Quasielastic Neutron Scattering Research Articles

Experimental analysis on dynamics of liquid molecules adjacent to particles in nanofluids

Quasi-elastic neutron scattering (QENS) and pulsed-field-gradient nuclear magnetic resonance (PFG-NMR) analyses of a nanofluid composed of silicon dioxide (SiO2) nanoparticles (sized 100, 300, or 500 nm) and a base fluid of ethylene glycol aqueous solution were performed. The aim was to elucidate the mechanism increase in the thermal conductivity of the nanofluid above its theoretical value. Typically, the self-diffusion coefficient of liquid molecules in nanofluids can indicate the effect of the nanoparticles on thermal transport in nanofluids as well as the molecular dynamics of the liquid surrounding the nanoparticles. At 298 and 333 K, the obtained experimental results indicate that SiO2 particles may decrease the self-diffusion coefficient of the liquid molecules in the ethylene glycol aqueous solution because of their highly restricted motion around these nanoparticles. The self-diffusion coefficient of the liquid molecules comprising 300 nm-sized particles is lower than that of the nanofluids comprising 100 and 500 nm-sized particles. At a constant temperature, the thermal conductivity increases as the self-diffusion coefficient of the liquid molecules decreases in the SiO2 nanofluids.

Microscopic dynamics of lithium diffusion in single crystal of the solid-state electrolyte La2/3−xLi3xTiO3 ( x=0.13 ) studied by quasielastic neutron scattering

Quasielastic neutron scattering (QENS) measurements combined with first principles based moleculardynamics calculations were conducted to study the dynamics of Li$^+$ ions in a solid-state electrolyte La$_{2/3-x}$Li$_{3x}$TiO$_{3}$ (LLTO) with $x=0.13$. By using a large $^7$Li-enriched single crystal sample, a QENS signal was clearly observed along the three principal axes [110], [111], and [001] at a temperature ($T$) of 600 K. Wave vector dependence of the linewidth of the QENS signal along each direction was explained well using the Chudley-Elliot model for jumps between the A sites of the perovskite lattice through the bottleneck square, which was also supported by molecular dynamics calculations. At $T=600$ K, the estimated self-diffusion coefficient of Li$^+$ ($D_{Li}$) in the $ab$ plane [$D^{ab}_{Li}=(6.8\pm0.5)\times 10^{-6}$ cm$^2$/s] was slightly larger than that along the $c$ axis [$D^{c}_{Li}=(4.4\pm0.3)\times 10^{-6}$ cm$^2$/s], suggesting quasi-isotropic diffusion, that is, the three-dimensional diffusion of Li$^+$ ions. The decrease in $D_{Li}$ with decreasing $T$ was reasonably explained by a thermal activation process with the activation energy determined from ionic-conductivity measurements. Furthermore, the estimated values of the self-diffusion coefficient of Li$^+$ ions are comparable to those in the sulfide-based Li$^+$ ion conductor, Li$_{7}$P$_{3}$S$_{11}$, although its ionic conductivity is 10 times larger than that for LLTO. The obtained microscopic information on Li$^+$ diffusion in LLTO clarifies how to understand the Li conduction mechanism in LLTO and Li$_{7}$P$_{3}$S$_{11}$ in a unified manner and can provide a way to increase the Li$^+$ ionic conductivity in oxide-based solid electrolytes.

Investigations of structural and dynamical mechanisms of ice formation regulated by graphene oxide nanosheets.

Recent research indicates that graphene oxide (GO) nanosheets can be used to regulate ice formation by controlling critical ice nucleus growth in water at supercooling temperatures. In addition, the study of ice formation mechanisms regulated by GO nanosheets, a good model system for antifreeze proteins (AFPs), will shed light on how AFPs regulate ice formation in nature. In this work, time-resolved small-angle x-ray scattering (TR-SAXS) and quasi-elastic neutron scattering (QENS) experiments were carried out to investigate the structural and dynamical mechanisms of ice formation regulated by GO nanosheets. Strikingly, a transient intermediate state was observed in TR-SAXS experiments that only exists in the aqueous dispersions with a larger GO size (11 nm). This serves as evidence that the size of GO is critical for regulating ice formation. Elastic neutron scattering results indicate that ice is formed in all samples and thermal hysteresis occurs in GO aqueous dispersions in both H2O and D2O. The structural and dynamics information about water molecules in GO, extracted from QENS, reveals different dynamical behaviors of water molecules in GO aqueous dispersions when approaching the ice formation temperature.

High Hydrogen Mobility in an Amide–Borohydride Compound Studied by Quasielastic Neutron Scattering

The hydrogen storage performance of reactive hydride composite can be significantly improved by the addition of and the subsequent formation of an amide–borohydride compound during hydrogen release. Herein, an investigation into the structure and anion motions of using synchrotron radiation powder X‐ray diffraction (SR‐PXD; 295–573 K) and quasielastic neutron scattering (QENS; 297–514 K) is described. The highest temperature studied with QENS (514 K) is above the melting point of . The neutron measurements confirm a long‐range diffusive motion of hydrogen‐containing species with the diffusion coefficient . Interestingly, this value is comparable to that of diffusion inferred from conductivity measurements. SR‐PXD confirms the recrystallization of from the melt into the α‐phase upon cooling. At temperatures below 514 K, localized rotational motions are observed that are attributed to tetrahedra units mainly undergoing rotations around the axes. The activation energy for this thermally activated process is found to be and respectively for the two instrumental resolutions utilized in the QENS measurements, corresponding to observation times of 55 and 14 ps.

Structural and dynamic studies of Pr(11BH4)3

Rare earth borohydrides RE (BH4)3 are studied in the context of energy storage, luminescence and magnetic applications. We have investigated the structural behavior of praseodymium borohydride Pr (11BH4)3 containing 11B isotope because of the previously reported negative thermal expansion. Differential scanning calorimetry (DSC), in-situ variable temperature synchrotron radiation powder X-ray diffraction (SR-PXD) and infrared studies reveal that Pr (11BH4)3 undergoes to a volume contraction during the phase transition from alpha α-Pr (11BH4)3 to rhombohedral r-Pr (11BH4)3 phase upon heating to 493 K. Surprisingly, the phase transition persists upon cooling at room temperature. Vibrational analysis also shows that the stretching frequency of BH4− anion does not change upon heating which indicates that the B–H bond length remains constant during the structural phase transition from α-Pr (11BH4)3 to r-Pr (11BH4)3 phase. Additionally, the energy barrier of reorientation motion of the BH4− anion in the α-phase was estimated to be ca 23 kJ/mol by quasi-elastic neutron scattering (QENS) and Raman spectroscopy.

Dynamic Processes and Mechanisms Involved in Relaxations of Single-Chain Nano-Particle Melts.

We present a combined study by quasielastic neutron scattering (QENS), dielectric and mechanical spectroscopy, calorimetry and wide-angle X-ray diffraction on single-chain nano-particles (SCNPs), using the corresponding linear precursor chains as reference, to elucidate the impact of internal bonds involving bulky cross-links on the properties of polymer melts. Internal cross-links do not appreciably alter local properties and fast dynamics. This is the case of the average inter-molecular distances, the β-relaxation and the extent of the atomic displacements at timescales faster than some picoseconds. Contrarily, the α-relaxation is slowed down with respect to the linear precursor, as detected by DSC, dielectric spectroscopy and QENS. QENS has also resolved broader response functions and stronger deviations from Gaussian behavior in the SCNPs melt, hinting at additional heterogeneities. The rheological properties are also clearly affected by internal cross-links. We discuss these results together with those previously reported on the deuterated counterpart samples and on SCNPs obtained through a different synthesis route to discern the effect of the nature of the cross-links on the modification of the diverse properties of the melts.

Experimental demonstration of the novel \u201cvan-Hove integral method (vHI)\u201d for measuring diffusive dynamics by elastic neutron scattering

Quasi-elastic neutron scattering (QENS)—based on the seminal work of Nobel Laureate Brockhouse—has been one of the major methods for studying pico-second to nano-second diffusive dynamics over the past 70 years. This is regarded as an “inelastic” method for dynamics. In contrast, we recently proposed a new neutron-scattering method for dynamics, which uses the elastic line of the scattering to access system dynamics directly in the time domain (Benedetto and Kearley in Sci Rep 9:11284, 2019). This new method has been denoted “vHI” that stands for “van Hove Integral”. The reason is that, under certain conditions, the measured elastic intensity corresponds to the running-time integral of the intermediate scattering function, Ileft( {Q,t} right), up to a time that is inversely proportional to the energy band-width incident on the sample. As a result, Ileft( {Q,t} right) is accessed from the time derivative of the measured vHI profile. vHI has been supported by numerical and Monte-Carlo simulations, but has been difficult to validate experimentally due to the lack of a suitable instrument. Here we show that vHI works in practice, which we achieved by using a simple modification to the standard QENS backscattering spectrometer methodology. Basically, we varied the neutron-energy band-widths incident at the sample via a step-wise variation of the frequency of the monochromator Doppler-drive. This provides a measurement of the vHI profile at the detectors. The same instrument and sample were also used in standard QENS mode for comparison. The intermediate scattering functions, Ileft( {Q,t} right), obtained by the two methods—vHI and QENS—are strikingly similar providing a direct experimental validation of the vHI method. Perhaps surprisingly, the counting statistics of the two methods are comparable even though the instrument used was expressly designed for QENS. This shows that the methodology modification adopted here can be used in practice to access vHI profiles at many of the backscattering spectrometers worldwide. We also show that partial integrations of the measured QENS spectrum cannot provide the vHI profile, which clarifies a common misconception. At the same time, we show a novel approach which does access Ileft( {Q,t} right) from QENS spectra.

Emergence of dynamical disorder and phase metastability in carbon nanobowls

The condensed phases of the carbon-based nanobowl corannulene are herein investigated in the temperature range 200–573 K, combining differential scanning calorimetry, synchrotron X-ray diffraction, and quasielastic neutron-scattering. For the first time, we identify the presence of a well-defined thermal event at 382 K, a figure well below a melting point of 540 K. Contrary to naïve expectation, detailed analysis of the neutron-scattering data below and above this pre-melting transition signals the emergence of correlated stochastic dynamics within both thermodynamically stable solid phases of the material. We find that these are progressively responsible for the suppression of molecular and supramolecular order over mesoscopic length scales, and are associated with the formation of high-symmetry rotor-like states exhibiting localized stochastic motions. Upon cooling from the melt, we have also discovered a robust hysteresis associated with the existence of hitherto-unknown metastable liquid (deep-supercooled) and disordered-solid phases. This behaviour is markedly different from that observed in the quintessential Buckminsterfullerene C60 or other chemically substituted fullerene adducts studied to date at this level of detail. These results evince new and yet-to-tapped opportunities for the use of the stable and metastable phases of carbon-based nanobowls in novel applications exploiting the emergence of dynamical disorder at the nanoscale.

Methanol dynamics in H-ZSM-5 with Si/Al ratio of 25: a quasi-elastic neutron scattering (QENS) study

Methanol dynamics in zeolite H-ZSM-5 (Si/Al of 25) with a methanol loading of ~ 30 molecules per unit cell has been studied at 298, 323, 348 and 373 K by incoherent quasi-elastic neutron scattering (QENS). The elastic incoherent structure factor (EISF) reveals that the majority of methanol is immobile, in the range between 70 and 80%, depending on the measurement temperature. At 298 K, ≈ 20% methanol is mobile on the instrumental timescale, exhibiting isotropic rotational dynamics with a rotational diffusion coefficient (DR) of 4.75 × 1010 s−1. Upon increasing the measurement temperature from 298 to 323 K, the nature of the methanol dynamics changes from rotational to translational diffusion dynamics. Similar translational diffusion rates are measured at 348 and 373 K, though with a larger mobile fraction as temperature increases. The translational diffusion is characterised as jump diffusion confined to a sphere with a radius close to that of a ZSM-5 channel. The diffusion coefficients may be calculated using either the Volino–Dianoux (VD) model of diffusion confined to a sphere, or the Chudley–Elliot (CE) jump diffusion model. The VD model gives rise to a self-diffusion co-efficient (Ds) of methanol in the range of 7.8–8.4 × 10–10 m2 s−1. The CE model gives a Ds of around 1.2 (± 0.1) × 10–9 m2 s−1 with a jump distance of 2.8 (either + 0.15 or − 0.1) Å and a residence time (τ) of ~ 10.8 (either + 0.1 or − 0.2) ps. A correlation between the present and earlier studies that report methanol dynamics in H-ZSM-5 with Si/Al of 36 is made, suggesting that with increasing Si/Al ratio, the mobile fraction of methanol increases while DR decreases.

Water and Ion Dynamics in Confined Media: A Multi-Scale Study of the Clay/Water Interface

This review details a large panel of experimental studies (Inelastic Neutron Scattering, Quasi-Elastic Neutron Scattering, Nuclear Magnetic Resonance relaxometry, Pulsed-Gradient Spin-Echo attenuation, Nuclear Magnetic Resonance Imaging, macroscopic diffusion experiments) used recently to probe, over a large distribution of characteristic times (from pico-second up to days), the dynamical properties of water molecules and neutralizing cations diffusing within clay/water interfacial media. The purpose of this review is not to describe these various experimental methods in detail but, rather, to investigate the specific dynamical information obtained by each of them concerning these clay/water interfacial media. In addition, this review also illustrates the various numerical methods (quantum Density Functional Theory, classical Molecular Dynamics, Brownian Dynamics, macroscopic differential equations) used to interpret these various experimental data by analyzing the corresponding multi-scale dynamical processes. The purpose of this multi-scale study is to perform a bottom-up analysis of the dynamical properties of confined ions and water molecules, by using complementary experimental and numerical studies covering a broad range of diffusion times (between pico-seconds up to days) and corresponding diffusion lengths (between Angstroms and centimeters). In the context of such a bottom-up approach, the numerical modeling of the dynamical properties of the diffusing probes is based on experimental or numerical investigations performed on a smaller scale, thus avoiding the use of empirical or fitted parameters.

Quasielastic Neutron Scattering for Analyzing Transport Dynamics of Chemically-Bound Hydrogen in Minerals

Quasielastic Neutron Scattering for Analyzing Transport Dynamics of Chemically-Bound Hydrogen in Minerals

Analysis and Comparison of Quasi-Elastic Neutron Scattering (QENS) Spectra Model

The Quasi-Elastic Neutron Scattering (QENS) experiment is a novel method to study confined water dynamics by measuring the neutron energy transfer ( E )and scattering vector (Q) after the neutron interacts with the sample target. By adopting a suitable theoretical model and performing nonlinear least-squares fitting analysis on the Quasi- Elastic Neutron scattering spectra, the relevant physical parameters describing the water dynamics can be obtained, and then the constrained water dynamics in the sample can be detected. There are many types of Quasi-Elastic Neutron Scattering spectra fitting analysis models, and the fitting effects of different models and the relevant physical parameters obtained to characterize water dynamic information are not the same. This paper uses the Jump-diffusion and Rotating-diffusion Model (JRM) and the revised Jump-diffusion and Rotating-diffusion Model (rJRM) to fit the QENS spectra of pure magnesium silicate (M-S-H) and pure calcium silicate (C-S-H) samples, respectively. The measurement temperatures of QENS spectra from M-S-H and C-S-H samples are 210K up to 280K and 230K up to 280K, respectively, the E ranges from -120 to 120μev and the Q value 0.3 A^(-1)~1.9 A^(-1). Different physical parameters describing the dynamic information of confined water can be obtained by using the two models for QENS spectra fitting analysis. Compared with the JRM model, the physical parameters obtained by using the rJRM model are more comprehensive, and it is suitable for all neutron energy transfer and scattering vector measurements. From the qualitative point of view, the QENS spectra fitting curve of rJRM model is more consistent with the original data points. From the quantitative point of view, the chi-square value fitted by the rJRM model is more consistent with the mathematical statistics law than the JRM model, and the time required for nonlinear fitting is shorter.

Microscopic insights on the structural and dynamical aspects of Imidazolium-based surface active ionic liquid micelles

Ionic liquids have drawn vast attention due to their extraordinary physicochemical properties and their relevance in a wide range of applications. As a result of their inherent amphiphilic nature, many ionic liquids are emerging as novel surfactants, being referred to as surface active ionic liquids (SAILs). Under suitable conditions in aqueous solution, these SAILs self-assemble to form nanostructures such as micelles and vesicles. Here, we report on the structure and dynamics of one such SAIL micellar system, 1-Decyl-3-methylimidazolium Bromide (DMIMBr), as studied using fully atomistic molecular dynamics (MD) simulation and quasi-elastic neutron scattering (QENS). Results are compared with a conventional surfactant, dodecyltrimethylammonium bromide (DTAB) micelles. MD simulations showed that while the structure of the DMIMBr micelle is very similar to that of DTAB, the conformational flexibility of the alkyl chains is starkly different. The alkyl chains in the SAIL are more ordered, having fewer gauche defects. This is consistent with experimental results obtained using QENS which also showed slower alkyl chain segmental dynamics. MD results also show restricted dynamics of the hydration water in DMIMBr micelles, of a sub-diffusive nature, suggesting stronger affinity of water molecules to the imidazolium moiety. Thus the decreased flexibility in the alkyl chains could arise from the slower hydration dynamics. In contrast, the lateral motion of the surfactant is found to be relatively faster in DMIMBr micelles than in DTAB micelles. The understanding gained from this study provides a microscopic insight about the dynamical aspects of SAIL micelles, which might be useful for related applications including micellar catalysis and nanoparticle synthesis.

Study on the dynamics of a vanadium doped LiFePO4 lithium‐ion battery using quasi‐elastic neutron scattering technique

AbstractThe investigation into the lithium diffusion in active electrode materials is especially interesting since it is directly connected with electrochemical performance of lithium‐ion battery. Quasi‐elastic neutron scattering (QENS) is a powerful experimental tool to study lithium diffusion dynamics. Here, Li0.99V0.01FePO4 (LFPV) cathode material is investigated using QENS technique. The QENS data showed that lithium diffusion can be well described in LFPV using a jump diffusion model. The Li self‐diffusion coefficient in LFPV material was estimated to be ~3 × 10−7 cm2/s at T = 600 K. This result is about 108 times faster than previous reports using electrochemical measurements, but similar to the molecular dynamic simulation. The slower Li ion diffusion might be due to the barrier at two phase boundary, grain boundary, and solid‐electrolyte interface.

Probing Dynamics of Water Mass Transfer in Organic Porous Photocatalyst Water-Splitting Materials by Neutron Spectroscopy.

The quest for efficient and economically accessible cleaner methods to develop sustainable carbon-free energy sources induced a keen interest in the production of hydrogen fuel. This can be achieved via the water-splitting process and by exploiting solar energy. However, the use of adequate photocatalysts is required to reach this goal. Covalent triazine-based frameworks (CTFs) are potential target photocatalysts for water splitting. Both electronic and structural characteristics of CTFs, particularly energy levels, optical band gaps, and porosities are directly relevant to water splitting and can be engineered through chemical design. Porosity can, in principle, be beneficial to water splitting by providing a larger surface area for the catalytic reactions to take place. However, porosity can also affect both charge transport within the photocatalyst and mass transfer of both reactants and products, thus impacting the overall kinetics of the reaction. Here, we focus on the link between chemical design and water (reactant) mass transfer, which plays a key role in the water uptake process and the subsequent hydrogen generation in practice. We use neutron spectroscopy to study the mass transfer of water in two porous CTFs, CTF-CN and CTF-2, that differ in the polarity of their struts. Quasi-elastic neutron scattering is used to quantify the amount of bound water and the translational diffusion of water. Inelastic neutron scattering measurements complement the quasi-elastic neutron scattering study and provide insights into the softness of the CTF structures and the changes in librational degrees of freedom of water in the porous CTFs. We show that two different types of interaction between water and CTFs take place in CTF-CN and CTF-2. CTF-CN exhibits a smaller surface area and lower water uptake due to its softer structure than CTF-2. However, the polar cyano group interacts locally with water leading to a large amount of bound water and a strong rearrangement of the water hydration monolayer, while water diffusion in CTF-2 is principally impacted by microporosity. The current study leads to new insights into the structure-dynamics–property relationship of CTF photocatalysts that pave the road for a better understanding of the guest–host interaction on the basis of water-splitting applications.

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.

Melittin exerts opposing effects on short- and long-range dynamics in bicontinuous microemulsions

Bicontinuous microemulsions (BμEs) are a promising biomembrane mimetic system for investigating the behavior of antimicrobial peptides (AMPs) and their delivery to open wounds to combat antibiotic-resistant microorganisms. The properties of the BμE host are in turn affected by the guest AMP and can deviate from those of the unperturbed BμEs, especially at higher AMP concentrations. Here we report the effect of an archetypal AMP, melittin, over a wide range of concentrations, on the nanoscopic dynamics of BμEs formed by water/sodium dodecyl sulfate (SDS)/1-pentanol/dodecane, investigated using quasi-elastic neutron scattering (QENS). Two distinct motions are observed, namely, (i) the lateral motion of the surfactant on the surface of the oil channels and (ii) the internal motion of the surfactants. It is found that melittin restricts both the lateral and the internal motion, thereby acting as a stiffening agent. The lateral motion is more strongly affected, at low concentration of melittin. The lateral diffusion coefficient decreased sharply, approaching a constant value at higher melittin concentration. These results are in sharp contrast with the recent dynamic light scattering and neutron spin echo results which showed that at the length and time scales longer than those probed in the current work, melittin enhanced the long-range collective and local undulation motions of BμEs. Considered together, our results indicate that incorporation of melittin modulates the dynamics differently depending on the spatial and temporal regimes, in which the dynamics are being probed. The addition of melittin at low concentrations increased the magnitude of the zeta potential, but further increase of the melittin concentration decreased it. This suggests that addition of melittin at low concentrations led to increase in the surfactant concentration, but did not affect the negative charge per surfactant molecule, while further addition of melittin led to ion pairing of melittin with the oppositely charged surfactant. This study therefore demonstrates how the addition of melittin hinders the lateral motion of surfactants as a result of the strong association between melittin and SDS, suggesting that the release of AMPs from BμE-based delivery vehicles may be hindered.

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...

Quasielastic Neutron Scattering and Molecular Dynamics Simulation Study on the Molecular Behaviour of Catechol in Zeolite Beta

The dynamics of catechol in zeolite Beta was studied using quesielastic neutron scattering (QENS) experiments and molecular dynamics simulations at 393 K, to understand the behaviour of phenolic monomers relevant in the catalytic conversion of lignin via metal nanoparticles supported on zeolites. Compared to previous work studying phenol, both methods observe that the presence of the second OH group in catechol can hinder mobility significantly, as explained by stronger hydrogen-bonding interactions between catechol and the Brønsted sites of the zeolite. The instrumental timescale of the QENS experiment allows us to probe rotational motion, and the catechol motions are best fit to an isotropic rotation model with a D^{rot} of 2.9 × 10^{10} s^{-1}. While this D^{rot} is within error of that measured for phenol, the fraction of molecules immobile on the instrumental timescale is found to be significantly higher for catechol. The MD simulations also exhibit this increased in ‘immobility’, showing that the long-range translational diffusion coefficients of catechol are lower than phenol by a factor of 7 in acidic zeolite Beta, and a factor of sim3 in the siliceous material, further illustrating the significance of Brønsted site H-bonding. Upon reproducing QENS observables from our simulations to probe rotational motions, a combination of two isotropic rotations was found to fit the MD-calculated EISF; one corresponds to the free rotation of catechol in the pore system of the zeolite, while the second rotation is used to approximate a restricted and rapid “rattling”, consistent with molecules anchored to the acid sites through their OH groups, the motion of which is too rapid to be observed by experiment.

Proton Dynamics in Palladium-Silver: An Inelastic Neutron Scattering Investigation.

Proton dynamics in Pd77Ag23 membranes is investigated by means of various neutron spectroscopic techniques, namely Quasi Elastic Neutron Scattering, Incoherent Inelastic Neutron Scattering, Neutron Transmission, and Deep Inelastic Neutron Scattering. Measurements carried out at the ISIS spallation neutron source using OSIRIS, MARI and VESUVIO spectrometers were performed at pressures of 1, 2, and 4 bar, and temperatures in the 330–673 K range. The energy interval spanned by the different instruments provides information on the proton dynamics in a time scale ranging from about 102 to 10−4 ps. The main finding is that the macroscopic diffusion process is determined by microscopic jump diffusion. In addition, the vibrational density of states of the H atoms in the metal lattice has been determined for a number of H concentrations and temperatures. These measurements follow a series of neutron diffraction experiments performed on the same sample and thus provide a complementary information for a thorough description of structural and dynamical properties of H-loaded Pd-Ag membranes.