In this work we study how the properties of ionic liquids change upon confinement between two walls at various nanometric distances. We also find a correlation between the dynamic properties and the ...structure of this system under these extremely nanoconfined circumstances. We report that for ethylammonium nitrate, the ionic structure inside the simulation boxes is a consequence of a subtle combination of ion packing, hydrogen bonding, electrostatic and van der Waals forces. We also study how the dynamical properties of this material change in these conditions, showing a decrease in the ionic mobility for very low slit sizes, recovering the bulk behavior as the distance between walls increases. Moreover, when short wall separations are considered, we show that the ionic mobility at short times is a minimum when the hydrogen bonding is also a minimum. Finally, we show that the effect of the interface in the long time ion dynamics only extends to a quite small region (ca. 1.35 nm) next to the walls. We show that the overall behavior of the nanoconfined liquid in the slit pore can be described by the superposition of a bulk and a confined simulation with a fitted wall separation. To our knowledge, there are no similar studies characterizing this kind of dense ionic systems in such a fine-grain way under these ultra-nanoconfined conditions.
•Ethylammonium nitrate ionic liquid under ultra-nanoconfinement between planar interfaces•Strong correlation between structure and dynamics•Structure determined by ion packing, hydrogen bonding, electrostatic and van der Waals forces•Slower dynamics for very low slit sizes (below 3 nm)•The spatial range of the interfacial effects in the ionic liquid dynamics is estimated to be 1.35 nm for EAN.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Mixtures of the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate with amphiphilic cosolvents, such as methanol and ethanol, nanoconfined between graphene walls are studied by means of ...molecular dynamics simulations and the results are compared with those of the pure ionic liquid and its mixtures with water confined in the same conditions. We investigate the adsorption of cosolvent molecules at the graphene walls as well as their distribution across the system. The results show that, due to a higher affinity of the polar groups to be close to the anions in combination with the electrostatic and excluded volume interactions, there exists a high tendency of the OH groups to lie close to the anode, inducing small changes in the first cation layer. The orientation of cosolvent molecules is found to be closely related to the alignment of the molecular dipole moment. We also investigate the lateral ionic distribution in the layers close to the electrodes, which shows a structural transition from liquid-like lamellar ordering to solid-like hexagonal patterns as the size of the cosolvent molecules increases leading to smaller position fluctuations of the ions. The dependence of the specific patterns on the nature of the electrodes is also studied. This study strongly suggests that the ionic patterns formed in the first ionic layers next to the charged interfaces are universal since their existence does not crucially depend on the atomic composition of the interfacial material, but only on the net charge density of the considered ionic layer, which significantly changes the ionic mobility in this region.
We report the first MD simulations of the 3D structure of the electric double layer of ionic liquid-alcohol mixtures.
In a recent paper we presented experimental measurements of the dynamic viscosity and specific electrical conductivity, for binary systems of 1-alkyl-3-methyl imidazolium tetrafluoroborate, CnMIMBF4, ...with water. In this paper we complete those measurements with four systems of CnMIMBF4 + ethanol, the alkyl chains of the ionic liquids (ILs) used being ethyl (EMIMBF4), butyl (BMIMBF4), hexyl (HMIMBF4), and octyl (OMIMBF4). As in aqueous systems, viscosity was measured at 288.15 K, 298.15 K, 308.15 K, and 318.15 K, while conductivity was measured at those four temperatures only for selected mixtures and at 298.15 K over the whole composition range. Note that EMIMBF4 is only partially miscible with ethanol at the studied temperatures and atmospheric pressure (while it is completely miscible in water). We calculate viscosity deviations and molar conductivity from the original experimental data, which are compared with the scarce previously published data for similar mixtures and with the corresponding aqueous systems. Viscosity and electrical conductivity are related between them using Walden’s rule, observing an increase of the resulting value with concentration. This behavior differs from that observed in the analogous aqueous systems.
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IJS, KILJ, NUK, PNG, UL, UM
This study investigated the influence of the aortic bifurcation anatomy on the endovascular treatment of abdominal aortic aneurysms using Excluder (W. L. Gore & Associates, Flagstaff, Ariz) ...bifurcated stent grafts.
This was a retrospective single-center study of patients treated with the Excluder stent graft. Analysis included anatomical factors of the aortic bifurcation (aortic bifurcation diameter ABD, calcification, thrombus), characteristics of the stent graft limbs (sum of stent graft limbs diameters SLD), and the SLD/ABD ratio. Narrow bifurcation was defined as ABD <20 mm. Primary outcomes were intraoperative stenosis, need for additional intraoperative measures, limb stenosis, and occlusion during follow-up.
The study included 232 patients. Mean ABD was 24.6 ± 6 mm, with 53 patients (23%) presenting with narrow bifurcation (range, 12.5-19.5 mm). Median SLD in these patients was 28 mm, and the SLD/ABD ratio was 1.64. Calcification involving >50% of the bifurcation circumference was present in 32% of the patients, with 17% presenting thrombus in this area. Of 53 patients with narrow bifurcation, intraoperative stenosis >50% occurred in three (5.7%), which required adjunctive treatment. Computed tomography at 1 month showed limb stenosis >50% in nine patients (17%). No limb occlusions were recorded with a median follow-up of 34 months. Multivariate analysis of the overall series showed a higher risk of limb stenosis on the computed tomography at 1 month in patients with peripheral artery disease (hazard ratio HR, 5.3; 95% confidence interval CI, 1.2-24.4; P = .032), narrow bifurcation (HR, 5.7; 95% CI, 2-15.8; P = .001), higher SLD/ABD ratio (HR, 29.3; 95% CI, 4-215.2; P = .001), and calcium >50% (HR, 3; 95% CI, 1.1-8; P = .03), and lower in bifurcations with thrombus (HR, 0.3; 95% CI, 0.1-0.8; P = .017).
Abdominal aortic aneurysms with narrow bifurcation can be treated with the bifurcated Excluder device without additional adjunctive measures. The presence of limb stenosis during follow-up is not associated with occlusion. Long-term follow-up studies are needed to confirm these results.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
In this paper spectrally resolved white light interferometry is applied for measuring the refractive index of different ionic liquids over a wide spectral band from 400 to 1000 nm. The measuring ...device is compound by a Michelson interferometer whose output is analyzed by means of two spectrometers. The first one is a homemade prism spectrometer which provides the interferogram produced by the sample over a wide continuum spectrum. The second one is a commercial diffraction grating spectrometer used to make high precision measurements of the displacement between the Michelson mirrors by interferometry. Both instruments combined allow the retrieval of the refractive index of the sample over a wide visible-near infrared continuum spectrum with deviations on the fourth decimal. A group of 14 different ionic liquids based on the 1-alkyl-3-methylimidazolium cation have been studied through this technique. The measured refractive index of the ionic liquids is used to calculate their electronic polarizability. This makes possible to gain insight into the microscopic behavior of the compounds. To give a better picture, the liquids have been classified in four groups and their refractive indices and polarizabilities are compared in order to find correlations between these magnitudes and the structure of the liquids.
•The refractive index of 14 ionic liquids is measured from 400 to 1000 nm.•The technique is fast and has high precision, with uncertainties Δn < 2 10−4.•The electronic polarizability is calculated from refractive index and density data.•Correlations and difference between the ionic liquids are established.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We perform molecular dynamics simulations of ionic liquids confined between graphene walls under a large variety of conditions (pure ionic liquids, mixtures with water and alcohols, mixtures with ...lithium salts and defective graphene walls). Our results show that the formation of striped and hexagonal patterns in the Stern layer can be considered as a general feature of ionic liquids at electrochemical interfaces, the transition between patterns being controlled by the net balance of charge in the innermost layer of adsorbed molecules. This explains previously reported experimental and computational results and, for the first time, why these pattern changes are triggered by any perturbation of the charge density at the innermost layer of the electric double layer (voltage and composition changes, and vacancies at the electrode walls, among others), which may help tuning electrode-ionic liquid interfaces. Using Monte Carlo simulations we show that such structures can be reproduced by a simple two-dimensional lattice model with only nearest-neighbour interactions, governed by highly screened ionic interactions and short-range and excluded volume interactions. We also show that the results of our simulations are consistent with those inferred from the Landau-Brazovskii theory of pattern formation in self-assembling systems. The presence of these patterns at the ionic liquid graphene-electrode interfaces may have a strong impact on the process of ionic transfer from the bulk mixtures to the electrodes, on the differential capacitance of the electrode-electrolyte double layer or on the rates of redox reactions at the electrodes, among other physicochemical properties, and is therefore an effect of great technological interest.
We perform molecular dynamics and Monte Carlo simulations of ionic liquids confined between graphene walls under a large variety of conditions, proving the occurrence of structural pattern transitions that can be explained using the Landau-Brazovskii theory.
The stability of binary mixtures of several protic ionic liquids (ethylammonium nitrate, ethylammonium acetate and ethylammonium tetrafluoroborate) with polyethylene oxide is studied by means of ...molecular dynamics simulations. The solubility range is seen to be wider for ethylammonium acetate, and the structure and single-particle dynamics of its ternary mixtures with lithium acetate are then studied. The structure of liquid mixtures of lithium acetate with the ionic liquid is seen to be seldom modified by the addition of the polymer, with very limited hydrogen bonding between the ionic liquid and the polymer taking place. Moreover, lithium is seen to be solvated in the liquid phase forming Li(ACE)4−3 tetrahedral complexes irrespective of the presence of the polymer, with very limited binding of metal cations to oxygen atoms in the polymer backbone. Hence, the registered single particle dynamics and lithium transport takes place in practically the same way as in the liquid phase with almost no interference of the polymer, contrarily to previously reported results for other ionic liquids.
•Ternary mixtures of a protic ionic liquid with a lithium salt and a polymer (PEO)•Miscibility range of mixtures with several protic ionic liquids•Structure and single-particle dynamics of bulk mixtures•Effect of the polymer presence in the distribution of lithium cations
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A molecular dynamics study of mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF
4
) with magnesium tetrafluoroborate (MgBF
4
2
) confined between two parallel graphene walls is ...reported. The structure of the system is analyzed by means of ionic density profiles, lateral structure of the first layer close to the graphene surface and angular orientations of imidazolium cations. Free energy profiles for divalent magnesium cations are calculated using two different methods in order to evaluate the height of the potential barriers near the walls, and the results are compared with those of mixtures of the same ionic liquid and a lithium salt (LiBF
4
). Preferential adsorption of magnesium cations is analyzed using a simple model and compared to that of lithium cations, and vibrational densities of states are calculated for the cations close to the walls analyzing the influence of the graphene surface charge. Our results indicate that magnesium cations next to the graphene wall have a roughly similar environment to that in the bulk. Moreover, they face higher potential barriers and are less adsorbed on the charged graphene walls than lithium cations. In other words, magnesium cations have a more stable solvation shell than lithium ones.
A molecular dynamics study of graphene-confined mixtures of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF
4
) with MgBF
4
2
is reported.
We perform molecular dynamics simulations of mixtures of a prototypical protic ionic liquid, ethylammonium nitrate, with lithium or magnesium nitrate (LiNO
3
/Mg(NO
3
)
2
) confined between two ...graphene walls. The structure of the system is analyzed by means of ionic density profiles, angular orientations of ethylammonium cations close to the wall and the lateral structure of the first layer close to the graphene wall. All these results are compared to those of the corresponding aprotic ionic liquid systems, analyzing the influence of the graphene wall charge in the structure of the protic and aprotic mixtures. Moreover, vibrational densities of states are calculated for the salt cations close to the walls. Finally, we investigate the structure of the mixture with Li salt near the interface using
ab initio
density functional theory, and the results are compared with those obtained by classical molecular dynamics simulations.
Hydrogen bonded protic ionic liquids improve the transport of electrochemically relevant cations to charged walls relative to aprotic ones.
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•We present transport properties for nine novel ionic liquids BMIMn-zM+z(SCN)n.•Metal cations are: Al, Mn, Fe, Cr, Ni, Hg, Zn, Co and Cu; and BMIM(SCN).•Ionic conductivity, viscosity ...and diffusion constant vs. temperature are given.•Comparison of the three magnitudes in pairs with classical equations agrees.•In contrast, great differences in the data presented for the different compounds.
In a previous paper some of us presented the structure and some properties of a new family of ionic liquids, ILs, with a common cation, 1-butyl-3-methyl imidazolium (the popular C4C1Im+ or BMIM+) and a variety of anions based in thiocyanate (SCN)−: one reference sample and ten with anionic metal complexes of different valences: AlIII, MnII, FeIII, CrIII, NiII, HgII, ZnII, CoII and CuI, resulting, respectively, BMIM(SCN), BMIM3 Al(SCN)6, BMIM4 Mn(SCN)6, BMIM3 Fe(SCN)6, BMIM3 Cr(SCN)6, BMIM4 Ni(SCN)6, BMIM2 Hg(SCN)4, BMIM2 Zn(SCN)4, BMIM2 Co(SCN)4 and BMIM3 Cu(SCN)4. In this paper we show experimental measurements of electrical conductivity of these ILs in a broad temperature range (about 90 K). Viscosity has been measured for six compounds in a wide temperature range. In addition, the diffusion coefficient for both ions forming the IL has been measured for some of the samples using NMR-Dosy technique. In spite of being very similar compounds from a chemical point of view, they present very different transport property values. Thus, viscosity varies more than two orders of magnitude among those metal thiocyanate ILs, being the highest for the compound with Al and the lowest for that with Hg. Moreover, differences between ionic conductivity and diffusion coefficient values extend more than one order of magnitude among the thiocyanate ILs. These three properties will be related in pairs, thus through Walden’s rule we compare molar conductivity and fluidity, while using Kohlrausch’s law and Nerst-Einstein equation molar conductivity and diffusion coefficient are related. Also, diffusion coefficient and fluidity (the inverse of viscosity) are compared by means of Stokes-Einstein relationship. In addition, we calculate the Laity interionic friction coefficients for both anions of the IL with Hg. Finally, a theoretical model is suggested to explain all the experimental evidences reported.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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