Quasi-elastic Neutron Scattering Measurements Research Articles

Evaluation of sample cell materials for aqueous solutions used in quasi-elastic neutron scattering measurements

For quasi-elastic neutron scattering (QENS) studies, sample cells made of pure or alloyed aluminium are frequently employed. Although the Al surface is protected by a passivating film, this film is not robust. Therefore, when the sample is an aqueous solution, chemical interactions between the Al surface and sample, promoted by corrosive entities such as chloride ions and certain conditions of pH, can compromise the integrity of the cell and interfere with the experiment. In this study, the corrosion susceptibilities of Al and its alloys were investigated by subjecting them to various treatments; the results were compared with those of other candidate materials with low chemical reactivity. This work showed that alloys with higher Al content and boehmite-coated surfaces are resistant to corrosion. In particular, for Al, the resistance is due to a reduction in the contact area achieved by reducing the surface roughness. QENS measurements of empty sample cells made of these materials revealed two results: (1) the profile of the cell fabricated with a copper-free Al alloy showed a minor dependence on the scattering vector magnitudeQand (2) reducing the real surface area of Al effectively suppresses its scattering intensity, while boehmite coating strengthens the scattering. Cells fabricated with Mo, Nb and single-crystal sapphire can be used as alternatives to Al because of their low scattering intensity and reduced dependence onQ.

Impact of Chemical Structure on the Dynamics of Mass Transfer of Water in Conjugated Microporous Polymers: A Neutron Spectroscopy Study.

Hydrogen fuel can contribute as a masterpiece in conceiving a robust carbon-free economic puzzle if cleaner methods to produce hydrogen become technically efficient and economically viable. Organic photocatalytic materials such as conjugated microporous materials (CMPs) are potential attractive candidates for water splitting as their energy levels and optical band gap as well as porosity are tunable through chemical synthesis. The performances of CMPs depend also on the mass transfer of reactants, intermediates, and products. Here, we study the mass transfer of water (H2O and D2O) and of triethylamine, which is used as a hole scavenger for hydrogen evolution, by means of neutron spectroscopy. We find that the stiffness of the nodes of the CMPs is correlated with an increase in trapped water, reflected by motions too slow to be quantified by quasi-elastic neutron scattering (QENS). Our study highlights that the addition of the polar sulfone group results in additional interactions between water and the CMP, as evidenced by inelastic neutron scattering (INS), leading to changes in the translational diffusion of water, as determined from the QENS measurements. No changes in triethylamine motions could be observed within the CMPs from the present investigations.

Simultaneous thermodynamic and dynamical characterisation using in situ calorimetry with neutron spectroscopy

Both Differential Scanning Calorimetry (DSC) and Quasi-elastic Neutron Scattering (QENS) are powerful analytical tools actively used in studies of phase transitions in complex solid and liquid systems. DSC is typical­ly used to map phase transition temperatures and identify sample states, and QENS provides information on the molecular scale dynamical motions, such as molecular self-diffusion or glassy dynamics, associated with such transitions. Both techniques provide highly valuable complementary information about the sample and in many cases it would be advantageous to measure in parallel with a view to linking the two observables. The biggest challenge is that the cell design which differs greatly between the two methods. Here we present a first attempt at designing a cryogenic system which will allow the simultaneous measurement of calorimetric transitions and QENS measurements, as tested on the neutron spectrometer IRIS at ISIS neutron scattering facility. The system temperature range is from 10 K to 300 K. We present and discuss the initial design of the system, preliminary test results, current challenges and limitations, and future directions.

Elastically Collective Nonlinear Langevin Equation Theory of Glass-Forming Liquids: Transient Localization, Thermodynamic Mapping, and Cooperativity.

We analyze multiple new issues concerning activated relaxation in glassy hard sphere fluids and molecular and polymer liquids based on the elastically collective nonlinear Langevin equation (ECNLE) theory. By invoking a high-temperature reference state, a near universality of the apparent dynamic localization length scale is predicted for liquids of widely varying fragility, a result that is relevant to recent simulation studies and quasi-elastic neutron-scattering measurements. In contrast, in the same format, a strongly nonuniversal behavior is found for the activation barrier that controls long-time relaxation. Two measures of cooperativity in the ECNLE theory are analyzed. A particle-level total displacement associated with the alpha relaxation event is found to be only of order 1-2 particle diameters and weakly increases with cooling. In contrast, an alternative cooperativity length is defined as the spatial scale required to essentially recover the full barrier and bulk alpha time. This length scale grows strongly with cooling because of the emergence in the deeply supercooled regime of collective long-range elastic fluctuations required to allow local hopping. It becomes very large as the laboratory Tg is approached, though it is relatively modest at degrees of supercooling accessible with molecular dynamics simulation. The alpha time is found to be exponentially related to this cooperativity length over an enormous number of decades of relaxation time that span the lightly to deeply supercooled regimes. Moreover, the effective barrier height increases almost linearly with the growing cooperativity length scale. An alternative calculation of the collective elastic barrier based on a literal continuum mechanics approach is shown to result in very little change of the theoretical results for bulk properties but leads to a much smaller and less temperature-sensitive cooperativity length scale.

Activation Energy of Organic Cation Rotation in CH3NH3PbI3 and CD3NH3PbI3: Quasi-Elastic Neutron Scattering Measurements and First-Principles Analysis Including Nuclear Quantum Effects.

The motion of CH3NH3+ cations in the low-temperature phase of the promising photovoltaic material methylammonium lead triiodide (CH3NH3PbI3) is investigated experimentally as well as theoretically, with a particular focus on the activation energy. Inelastic and quasi-elastic neutron scattering measurements reveal an activation energy of ∼48 meV. Through a combination of experiments and first-principles calculations, we attribute this activation energy to the relative rotation of CH3 against an NH3 group that stays bound to the inorganic cage. The inclusion of nuclear quantum effects through path integral molecular dynamics gives an activation energy of ∼42 meV, in good agreement with the neutron scattering experiments. For deuterated samples (CD3NH3PbI3), both theory and experiment observe a higher activation energy for the rotation of CD3 against NH3, which results from the smaller nuclear quantum effects in CD3. The rotation of the NH3 group, which is bound to the inorganic cage via strong hydrogen bonding, is unlikely to occur at low temperatures due to its high energy barrier of ∼120 meV.

Water dynamics in rigid ionomer networks.

The dynamics of water within ionic polymer networks formed by sulfonated poly(phenylene) (SPP), as revealed by quasi-elastic neutron scattering (QENS), is presented. These polymers are distinguished from other ionic macromolecules by their rigidity and therefore in their network structure. QENS measurements as a function of temperature as the fraction of ionic groups and humidity were varied have shown that the polymer molecules are immobile while absorbed water molecules remain dynamic. The water molecules occupy multiple sites, either bound or loosely constrained, and bounce between the two. With increasing temperature and hydration levels, the system becomes more dynamic. Water molecules remain mobile even at subzero temperatures, illustrating the applicability of the SPP membrane for selective transport over a broad temperature range.

How mobile are dye adsorbates and acetonitrile molecules on the surface of TiO2 nanoparticles? A quasi-elastic neutron scattering study.

Motions of molecules adsorbed to surfaces may control the rate of charge transport within monolayers in systems such as dye sensitized solar cells. We used quasi-elastic neutron scattering (QENS) to evaluate the possible dynamics of two small dye moieties, isonicotinic acid (INA) and bis-isonicotinic acid (BINA), attached to TiO2 nanoparticles via carboxylate groups. The scattering data indicate that moieties are immobile and do not rotate around the anchoring groups on timescales between around 10 ps and a few ns (corresponding to the instrumental range). This gives an upper limit for the rate at which conformational fluctuations can assist charge transport between anchored molecules. Our observations suggest that if the conformation of larger dye molecules varies with time, it does so on longer timescales and/or in parts of the molecule which are not directly connected to the anchoring group. The QENS measurements also indicate that several layers of acetonitrile solvent molecules are immobilized at the interface with the TiO2 on the measurement time scale, in reasonable agreement with recent classical molecular dynamics results.

Dynamics Study of Lithium Ion Diffusion in Super Lithium Ion Conductors, Li10GeP2S12 (LGPS)

Fast ionic conduction in solid electrolytes plays a key role in feasibility of the all-solid-state battery system. Among the lithium ion conductors, the Li10GeP2S12 (LGPS) system shows the conductivity comparable to organic liquid electrolytes [1]. The recent study focused on the synthesis of solid solutions of this material, which might introduce either lithium vacancy or interstitial lithium ions and might affect its ionic conductivity and electrochemical stability. The crystal structures of the solid solution were studied using neutron diffraction technique. Their conduction pathway was estimated using Maximum Entropy Method (MEM) based on the structure information. These results indicate the lithium conduction pathway in LGPS is one-dimensional pathway along c axis at room temperature, and three-dimensional one at higher temperature [2]. However, the results of MEM provided only the space area of possible lithium ion conduction. Then, the study of lithium diffusive behaviors is necessary to understand lithium ionic conductivity in more details. The dynamics of lithium ion diffusions can be obtained directly by using the Quasielastic Neutron Scattering (QENS) technique because the quasielastic scattering spectrum is a broadening of elastic peak caused by the diffusion of atoms or ions within a material. When ions cause diffusion motions on a fixed sublattice, the quasielastic scattering spectra can exhibit a Q-dependence, which provides information on the dynamical structure of the ions diffusion. In this study, the QENS measurements were performed using the high-resolution Si crystal analyzer TOF type near-backscattering spectrometer, DNA, at MLF/J-PARC, Tokai, Ibaraki, Japan, at the energy resolution of 3.6 µeV [3]. S(Q,ω) spectra from 150 to 640 K were collected. After the analyzed those using jump-diffuse model [4,5], self-diffusion constants, jump length and mean residence time of conduction lithium ions in LGPS system were determined. The jump length was 1.73 Å at 473K and 2.72 Å at 640 K respectively. The jump length at 473 K was consistent with conduction along caxis. The jump length at 640 K also corresponded to the three dimensional conduction model. In this presentation, the mechanism of lithium ion diffusion in LGPS system will be discussed.

Difference in the hydration water mobility around F-actin and myosin subfragment-1 studied by quasielastic neutron scattering

Hydration water is essential for a protein to perform its biological function properly. In this study, the dynamics of hydration water around F-actin and myosin subfragment-1 (S1), which are the partner proteins playing a major role in various cellular functions related to cell motility including muscle contraction, was characterized by incoherent quasielastic neutron scattering (QENS). The QENS measurements on the D2O- and H2O-solution samples of F-actin and S1 provided the spectra of hydration water, from which the translational diffusion coefficient (DT), the residence time (τT), and the rotational correlation time (τR) were evaluated. The DT value of the hydration water of S1 was found to be much smaller than that of the hydration water of F-actin while the τT values were similar between S1 and F-actin. On the other hand, the τR values of the hydration water of S1 was found to be larger than that of the hydration water of F-actin. It was also found that the DT and τR values of the hydration water of F-actin are similar to those of bulk water. These results suggest a significant difference in mobility of the hydration water between S1 and F-actin: S1 has the typical hydration water, the mobility of which is reduced compared with that of bulk water, while F-actin has the unique hydration water, the mobility of which is close to that of bulk water rather than the typical hydration water around proteins.

Diffusion of H2, CO2, and Their Mixtures in the Porous Zirconium Based Metal–Organic Framework MIL-140A(Zr): Combination of Quasi-Elastic Neutron Scattering Measurements and Molecular Dynamics Simulations

The diffusivity of H2 and CO2 in the small pore Zr based metal–organic framework (MOF) MIL-140A(Zr) has been evaluated using a combination of quasi-elastic neutron scattering measurements and molecular dynamics simulations. These two techniques were used to determine the self-diffusivities of H2, and the corrected and transport diffusivities of CO2, as single components and binary mixture. H2 was shown to be the faster of the two gases to diffuse through the narrow triangular channel of MIL-140A(Zr), its self-diffusivity value being 1 order of magnitude higher than that of CO2, at the same temperature. In this case, although no specific interaction sites are present, the CO2 interacts more strongly with the pore wall than H2, partly a consequence of its greater kinetic radius, which renders it slower than H2. In the context of a binary mixture, H2 still diffuses faster between the two, although with a slightly lower self-diffusivity, while that of CO2 increases slightly. However, the difference in terms o...

Monitoring the dynamics of miscible P3HT:PCBM blends: A quasi elastic neutron scattering study of organic photovoltaic active layers

This work addresses the detailed molecular dynamic behavior of miscible blends of Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and their pure counterparts by quasi-elastic neutron scattering measurements (QENS). The study provides the measure of relaxation processes on pico-to-nanosecond time scales. A single relaxation process was observed in pure P3HT and PCBM while two relaxation processes, one fast and one slow, were observed in the blends. The fast process was attributed to the dynamics of P3HT while the slow process was correlated to the dynamics of PCBM. The results show that the relaxation process is a balance between two opposing effects: increased mobility due to thermal activation of P3HT molecules and decrease mobility due to the presence of PCBM which is correlated to the percent crystallinity of P3HT and local packing density of PCBM in the amorphous phase. The threshold for the domination of the thermally activated relaxation is between 5 and 9 vol.% of PCBM loading. Two distinct spatial dependences of the relaxation processes, in which the crossover length scale depends neither on temperature nor composition, were observed for all the samples. They were attributed to the collective motions of the hexyl side chains and the rotational motions of the C–C single bonds of the side chains. These results provide an understanding of the effects of PCBM loading and temperature on the dynamics of the polymer-fullerene blends which provides a tool to optimize the efficiency of charge carrier and exciton transport within the organic photovoltaic (OPV) active layer to improve the high performance of organic solar cells.

Anion Reorientations in the Superionic Conducting Phase of Na2B12H12

Quasielastic neutron scattering (QENS) methods were used to characterize the reorientational dynamics of the dodecahydro-closo-dodecaborate (B12H122–) anions in the high-temperature, superionic conducting phase of Na2B12H12. The icosahedral anions in this disordered cubic phase were found to undergo rapid reorientational motions, on the order of 1011 jumps s–1 above 530 K, consistent with previous NMR measurements and neutron elastic-scattering fixed-window scans. QENS measurements as a function of the neutron momentum transfer suggest a reorientational mechanism dominated by small-angle jumps around a single axis. The results show a relatively low activation energy for reorientation of 259 meV (25 kJ mol–1).

Effect of Surface Passivation in Spinel Slurry Toward Hydrolysis: Neutron Scattering and Rheological Studies

Aqueous colloidal forming of magnesium aluminate (MgAl2O4) spinel offers much potential for various applications; however, these advantages are generally offset by the basic nature of the powder and its affinity for hydrolysis. Hydrolysis in the presence of water generally imparts surface chemical changes resulting in the degradation of colloidal stability. In the present study, spinel powders were subjected to thermally assisted surface passivation and evaluated for the effectiveness of preventing hydrolysis through quasielastic neutron scattering (QENS) technique and correlated with rheological measurements. In order to evaluate the extent of hydrolysis, spinel slurries prepared with (SP) and without surface passivation (WSP) were studied by rheological and QENS measurements at regular intervals of time. While WSP slurry exhibited a steep enhancement in viscosity from 1.02 to 19.4 Pa · s and fraction of the elastic intensity from 0.20 to 0.38 for 96 and 200 hours, respectively, a negligible change in viscosity for SP slurries from 0.313 to 0.345 Pa · s and fraction of the elastic intensity from 0.16 to 0.17 for the similar period confirmed the inhibition of hydrolysis, revealing change in surface chemistry due to hydrolysis. Microscopic details as obtained from neutron scattering data revealed that dynamical behavior of water molecules in both the slurries could be described very well by the Singwi–Sjolander model of jump diffusion. Further analysis showed lower diffusivity ∼1.82 × 10−5 cm2/sec and higher residence time ∼6.39 ps for WSP slurry in comparison with 2.16 × 10−5 cm2/sec and 5.80 ps, complimenting the inhibition of hydrolysis in case of SP slurry.

Ion Conducting Behavior in Secondary Battery Materials Detected by Quasi-elastic Neutron Scattering Measurements

Ionic conducting behaviors in secondary battery materials, i.e. cathode and solid electrolyte, were studied with quasi-elastic neutron scattering (QENS) measurements. Although the incoherent scattering length for Li and Na is lower by two orders of magnitude than that for H, the QENS spectra were clearly detected using the combination of an intense neutron source and a low background spectrometer. The fundamental parameters, such as, the activation energy, the jump distance, and the diffusion coefficient were obtained by analyzing QENS spectra. These parameters are consistent with the previous results estimated by muon-spin relaxation (μSR) measurements and first principles calculations.

Li diffusive behavior of garnet-type oxides studied by muon-spin relaxation and QENS

A diffusive behavior of Li+ ion in a garnet-type oxide, Li5 + xLa3ZrxNb2 − x012 with x = 0–2, has been investigated by both a positive muon-spin relaxation (μ+SR) and quasi-elastic neutron scattering (QENS) technique using powder samples. The μ+SR results revealed that Li+ ions start to diffuse above ~ 150 K for the whole samples measured. The activation energy of Li diffusion (Ea) estimated from the μ+SR data was in good agreement with Ea obtained by the QENS measurements. However, both Eas were about a half of Ea of ionic conductivity of Li+ (σLi), which was evaluated by AC-impedance measurements on sintered pellets. This indicated the serious effect of grain boundary and/or surface on Ea. Furthermore, since the diffusion coefficient of Li+ estimated by μ+SR is roughly independent of x, the number of mobile Li+ in the garnet lattice was found to be the predominant parameter to determine σLi.

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.

Characterization of Morphology and Active Agent Mobility within Hybrid Silica Sol–Gel Composites

The porous properties of sol–gels make them attractive choices for developing functional materials requiring the controlled release of entrapped active agents for a range of applications that include protective coatings, sensors, self-healing films, and drug delivery. In this study, we investigate the properties of sodium benzoate as a model active agent entrapped within a mesoporous silica matrix formed from the biocompatible precursor diglycerylsilane (DGS). Quasi-elastic neutron scattering (QENS) is used to measure the mobility and diffusion of the mobile species in the gels, whereas small-angle neutron scattering (SANS) provides key information on the structural features of the gels. QENS measurements indicate that the diffusivity of the benzoate species decreases approximately 4-fold, from 14.3 × 10–10 m2 s–1 in bulk solution to 3.3 × 10–10 m2 s–1 following entrapment within DGS-derived sol–gels. A similar trend is exhibited by water entrapped within the porous network. However, subsequent detailed a...

ChemInform Abstract: Quasielastic Neutron Scattering Measurements of n-Butane in Its Crystalline, Plastic, and Liquid Phases

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Dynamics of Propylene adsorbed in Na-Y and Na-ZSM5 Zeolites: A QENS and MD Simulation Study

Abstract Here we report dynamics of propylene (smallest asymmetric hydrocarbon) adsorbed in two different host systems – Na-Y and Na-ZSM5 zeolites as studied by quasielastic neutron scattering (QENS) techniques and molecular dynamics (MD) simulation techniques. MD simulation studies suggested that the rotational motion of propylene is much faster than the translation. Therefore, two different spectrometers were used to determine the translational and rotational contributions. Analysis of the QENS data (ΔE~200 μeV) revealed that the translational motion of propylene in Na-ZSM5 zeolite is a factor of 3 slower than that in Na-Y zeolite. This is consistent with the smaller void volume available in Na-ZSM5 zeolite as also the fact that the adsorption of propylene is stronger in Na-ZSM5 as compared to that in Na-Y zeolite as indicated in the Fourier Transformed Infra Red (FTIR) studies. This result is further corroborated by the MD simulation studies. It was found that the translation motion occurs at three time scales in both the systems, only one of which corresponds to that observed through the QENS measurements. To probe the faster rotational motion experiments were carried out on a Triple axis spectrometer with wider energy window (ΔE~3meV). The variation of the elastic incoherent structure factor (EISF) suggests that the observed QE broadening corresponds to isotropic rotational motion of propylene in both the hosts. Rotational diffusion coefficients of propylene molecules are found to be of the same order in both zeolites. Trajectories obtained from MD simulation corresponding to the rotational motion revealed that although on a large time scale, the rotation appears isotropic, but at short time scales the channel structure of the Na-ZSM5 restrict the rotation of propylene molecules. This is in contrast with propylene adsorbed in Na-Y zeolite where rotation remains isotropic even at short time scale. A comparison with other hydrocarbon-zeolite systems as studied by us is also presented here.

Translational and Rotational Dynamics of Monosaccharide Solutions

Molecular dynamics computer simulations have been carried out on aqueous solutions of glucose at concentrations bracketing those previously measured with quasi-elastic neutron scattering (QENS), in order to investigate the motions and interactions of the sugar and water molecules. In addition, QENS measurements have been carried out on fructose solutions to determine whether the effects previously observed for glucose apply to monosaccharide solutions. The simulations indicate a dynamical analogy between higher solute concentration and lower temperature that could provide a key explanation of the bioprotective phenomena observed in many living organisms. The experimental results on fructose solutions show qualitatively similar behavior to the glucose solutions. The dynamics of the water molecules are essentially the same, while the translational diffusion of the sugar molecules is slightly faster in the fructose solutions.