Reiner Zorn

Forschungszentrum Jülich · Jülich Centre for Neutron Science (JCNS)

To describe the properties of glass-forming liquids, the concepts of a cooperativity length or the size of cooperatively rearranging regions are widely employed. Their knowledge is of outstanding importance for the understanding of both thermodynamic and kinetic properties of the systems under consideration and the mechanisms of crystallization pro...

The molecular dynamics of two addition type polynorbornenes, exo‐PNBSi and PTCNSi1, bearing microporosity has been investigated by broadband dielectric spectroscopy, fast scanning calorimetry, and neutron scattering. Both polymers have the same side groups but different backbones. Due to their favorable transport properties, these polymers have pot...

The origin of a well-known feature in relaxation data seen in many glass-forming materials has now — possibly — been resolved by means of computer simulations.

The molecular dynamics of addition-type poly(tricyclononenes) with Si-substituted bulky side groups has been investigated by a combination of neutron time-of-flight and neutron backscattering spectroscopy on a time scale from 0.1 ps to ca. 3 ns. The investigated poly(tricyclononenes) PTCNSi1 and PTCNSi2g both bear a high microporosity which makes t...

The microscopic diffusion and the low frequency density of states (VDOS) of PIM-EA-TB(CH3) are investigated by inelastic and quasi-elastic neutron scattering where also the demethylated counterpart of PIM-EA-TB(H2) is considered. These intrinsic microporous polymers are characterized by large BET surface area values of several hundred m2/g and pore...

In quasieleastic neutron scattering spectrometers one usually faces a trade-off between energy resolution and counting statistics. If the resolution is improved the intensity at the detectors reduces and vice versa. It is not immediately clear how to weigh both factors against each other. In this paper it is proposed to use the maximum time obtaina...

Converting neutron scattering data to real-space time-dependent structures can only be achieved through suitable models, which is particularly challenging for geometrically disordered structures. We address this problem by introducing time-dependent clipped Gaussian field models. General expressions are derived for all space- and time-correlation f...

Converting neutron scattering data to real-space time-dependent structures can only be achieved through suitable models, which is particularly challenging for geometrically disordered structures. We address this problem by introducing time-dependent clipped Gaussian field models. General expressions are derived for all space- and time-correlation f...

Inelastic incoherent neutron time-of flight scattering was employed to measure the low frequency density of states for a series of addition polymerized polynorbornenes with bulky side groups. The rigid main chain in combination with the bulky side groups give rise to a microporosity of these polymers in the solid state. The microporosity characteri...

Quasielastic neutron scattering by employing a combination of time-of-flight and backscattering techniques is carried out to explore the molecular mobility of a polymer of intrinsic microporosity (PIM-1) on microscopic timescales in comparison with a high-performance polyimide. Molecular fluctuations can change the structure of the temporary networ...

The molecular dynamics of the triphenylene-based discotic liquid crystal HAT6 is investigated by broadband dielectric spectroscopy, advanced dynamical calorimetry and neutron scattering. Differential scanning calorimetry in combination with X-ray scattering reveals that HAT6 has a plastic crystalline phase at low temperatures, a hexagonally ordered...

The present study focuses on quasielastic neutron scattering (QENS) of the proton dynamics in phosphoric acid (PA) inside the catalytic layer of high-temperature polymer electrolyte fuel cells (HT-PEFCs). The nanosecond proton dynamics is investigated on the local length scale around operating temperatures (300 K–430 K) using neutron backscattering...

The tracer diffusion coefficient of six different permanent gases in polymer-grafted nanoparticle (GNP) membranes, i.e., neat GNP constructs with no solvent, show a maximum as a function of the grafted chain length at fixed grafting density. This trend is reproduced for two different NP sizes and three different polymer chemistries. We postulate th...

A combination of different complementary methods is employed to investigate scaling of the molecular dynamics of two different liquid crystals. Each method is sensitive to different kind of fluctuations and provides therefore a different window to look at the molecular dynamics. In detail, broadband dielectric spectroscopy is combined with specific...

High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) have been studied with quasielastic neutron scattering, which gives access to the proton diffusion in the fuel cell on local length- and timescales. So far, the different components such as the proton conducting membrane and the electrode layers have been studied separately. Here we show th...

The performance of fuel cells depends largely on the proton diffusion in the proton conducting membrane, the core of a fuel cell. High temperature polymer electrolyte fuel cells are based on a polymer membrane swollen with phosphoric acid as the electrolyte, where proton conduction takes place. We studied the proton diffusion in such membranes with...

Polymers with intrinsic microporosity are promising candidates for the active separation layer in gas separation membranes. Here, the vibrational density of states (VDOS) for PIM-1, the prototypical polymer with intrinsic microporosity, is investigated by means of inelastic neutron scattering. The results are compared to data measured for a more co...

Small angle scattering with X-rays (SAXS) and neutrons (SANS) is used as a powerful tool to investigate different components of fuel cells or even groups such as membrane electrode assemblies (MEAs) (1,2). In particular, the structure of electrode layers and membrane electrode assemblies of High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs)...

A recent model for unentangled polymer chains in confinement [M. Dolgushev and M. Krutyeva, Macromol. Theory Simul. 21, 565 (2012)] is scrutinized by small-angle neutron scattering (SANS) with respect to its static prediction, the single-chain structure factor. We find a remarkable agreement although the model simplifies the effect of the confineme...

The aim of this paper is to decide which of the two possible thermodynamic expressions for the cooperativity length in glass forming liquids is the correct one. In the derivation of these two expressions , the occurrence of temperature fluctuations in the considered nanoscale subsystems is either included or neglected. Consequently, our analysis gi...

In this work, the structural properties of pristine and phosphoric acid doped poly(2,5-benzimidazole) membranes have been investigated by small angle neutron- and X-ray scattering, X-ray diffraction, polarized light microscopy and transmission electron microscopy. The results of our investigation demonstrate formation of crystalline regions with a...

An in situ ¹H NMR study has been carried out to examine the anionic initiation mechanism of 1,3-butadiene and tert-butyllithium (t-BuLi) using n-heptane as solvent. Additionally, mixtures of model compounds have been investigated ex situ to simulate very early stages of polymerization. The analysis of the NMR spectra in combination with density fun...

The effect of a nanometer scale confinement (pore sizes 7.5 nm down to 2.5 nm) on the vibrational density of states (VDOS) and on the molecular dynamics of Poly(dimethyl siloxane) (PDMS) and Poly(methyl phenyl siloxane) (PMPS) is studied by inelastic neutron scattering. The high penetration depth of neutrons makes neutron scattering a suitable tool...

The present study focuses on structural and dynamical properties of the catalytic layer for high-temperature polymer electrolyte fuel cells (HT-PEFC). The catalytic layer is a composite material containing nanoporous carbon, poly(tetrafluoroethylene) (PTFE) and platinum (Pt) nanoparticles. The structure of the catalyst is investigated using small a...

The structural properties and proton transport processes of High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) are studied on a broad range of length- and timescales with different neutron scattering techniques. We show structural properties of the proton conducting membrane and of the catalyst layer. Proton transport is measured with quasi...

The conception, design and optimization of fuel cells in general requires a good knowledge of the underlying physical processes on all length scales. In this contribution we focus on High Temperature Polymer Electrolyte Fuel Cells (HT-PEFCs) based on a proton conducting membrane such as poly2,2’-m-(phenylene)-5,5’-bibenzimidazole (PBI) doped with p...

In- and quasielastic neutron scattering is employed to investigate both the vibrational density of states and the molecular dynamics of two homologous discotic liquid crystals (DLC) with different length of the alkyl side chain based on a triphenylene derivate. For both compounds characteristic low frequency excess contributions to the vibrational...

The mechanism of proton conductivity in high temperature polymer electrolyte fuel cells (HT-PEFCs) has been investigated with macroscopic conductivity measurements and on a microscopic scale with quasielastic neutron scattering techniques. Polybenzimidazole membranes, which are used in HT-PEFCs, are doped with phosphoric acid (PA) to achieve the de...

Literature data for picosecond mean square displacements show that the anharmonicity explains only about half of the fragility (with different fractions for different glass formers). The other half must be ascribed to the Adam-Gibbs mechanism of a growing cooperatively rearranging region. One can measure both influences separately by a simultaneous...

Molecular dynamics is often studied by broad band dielectric spectroscopy (BDS) because of the wide dynamic range available and the large number of processes resulting in electrical dipole fluctuations and with that in a dielectrically detectable relaxation process. Calorimetry on the other hand is an effective analytical tool to characterize phase...

Neutron scattering is employed to investigate the vibrational density of states (VDOS) of the discotic liquid crystal 2,3,6,7,10,11-hexakis[hexyloxy] triphenylene (HAT6) confined to the pores of alumina oxide membranes with different pore sizes. Additionally, the phase transitions were studied by differential scanning calorimetry. The transitions w...

The vibrational density of states of a series of homologous triphenylene-based discotic liquid crystals HATn (n = 5, 6, 8, 10, 12) depending on the length of the aliphatic side chain is investigated by means of inelastic neutron scattering. All studied materials have a plastic crystalline phase at low temperatures, followed by a hexagonally ordered...

In this paper the scattering from an ideal polymer chain in strong confinement () is calculated. It is possible to derive analytical closed-form expressions analogous to the Debye form factor. The results can be written in terms of one hypergeometric function 2F2 for all geometries (channel, film, unconfined). It is shown that the result is consist...

The Lindemann criterion is reformulated in terms of the average shear modulus $G_c$ of the melting crystal, indicating a critical melting shear strain which is necessary to form the many different inherent states of the liquid. In glass formers with covalent bonds, one has to distinguish between soft and hard degrees of freedom to reach agreement....

In this work, 1H NMR was used to examine the anionic copolymerization kinetics of ethylene oxide and 1,2-butylene oxide. The in situ NMR technique allows monitoring the concentration profiles of both monomers simultaneously. A series of polymerization experiments at different monomer and initiator concentrations were done in order to determine the...

For high resolution time-of-flight neutron scattering spectrometers, a significant contribution to the instrumental resolution broadening will be due to the flight path uncertainty induced by the sample size. In linear approximation, this contribution is an additional convolution of the resolution function with the scaled distribution of flight pat...

We present incoherent quasi-elastic neutron scattering measurements in a wave vector transfer range from 0.4 Å(-1) to 1.6Å (-1) on liquid n-hexane confined in cylindrical, parallel-aligned nanochannels of 6 nm mean diameter and 260 μm length in monolithic, mesoporous silicon. They are complemented with, and compared to, measurements on the bulk sys...

We present a new approach to a unified description of the dielectric end-to-end vector and the viscoelastic stress relaxation of entangled homopolymer melts in terms of the tube model. The comparison and quantitative analysis of carefully recorded viscoelastic and dielectric relaxation spectra evidence that the dielectric mode distribution is compl...

The effect of a nanometer confinement on the vibrational and molecular dynamics of a liquid crystals E7 was studied by dielectric spectroscopy (DS) and neutron scattering (NS). E7 undergoes a glass transition phenomenon besides the nematic to isotropic phase transition. As confining host a molecular sieve of the MCM-41 type is used having cylindric...

Neutron spectroscopy is an important method for the study of microscopic dynamics because it captures the spatial as well as the temporal aspects of the atomic or molecular motion. In this article techniques will be presented which are of special importance for the study of confined systems. Many of these are based on the fact that neutron scatteri...

The vibrational density of states (VDOS) of disordered systems shows a low-frequency excess, the so-called boson peak. Experiments show a change in the shape of the boson peak when the systems are spatially confined. Depending on the type of confinement (hard or soft) the low-frequency wing of the boson peak is either suppressed or enhanced. Here,...

Neutron scattering elastic scans are a common technique to obtain an overview of the microscopic dynamics over a wide range of a control parameter, in most cases the temperature. The data evaluation usually aims at calculating the mean-square displacement 〈r2〉 of the scatterers. Unless there is a clear separation of fast and slow dynamics, this mea...

Poly(bismethoxyphosphazene) (PBMP) was synthesized, giving polymer melts with Tg = −70.9 °C. The chain dynamics of melts and DMF solutions of poly(bismethoxyphosphazene) (PBMP) was investigated by Small-Angle Neutron Scattering (SANS). The radius of gyration Rg was found as 144.7 ± 0.2 Å, and the average MW from SANS was 95000 Da. DMF revealed to b...

We have studied the microscopic dynamics of a glass-forming liquid in the soft confinement formed by microemulsion droplets using inelastic neutron scattering. The confined liquid was propylene glycol, the outer, hydrophobic phase was decalin, and the surfactantsodium dioctylsulfosuccinate (AOT) with the same composition used before with other spec...

In this article we present inelastic neutron scattering (INS) experiments on different systems of confined glass‐formers. The aim of these experiments is to study the influence of spatial restriction on the microscopic dynamics related to the glass transition. Such results could be helpful for the detection of a currently speculated cooperativity l...

The molecular dynamics of glass-forming poly(methyl phenyl siloxane) (PMPS) is studied by thermal (10−3–5 × 102 Hz), dielectric (10−3–109 Hz) and neutron (5 × 108–1012 Hz) spectroscopy. Because of the broad frequency range of 15 orders of magnitude the study provides a precise determination of glassy dynamics in a wide temperature range using diffe...

Atomic mean-square displacements for frequencies above 1011 Hz have been determined from neutron time-of-flight data in the glassy, liquid and crystalline phase of selenium. As in many other substances, the difference between the values in the disordered and the ordered phase shows a strong increase with increasing temperature, setting in at about...

The dielectric response (1 MHz ÷ 10 GHz) and the structure of a water-oil emulsion were studied as a function of temperature. It was observed that the water component causes the dielectric loss of the emulsion in the crystalline gel phase at low temperatures. However, the dielectric loss decreases discontinuously at the gel-microemulsion transition...

Neutron scattering elastic scans are a time-efficient method to obtain an overview of the dependence of the microscopic dynamics on a control parameter, usually the temperature. In the conventional treatment of elastic scan data multiple scattering is ignored. This leads to an inconsistency at low wave vector Q which is resolved by an additional fi...

The effect of a nanometer confinement on the molecular dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by dielectric spectroscopy (DS), temperature modulated DSC (TMDSC) and neutron scattering (NS). Nanoporous glasses with pore sizes of 2.5–20 nm have been used. DS and TMDSC experiments show that for PMPS in 7.5 nm pores the molecular d...

We have studied the influence of plasticization on the microscopic dynamics of a glass-forming polymer. For this purpose we studied polyvinylchloride (PVC) with and without the commercially used plasticizer dioctylphthalate (DOP). We used dielectric spectroscopy and inelastic neutron scattering employing the neutron spin echo (NSE) technique. For b...

We derive an energy landscape interpretation of dielectric relaxation times in undercooled liquids, comparing it to the traditional Debye and Gemant-DiMarzio-Bishop pictures. The interaction between different local structural rearrangements in the energy landscape explains qualitatively the recently observed splitting of the flow process into an in...

We have investigated the short-range order in 1,4-polybutadiene by combining fully atomistic MD simulations and neutron diffraction with polarization analysis on isotopically labeled samples. Thereby the structure factor corresponding to the fully deuterated sample and the partial structure factor of the fully protonated polymer have been obtained....

Inelastic neutron scattering was employed over recent years to investigate the influence of spatial confinement on the dynamics of glass-forming systems. We review the common phenomena observed by neutron scattering in such different confining hosts like porous glasses, molecular sieves, clays or free standing polymer films, which impose a spatial...

Dielectric spectroscopy in combination with temperature modulated differential scanning calorimetry and quasielastic/inelastic neutron scattering are employed to investigate the molecular (glassy) dynamics of poly(dimethyl siloxane) (PDMS) and poly(methyl phenyl siloxane) (PMPS) confined to random nanoporous glasses with nominal pore sizes between...

The Research Center Jülich FZJ has a strong tradition in research with neutrons encompassing the design of next generation neutron sources, the development of instruments, and methods, to the application of neutron scattering in upcoming scientific areas. Jülich was task leader for beam transport, target system, and safety of the European Spallatio...

Neutron spin echo (NSE) is characterized by a broad variety of new developments. The obvious trend is towards the highest possible energy resolution at the highest possible wavelengths by further developing the generic IN11 design. The planned NSE spectrometer at the SNS will further push the limits of NSE reaching Fourier times as long as 1 μs. On...

We studied the dynamics of dissolved water in aluminosilicate glasses with the compositions NaAlSi3O8·0.3H2O , NaAlSi3O8·1.3H2O and Ca0.5AlSi3O8·1.3H2O using quasielastic neutron scattering. As shown by near-infrared spectroscopy on these samples, H2O molecules are the predominant hydrous species in the water-rich glasses whereas OH groups bound to...

In current solid state theory the understanding of the crystalline state of matter is much more developed than that of the amorphous state. Amorphous materials constitute a large part of condensed matter. A theoretical understanding is of immense importance for basic science as well as application purposes: silicate glasses in windows, bottles etc....

In this article, results on the microscopic dynamics of a low-molecular glass former and a polymer confined in nanoporous silica obtained by inelastic neutron scattering are presented. By combining time-of-flight spectroscopy and backscattering spectroscopy we are able to cover a large dynamical range, from the low-frequency vibrations to the α rel...

The glassy dynamics of poly(propylene glycol) (PPG) and poly(methyl phenyl siloxane) (PMPS) confined to nanoporous glasses (pore sizes 2.5–20 nm) investigated by dielectric spectroscopy, temperature modulated DSC and neutron scattering is compared. For both systems the relaxation rates estimated from dielectric spectroscopy and temperature modulate...

NO ABSTRACT

The glassy dynamics of poly(propylene glycol) (PPG) and poly(dimethyl siloxane) (PDMS) confined to a nanoporous host system revealed by dielectric spectroscopy, temperature-modulated DSC and neutron scattering is compared. For both systems the relaxation rates estimated from dielectric spectroscopy and temperature-modulated DSC agree quantitatively...

The microscopic dynamics of glass-forming materials, especially polymers, is a topic of strong current interest and often heated debate. In this review an overview of the most common dynamical phenomena in glass-forming polymers will be presented: α relaxation, β relaxation, 'boson peak', and 'fast process' (βfast relaxation). The experimental resu...

In this paper, we have combined molecular dynamics simulation and neutron diffraction experiments with polarization analysis, to unravel the different atomic correlations contributing to the total and partial static structure factors of polyisoprene (PI). Four different PI samples have been investigated: PId3 (methyl group deuterated and main chain...

The effect of a nanometer confinement on the molecular dynamics of poly(methyl phenyl siloxane) (PMPS) was studied by dielectric spectroscopy (DS), temperature modulated DSC (TMDSC) and neutron scattering (NS). DS and TMDSC experiments show that for PMPS in 7.5 nm pores the molecular dynamics is faster than in the bulk which originates from an inhe...

Since 1997 the Institutes of Neutron Scattering and Scattering Methods at Forschungszentrum Julich (Germany) have organized a hands-on laboratory course for students of physics, chemistry, and other natural sciences. In the beginning, this course was held mainly for students of the co-organizing universities of Aachen and Munster. While still being...

Fully atomistic molecular dynamic simulations were carried out by using the Insight (Insight II 4.0.0 P version) and the Discover-3 programs from MSI with the polymer consortium force field. The model system used in these simulations was built using the Amorphous Cell module. The polymer system simulated was glassy polyisoprene (PI) as used in prev...

In this article we present results on the microscopic dynamics of a glass-forming liquid (salol) confined in microporous silica glass (Gelsil) obtained by inelastic neutron scattering. By combining different methods we are able to cover a large dynamical range, from the low-frequency vibrations to the α-relaxation. The most prominent effect was obs...

In this article a simple-to-use analytic procedure for the correction of multiple scattering effects in polarized neutron diffraction experiments is presented. It is demonstrated that assuming (i) same scattering probabilities for multiple scattering of different order (>1) and (ii) isotropic multiple scattering the correction reduces to a linear t...

In this paper a novel way to quantify "nonexponential" relaxations is described. So far, this has been done in two ways: (1) by fitting empirical functions with a small number of parameters, (2) by calculation of the underlying distribution function g(ln tau) of (exponential) relaxations using regularization methods. The method described here is in...

Literature mechanical relaxation data of two glasses, vitreous silica and poly(methyl methacrylate) (PMMA), an amorphous polymer, are interpreted in terms of the Gilroy-Phillips model. For frequencies up to 1 GHz, one finds a temperature-independent barrier density function f(V) at all temperatures in the glass phase. If one looks at still higher f...

In this paper the microscopic dynamics of methyl side groups in polyisoprene is studied by means of inelastic neutron scattering. By combining time-of-flight and backscattering technique a range of four decades can be obtained (0.2 ps-2 ns). The two experimental results were combined in the time domain by using an inverse Fourier transform. Multipl...

The structural dynamics of a polymer electrolyte model material, poly(prolyene oxide) (PPO)–LiClO4 (and PPO for reference), has for the first time been studied using coherent quasielastic neutron scattering. By a combination of neutron spin echo and inverse time-of-flight techniques we investigate the relaxation function in an experimental time win...

We examined the dynamics of amphiphilic polymer micelles of the diblock copolymer HOVE-NBVE (hydroxyethylvinyl ether as a hydrophilic segment and n-butylvinyl ether as a hydrophobic segment) in aqueous solution using the neutron spin-echo (NSE) technique. The time-correlation function obtained for the polymer micelles was well fitted by double expo...