Effect of protonation on the solvation structure of solute N-butylamine in an aprotic ionic liquid

Significant change in the solvation structure by protonation reaction in the ionic liquid [C₂mIm][TFSA].

Lysozyme Solubility and Conformation in Neat Ionic Liquids and Their Mixtures with Water

The room temperature solubility of a number of model proteins is assessed for a diverse set of neat ionic liquids (ILs). For two soluble protein-IL pairs, lysozyme in [C2MIM][EtSO4] (1-ethyl-3-methylimidazolium ethylsulfate) and in [C2,4,4,4P][Et2PO4] (tributyl(ethyl)phosphonium diethylphosphate), protein solubility and structure at various temperatures are probed by dynamic light scattering (assessing dissolved molecular size), turbidimetry (reflecting degree of solubility), and Fourier transform infrared spectroscopy (uncovering helical secondary structure). As compared to aqueous environments, [C2,4,4,4P][Et2PO4] thermally stabilizes protein size and secondary structure while [C2MIM][EtSO4] does the opposite. Lysozyme denatured in [C2MIM][EtSO4] does not aggregate, presumably due to an absence of hydrophobic interactions, and the denaturation appears thermally reversible. Both ILs at room temperature are miscible with water in all proportions, but to create the corresponding ternary mixtures with protein, the order of mixing is important. Mixed to avoid additions of water to IL-dissolved protein, stable solutions are obtained with [C2MIM][EtSO4] at all solvent compositions. When water is added to IL-rich solutions, liquid-liquid demixing is noted.

Self-Assembly of Polyether Diblock Copolymers in Water and Ionic Liquids

Here the thermoresponsive self-assembly of diblock copolymers comprising poly(ethyl glycidyl ether) (PEGE) and poly(ethylene oxide) (PEO) in water and ionic liquids (ILs) is investigated. PEGE undergoes lower critical solution temperature (LCST) phase separation in both water and 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)amide ([C2 mim][NTf2 ]), while PEO is a compatible segment for these solvents. The diblock copolymers, PEGE-b-PEO, undergo thermosensitive unimer-micelle transitions at temperatures close to the LCST point (TLCST ) of the PEGE homopolymer in water but not in [C2 mim][NTf2 ], even at temperatures much higher than TLCST . The difference in the thermoresponsivity of these solutions is explored using differential scanning calorimetry results from rather small magnitudes of the thermodynamic parameters for the phase transition of the PEGE segment in [C2 mim][NTf2 ], compared with those in water. Due to such small magnitudes, TLCST of the PEGE segment for the block copolymers in the IL is greatly affected by the elongation of soluble PEO segments.

Doubly thermo-responsive copolymers in ionic liquid

We report the behaviour of thermoresponsive block copolymers of n-butyl acrylate and N-alkyl acrylamides in [C2mim][NTf2]. Poly(N-isopropylacrylamide) exhibits an upper critical solution temperature in [C2mim][NTf2] whereas poly(n-butyl acrylate) has a lower critical solution temperature. Consequently, these polymers exhibit double thermo-responsiveness correlated with the macromolecular structure. Moreover, a switching from micellar to reverse micellar structures was induced by a change in temperature. This property enables the development of reversible shuttles between ionic liquids and water.

Structural effect of glyme–Li+ salt solvate ionic liquids on the conformation of poly(ethylene oxide)

Conformation of poly(ethylene oxide) in solvate ionic liquids is affected by the solvent structure.

SANS study on the solvated structure and molecular interactions of a thermo-responsive polymer in a room temperature ionic liquid

We have utilized SANS to quantitatively characterize the LCST-type phase behavior of PPhEtMA in d₈-[C₂mIm⁺][TFSA⁻].

Dissolved chloride markedly changes the nanostructure of the protic ionic liquids propylammonium and ethanolammonium nitrate

The bulk nanostructure of 15 mol% propylammonium chloride (PACl) dissolved in propylammonium nitrate (PAN) and 15 mol% ethanolammonium chloride (EtACl) in ethanolammonium nitrate (EtAN) has been determined using neutron diffraction with empirical potential structure refinement fits.

Adsorption of Polyether Block Copolymers at Silica-Water and Silica-Ethylammonium Nitrate Interfaces

Atomic force microscope (AFM) force curves and images are used to characterize the adsorbed layer structure formed by a series of diblock copolymers with solvophilic poly(ethylene oxide) (PEO) and solvophobic poly(ethyl glycidyl ether) (PEGE) blocks at silica-water and silica-ethylammoniun nitrate (EAN, a room temperature ionic liquid (IL)) interfaces. The diblock polyethers examined are EGE109EO54, EGE113EO115, and EGE104EO178. These experiments reveal how adsorbed layer structure varies as the length of the EO block varies while the EGE block length is kept approximately constant; water is a better solvent for PEO than EAN, so higher curvature structures are found at the interface of silica with water than with EAN. At silica-water interfaces, EGE109EO54 forms a bilayer and EGE113EO115 forms elongated aggregates, while a well-ordered array of spheres is present for EGE104EO178. EGE109EO54 does not adsorb at the silica-EAN interface because the EO chain is too short to compete with the ethylammonium cation for surface adsorption sites. However, EGE113EO115 and EGE104EO178 do adsorb and form a bilayer and elongated aggregates, respectively.

Two-dimensional photonic crystal chemical and biomolecular sensors

We review recent progress in the development of two-dimensional (2-D) photonic crystal (PC) materials for chemical and biological sensing applications. Self-assembly methods were developed in our laboratory to fabricate 2-D particle array monolayers on mercury and water surfaces. These hexagonal arrays strongly forward Bragg diffract light to report on their array spacings. By embedding these 2-D arrays onto responsive hydrogel surfaces, 2-D PC sensing materials can be fabricated. The 2-D PC sensors utilize responsive polymer hydrogels that are chemically functionalized to show volume phase transitions in selective response to particular chemical species. Novel hydrogels were also developed in our laboratory by cross-linking proteins while preserving their native structures to maintain their selective binding affinities. The volume phase transitions swell or shrink the hydrogels, which alter their 2-D array spacings, and shift their diffraction wavelengths. These shifts can be visually detected or spectrally measured. These 2-D PC sensing materials have been used for the detection of many analytes, such as pH, surfactants, metal ions, proteins, anionic drugs, and ammonia. We are exploring the use of organogels that use low vapor pressure ionic liquids as their mobile phases for sensing atmospheric analytes.

Thermoreversible partitioning of poly(ethylene oxide)s between water and a hydrophobic ionic liquid

We describe a poly(ethylene oxide) (PEO) homopolymer "shuttle" between water and a hydrophobic ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMIM][TFSI]). PEO homopolymers with varying molecular weight transferred reversibly and quantitatively between water at room temperature and [EMIM][TFSI] at an elevated temperature. The temperature of the transfer from water to [EMIM][TFSI] shows a linear dependence on PEO molecular weight and a dependence on polymer concentration consistent with expectation based on Flory-Huggins theory. These results are also consistent with the previously observed lower critical solution temperature (LCST) behavior of PEO in water. Dynamic light scattering study of the concentration and temperature dependence of the swelling degree of PEO corona of polybutadiene (PB)-PEO block copolymer micelles indicates that the solvent quality of [EMIM][TFSI] for PEO remains essentially the same as a good solvent over the temperature range of the PEO shuttle. Fundamental understanding of the PEO shuttle is of significance in development of systems for phase transfer of reagents and reaction products between ionic liquids and water.

Solubility of poly(methyl methacrylate) in ionic liquids in relation to solvent parameters

The solubility of poly(methyl methacrylate) (PMMA) in 1-alkyl-3-methylimidazolium ionic liquids (ILs) with different anionic structures has been explored. Nearly monodisperse PMMA-grafted silica nanoparticles (PMMA-g-NPs) were used as a measurement probe for evaluating the PMMA solubility in ILs. The hydrodynamic radius (Rh) of PMMA-g-NPs was measured in the ILs by dynamic light scattering (DLS). Changes in Rh and colloidal stability, that is, the PMMA-solubility change in the ILs, were observed depending on the ionic structures of the ILs. The solubility was mainly affected by the anionic structures of the ILs rather than by the alkyl chain length of the cationic structure. Solvent parameters, including Lewis basicity, solubility parameters, and a hydrophobicity parameter, were used to discuss the change in the PMMA solubility in ILs with different ionic structures. By considering the PMMA solubility in the ILs using these parameters, it was found that there is a good correlation between the PMMA solubility and the hydrophobicity parameter of the anions. Although the change in the PMMA solubility with different cationic structures was not remarkable, the hydrophobicity of the cations also played a role in the solvation of PMMA by providing a low-polarity environment adequate to dissolve PMMA.

Responsive ionic liquid–polymer 2D photonic crystal gas sensors

Responsive polymer–ionic liquid systems that are stable with respect to ambient conditions and capable of detecting gases.

Recent aspects of self-oscillating polymeric materials: designing self-oscillating polymers coupled with supramolecular chemistry and ionic liquid science

Herein, we summarise the recent developments in self-oscillating polymeric materials based on the concepts of supramolecular chemistry, where aggregates of molecular building blocks with non-covalent bonds evolve the temporal or spatiotemporal structure.

Thermoreversible nanogel shuttle between ionic liquid and aqueous phases

We describe a nanogel that can reversibly shuttle between a hydrophobic ionic liquid (IL) phase and an aqueous phase in response to temperature changes. A thermosensitive diblock copolymer, consisting of poly(ethylene oxide) (PEO) as the first segment and a random copolymer of N-isopropylacrylamide (NIPAm) and N-acryloyloxysuccinimide (NAS) as the second segment, was prepared as a nanogel precursor using anionic ring-opening polymerization of EO followed by reversible addition-fragmentation chain-transfer (RAFT) polymerization of NIPAm and NAS. After the micellization of the diblock copolymer in an aqueous solution upon heating to temperatures higher than the lower critical solution temperature (LCST) of the second segment, a coupling reaction of the NAS group of the P(NIPAm-r-NAS) core with ethylenediamine gave a nanogel with a well-solvated PEO corona. The nanogel exhibited contrasting thermosensitivities in the aqueous and IL phases. Dynamic light scattering measurements revealed that the nanogel exhibited LCST phase behavior (low-temperature-swollen/high-temperature-shrunken) in the aqueous phase and the opposite upper critical solution temperature (UCST) phase behavior (high-temperature-swollen/low-temperature-shrunken) in hydrophobic ILs. The nanogel favored the aqueous phase at low temperatures and the IL phase at high temperatures because of the solubility changes in the PEO corona. Upon increasing the temperature, the nanogel underwent a swollen-to-shrunken phase change in the aqueous phase, a transfer from the aqueous phase to the IL phase, and a shrunken-to-swollen phase change in the IL phase. These processes were thermally reversible, which made the round-trip shuttling of the nanogel between the aqueous and IL phases possible.

Formation of heterogeneous polymer films via simultaneous or sequential depositions of soluble and insoluble monomers onto ionic liquids

In this paper, we studied the formation of heterogeneous polymer films on ionic liquid (IL) substrates via the simultaneous or sequential depositions of monomers that are either soluble or insoluble in the liquid. We found that the insoluble monomer 1H,1H,2H,2H-perfluorodecyl acrylate (PFDA) only polymerizes at the IL surface, while the soluble monomer ethylene glycol diacrylate (EGDA) can polymerize at both the IL surface and within the bulk liquid. The polymer chains that form within the bulk liquid entrap IL as they integrate into the polymer film formed at the IL surface, resulting in heterogeneous films that contain IL on the bottom side. Varying the order in which the soluble and insoluble monomers were introduced into the system led to different film structures. When the insoluble monomer was introduced first, a film formed at the surface and the soluble monomer then diffused through this film and polymerized within the bulk, leading to a sandwich structure. When the soluble monomer was introduced first, a layered film was formed whose structure followed the order in which the monomers were introduced. When the two monomers were introduced simultaneously, the soluble monomer polymerized in the bulk while a copolymer film formed at the surface. This study provides an understanding of how to control the composition of layered polymer films deposited onto IL substrates in order to develop new composite materials for separation and electrochemical applications.

Solvent nanostructure, the solvophobic effect and amphiphile self-assembly in ionic liquids

The ability of ionic liquids (ILs) to support amphiphile self-assembly into a range of mesophase structures has been established as a widespread phenomenon. From the ILs evaluated as self-assembly media, the vast majority have supported some lyotropic liquid crystal phase formation. Many neat ionic liquids have been shown to segregate into polar and non-polar domains to form a nanostructured liquid. A very strong correlation between the nanostructure of the ionic liquid and its characteristics as an amphiphile self-assembly solvent has been found. In this review we discuss ionic liquids as amphiphile self-assembly media, and identify trends that can be used to distinguish which ionic liquids are likely to have good promotion properties as self-assembly media. In particular these trends focus on the nanostructure of neat ionic liquids, their solvent cohesive energy density, and the related solvophobic effect. We forecast that many more ILs will be identified as amphiphile self-assembly solvents in the future.

Conductivity and Solvation Dynamics in Ionic Liquids

It was shown recently that a simple dielectric continuum model predicts the integral solvation time of a dipolar solute ⟨τsolv⟩ to be inversely proportional to the electrical conductivity σ0 of an ionic solvent or solution. In this Letter, we provide a more general derivation of this connection and show that available data on coumarin 153 (C153) in ionic liquids generally support this prediction. The relationship between solvation time and conductivity can be expressed by ln(⟨τsolv⟩/ps) = 4.37 - 0.92 ln (σ0/S m(-1)) in 34 common ionic liquids.

Chemical propulsion using ionic liquids

Chemical propulsion generates motion by directly converting locally stored chemical energy into mechanical energy. Here, we describe chemically driven autonomous motion generated by using imidazolium-based ionic liquids on a water surface. From measurements of the driving force of a locomotor loaded with an ionic liquid and observations of convection on the water surface originating from the ionic liquid container of the locomotor, the driving mechanism of the motion is found to be due to the Marangoni effect that arises from the anisotropic distribution of ionic liquids on the water surface. The maximum driving force and the force-generation duration are determined by the surface activity of the ionic liquid and the solubility of the ionic liquid in water, respectively. Because of the special properties of ionic liquids, a chemical locomotor driven by ionic liquids is promising for realizing autonomous micromachines and nanomachines that are safe and environmentally friendly.