Incoherent Quasi-elastic Neutron Scattering Research Articles

Proton Diffusion in Liquid 1,2,3-Triazole Studied by Incoherent Quasi-Elastic Neutron Scattering.

Improving the proton transport in polymer electrolytes impacts the performance of next-generation solid-state batteries. However, little is known about proton conductivity in nonaqueous systems due to the lack of an appropriate level of fundamental understanding. Here, we studied the proton transport in small molecules with dynamic hydrogen bonding, 1,2,3-triazole, as a model system of proton hopping in a nonaqueous environment using incoherent quasi-elastic neutron scattering. By using the jump-diffusion model, we identified the elementary jump-diffusion motion of protons at a much shorter length scale than those by nuclear magnetic resonance and impedance spectroscopy for the estimated long-range diffusion. In addition, a spatially restricted diffusive motion was observed, indicating that proton motion in 1,2,3-triazole is complex with various local correlated dynamics. These correlated dynamics will be important in elucidating the nature of the proton dynamics in nonaqueous systems.

Quasielastic Neutron Scattering Study on Polymorphism of Glycerol Deuterated Triacylglycerols: Comparison with Saturated, Trans-unsaturated and Cis-unsaturated Triacylglycerols

The relationship between the polymorphism and dynamic properties of acyl chains in triacylglycerols (TAGs) was studied using incoherent quasielastic neutron scattering (IQENS). The influence of cis...

Molecular Basis of Water Activity in Glycerol-Water Mixtures.

Water activity (Aw) is a reliable indication of the microbial growth, enzymatic activity, preservation, and quality of foods. However, a molecular basis of Aw is still under debate in multiple related disciplines. Glycerol–water mixtures can provide a variation of Aws by controlling the ratio of glycerol and water. In this study, the molecular basis of Aw was examined by using differential scanning calorimetry (DSC), attenuated total reflection Fourier-transform infrared spectroscopy (ATR-IR), and incoherent quasi-elastic neutron scattering (IQENS) based on moisture sorption isotherms of glycerol–water mixtures. Three regions were identified and classified based on DSC results. DSC showed that bulk-like water existed at Aw > ≈ 0.7 at 27°C. Hydrogen bonding related molecular vibrations were analyzed by ATR-IR, which indicated that the OH stretching in water molecules is significantly different for Aw > ≈ 0.7. Translational diffusive and/or rotational motions in time and space analyzed by IQENS appeared when Aw > ≈ 0.7, and are correlated with hydrogen bonding related local vibrational dynamics in the glycerol–water mixtures. More importantly, Aw values of glycerol–water mixtures can be explained by the hydrogen bonding network and molecular dynamics of water in the solution. We discuss the implications of Aw in the preservation of food at the molecular level.

Molecular Dynamics of POPC Phospholipid Bilayers through the Gel to Fluid Phase Transition: An Incoherent Quasi-Elastic Neutron Scattering Study

The microscopic dynamics for the gel and liquid-crystalline phase of highly aligned D2O-hydrated bilayers of 1-palmitoyl-oleoyl-sn-glycero-phosphocholine (POPC) were investigated in the temperature range from 248 to 273 K by using incoherent quasi-elastic neutrons scattering (QENS). We develop a model for describing the molecular motions of the liquid phase occurring in the 0.3 to 350 ps time range. Accordingly, the complex dynamics of hydrogen are described in terms of simple dynamical processes involving different parts of the phospholipid chain. The analysis of the data evidences the existence of three different motions: the fast motion of hydrogen vibrating around the carbon atoms, the intermediate motion of carbon atoms in the acyl chains, and the slower translational motion of the entire phospholipid molecule. The influence of the temperature on these dynamical processes is investigated. In particular, by going from gel to liquid-crystalline phase, we reveal an increase of the segmental motion mainly affecting the terminal part of the acyl chains and a change of the diffusional dynamics from a localized rattling-like motion to a confined diffusion.

The measurement of self-diffusion coefficients in liquid metals with quasielastic neutron scattering

Quasielastic incoherent neutron scattering (QENS) has proven to be a versatile tool to study self diffusion of atoms in liquid metals. Here it is shown, that coherent contributions to the signal in the smallq limit appear as aflat and energy independent constant to the QENS signal in single-component liquid metals even for systems with a small incoherent scattering cross section, like aluminum. Container-less processing via electromagnetic or electrostatic levitation devices, especially designed for QENS, enables the in-situ measurement on liquid metallic droplets of sizes between 5mm to 10mm in diameter. This gives access to the study of chemically reactive, refractory metallic melts and extends the accessible temperature range to undercoolings of several hundred Kelvin below the respective melting point. Compared to experiments using a thin-walled crucible giving hollow-cylindrical sample geometry it is shown that multiple scattering on levitated droplets is negligible for the analysis of the self-diffusion coefficient. QENS results of liquid germanium and 73 germanium isotope mixtures, titanium, nickel, copper and aluminum are reviewed. The self-diffusion coefficients of these systems are best described by an Arrhenius-type temperature dependence around their respective melting points.

Microscopic dynamics of glycerol: a QENS study

We report on a quasielastic incoherent neutron scattering (QENS) experiment on liquid glycerol. QENS data were collected at the temperature T=380 K and with a resolution (FWHM) R=55μeV. The analysis of the quasielastic signal enables us to draw a consistent picture of the diffusive mechanism on a picosecond time scale and to compare with most recent models for glycerol dynamics. Model selection, performed with the fitting algorithm FABADA, gives us a preliminary description about the motions of the glycerol molecules in its liquid state.

Polymer Diffusion in Microgels with Upper Critical Solution Temperature as Studied by Incoherent Neutron Scattering

Poly(acrylic-acrylamide) interpenetrated microgels present continuous phase transition from collapsed to swollen state around 42 °C. The upper critical solution temperature (UCST) of this polymeric system has prompted scientists to consider them candidates for its use in biological applications such as smart drug delivery devices since the swelling of the polymer matrix would permit the release of the drug previously entrapped within the microgels. In these systems the increment of the temperature can break inter-chain interactions, mainly hydrogen bonds, which reduce the elastic tension that stabilizes the microgel, favoring the polymer swelling. The microgel molecular dynamics at the UCST can be investigated using Incoherent Elastic (IENS) and Quasielastic Neutron Scattering (IQNS). From the analysis of the IQNS data we obtained that the diffusion coefficient of the polymer segments depends on the composition of the interpenetrated matrix. Thus, at room temperature, microgels with a polymer composition of 50% of each component present a diffusion coefficient 1·10−12 m2/s, while for the microgels formed by only one component the diffusion coefficient is 5.10−10 m2/s. This huge difference in the diffusion coefficient is conspicuously reduced when temperature increases, and we attribute this effect to the breaking of the inter-chain interaction. By means of FTIR-ATR analysis we have identified the groups that are involved in this phenomenon and we associate the breaking of the polyacrylic-polyacrylamide interactions with the swelling of the microgels.

Vibrations and reorientations of H2O molecules in [Sr(H2O)6]Cl2 studied by Raman light scattering, incoherent inelastic neutron scattering and proton magnetic resonance

Vibrational–reorientational dynamics of H2O ligands in the high- and low-temperature phases of [Sr(H2O)6]Cl2 was investigated by Raman Spectroscopy (RS), proton magnetic resonance (1H NMR), quasielastic and inelastic incoherent Neutron Scattering (QENS and IINS) methods. Neutron powder diffraction (NPD) measurements, performed simultaneously with QENS, did not indicated a change of the crystal structure at the phase transition (detected earlier by differential scanning calorimetry (DSC) at TCh=252.9K (on heating) and at TCc=226.5K (on cooling)). Temperature dependence of the full-width at half-maximum (FWHM) of νs(OH) band at ca. 3248cm−1 in the RS spectra indicated small discontinuity in the vicinity of phase transition temperature, what suggests that the observed phase transition may be associated with a change of the H2O reorientational dynamics. However, an activation energy value (Ea) for the reorientational motions of H2O ligands in both phases is nearly the same and equals to ca. 8 kJmol−1. The QENS peaks, registered for low temperature phase do not show any broadening. However, in the high temperature phase a small QENS broadening is clearly visible, what implies that the reorientational dynamics of H2O ligands undergoes a change at the phase transition. 1H NMR line is a superposition of two powder Pake doublets, differentiated by a dipolar broadening, suggesting that there are two types of the water molecules in the crystal lattice of [Sr(H2O)6]Cl2 which are structurally not equivalent average distances between the interacting protons are: 1.39 and 1.18Å. However, their reorientational dynamics is very similar (τc=3.3⋅10−10s). Activation energies for the reorientational motion of these both kinds of H2O ligands have nearly the same values in an experimental error limit: and equal to ca. 40kJmole−1. The phase transition is not seen in the 1H NMR spectra temperature dependencies. Infrared (IR), Raman (RS) and inelastic incoherent neutron scattering (IINS) spectra were calculated by the DFT method and quite a good agreement with the experimental data was obtained.

Diffusive Properties of , -Trehalose-Water Solutions

In the present work the results of an experimental study on trehalose aqueous solutions, performed by means of Photon Correlation Spectroscopy and Incoherent Quasi Elastic Neutron Scattering measurements, are reported and discussed. The experimental findings allow to separate the self- and collective contributions, revealing the presence of two distinct translational diffusive mechanisms which have been assigned to the continuous translational diffusion of the trehalose molecules and to the translational jump diffusion of the water molecules. Furthermore, the comparison between the self- and the collective diffusion coefficient, furnishes useful information on the interaction nature among the hydrated trehalose molecules.

Molecular Dynamics and Macroscopic Properties of Magnetic Microgels

Thermo-sensitive microgels based on poly(N-isopropyl acrylamide) (PNIPAM) were covered with nanoparticles of γ-Fe2O3 with size around 6 nm. When the inorganic cover was 18% (w/w) respect the polymer part, the microgels presented magnetic properties in addition to their inherent thermo-sensitivity. The interactions existing between the magnetic nanoparticles and the polymer matrix provoke the shifting of the microgel volume transition to higher temperatures when the amount of γ-Fe2O3 increases. The study performed using incoherent quasielastic neutron scattering (IQNS) confirms that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both, the mean square displacement of the polymer segments and the diffusive motion of the polymer chains, decrease as the iron oxide content increases. The reduction of vibrational and diffusional motions of the polymer chains is attributed to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles that explains the reduction of the swelling capacity of the microgels and the shift of the polymer volume transition to higher temperatures with increasing the iron content.

ChemInform Abstract: Neutron Investigation of Reorientations in Organic Molecular Compounds

Abstract The application of the Incoherent Quasielastic Neutron Scattering (IQNS) technique to the study of the dynamic disorder in molecular crystals is illustrated by a series of recent experiments. First, some basic principles of incoherent neutron scattering from organic hydrogenous compounds are outlined. The Elastic Incoherent Structure Factor (EISF), a fundamental quantity directly related to the spatial average distribution of the scatterers, is introduced. An illustration of the isotropic rotational model is provided by the case of norbornane. A comparison is made with a related compound, norbornadiene, the latter providing evidence of a strong translation—rotation coupling. The case of deformable molecules is illustrated with different analyses of the dynamics of alkyl chains in various situations. The flexibility of the chains is analysed for tetracarboxylate complexes in liquid-crystal phases, decylammonium and alkylene diammonium molecules in perovskite-type layered crystalline structures, and nonadecane in its rotator phase. Some studies related to alkanes in inclusion compounds are also covered. The final part of the paper is devoted to recent studies of glassy and metastable phases, and also to critical phenomena. We report on the dynamics of the cyanoadamantane molecules in the quenched glassy phase and on the modifications observed by aging of the sample. In the case of p-terphenyl, long-range correlations appear when approaching the phase transition on cooling and contribute to the scattered intensity. We conclude with a description of the rich polymorphism of methoxybenzylidenebutylaniline, where the quenched degrees of freedom are progressively relaxed in a succession of metastable phases.

Thermal Motion in Water + Electrolyte Solutions According to Quasi-Elastic Incoherent Neutron Scattering Data

The main attention of this article is focused on the study of the physical mechanisms of thermal motion in water and water + electrolyte solutions that lead to the broadening of the incoherent neutron scattering peak. It is taken into account that the neutron peak has a diffusion nature and is described by a Lorentzian line shape only for wave vectors k having magnitudes |k| ≡ k ≪ 1/a, where a is the interparticle spacing. A modified version of the theory developed by Singwi and Sjolander (Phys. Rev. 1960, 119, 863) for the description of the Lorentzian half-width is proposed. It is shown that for k > 1/a, the neutron peak is described by a Gaussian line shape whose half-width is proportional to the average thermal velocity of the Lagrange particles. The relevant theoretical parameters can be determined by fitting experimental data for the half-width of the neutron peak. In such a way, the self-diffusion coefficients of water molecules, their collective parts, and the residence times as well as the radii ...

Incoherent Quasielastic Neutron Scattering study of hydrogen diffusion in thorium–zirconium hydrides

Monophase thorium–zirconium hydrides (ThZr 2H x ) have been fabricated starting from a metallic alloy and the hydrogen stoichiometry determined by X-ray diffraction. Incoherent Quasielastic Neutron Scattering (IQNS) on the hydrides was conducted over the temperature range 650–750 K at the Backscattering Silicon Spectrometer (BASIS) at the Spallation Neutron Source (SNS) at ORNL. The isotropic Chudley–Elliott model was utilized to analyze the quasielastic linewidth broadening data as function of momentum transfer. The diffusion coefficient and average jump distance of hydrogen atoms in ThZr 2H 5.6 and ThZr 2H 6.2 were extracted from the measurements.

Investigation of the Relationship between Hydrogen Bonds and Macroscopic Properties in Hybrid Core−Shell γ-Fe2O3−P(NIPAM-AAS) Microgels

We investigate in a hybrid material the interactions existing between magnetic nanoparticles of gamma-Fe(2)O(3) and the polymer matrix constituted by core-shell poly(N-isopropylacrylamide-sodium acrylate) microgels. These interactions provoke the shifting of the microgel volume phase transition to higher temperatures when the amount of gamma-Fe(2)O(3) increases. The study was performed using different techniques such as incoherent quasi-elastic neutron scattering (IQNS), infrared spectroscopy (FTIR-ATR), and dynamic light scattering (DLS). Below the low critical solution temperature (LCST) of the polymer, the IQNS data confirm that the presence of inorganic nanoparticles affects the PNIPAM chain motions. Thus, in the swollen state both the mean-square displacement of the polymer segments and the diffusive motion of the polymer chains decrease as the iron oxide content increases. The FTIR-ATR study indicates that the reduction of vibrational and diffusional motions of the polymer chains is due to the formation of hydrogen bonds between the amide groups of the polymer matrix and the OH groups of the magnetic nanoparticles. The creation of this hybrid complex would explain the reduction of the swelling capacity with increasing the iron content in the microgels. Furthermore, this interaction could also explain the shift of the polymer LCST to higher temperatures as due to the extra energy required by the system to break the hydrogen bonds prior to the PNIPAM collapse.

Dynamics of functionalized single wall carbon nanotubes in solution studied by incoherentneutron scattering experiments

We have studied, by incoherent neutron scattering experiments, the dynamics of acolloidal suspension of functionalized single wall carbon nanotubes (SWNTs).The nanotubes have been functionalized with pentyl ester groups attached atthe ends and suspended in deuterated toluene with a concentration of 2.6 mgSWNT/1 ml of deuterated toluene. The experimental techniques were incoherent elastic neutron scattering(IENS) and incoherent quasielastic neutron scattering (IQNS). In the temperature rangebetween 4 K and 300 K, three phases were observed by IENS measurements: a solid phase forT<Tg, an undercooledliquid phase for Tg<T<Tm anda liquid phase for T>Tm. Furthermore, in the high temperature range of the undercooled liquidphase, hysteresis loops in the heating and cooling scans were observed. Thelower limit of the hysteresis loop defines the critical crossover temperatureTc. IQNS measurements in the liquid phase and a cooling scan of the undercooledliquid phase were performed. Three different quasielastic peaks were identified,two in the liquid phase and another one in the undercooled liquid phase. Thewidths of the quasielastic peaks are discussed as a generalized diffusion functionwhich can be factorized as a temperature dependent diffusion function and aQ dependent structure function. From the comparison of the diffusion function with theviscosity of toluene, we conclude that two components are in the long-time rangeBrownian motion and the other one in the short-time range Brownian motion.

Incoherent Quasielastic Neutron Scattering Study on the Polymorphism of Tristearin: Dynamical Properties of Hydrocarbon Chains

Dynamical properties of acyl chains in the three polymorphic phases alpha, beta', and beta of tristearin [C(3)H(5)(OCOC(17)H(35))3] have been studied by means of incoherent quasielastic neutron scattering (IQNS) using selectively deuterated samples. The mean square displacement of hydrogen atoms, <U2>, was estimated from the scattering vector Q dependence of the elastic scattering component under the harmonic approximation. It was shown that the temperature dependence of <U2> was significantly different between the three phases. There was no marked difference in <U2> between these phases up to 193 K, and the <U2> value increased linearly with temperature. Although the beta phase remained linear up to 293 K, the alpha and beta' phases started to show a nonlinear increase around 200 K, suggesting an anharmonic nature of molecular motions. The alpha phase exhibited the most conspicuous temperature dependence. These characteristics were ascribable to the difference in the lateral packing of acyl chains. Compared with the beta phase which has a tightly packed T// subcell, the beta' and alpha phases have looser O perpendicular and H subcells, respectively. The molecular motion in the alpha phase was analyzed using the model of uniaxial rotational diffusion in a onefold cosine potential. It has been clarified that the rotational fluctuation about the chain axis in the alpha phase is rather restricted compared with that in the rotator phase of n-alkanes.

Diffusive dynamics of water in ion-exchanged zeolites

In this paper, an incoherent quasi-elastic neutron scattering (IQENS) study of the single-particle dynamics of water in fully hydrated Na-A and Mg50-A zeolites at T = 293 K and T = 333 K is presented. In order to probe different time scales, measurements were made at two resolutions, ∼8 µeV and ∼28 µeV. The high-resolution data allowed us to investigate the slower dynamics, which is mainly translational. The low-resolution spectra were used to probe the faster dynamics and distinguish between diffusional and rotational motion. We found that the partial exchange of Na+ with Mg2+ induces: (a) an increase of the available volume for diffusion; (b) a decrease of the fraction of water molecules taking part in the observed jump diffusion process; and (c) a shortening of the residence time.

Iqens study of the influence of confinement on diffusional dynamics of propylene glycol

The modification, compared to the bulk state, of the dynamics of liquids in confined geometry has attracted considerable interest in scientific research, also because of the close connection with many relevant technological problems, such as the building of optical switches, membrane separation, catalysis and tertiary oil recovery. We report the preliminary results of an Incoherent Quasi Elastic Neutron Scattering (IQENS) investigation on propylene glycol (PG: H[OCH(CH 3)CH 2]OH), a low molecular weight polymer, both in the bulk and in the confined state, in order to show the different dynamical behaviour of this system as a consequence of the presence of an interface. In particular PG was confined in 26 Å pores of a porous sol–gel glass with unmodified and modified inner surface, trying to distinguish the different role played by hydrophobic and hydrophilic confinement on its diffusive motion. The data have been interpreted in the framework of the well known Volino–Dianoux model for confined diffusion, and compared with the most recent literature in this field.

Diffusional and vibrational dynamics of water in NaA zeolites by neutron and Fouriertransform infrared spectroscopy

This paper reports the most recent results of a detailed spectroscopic analysis of waterconfined in NaA zeolitic matrix, performed, as a function of temperature andhydration level, by means of the simultaneous use of incoherent quasi-elasticneutron scattering (IQENS) and Fourier transform infrared (FT-IR) absorption.The diffusive process reveals a rather wide distribution of relaxation times. Furthermore, we observeda Q-dependence of the mean relaxation time which does not disagree with the mode coupling theory for associated liquids.As far as vibrational dynamics is concerned, the spectral substructure of theH2O bending(1500–1800 cm−1) andO–Hstretching (3000–3800 cm−1) bands has been interpreted in the framework of actual theories for associated liquids andon the basis of previous measurements performed, by Raman scattering, on water confinedin a controlled silica glass (GelSil). From a comparison of the results in these twocases, the ‘structure-maker’ role on confined water, played by the NaA zeolite,and the ‘structure-breaker’ role, played by the GelSil, have been clearly shown.

Vibrational and diffusional dynamics of water in Mg50-A zeolites by spectroscopic investigation

The spectral substructure of the O–H stretching mode of water confined in Mg50-A zeolites is demonstrated, in full hydration conditions and in the temperature range 20–80°C, using Fourier transform Infrared (FT-IR) spectroscopy. Band shapes have been fitted to individual components, according to the actual theories for associated liquids, and three major constituent peaks were derived, at 3230 cm−1 (ω1), 3460 cm−1 (ω2), and 3600 cm−1 (ω3). They have been related, respectively, to an ice-like molecular environment and other hydrogen-bonding configurations. A detailed quantitative analysis of their centre frequencies and relative intensities, traced over the full temperature range investigated, has led to the conclusion that these subbands show direct evidence, under confinement, of bifurcated hydrogen bonds (BHB) among three water molecules as a main feature of the structure of liquid water. The most interesting result comes from the observation, at all temperatures, of the tetrahedral connectivity typical of bulk water. In this sense, we attributed to the zeolitic surface a ‘structure-maker’ role on physisorbed water. This role becomes particularly relevant at the lowest temperature, where the ice-like contribution appears to be the favoured one even under confinement. Furthermore, preliminary results are presented of an incoherent quasi-elastic neutron scattering (IQENS) investigation of the diffusional dynamics of water in the same system, at T=20°C, analysed in the framework of the Confined Diffusion Model (CDM).