IL system to give a more ordered solution structure. This behavior might be ascribed to negative mixing entropy in the solution state, which is key to the lower critical solution temperature (LCST)-type phase behavior in the PBnMA/IL solutions.