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[EN] A combined study of inelastic neutron scattering and ab initio molecular dynamics simulations has been performed in order to study the water-acid site interaction in zeolite chabazite with a ratio Si/Al = 16 that corresponds to 2 protons/uc with two different water coverages with the number of water molecules being lower and higher than that of proton sites. These results have provided a clear picture of the water-acid site interaction, and it has been demonstrated that there are two regimens of water adsorption, which depend on the water loading. (i) At low water coverage (water/acid site similar to 0.5), the main interactions between water and the zeolitic acid sites are established through hydrogen bond and there is no proton transference to water. (ii) At relatively high water loading (water/acid site similar to 3), the clustering of water molecules and hydronioum cations formed by the complete transference of the zeolitic proton to the water molecules has been observed. The formation of water-hydronium clusters interacting with oxygen atoms of the zeolite framework provides the stabilization energy needed for the protonation of water molecules confined in the cavities of chabazite. These results are the experimental evidence obtained from INS of proton transfer from the zeolitic acid site and the hydronium formation and are in agreement with a previous computational study (Phys. Chem. Chem. Phys. 2009, 11, 1702-1712) and very recent solid state NMR spectroscopy studies (J. Am. Chem. Soc. 2019, 141, 3444-3455). The inspection of the low energy bands (translational and optic modes) and librational bands of the experimental results allows obtaining information about the Hbond network of the hydronium-water cluster

A combined study of inelastic neutron scattering and ab initio molecular dynamics simulations has been performed in order to study the water-acid site interaction in zeolite chabazite with a ratio Si/Al = 16 that corresponds to 2 protons/uc with two different water coverages with the number of water molecules being lower and higher than that of proton sites. These results have provided a clear picture of the water-acid site interaction, and it has been demonstrated that there are two regimens of water adsorption, which depend on the water loading. (i) At low water coverage (water/acid site ∼0.5), the main interactions between water and the zeolitic acid sites are established through hydrogen bond and there is no proton transference to water. (ii) At relatively high water loading (water/acid site ∼3), the clustering of water molecules and hydronioum cations formed by the complete transference of the zeolitic proton to the water molecules has been observed. The formation of water-hydronium clusters interacting with oxygen atoms of the zeolite framework provides the stabilization energy needed for the protonation of water molecules confined in the cavities of chabazite. These results are the experimental evidence obtained from INS of proton transfer from the zeolitic acid site and the hydronium formation and are in agreement with a previous computational study (Phys. Chem. Chem. Phys. 2009, 11, 1702-1712) and very recent solid state NMR spectroscopy studies (J. Am. Chem. Soc. 2019, 141, 3444-3455). The inspection of the low energy bands (translational and optic modes) and librational bands of the experimental results allows obtaining information about the H-bond network of the hydronium-water cluster.

The functionalization of carbon nanotubes with fluorescent molecules is a standard procedure in many toxicity studies aiming at knowing their distribution within cells or whole organisms. Nevertheless, there is a lack of knowledge concerning the efficiency of the grafting processes, and more specifically concerning the question of the competition between covalent and non-covalent grafting. In this work, we investigated the grafting process of the fluorescein isothiocyanate (FITC) onto double-walled carbon nanotubes (DWNTs) using X-ray photoelectron spectroscopy, inelastic neutron scattering spectroscopy and computational simulations.We demonstrated that both covalent and non-covalent grafting occurred during the functionalization with the FITC. Moreover, we showed that a significant fraction of the fluorophore remained simply adsorbed onto the DWNTs despite thorough washing steps, which raises concerning questions about the use of this fluorophore in some toxicity studies and its possible ability to mislead their conclusions.

In amorphous materials, such as xerogels, the properties are the key to most of their applications. Therefore, it is of great importance to get insight into the xerogel structure. In order to achieve a better understanding of structure formation in methyl-silica xerogels and thus be able to better influence the properties of these materials, we have chosen the molecular approach to model the hybrid–xerogel structure using the density functional theory. A theoretical cage model for hybrid xerogels was performed from the PBEPBE/6-31G(d,p) method. The model could explain the presence of ordered domains in the structure. A comprehensive listing of all IR and 29Si NMR assignments is provided. The effects in the structure of the organic functional groups incorporated on the host structure network are investigated using inelastic neutron scattering spectroscopy (INS). The combination of experiments and modeling permitted an analysis of the INS studies, including unique INS assignments, contributing to the understanding of the skeletal SiO2 network of silica xerogels and so to obtain information about the structure of this material.

Discrimination between different gases is an essential aspect for industrial and environmental applications involving sensing and separation. Several classes of porous materials have been used in this context, including zeolites and more recently MOFs. However, to reach high selectivities for the separation of gas mixtures is a challenging task that often requires the understanding of the specific interactions established between the porous framework and the gases. Here we propose an approach to obtain an enhanced selectivity based on the use of compartmentalized coordination polymers, named CCP-1 and CCP-2, which are crystalline materials comprising isolated discrete cavities. These compartmentalized materials are excellent candidates for the selective separation of CO2 from methane and nitrogen. A complete understanding of the sorption process is accomplished with the use of complementary experimental techniques including X-ray diffraction, adsorption studies, inelastic- and quasi-elastic neutron scattering, magnetic measurements and molecular dynamics calculations.

Transformation of deuterated ethanol from the plastic crystal phase into the monoclinic one is investigated by means of a singular setup combining simultaneously dielectric spectroscopy with neutron diffraction. We postulate that a dynamic transition from plastic crystal to supercooled liquid-like configuration through a deep reorganization of the hydrogen-bonding network must take place as a previous step of the crystallization process. Once these precursor regions are formed, subsequent crystalline nucleation and growth develop with time. © 2014 AIP Publishing LLC.

Here we present an experimental setup to obtain information on structural and dynamical changes in liquids during crystallization. This setup consists in a sample cell that allows performing simultaneous measurements of neutron diffraction and dielectric spectroscopy experiments. The capabilities of the technique have been probed by following in real time the crystallization process of a model liquid: the isopropanol. By performing the simultaneous experiment information can be obtained from both phases, amorphous and crystalline, and therefore it can provide a complete description of the changes occurring during a crystallization process. The use of this setup allowed us to demonstrate that a breakage of the hydrogen-bond network is a precursor step for the crystallization of isopropanol. © 2005 American Institute of Physics.

Transformation of deuterated ethanol from supercooled liquid into a plastic crystal or rotator phase is investigated by means of a particular experimental setup combining simultaneously dielectric spectroscopy with neutron diffraction techniques. We demonstrate that, previous to the growth of the bcc lattice of the plastic crystal phase, the formation of a precursor or intermediate phase through a liquid-liquid phase separation takes place. Once this precursor phase is formed, subsequent (plastic) crystalline nucleation and growth is expected to develop.

The stochastic dynamics in molten nickel is studied by neutron scattering. The quasielastic spectrum shows two distinct components having disparate linewidths. The wave-vector dependence of the narrow component is shown to arise from incoherent scattering at low momentum transfers. In turn, the spectral half-width of the wider component shows a modulation with wave vector characteristic of coherent quasielastic scattering. The analysis of both components provides direct experimental estimates for the self-diffusion coefficient, as well as the effective particle diameter. The experimental data are then used to validate computer simulation results which are derived using an embedded-atom potential. Such results are also employed to explore regions in frequency-wave-vector space not easily amenable to experiment. In addition, simulation results are also compared with data pertaining to the collective motions. Such an exercise reveals the need to develop a further level in the memory function expansion of the coherent dynamic structure factor. The implications of such findings for our current understanding of the dynamics of liquid metals are finally assessed. © 2007 The American Physical Society.

The spectra of collective excitations of liquid and glassy tellurium have been studied by means of inelastic neutron scattering. Here we report on the dynamics of liquid Te as measured at two different temperatures, just above melting (Tm =723 K) and at ∼1000 K as well as the glass that is studied at room temperature. Estimates for the velocity of propagating excitations for both temperatures have been obtained from the experimental data, and a contrasting behavior is found with respect to anomalies shown by the adiabatic sound velocity measured by ultrasound methods. The origin of such differences is finally discussed. © 2006 The American Physical Society.

Dielectric spectroscopy and neutron diffraction experiments in acetone have been performed in order to clarify the dynamical behavior and the structural changes associated to the unsolved thermal transition that takes place in the solid state around 130 K. The combination of dielectric experiments with neutron diffraction reveals the existence of a dielectric process in the stable crystalline phase of acetone. The evolution with temperature of the dielectric process, within the temperature range where the peak of the heat capacity was reported, supports that the transition is not of order-disorder type. The origin of the dielectric dispersion has been assigned to structural defects in the orthorhombic crystal phase of acetone. © 2005 Elsevier B.V. All rights reserved.

Structural measurements combined with dynamical techniques were performed for investigating isopropanol crystallization in real time. Time resolved neutron diffraction, neutron scattering, and dielectric spectroscopy were also used for analyzing the hydrogen-bond network. A sample holder was designed from insulating anodized aluminum to perform neutron diffraction measurements. A breakage of the hydrogen-bond network was found to be the precursor step for the crystallization of isopropanol, as shown by the results.  2004 The American Physical Society

The origin of the three broad bands appearing in the dielectric spectra of molecular glass formers is tracked down to microscopic scales by means of neutron-scattering and molecular-dynamics simulations. Three distinct regimes are also seen in the neutron quasielastic spectrum and are shown to arise from well-separated time regions appearing in the single-particle dipole autocorrelation function derived from simulations. ©2004 American Physical Society