RESUMO
Electret materials with high deformability largely extend their applications such as wearable devices and actuators. Meanwhile, the deformability of currently reported electrets is somewhat limited except for a liquid electret that requires synthetic procedures with relatively low product yield. Here, we report a polymer-based electret with infinite deformability, which is simply prepared by corona-discharging on the mixture of two commercially available polymers, i.e., polybutenes (PB) as a liquid polyolefin and polypropylene-graft-maleic anhydride (MPP) as a solute. The charge retention mechanism of the PB/MPP electret was both experimentally and computationally elucidated from the views of molecular and nanoscale structures, and transport properties. Contrary to the ease of the preparation, the charge retention mechanism was complicated. The results of quantum chemical calculations and X-ray scattering indicated that the succinic anhydride polar moieties in MPP act as a charge trap site while how they distribute in the non-polar matrix also matters. Transport property measurements revealed the strong connection between complex viscosity and the relaxation time of the charge decay of the PB/MPP electret. Finally, we fabricated a simple piezoelectric device consisting of the PB/MPP electret. It was demonstrated that the piezoelectric performance of the PB/MPP electret is comparable to that of a conventional solid electret.
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We investigated nano-structural changes of cellulose dissolved in 1-ethyl-3-methylimidazolium acetate-an ionic liquid (IL)-using a small angle X-ray scattering (SAXS) technique over the entire concentration range (0-100 mol %). Fibril structures of cellulose disappeared at 40 mol % of cellulose, which is a significantly higher concentration than the maximum concentration of dissolution (24-28 mol %) previously determined in this IL. This behavior is explained by the presence of the anion bridging, whereby an anion prefers to interact with multiple OH groups of different cellulose molecules at high concentrations, discovered in our recent work. Furthermore, we observed the emergence of two aggregated nano-structures in the concentration range of 30-80 mol %. The diameter of one structure was 12-20 nm, dependent on concentration, which is ascribed to cellulose chain entanglement. In contrast, the other with 4.1 nm diameter exhibited concentration independence and is reminiscent of a cellulose microfibril, reflecting the occurrence of nanofibrillation. These results contribute to an understanding of the dissolution mechanism of cellulose in ILs. Finally, we unexpectedly proposed a novel cellulose/IL composite: the cellulose/IL mixtures of 30-50 mol % that possess liquid crystallinity are sufficiently hard to be moldable.
Assuntos
Celulose/química , Imidazóis/química , Líquidos Iônicos/química , Nanoestruturas/química , Tamanho da Partícula , Espalhamento a Baixo ÂnguloRESUMO
Ionic liquids with cationic organosilicon groups have been shown to have a number of useful properties, including reduced viscosities relative to the homologous cations with hydrocarbon substituents on the cations. We report structural and dynamical properties of four ionic liquids having a trimethylsilylpropyl functional group, including 1-methyl-3-trimethylsilylpropylimidazolium (Si-C3-mim+) cation paired with three anions: bis(fluorosulfonyl)imide (FSI-), bis(trifluoromethanesulfonyl)imide (NTf2-), and bis(pentafluoroethanesulfonyl)imide (BETI-), as well as the analogous N-methyl-N-trimethylsilylpropylpyrrolidinium (Si-C3-pyrr+) cation paired with NTf2-. This choice of ionic liquids permits us to systematically study how increasing the size and hydrophobicity of the anions affects the structural and transport properties of the liquid. Structure factors for the ionic liquids were measured using high energy X-ray diffraction and calculated from molecular dynamics simulations. The liquid structure factors reveal first sharp diffraction peaks (FSDPs) for each of the four ionic liquids studied. Interestingly, the domain size for Si-C3-mim+/NTf2- indicated by the maxima for these peaks is larger than for the more polar ionic liquid with a similar chain length, 1-pentamethyldisiloxymethyl-3-methyl-imidazolium bis(trifluoromethanesulfonyl)imide (SiOSi-mim+/NTf2-). For the series of Si-C3-mim+ ionic liquids, as the size of the anion increases, the position of FSDP indicates that the intermediate range order domains decrease in size, contrary to expectation. Diffusivities for the anions and cations are compared for a series of both hydrocarbon-substituted and silicon-substituted cations. All of the anions show the same scaling with temperature, size, and viscosity, while the cations show two distinct trends-one for hydrocarbon-substituted cations and another for organosilicon-substituted cations, with the latter displaying increased friction.
RESUMO
We report the results of a comprehensive (81)Br NMR spectroscopic study of the structure and dynamics of two room temperature ionic liquids (RTILs), 1-butyl-3-methylimidazolium bromide ([C(4)mim]Br) and 1-butyl-2,3-dimethylimidazolium bromide ([C(4)C(1)mim]Br), in both liquid and crystalline states. NMR parameters in the gas phase are also simulated for stable ion pairs using quantum chemical calculations. The combination of (81)Br spin-lattice and spin-spin relaxation measurements in the motionally narrowed region of the stable liquid state provides information on the correlation time of the translational motion of the cation. (81) Br quadrupolar coupling constants (C(Q)) of the two RTILs were estimated to be 6.22 and 6.52 MHz in the crystalline state which were reduced by nearly 50% in the liquid state, although in the gas phase, the values are higher and span the range of 7-53 MHz depending on ion pair structure. The C(Q) can be correlated with the distance between the cation-anion pairs in all the three states. The (81)Br C(Q) values of the bromide anion in the liquid state indicate the presence of some structural order in these RTILs, the degree of which decreases with increasing temperature. On the other hand, the ionicity of these RTILs is estimated from the combined knowledge of the isotropic chemical shift and the appropriate mean energy of the excited state. [C(4)C(1)mim]Br has higher ionicity than [C(4)mim]Br in the gas phase, while the situation is reverse for the liquid and the crystalline states.
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R(+)-α-lipoic acid (RALA) is a naturally-occurring substance, and its protein-bound form plays significant role in the energy metabolism in the mitochondria. RALA is vulnerable to a variety of physical stimuli, including heat and UV light, which prompted us to study the stability of its complexes with cyclodextrins (CDs). In this study, we have prepared and purified a crystalline RALA-αCD complex and evaluated its properties in the solid state. The results of ¹H NMR and PXRD analyses indicated that the crystalline RALA-αCD complex is a channel type complex with a molar ratio of 2:3 (RALA:α-CD). Attenuated total reflection/Fourier transform infrared analysis of the complex showed the shift of the C=O stretching vibration of RALA due to the formation of the RALA-αCD complex. Raman spectroscopic analysis revealed the significant weakness of the S-S and C-S stretching vibrations of RALA in the RALA-αCD complex implying that the dithiolane ring of RALA is almost enclosed in glucose ring of α-CD. Extent of this effect was dependent on the direction of the excitation laser to the hexagonal morphology of the crystal. Solid-state NMR analysis allowed for the chemical shift of the C=O peak to be precisely determined. These results suggested that RALA was positioned in the α-CD cavity with its 1,2-dithiolane ring orientated perpendicular to the plane of the α-CD ring.
Assuntos
Ácido Tióctico/química , alfa-Ciclodextrinas/química , Cristalização , Espectroscopia de Ressonância Magnética , Microscopia Eletrônica de Varredura , Espectroscopia de Infravermelho com Transformada de Fourier , Análise Espectral Raman , Difração de Raios XRESUMO
The excited-state intramolecular proton transfer (ESIPT) reaction of 4'-N,N,-diethylamino-3-hydroxyflavone (C2HF) was studied using time-resolved fluorescence measurements in ionic liquids (ILs) of various anions with a fixed cation (1-ethyl-3-methylimidazolium [C2mim]+). C2HF showed an ESIPT reaction from the normal excited state (N*; keto form) to the tautomer excited state (T*; enol form) where both states are emissive. The ESIPT rate and yield were obtained by analyzing the time-resolved fluorescence spectra measured using the optical Kerr gate method. Both the ESIPT rate and yield decreased with increasing hydrogen-bond accepting ability of the anion. According to density functional theory calculations, the complex formation energy between C2HF and the anion became significantly negative with increasing the hydrogen-bond accepting ability of anion. The pseudoequilibrium constant between N* and T* ([T*]/[N*]) in the electronic excited state decreased with increasing hydrogen-bond accepting ability of the anion, while it increased with increasing the alkyl-chain length of alkyl sulfonate. The excitation wavelength dependence of the ESIPT rate and yield was studied for C2HF in [C2mim][C6H13SO3]. The ESIPT yield decreased by nearly a factor of 2 with increasing excitation wavelength from 360 to 425 nm, although the change in the ESIPT rate was small. The solvation heterogeneity due to the alkyl chain in the anion was considered to be the reason for the excitation wavelength dependence.
RESUMO
Translational diffusion coefficients of carbon monoxide (CO), diphenylacetylene (DPA), and diphenylcyclopropenone (DPCP) were determined in mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate ([C4mim]BF4) and water using transient grating spectroscopy at different mole fractions of water (xw). While DPA exhibited a larger diffusion coefficient than DPCP at low water mole fractions (xw < 0.7), as observed for conventional liquids and ionic liquids (ILs), it was smaller at high mole fractions (xw > 0.9). The apparent molecular radius of DPA determined using the Stokes-Einstein equation at xw > 0.9 is close to the radius of an IL cluster in a water pool as determined from small-angle neutron scattering experiments (J. Bowers et al., Langmuir, 2004, 20, 2192-2198), suggesting that the DPA molecules are trapped in IL clusters in the water pool and move together. The solvation state of DPCP in the mixture was studied using Raman spectroscopy. Dramatically strong water/DPCP hydrogen bonding was observed at higher water mole fractions, suggesting that DPCP is located near the cluster interfaces. The large diffusion coefficient of DPCP suggests that hopping of DPCP between IL clusters occurs through hydrogen bonding with water.
RESUMO
Ionic liquids (ILs) are salts with an extremely low melting point. Substantial efforts have been made to address their low melting point from the enthalpic standpoint (i.e. interionic interactions). However, this question is still open. In this study, we report our findings that entropic (large fusion entropy), rather than enthalpic, contributions are primarily responsible for lowering the melting point in many cases, based on a large thermodynamic dataset. We have established a computational protocol using molecular dynamics simulations to decompose fusion entropy into kinetic (translational, rotational, and intramolecular vibrational) and structural (conformational and configurational) terms and successfully applied this approach for two representatives of ILs and NaCl. It is revealed that large structural contribution, particularly configurational entropy in the liquid state, plays a deterministic role in the large fusion entropy and consequently the low melting point of the ILs.
RESUMO
We investigated the rotational dynamics of two imidazolium-based ionic liquids, 1-butyl-3-methylimidazolium bromide ([C(4)mim]Br) and 1-butyl-2,3-dimethylimidazolium bromide ([C(4)C(1)mim]Br), to reveal the effects of methylation at position 2 of the imidazolium ring (C(2) methylation). The rotational correlation time (τ(local)) for each carbon in the cations is derived from the spin-lattice relaxation time of (13)C nuclear magnetic resonance. The τ(local) results obtained here provide three principle insights into the rotational dynamics of ionic liquids. First, all τ(local) values for [C(4)C(1)mim]Br are greater than those for [C(4)mim]Br owing to a viscosity increase due to C(2) methylation. Second, the rate of change in τ(local) on C(2) methylation differs among the carbons in the cation, which indicates that each carbon has a different microviscosity. Third, the τ(local) increase in the (13)C at the root of the butyl group on C(2) methylation is very small compared to both intuitive prediction and the results from quantum chemical calculations. This indicates that the motion of the butyl group root in [C(4)C(1)mim]Br is not significantly inhibited by the methyl group at the position 2 of the imidazolium ring. The finding provides conclusive information on the origin of the increases in the melting point on C(2) methylation. Hunt previously found through calculation that decreases in entropy are caused by two factors, namely, reductions in the rotational mobility of the butyl group and in the number of stable anion interaction sites with C(2) methylation, resulting in an increase in melting point and viscosity. Our finding experimentally illustrates that the origin of the increases in melting point is not the inhibition of butyl group motion and that the reduction in stable anion interaction sites plays a major role in the increases. Additionally, it is suggested that the viscosity increase on C(2) methylation can be interpreted in the same manner.
Assuntos
Imidazóis/química , Líquidos Iônicos/química , Termodinâmica , Cátions/química , Espectroscopia de Ressonância Magnética , Metilação , RotaçãoRESUMO
The excited-state intramolecular proton transfer (ESIPT) of 4'-N,N-dialkylamino-3-hydroxyflavone (CnHF) having different alkyl chain lengths (ethyl, butyl, and octyl chains) was investigated in ionic liquids (ILs) by steady-state fluorescence and transient absorption spectroscopy. Upon photoexcitation, CnHF underwent ESIPT from the normal form to the tautomer form, and dual emissions from both states were detected. For C4HF and C8HF, the tautomerization yields determined from the fluorescence intensity ratios increased with the increasing number of alkyl chain carbon atoms in the cation and on reducing the excitation wavelength as reported for C2HF [K. Suda et al., J. Phys. Chem. B. 117, 12567 (2013)]. The transient absorption spectra of CnHF were measured at excitation wavelengths of 360, 400, and 450 nm. The ESIPT rate determined from the induced emission of the tautomer was correlated with the tautomerization yield for C2HF and C4HF. In addition, the recovery of the ground-state bleach was found to be strongly dependent on the excitation wavelength. This result indicates that the solvated state of the molecule before photoexcitation is dependent on the excitation wavelengths. The time constant for the ground-state relaxation was slower than that for the excited state.
RESUMO
Non-flammable and highly concentrated electrolyte solutions were designed using tris(2,2,2-trifluoroethyl) phosphate (TFEP) as a main solvent toward a radical improvement in the safety and energy density of lithium-ion batteries. Unlike conventional carbonate ester-based solutions, simple TFEP-based electrolyte solutions were not intrinsically compatible with 5â V-class LiNi0.5 Mn1.5 O4 positive electrodes, even at high concentrations. Based on the degradation mechanism that was analyzed by Raman spectroscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy, a fluorinated diluent of methyl 3,3,3-trifluoropropionate (FMP) was introduced to suppress the decomposition of LiBF4 and TFEP at high potentials. A nearly saturated LiBF4 /TFEP+FMP electrolyte solution with a specific composition improved the charge and discharge performance of a LiNi0.5 Mn1.5 O4 electrode, and the solution structure was studied by pulsed-field-gradient NMR spectroscopy.
RESUMO
The rotational dynamics of carbon monoxide (CO) in ionic liquids (ILs) was investigated by nuclear magnetic resonance (NMR) relaxation measurements and molecular dynamics (MD) simulations. NMR spin-lattice relaxation time measurements were performed for 17O-enriched CO in 10 ILs (four imidazolium-cation-based, four phosphonium-cation-based, and two ammonium-cation-based ILs, all paired with the bis(trifluorosulfonylmethane)imide anion). In combination with previously reported data for five ILs and viscosity data, our results indicated that the obtained rotational relaxation times (τ2R) were much smaller than those predicted using the Stokes-Einstein-Debye (SED) theory. For the same viscosity/temperature values, the τ2R-1 value increased linearly with increasing carbon number of the alkyl group in the cation. The deviation from the SED equation was due to the insensitivity of τ2R to the carbon number, even though a higher carbon number generally leads to higher viscosity values for ILs. To investigate the unique rotational properties of CO in the ILs, MD simulations were performed on five representative ILs (two imidazolium, two phosphonium, and one ammonium) containing CO solutes. From rotational correlation function analyses, the CO rotation mainly occurred in a free rotation-like manner within 1 ps, which explained the relative insensitivity of CO rotation to viscosity. In the subsequent time scale (>1 ps), the minor component of the CO rotation was discriminated among different ILs. It was strongly suggested that, because CO preferably locates in the outer part of the alkyl groups in the cation, the slow CO rotation is correlated with the outer alkyl dynamics, which are decoupled from the whole cation rotation.
RESUMO
Most ionic liquids (ILs) are characterized by the presence of some kind of isomer for component ions. We investigated the liquid and crystalline structures of 1-isopropyl-3-methylimidazolium halides ([i-C3mim]X, X = Br, I) by means of Raman scattering measurements backed up by density functional theory (DFT) calculations. The DFT calculations indicated that there are two stable rotational isomers of [i-C3mim](+), one of an asymmetric form (Asym) and the other a symmetric one (Sym). For both salts, it was revealed that Asym and Sym coexist in liquid states, in contrast to the presence of only Asym in crystalline states. We determined the isomer populations and showed that Asym is dominant in the liquid states of both salts (approximately 7/3). Conformational changes in [i-C 3mim](+) during the crystallizing and melting processes were observed by conducting simultaneous measurements using the techniques of Raman spectroscopy and calorimetry. We have revealed that the conformational change from Asym to Sym occurs gradually, with linking to melting in the premelting region. This is a conclusive observation of the structural changes of ILs in the premelting region and demonstrates the conformational changes between isomers during the crystallizing and melting processes.
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Cellulose triacetate was synthesised by the transesterification reaction of mild acid-pretreated lignocellulosic biomass with a stable acetylating reagent (isopropenyl acetate, IPA) in an ionic liquid (1-ethyl-3-methylimidazolium acetate, EmimOAc) which enabled the dissolution of lignocellulose as well as the organocatalytic reaction. The homogeneous acetylation of pretreated sugar-cane bagasse was carried out under mild conditions (80 °C, 30 min), and the subsequent reprecipitation processes led to enriched cellulose triacetate with a high degree of substitution (DS; 2.98) and glucose purity (â¼90%) along with production of lignin acetate.
RESUMO
High loading of cellulose in ionic liquid (IL) pretreatment is potentially a key technique for cellulose conversion to glucose in biorefining. In this work, to expand the potential use of this high loading technique, the accessibility of microcrystalline cellulose pretreated with an IL across a wide cellulose loading range (5-50mol%) and its relationship with the hydrolytic reactivity were comprehensively investigated. The results show that the estimated cellulose accessibility based on the crystallinity and specific surface area was notably higher in 25mol% loading than that for a conventional loading of 5mol%. Consistently, acid-catalyzed glucose conversion was faster at this high loading, showing that a higher cellulose loading improves the pretreatment efficiency. In contrast, enzymatic hydrolysis was not enhanced by a high cellulose loading. A key difference between the activities in these two hydrolytic reactions is the catalyst size.
RESUMO
We performed structural investigations of cellulose mixed with 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]) in the entire concentration range (0-100 mol %) by wide-angle X-ray scattering with the aid of quantum chemical calculations and 13C solid-state NMR spectroscopy. We particularly focused on a highly concentrated region (≥30 mol %), which has previously been overlooked. At concentrations of 15-30 mol %, a periodic peak corresponding to cellulose chain alignment emerged; this is associated with a lyotropic cholesteric liquid-crystalline phase. At concentrations of ≥30 mol %, the structure is transformed into ordered layers where OAc anions and Emim cations intercalate. This transformation is found to be driven by a change in the interaction between the IL anions and the OH groups of cellulose. At low concentrations, the anion mainly interacts with the OH group of cellulose in a 1:1 ratio, as previously reported; at high concentrations, the anions bridge the OH groups of two cellulose chains.
RESUMO
The flexibility and conformational variety of the butyl group in cations of ionic liquids (ILs) play an important role in dictating the macroscopic and microscopic properties of ILs. Here we calculate potential energy surfaces for the dihedral angles of the butyl group in four different types of cyclic cations, imidazolium, pyridinium, pyrrolidinium, and piperidinium, using the density functional theory method. The calculation results highlight the role of the butyl group in these cations by comparison of five-membered and six-membered rings, and of aromatic and alicyclic rings, in terms of stable conformations and rotational barriers. A striking result is that the butyl group rotation in pyrrolidinium induces pseudorotation of the ring whereas such a phenomenon does not occur in piperidinium. This difference is thought to be because of the relationship in rotational activation energy between the butyl group (10-40 kJ mol-1) and the ring (<6 kJ mol-1 for pyrrolidinium and 40-50 kJ mol-1 for piperidinium). The calculated stable conformers are compared with the ones observed in crystals recorded in the Cambridge Structural Database. Although conformers with lower calculated energy generally have higher chances to be experimentally observed, roughly independent of the cation structure, some calculated conformers deviate from this trend and show very low population. It is found that not only low energy but also high rotational activation energy (i.e., long lifetime) is required to observe conformers in crystalline states. In the last part of this article, to identify conformers in real systems, the applicability of the calculated Raman bands of cations with different butyl group conformations is discussed.
RESUMO
Choline acetate (ChOAc), a cholinium ionic liquid (IL), was compared with 1-ethyl-3-methylimidazolium acetate (EmimOAc) with regard to biomass pretreatment, inhibition on cellulase and yeast, residuals in pretreated biomass, and saccharification and fermentation of pretreated biomass. Irrespective of ChOAc and EmimOAc, cellulose and hemicellulose saccharification of the IL-pretreated bagasse were over 90% and 60%, respectively. Median effective concentrations (EC50) based on cellulase activity were 32 wt% and 16 wt% for ChOAc and EmimOAc, respectively. The EC50 based on yeast growth were 3.1 wt% and 0.3 wt% for ChOAc and EmimOAc respectively. The residuals in IL-pretreated bagasse were 10% and 23% for ChOAc and EmimOAc, respectively, when washed 2 times after pretreatment. Ethanol yield on a bagasse basis were 60% and 24% for ChOAc and EmimOAc, respectively, in the saccharification and fermentation of IL-pretreated bagasse when washed 2 times. ChOAc-pretreated bagasse could be saccharified and fermented with fewer wash times than EmimOAc-pretreated bagasse.
Assuntos
Metabolismo dos Carboidratos/efeitos dos fármacos , Celulose/química , Etanol/metabolismo , Fermentação/efeitos dos fármacos , Imidazóis/farmacologia , Líquidos Iônicos/farmacologia , Eliminação de Resíduos Líquidos/métodos , Biomassa , Celulase/metabolismo , Celulose/metabolismo , Saccharomyces cerevisiae/citologia , Saccharomyces cerevisiae/efeitos dos fármacos , Saccharomyces cerevisiae/metabolismoRESUMO
Choline acetate (ChOAc), a cholinium ionic liquid (IL), showed almost the same bagasse pretreatment capability as 1-ethyl-3-methylimidazolium acetate (EmimOAc), a conventional imidazolium IL used for biomass pretreatment. Moreover, ChOAc showed less of an inhibitory effect on cellulase than EmimOAc. Thus, ChOAc was used for IL/ultrasound-assisted pretreatment and in situ enzymatic saccharification, where IL was not washed out from the pretreated bagasse but diluted with the addition of a buffer solution. When in situ saccharification was performed for 48h in the presence of 10% ChOAc, the cellulose and hemicellulose saccharification percentages were 80% and 72%, respectively. When ChOAc was increased to 20%, the saccharification percentages were 72% and 53%, respectively. However, the values were just 28% and 2%, respectively, in case of 20% EmimOAc. A glucose/xylose solution free from IL and ChOAc aqueous solution without these sugars could be recovered separately by electrodialysis of the hydrolysate of in situ saccharification.
Assuntos
Acetatos/química , Celulose/química , Colina/química , Biomassa , Biotecnologia , Celulase , Imidazóis , Líquidos Iônicos , Polissacarídeos , Ultrassom , Difração de Raios XRESUMO
The ionic dynamics of the room temperature ionic liquid 1-butyl-3-methylimdiazolium bis((trifluoromethyl)sulfonyl)amide ([C(4)mim]NTf(2)) is studied using (13)C and (1)H nuclear magnetic resonance (NMR) spectroscopy over a wide temperature range encompassing the glassy and liquid states. The temperature dependence of the (13)C spin-lattice relaxation time is analyzed with four different models to derive the rotational dynamics of the RTIL in the nano to picosecond range. It was found that the extended model-free approach bridges the data obtained from the BPP and DC models, and describes ion dynamics of the RTIL well. Three different motions are observed based on the approach: an overall ion rotation, a slow and a fast local rotational motion. The time scale of the slow local rotational motion, particularly of the imidazolium ring carbons, is strongly coupled to the time scale of the overall ion rotation, above the melting point. Below the melting point these two time scales show strong decoupling and the local rotation displays nanosecond dynamics in the glassy state. The analyses of the second moment (M(2)) of the (1)H and (13)C nuclides indicate that, in addition to the axial rotations of the two methyl groups (cation) and the CF(3) group (anion), all (13)C sites including the imidazolium ring carbon and CF(3) show evidence of mobility, even in the glassy state.