RESUMEN

The methoxy analogue of a trans-stilbene compound - 2,3,3',4'-tetramethoxy-trans-stilbene - was selected to characterize its crystallographic structure, intermolecular interactions and molecular dynamics. The sample was studied using single-crystal X-ray diffraction (XRD), infrared spectroscopy (FT-IR), liquid and solid-state 1H and 13C nuclear magnetic resonance (NMR) and quasielastic neutron scattering (QENS). The compound crystallized in the orthorhombic Pbca space group. The experimental methods were supported by theoretical calculations, density functional theory (plane-wave DFT) and molecular dynamics simulations (MD) methods. Combining several experimental and simulation techniques allowed the detailed analysis of molecular reorientations and provided a consistent picture of the molecular dynamics. The internal molecular mobility of the studied compound can be associated with the reorientational dynamics of four methyl groups. Interestingly, a large diversity of the energy barriers was observed - one methyl group reoriented across low activation barriers (∼3 kJ mol-1), while three methyl groups exhibited a high activation energy (10-14 kJ mol-1) and they are characterised by very different correlation times differing by almost two orders of magnitude at room temperature. The intramolecular interactions mainly influence the activation barriers.

RESUMEN

Design of new functional materials with fast Mg-ion mobility is crucial for the development of competitive solid-state magnesium batteries. Herein, we present new nanocomposites, Mg(BH4)2·1.6NH3-Al2O3, reaching a high magnesium conductivity of σ(Mg2+) = 2.5 × 10-5 S cm-1 at 22 °C assigned to favorable interfaces between amorphous state Mg(BH4)2·1.6NH3; inert and insulating Al2O3 nanoparticles; and a minor fraction of crystalline material, mainly Mg(BH4)2·2NH3. Furthermore, quasi-elastic neutron scattering reveals that the Mg2+-ion mobility in the solid state appears to be correlated to relatively slow motion of NH3 molecules rather than the fast dynamics of BH4- complexes. The nanocomposite is compatible with a metallic Mg anode and shows stable Mg2+ stripping/plating in a symmetric cell and an electrochemical stability of ∼1.2 V. The nanocomposite has high mechanical stability and ductility and is a promising Mg2+ electrolyte for future solid-state magnesium batteries.

RESUMEN

Over the last couple of decades, deep eutectic solvents (DESs) have emerged as novel alternatives to ionic liquids that are extensively used in the synthesis of innovative materials, metal processing, catalysis, etc. However, their usage is limited, primarily because of their large viscosity and poor conductivity. Therefore, an understanding of the molecular origin of these transport properties is essential to improve their industrial applicability. Here, we present the report of the nanoscopic diffusion mechanism of acetamide in a DES synthesized with lithium perchlorate as studied using neutron scattering and molecular dynamics (MD) simulation techniques. A diffusion model is constructed with the help of MD simulation data comprising two distinct processes, corresponding to long-range jump diffusion and localized diffusion within a restricted volume. This diffusion model is validated through the analysis of neutron scattering data in the acetamide based DES (ADES) and molten acetamide. Although ADES has a remarkably lower freezing point compared to pure acetamide, the molecular mobility is found to be enormously restricted in the former. Particularly, the long-range jump diffusion process of acetamide is slower by a factor of 3 in ADES in comparison with molten acetamide. Further, the geometry of localized diffusion is found to be unaltered, but the dynamics is observed to be slightly slower in ADES. The diffusion model is found to be consistent over a wide temperature range for the ADES. Both long-range and localized diffusion show Arrhenius dependence with temperature in ADES. MD simulation analysis reveals that the long-range diffusion in ADES is restricted mainly due to the formation of hydrogen bond mediated complexes between the ionic species of the salt and acetamide molecules. Hence, the origin of higher viscosity observed in ADES can be attributed to the complexation in the ADES. The complex formation also explains the inhibition of the crystallization process while cooling and thereby results in depression of the freezing point of ADES.

RESUMEN

Coupling between dynamical heterogeneity of ionic liquids and their structural periodicity on different length-scales can be directly probed by quasielastic neutron scattering with polarization analysis. The technique provides the tools to investigate single-particle and cooperative ion motions separately and, thus, dynamics of ion associations affecting the net charge transport can be experimentally explored. The focus of this study is the structure-dynamic relationship in the protic ionic liquid, triethylammonium triflate, characterized by strong hydrogen bonds between cations and anions. The site-selective deuterium/hydrogen-isotope substitution was applied to modulate the relative contributions of different atom groups to the total coherent and incoherent scattering signal. This approach in combination with molecular dynamics simulations allowed us to obtain a sophisticated description of cation self-diffusion and confined ion pair dynamics from the incoherent spectral component by using the acidic proton as a tagged particle. The coherent contribution of the neutron spectra demonstrated substantial ion association leading to collective ion migration that preserves charge alteration on picosecond time scale, as well as correlation of the localized dynamics occurring between adjacent ions.

RESUMEN

Coordination complexes of magnesium borohydride show promising properties as solid electrolytes for magnesium ion batteries and warrant a thorough microscopic description of factors governing their mobility properties. Here, the dynamics of Mg(BH4)2-diglyme0.5 on the atomic level are investigated by means of quasielastic neutron scattering supported by density functional theory calculations and IR and NMR spectroscopy. Employing deuterium labeling, we can unambiguously separate all the hydrogen-containing electrolyte components, which facilitate Mg2+ transport, and provide a detailed analytical description of their motions on the picosecond time scale. The planar diglyme chain coordinating the central Mg atom appears to be flexible, while two dynamically different groups of [BH4]- anions undergo reorientations. The latter has important implications for the thermal stability and conductivity of Mg(BH4)2-diglyme0.5 and demonstrates that the presence of excess Mg(BH4)2 units in partially chelated Mg complexes may improve the overall performance of related solid-state electrolytes.

RESUMEN

Changing the number of carbon atoms in the substituents of ionic liquids (ILs) is a way to shift the balance between Coulomb and van der Waals forces and, thus, to tune physicochemical properties. Here we address this topic on the microscopic level by employing quasielastic neutron scattering (QENS) and provide information about the stochastic ionic motions in the N-alkylpyridinium based ILs in a relatively expanded time range, from short time (subpicosecond) particle rattling to long time diffusive regime (hundreds of picoseconds). We have systematically investigated the effect of the alkyl chain length on the picosecond dynamics by employing partial deuteration of the samples and varying the number of carbon atoms in the alkyl substituent. The localized dynamics of the side groups have appeared to be enhanced for bulkier cations, which is opposite to the trend observed for the translational motion. This result highlights the role of the conformational flexibility of the alkyl group on the dynamical properties of ILs.

RESUMEN

Phonons in condensed matter materials transmit energy through atomic lattices as coherent vibrational waves. Like electronic and photonic properties, an improved understanding of phononic properties is essential for the development of functional materials, including thermoelectric materials. Recently, an Einstein rattling mode was found in thermoelectric material Na0.8CoO2, due to the large displacement of Na between the [CoO2] layers. In this work, we have realized a different type of rattler in another thermoelectric material Ca3Co4O9 by chemical doping, which possesses the same [CoO2] layer as Na0.8CoO2. It remarkably suppressed the thermal conductivity while enhancing its electrical conductivity. This new type of rattler was investigated by inelastic neutron scattering experiments in conjunction with ab-initio molecular dynamics simulations. We found that the large mass of dopant rather than the large displacement is responsible for such rattling in present study, which is fundamentally different from skutterudites, clathrates as well as Na analogue. We have also tentatively studied the phonon band structure of this material by DFT lattice dynamics simulation, showing the relative contribution to phonons in the distinct layers of Ca3Co4O9.

RESUMEN

Quasielastic neutron scattering (QENS) in combination with deuterium labeling allows for studying protonated "highlighted" species and extracting detailed information about tangled stochastic processes. This approach has been applied to examine proton dynamics in the protic ionic liquid, triethylammonium triflate. The temperature range covered during the experiments (2-440 K) included two melting transitions correspondingly reflected in the global and localized dynamics of the cation. To focus on the dynamics of the acidic proton, QENS spectra of the sample with the deuterated alkyl side chains were analyzed. The remaining hydrogen atom served as a tagged particle for investigating both global long-range motion of the cation and specific dynamics of the proton and, thus, provided insight into the transport properties of triethylammonium triflate, which is important for designing electrochemical devices.

RESUMEN

Quasielastic neutron scattering with polarized neutrons allows for an experimental separation of single-particle and collective processes, as contained in the incoherent and coherent scattering contributions. This technique was used to investigate the dynamical processes in the pyridinium-based ionic liquid 1-butylpyridinium bis(trifluoromethylsulfonyl)-imide. We observed two diffusion processes with different time scales. The slower diffusional process was present in both the coherent and the incoherent contribution, meaning that this process has at least a partial collective nature. The second faster localized process is only present in the incoherent scattering contribution. We conclude that it is a true single-particle process on a shorter time scale.

RESUMEN

Quasielastic neutron scattering (QENS) has been used to study the cation dynamics in the pyridinium based ionic liquid (IL) 1-N-butylpyridinium bis((trifluoromethyl)sulfonyl)imide (BuPy-Tf(2)N). This IL allows for a detailed investigation of the dynamics of the cations only, due to the huge incoherent scattering cross section of the cation (σ(inc)(cation) >> σ(inc)(anion)). The measured spectra can be decomposed into two Lorentzian lines, indicative of two distinct dynamic processes. The slower of these two processes is diffusive in nature, whereas the faster one can be attributed to localized motions. The temperature dependence of the diffusion coefficient of the slow process follows an Arrhenius law, with an activation energy of E(A) = 14.8 ± 0.3 kJ/mol. Furthermore, we present here results from experiments with polarized neutrons. These experiments clearly show that the slower of the two observed processes is coherent, while the faster one is incoherent in nature.

RESUMEN

The dynamics of water in human red blood cells was measured with quasielastic incoherent neutron scattering in the temperature range between 290 and 320 K. Neutron spectrometers with time resolutions of 40, 13, and 7 ps were combined to cover time scales of bulk water dynamics to reduced mobility interfacial water motions. A major fraction of approximately 90% of cell water is characterized by a translational diffusion coefficient similar to bulk water. A minor fraction of approximately 10% of cellular water exhibits reduced dynamics. This slow water fraction was attributed to dynamically bound water on the surface of hemoglobin which accounts for approximately half of the hydration layer.

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