ABSTRACT
The unique electronic properties of topological quantum materials, such as protected surface states and exotic quasiparticles, can provide an out-of-plane spin-polarized current needed for external field-free magnetization switching of magnets with perpendicular magnetic anisotropy. Conventional spin-orbit torque (SOT) materials provide only an in-plane spin-polarized current, and recently explored materials with lower crystal symmetries provide very low out-of-plane spin-polarized current components, which are not suitable for energy-efficient SOT applications. Here, we demonstrate a large out-of-plane damping-like SOT at room temperature using the topological Weyl semimetal candidate TaIrTe4 with a lower crystal symmetry. We performed spin-torque ferromagnetic resonance (STFMR) and second harmonic Hall measurements on devices based on TaIrTe4/Ni80Fe20 heterostructures and observed a large out-of-plane damping-like SOT efficiency. The out-of-plane spin Hall conductivity is estimated to be (4.05 ± 0.23)×104 (â / 2e) (Ωm)-1, which is an order of magnitude higher than the reported values in other materials.
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The dynamical properties of four protic ionic liquids, based on the ethyltriazolium ([C2HTr124]) and the ethylimidazolium ([C2HIm]) cation, were investigated. The associated anions were the triflate ([TfO]) and the bistriflimide ([TFSI]). Ionic conductivity values and self-diffusion coefficients were measured and discussed, extending the discussion to the concept of fragility. Furthermore, in order to allow the measurement of the ionic conductivity of very small volumes (<0.5 mL) of ionic liquid under an inert and dry atmosphere, a new setup was developed. It was found that the cation nature strongly affected the transport properties, the [C2HTr124] cation resulting in slower dynamics than the [C2HIm] one. This was concluded from both conductivity and diffusivity measurements while for both properties, the anion had a lesser effect. By fitting the conductivity data with the Vogel-Fulcher-Tammann (VFT) equation, we could also estimate the fragility of these ionic liquids, which all fell in the range of very fragile glass-forming materials. Finally, the slower dynamics observed in the triazolium-based ionic liquids can be rationalized by the stronger interactions that this cation establishes with both anions, as deduced from the frequency analysis of relevant Raman signatures and density functional theory (DFT) calculations.
Subject(s)
Ionic Liquids , Anions , Cations , Electric Conductivity , GlassABSTRACT
Objetivo: Evaluar la gravedad pulmonar de pacientes con Covid-19 a través de la correlación del puntaje SOFA pulmonar con el de afectación pulmonar en Tomografía Computarizada de Tórax. Método: Se trata de un estudio epidemiológico retrospectivo analítico descriptivo realizado en una Unidad de Cuidados Intensivos que buscó analizar el compromiso pulmonar de pacientes con Covid a través del cálculo del SOFA pulmonar relacionando la Tomografía de Tórax y si estos tenían relación con el desenlace clínico. Resultados: La población de estudio incluyó a 704 pacientes, de los cuales el 43,7% eran mujeres y el 56,2% hombres, con una edad media de 61 años y una estancia media de 13 días. La mayoría de la población presentó afectación pulmonar del 75%, puntuación SOFA pulmonar de 2 y relación PaO²/FiO² entre 100 y 200. Conclusión: Los pacientes que tenían afectación pulmonar más extensa en consecuencia tenían menor relación PaO²/FiO² y permanecían hospitalizados por un tiempo más largo con una mayor incidencia de muerte. (AUI)
Objective: To evaluate the pulmonary severity of COVID-19 patients throug the SOFA score computed with pulmonary involvement in Chest Computed Tomography. Method: This is a descriptive epidemiological study conducted out in an Intensive Care Unit, which aimed to study the pulmonary treatment of COVID-19 patients through the calculation of the pulmonary SOFA score relating to Chest Tomography and whether these were related to clinical treatment. Results: The study population consisted of 704 patients, of which 43.7% were women and 56.2% men, with a mean age of 61 years and a mean hospitalization time of 13 days. Most patients had a pulmonary behavior of 75%, a pulmonary SOFA score of 2 and a PaO²/FiO² ratio between 100 and 200. Conclusion: Patients who had more extensive pulmonary involvement/consequently had a lower PaO²/FiO² ratio and remained longer hospitalized with a higher incidence of death. (AU)
Subject(s)
Humans , Male , Female , Young Adult , Adult , Middle Aged , Aged , Aged, 80 and over , Intensive Care Units , Pandemics , Coronavirus Infections/epidemiology , Epidemiology, Descriptive , Retrospective Studies , Brazil , Tomography, X-Ray Computed , Organ Dysfunction ScoresABSTRACT
NONO (Non-Pou Domain-Containing Octamer-Binding Protein) gene maps on chromosome Xq13.1 and hemizygous loss-of-function nucleotide variants are associated with an emerging syndromic form of intellectual developmental disorder (MRXS34; MIM #300967), characterized by developmental delay, intellectual disability, poor language, dysmorphic facial features, and microcephaly. Structural brain malformation, such as corpus callosum and cerebellar abnormalities, and heart defects, in particular left ventricular non-compaction (LVNC), represent the most recurrent congenital malformations, recorded both in about 80% of patients, and can be considered the distinctive imaging findings of this disorder. We present on a further case of NONO-related disease; prenatally diagnosed in a fetus with complete corpus callosum agenesis; absence of septum pellucidum; pericallosal artery; LVNC and Ebstein's anomaly. A high-resolution microarray analysis demonstrated the presence of a deletion affecting the NONO 3'UTR; leading to a marked hypoexpression of the gene and the complete absence of the protein in cultured amniocytes. This case expands the mutational spectrum of MRXS34, advises to evaluate NONO variants in pre- and postnatal diagnosis of subjects affected by LVNC and other heart defects, especially if associated with corpus callosum anomalies and confirm that CNVs (Copy Number Variants) represent a non-negligible cause of Mendelian disorders.
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We report the behavior of the protic and surface active ionic liquid octylimidazolium bis(trifluoromethylsulfonyl)imide, [HC8Im][TFSI], in bulk and inside silica nanochannels, at the interface with the conductive substrate indium tin oxide (ITO) upon applied potential. The two distinct cases of the ionic liquid being in contact with a bare ITO substrate and an ITO substrate covered with a thin film of mesoporous silica containing vertically-aligned channel-like pores have been investigated. These correspond to the behavior of the bulk ionic liquid and the ionic liquid confined within nanochannels (approximately 3.5 nm wide and 65 nm long). Broadband dielectric spectroscopy (BDS) and electrochemical impedance spectroscopy (EIS) have been used as the experimental methods, while modelling with equivalent circuits has been applied to evaluate the experimental results. Thus, this study does not only show a functional ionic liquid/silica hybrid material, but also presents an in-depth electrochemical characterization revealing an enhanced specific capacitance at the confined-IL/ITO interface (â¼16 µF cm-2) as compared to the case of bulk IL/ITO (â¼6 µF cm-2). This suggests that local structure and ion ordering inside the nanochannels of silica are different from that of the bulk ionic liquid, favoring denser ionic packing and a higher specific capacitance at the metal interface.
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Binary mixtures based on the two protic ionic liquids 1-ethylimidazolium triflate ([C2HIm][TfO]) and 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide ([C2HIm][TFSI]) have been investigated, with focus on phase behavior, ionic conductivity, and intermolecular interactions as a function of composition (χ TFSI indicating the mole fraction of the added compound). It is found that on addition of [C2HIm][TFSI] to [C2HIm][TfO], the melting temperature is first decreased (0 < χ ≤ 0.3) and then suppressed (0.3 < χ ≤ 0.8) resulting in mixtures with no phase transitions. These mixtures display a wide temperature range of the liquid state and should be interesting for use in devices operating at extreme temperatures. The ionic conductivity does not vary significantly across the composition range analyzed, as evidenced in the comparative Arrhenius plot. The activation energy, E a , estimated by fitting with the Arrhenius relation in a limited temperature range (between 60 and 140 °C) varies marginally and keeps values between 0.17 and 0.21 eV. These marginal differences can be rationalized by the initially very similar values of the two neat protic ionic liquids. Vibrational spectroscopy, including both Raman and infrared spectroscopies, reveals weakening of the cation-anion interactions for increasing content of [C2HIm][TFSI], which is reflected by the blue shift of the average N-H stretching mode and the red shift of the S-O stretching mode in the TfO anion. These trends correlate with the higher disorder in the mixtures observed by DSC and are evidenced by the decrease and suppression of the melting temperature as the amount of [C2HIm][TFSI] is increased.
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INTRODUCTION: The term placenta praevia defines a placenta that lies over the internal os, whereas the term low-lying placenta identifies a placenta that is partially implanted in the lower uterine segment with the inferior placental edge located at 1-20 mm from the internal cervical os (internal-os-distance). The most appropriate mode of birth in women with low-lying placenta is still controversial, with the majority of them undergoing caesarean section. The current project aims to evaluate the rate of vaginal birth and caesarean section in labour due to bleeding by offering a trial of labour to all women with an internal-os-distance >5 mm as assessed by transvaginal sonography in the late third trimester. METHODS AND ANALYSIS: The MODEL-PLACENTA is a prospective, multicentre, 1:3 matched case-control study involving 17 Maternity Units across Lombardy and Emilia-Romagna regions, Italy. The study includes women with a placenta located in the lower uterine segment at the second trimester scan. Women with a normally located placenta will be enrolled as controls. A sample size of 30 women with an internal-os-distance >5 mm at the late third trimester scan is needed at each participating Unit. Since the incidence of low-lying placenta decreases from 2% in the second trimester to 0.4% at the end of pregnancy, 150 women should be recruited at each centre at the second trimester scan. A vaginal birth rate ≥60% in women with an internal-os-distance >5 mm will be considered appropriate to start routinely admitting to labour these women. ETHICS AND DISSEMINATION: Ethical approval for the study was given by the Brianza Ethics Committee (No 3157, 2019). Written informed consent will be obtained from study participants. Results will be disseminated by publication in peer-reviewed journals and presentation in international conferences. TRIAL REGISTRATION NUMBER: NCT04827433 (pre-results stage).
Subject(s)
Cesarean Section , Placenta Previa , Case-Control Studies , Female , Humans , Multicenter Studies as Topic , Placenta/diagnostic imaging , Placenta Previa/diagnostic imaging , Placenta Previa/epidemiology , Pregnancy , Prospective Studies , Ultrasonography, Prenatal/methodsABSTRACT
We report the structure and charge transport properties of a novel solid-state proton conductor obtained by acid-base chemistry via proton transfer from 12-tungstophosphoric acid to imidazole. The resulting material (henceforth named Imid3WP) is a solid salt hydrate that, at room temperature, includes four water molecules per structural unit. To our knowledge, this is the first attempt to tune the properties of a heteropolyacid-based solid-state proton conductor by means of a mixture of water and imidazole, interpolating between water-based and ionic liquid-based proton conductors of high thermal and electrochemical stability. The proton conductivity of Imid3WP·4H2O measured at truly anhydrous conditions reads 0.8 × 10-6 S cm-1 at 322 K, which is higher than the conductivity reported for any other related salt hydrate, despite the lower hydration. In the pseudoanhydrous state, that is, for Imid3WP·2H2O, the proton conductivity is still remarkable and, judging from the low activation energy (Ea = 0.26 eV), attributed to structural diffusion of protons. From complementary X-ray diffraction data, vibrational spectroscopy, and solid-state NMR experiments, the local structure of this salt hydrate was resolved, with imidazolium cations preferably orienting flat on the surface of the tungstophosphate anions, thus achieving a densely packed solid material, and water molecules of hydration that establish extremely strong hydrogen bonds. Computational results confirm these structural details and also evidence that the path of lowest energy for the proton transfer involves primarily imidazole and water molecules, while the proximate Keggin anion contributes with reducing the energy barrier for this particular pathway.
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O objetivo do estudo foi analisar a percepção sobre o mercado de trabalho entre ingressantes e formandos do curso de Enfermagem de uma universidade pública. O estudo qualitativo foi realizado com ingressantes (2019) e formandos (2018) do curso de Enfermagem da Universidade Estadual de Ponta Grossa. A amostra foi definida pelo método de saturação, a coleta de dados gravada com roteiro-guia. O material transcrito recebeu análise temática de conteúdo. Sobre o mercado de trabalho foram identificadas as categorias: mercado de trabalho amplo, mercado de trabalho saturado, mercado de trabalho exigente e mercado de trabalho desvalorizado. O mercado amplo deriva da percepção de diversidade no campo de atuação, porém houve sentimento de saturação, e por isto, exige experiência e maior formação profissional, tornando-o desvalorizado, principalmente no retorno financeiro. Houve uma percepção aproximada entre ingressantes e formandos sobre o mercado de trabalho em Enfermagem. Sendo assim, ao escolher o curso, o estudante tem ciência das dificuldades enfrentadas no mercado de trabalho relacionado à profissão. (AU)
The aim of the study was to analyze the perception of the labor market among incoming academics and graduatesof the Nursing course at a public university. The qualitative study was conducted with freshmen (2019) and graduates (2018) of the Nursing course at the State University of Ponta Grossa. The sample was defined by the saturation method, the data collection recorded with a guide script. The transcribed material received thematic content analysis. On the labor market, the following categories were identified: broad labor market, saturated labor market, demanding labor market and undervalued labor market. The broad market derives from the perception of diversity in the field, but there was a feeling of saturation, which is why it requires experience and greater professional training, making it devalued, especially in terms of financial return. There was an approximate perception between new students and graduates about the job market in Nursing. Thus, when choosing the course, the student is aware of the difficulties faced in the job market related to the profession. (AU)
Subject(s)
Humans , Perception , Students , Education, Nursing , Job MarketABSTRACT
Preoperative anxiety is a common reaction exhibited by up to 80% of patients who are scheduled for surgical procedures and characterized by psychological and physical changes which may affect their perioperative period. Our aim is to report the most up-to-date evidence on preoperative anxiety in brain surgery patients through a systematic analysis of the studies produced in the last decades. We performed a systematic review of literature by searching PubMed, Embase, and Cochrane Library databases. Data were extracted using the Population, Intervention, Comparison, Outcome framework and critically analyzed. PRISMA guidelines were applied, and the risk of bias of the included studies was assessed using the Risk of bias (RoB) 2 and ROBINS tools, as was the methodological quality, following GRADE criteria. We included 27 articles, accounting for 2558 patients in twelve different countries. The prevalence of preoperative anxiety ranged from 17 up to 89%, higher in female patients. Preoperative anxiety was associated with lower quality of life and cognitive performance, higher need for information, poorer memory and attention, longer hospitalization, depressive symptoms, and increase of physical disability; no correlation with survival rate was found. Seven randomized controlled trials attested the efficacy of acupuncture, music therapy, virtual reality, and pharmacological support in lowering anxiety levels. Preoperative anxiety is a common phenomenon that could negatively affect the perioperative period of brain surgery patients: this is something that should not be neglected to achieve better care through early prevention and optimal management.
Subject(s)
Music Therapy , Quality of Life , Anxiety/epidemiology , Brain , Female , HumansABSTRACT
Manufacturing new electrolytes with high ionic conductivity has been a crucial challenge in the development and large-scale distribution of fuel cell devices. In this work, we present two Nafion composite membranes containing a non-stoichiometric calcium titanate perovskite (CaTiO3-δ) as a filler. These membranes are proposed as a proton exchange electrolyte for Polymer Electrolyte Membrane (PEM) fuel cell devices. More precisely, two different perovskite concentrations of 5 wt% and 10 wt%, with respect to Nafion, are considered. The structural, morphological, and chemical properties of the composite membranes are studied, revealing an inhomogeneous distribution of the filler within the polymer matrix. Direct methanol fuel cell (DMFC) tests, at 110 °C and 2 M methanol concentration, were also performed. It was observed that the membrane containing 5 wt% of the additive allows the highest cell performance in comparison to the other samples, with a maximum power density of about 70 mW cm-2 at 200 mA cm-2. Consequently, the ability of the perovskite structure to support proton carriers is here confirmed, suggesting an interesting strategy to obtain successful materials for electrochemical devices.
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Polarised Raman spectroscopy is used to characterise the local structure in single crystals of zeotypes, namely silicalite-1 and ZSM-5, which share the MFI framework structure. Attributes favourable for applying polarised Raman spectroscopy are the orthogonal axes of these single crystals and their size, i.e. 10 to 30 micrometers in all three directions. We show that the intensity of certain vibrational modes in silicalite-1 depends on the polarisation of the incident light, reflecting the anisotropic character of the molecular bonds contributing to these vibrations. Using these observations, and by estimating the depolarisation ratio (ρ) and the pseudo-order factor (f), we propose a more accurate assignment of the Raman active modes. More precisely, Raman intensities peaked at 294, 360, 383 and 472 cm-1 are attributed to bending modes in 10-, 6-, 5- and 4-membered rings, respectively. In the region of stretching modes, the vibration at 832 cm-1 is assigned to Si-O-Si bonds shared between 5-membered rings, which have an orientation parallel to the a-axis of the crystal. By virtue of having a strongly polarised character, the modes at 472 and 832 cm-1 can be used as orientational indicators. The proposed assignment is supported by the good agreement between experimental and simulated polar plots, where Raman intensities are plotted as a function of the polarisation angle of the incident light. Finally, upon partial substitution of Si atoms by Al, the crystalline structure is maintained and almost no spectroscopic changes are observed. The only significant difference is the increased width of most vibrational modes, which is consistent with the local lower symmetry. This is also seen in the angular dependence of selected vibrational modes that compared to the case of pure silicalite-1 appear less polarised. In the Raman spectrum of ZSM-5 a new feature at 974 cm-1 is observed, which we attribute to Al-OH stretching. In the high frequency range, the O-H stretching modes are observed which arise from the Si-O(H)-Al Brønsted acid sites. The intensity of the characteristic mode at 3611 cm-1 reveals an anisotropic character as well, which is in line with previous findings from solid state NMR that Al atoms distribute nonrandomly within the MFI framework structure.
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We investigate the effect of adding different molecular cosolvents, water or imidazole, to the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide, i.e., [C2HIm][TFSI]. We explore how the added cosolvent distributes within the ionic liquid by means of molecular dynamics simulations and X-ray scattering. We also analyze the degree of short-range heterogeneity in the resulting mixtures, finding that while imidazole easily mixes with the protic ionic liquid, water tends to form small clusters in its own water-rich domains. These differences are rationalized by invoking the nature of intermolecular interactions. In aqueous mixtures water-water hydrogen bonds are more likely to form than water-ion hydrogen bonds (water-TFSI bonds being particularly weak), while imidazole can interact with both cations and anions. Hence, the cation-anion association is negligibly influenced by the presence of water, whereas the addition of imidazole creates solvent-separated ion pairs and is thus able to also increase the ionicity. As a consequence of these structural and interactional features, transport properties like self-diffusion and ionic conductivity also show different composition dependencies. While the mobility of both ions and solvent is increased considerably by the addition of water, upon adding imidazole this property changes significantly only for molar fractions of imidazole above 0.6. At these molar fractions, which correspond to a base-excess composition, the imidazole/[C2HIm][TFSI] mixture behaves as a glass-forming liquid with suppressed phase transitions, while homomixtures such as imidazole/[HIm][TFSI] can display a eutectic point.
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A composite membrane based on a Nafion polymer matrix incorporating a non-stoichiometric calcium titanium oxide (CaTiO3-δ) additive was synthesized and characterized by means of thermal analysis, dynamic mechanical analysis, and broadband dielectric spectroscopy at different filler contents; namely two concentrations of 5 and 10 wt.% of the CaTiO3-δ additive, with respect to the dry Nafion content, were considered. The membrane with the lower amount of additive displayed the highest water affinity and the highest conductivity, indicating that a too-high dose of additive can be detrimental for these particular properties. The mechanical properties of the composite membranes are similar to those of the plain Nafion membrane and are even slightly improved by the filler addition. These findings indicate that perovskite oxides can be useful as a water-retention and reinforcing additive in low-humidity proton-exchange membranes.
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Protic ionic liquids (PILs) are proposed as alternative anhydrous proton conducting electrolytes for intermediate temperature fuel cells. One of the key factors in their performance as electrolytes, as far as charge transport is concerned, is their proton conductivity. Noting the success of water-containing electrolytes and recognising faster proton mobility than structural relaxation (via mechanisms such as Grotthuss) as their advantage, such an advantage is envisaged for PILs and in some cases deduced. As extended hydrogen bond networks and proton exchange are at the heart of these mechanisms, here we report our results on a prototypical characterisation of proton exchange in a PIL (C2HimNTf2)-water mixture. NMR lineshape analysis and exchange spectroscopy (EXSY) are used to quantify the proton exchange rate. The obtained exchange rate is then used to explain the diffusion behaviour of the exchangeable proton as measured by pulse field gradient NMR methods; a marginal anomaly in the translational dynamics of the exchangeable proton in the form of a faster NH proton is observed. As far as we know this is the first report on systematic characterisation of proton exchange in PILs with the aim of understanding its effect on translational motion as a way of discerning exchange related mobility anomalies.
ABSTRACT
Protic ionic liquids are known to form extended hydrogen-bonded networks that can lead to properties different from those encountered in the aprotic analogous liquids, in particular with respect to the structure and transport behavior. In this context, the present paper focuses on a wide series of 1-alkyl-imidazolium bis(trifluoromethylsulfonyl)imide ionic liquids, [HC nIm][TFSI], with the alkyl chain length ( n) on the imidazolium cation varying from ethyl ( n = 2) to dodecyl ( n = 12). A combination of several methods, such as vibrational spectroscopy, wide-angle X-ray scattering (WAXS), broadband dielectric spectroscopy, and 1H NMR spectroscopy, is used to understand the correlation between local cation-anion coordination, nature of nanosegregation, and transport properties. The results indicate the propensity of the -NH site on the cation to form stronger H-bonds with the anion as the alkyl chain length increases. In addition, the position and width of the scattering peak q1 (or the pre-peak), resolved by WAXS and due to the nanosegregation of the polar from the nonpolar domains, are clearly dependent on the alkyl chain length. However, we find no evidence from pulsed-field gradient NMR of a proton motion decoupled from molecular diffusion, hypothesized to be facilitated by the longer N-H bonds localized in the segregated ionic domains. Finally, for all protic ionic liquids investigated, the ionic conductivity displays a Vogel-Fulcher-Tammann dependence on inverse temperature, with an activation energy Ea that also depends on the alkyl chain length, although not strictly linearly.
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Measuring temperature and heat flux is important for regulating any physical, chemical, and biological processes. Traditional thermopiles can provide accurate and stable temperature reading but they are based on brittle inorganic materials with low Seebeck coefficient, and are difficult to manufacture over large areas. Recently, polymer electrolytes have been proposed for thermoelectric applications because of their giant ionic Seebeck coefficient, high flexibility and ease of manufacturing. However, the materials reported to date have positive Seebeck coefficients, hampering the design of ultra-sensitive ionic thermopiles. Here we report an "ambipolar" ionic polymer gel with giant negative ionic Seebeck coefficient. The latter can be tuned from negative to positive by adjusting the gel composition. We show that the ion-polymer matrix interaction is crucial to control the sign and magnitude of the ionic Seebeck coefficient. The ambipolar gel can be easily screen printed, enabling large-area device manufacturing at low cost.
ABSTRACT
The binary mixture based on the protic ionic liquid (PIL) ethylimidazolium triflate (C2HImTfO) and the diol compound ethylene glycol (EG) has been investigated in the whole composition range from pure PIL to pure EG. At 30 °C the addition of EG increases both the ionic conductivity and the self-diffusivity of the ions. These quantities, however, change at different rates suggesting that the ionicity of the system is composition dependent. This behaviour is explained by means of new intermolecular forces established when a second compound like EG is introduced into the ionic network. More specifically, a complex H-bonded network is formed that involves the -NH group of the cation, the -OH group of EG and the -SO3 group of the anion. This configuration may increase the fluidity of the mixture but not necessarily the ionic dissociation. Moreover, diffusion NMR results indicate the occurrence of local proton dynamics, which arise from a proton exchange between the -NH of the cation and the -OH of EG, providing the requisite for a long-range Grotthuss mechanism of proton transport.
ABSTRACT
We report enhanced protonic and ionic dynamics in an imidazole/protic ionic liquid mixture confined within the nanopores of silica particles. The ionic liquid is 1-octylimidazolium bis(trifluoromethanesulfonyl)imide ([HC8Im][TFSI]), while the silica particles are microsized and characterized by internal well connected nanopores. We demonstrate that the addition of imidazole is crucial to promote a proton motion decoupled from molecular diffusion, which occurs due to the establishment of new N-HN hydrogen bonds and fast proton exchange events in the ionic domains, as evidenced by both infrared and 1H NMR spectroscopy. An additional reason for the decoupled motion of protons is the nanosegregated structure adopted by the liquid imidazole/[HC8Im][TFSI] mixture, with segregated polar and non-polar nano-domains, as clearly shown by WAXS data. This arrangement, promoted by the length of the octyl group and thus by significant chain-chain interactions, reduces the mobility of molecules (Dmol) more than that of protons (DH), which is manifested by DH/Dmol ratios greater than three. Once included into the nanopores of hydrophobic silica microparticles, the nanostructure of the liquid mixture is preserved with slightly larger ionic domains, but effects on the non-polar ones are unclear. This results in a further enhancement of proton motion with localised paths of conduction. These findings demonstrate significant progress in the design of proton conducting materials via tailor-made molecular structures as well as by smart exploitation of confinement effects. Compared to other imidazole-based proton conducting materials that are crystalline up to 90 °C or above, the gel materials that we propose are useful for applications at room temperature, and can thus find applications in e.g. intermediate temperature proton exchange fuel cells.
ABSTRACT
This paper extends the study of the induced temperature change in the mesostructure and in the physical properties occurring in aqueous mixtures of the ionic liquid 1-ethyl-3-methyl imidazolium octyl-sulfate [EMIm][OSO4]. For some compositions, these mixtures undergo a phase transition between the liquid (isotropic in the mesoscale) and the mesomorphic state (lyotropic liquid crystalline) at about room temperature. The behavior of mixtures doped with a divalent metal sulfate was investigated in order to observe their applicability as electrolytes. Calcium sulfate salt is almost insoluble even in the 20 wt% water mixture. The magnesium salt, in contrast, can be dissolved up to concentrations of 730 ppm in the same mixture and it has a profound impact on its properties. Six aqueous mixtures (with water content from 10 wt% to 33 wt%) of [EMIm][OSO4] were saturated with magnesium sulfate salt, producing the ternary mixture [EMIm][OSO4] + H2O + MgSO4. Viscosity, density and ionic conductivity for these samples were measured from 10 °C to 90 °C. In addition, SAXS, FTIR, diffussion NMR and Raman spectroscopy of the most interesting samples have been performed, and structural data indicate a transition between a hexagonal lyotropic liquid crystalline phase below and an isotropic solution phase above room temperature. The octyl sulfate anions of the cylindrical micelles in the hexagonal phase are coordinated with water molecules through H-bonds (about four per sulfate anion), while the [EMIm] cations seem to be poorly coordinated and so free to move. Inorganic salt addition reinforces that network, increasing the phase transition temperature.