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  • 1
    Online Resource
    Online Resource
    SPHERES, Jülich's high-flux neutron backscattering spectrometer at FRM II
    AIP Publishing ; 2012
    In:  Review of Scientific Instruments Vol. 83, No. 7 ( 2012-07-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 83, No. 7 ( 2012-07-01)
    Abstract: SPHERES is a third-generation neutron backscattering spectrometer, located at the 20 MW German neutron source FRM II and operated by the Jülich Centre for Neutron Science. It offers an energy resolution (fwhm) better than 0.65 μeV, a dynamic range of ± 31 μeV, and a signal-to-noise ratio of up to 1750:1.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.4732806
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2012
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
    SSG: 11
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  • 2
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    Reduced-mobility layers with high internal mobility in poly(ethylene oxide)–silica nanocomposites
    AIP Publishing ; 2017
    In:  The Journal of Chemical Physics Vol. 146, No. 20 ( 2017-05-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 146, No. 20 ( 2017-05-28)
    Abstract: A series of poly(ethylene oxide) nanocomposites with spherical silica was studied by proton NMR spectroscopy, identifying and characterizing reduced-mobility components arising from either room-temperature lateral adsorption or possibly end-group mediated high-temperature bonding to the silica surface. The study complements earlier neutron-scattering results for some of the samples. The estimated thickness of a layer characterized by significant internal mobility resembling backbone rotation ranges from 2 nm for longer (20 k) chains adsorbed on 42 nm diameter particles to 0.5 nm and below for shorter (2 k) chains on 13 nm particles. In the latter case, even lower adsorbed amounts are found when hydroxy endgroups are replaced by methyl endgroups. Both heating and water addition do not lead to significant changes of the observables, in contrast to other systems such as acrylate polymers adsorbed to silica, where temperature- and solvent-induced softening associated with a glass transition temperature gradient was evidenced. We highlight the actual agreement and complementarity of NMR and neutron scattering results, with the earlier ambiguities mainly arising from different sensitivities to the component fractions and the details of their mobility.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.4974768
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2017
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 3
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    Fractal diffusion in high temperature polymer electrolyte fuel cell membranes
    AIP Publishing ; 2018
    In:  The Journal of Chemical Physics Vol. 148, No. 20 ( 2018-05-28)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 148, No. 20 ( 2018-05-28)
    Abstract: 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 neutron scattering techniques which are especially sensitive to the proton contribution. Time of flight spectroscopy and backscattering spectroscopy have been combined to cover a broad dynamic range. In order to selectively observe the diffusion of protons potentially contributing to the ion conductivity, two samples were prepared, where in one of the samples the phosphoric acid was used with hydrogen replaced by deuterium. The scattering data from the two samples were subtracted in a suitable way after measurement. Thereby subdiffusive behavior of the proton diffusion has been observed and interpreted in terms of a model of fractal diffusion. For this purpose, a scattering function for fractal diffusion has been developed. The fractal diffusion dimension dw and the Hausdorff dimension df have been determined on the length scales covered in the neutron scattering experiments.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.5018717
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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  • 4
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    Neutron scattering study of the dynamics of a polymer melt under nanoscopic confinement
    AIP Publishing ; 2009
    In:  The Journal of Chemical Physics Vol. 131, No. 17 ( 2009-11-07)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 131, No. 17 ( 2009-11-07)
    Abstract: Poly(ethylene oxide) confined in an anodic aluminum oxide solid matrix has been studied by different neutron scattering techniques in the momentum transfer (Q⃗) range 0.2≤Q=|Q⃗|≤1.9 Å−1. The cylindrical pores of the matrix present a diameter (40 nm) much smaller than their length (150 μm) and are parallel and hexagonally ordered. In particular, we investigated the neutron intensity scattered for two orientations of the sample with respect to the incident beam, for which the Q⃗ direction was either parallel or perpendicular to the pores for a scattering angle of 90°. Diffuse neutron scattering at room temperature has shown that the aluminum oxide has amorphous structure and the polymer in the nanoporous matrix is partially crystallized. Concerning the dynamical behavior, for Q & lt;1 Å−1, the spectra show Rouse-like motions indistinguishable from those in the bulk within the uncertainties. In the high-Q limit we observe a slowing down of the dynamics with respect to the bulk behavior that evidences an effect of confinement. This effect is more pronounced for molecular displacements perpendicular to the pore axis than for parallel displacements. Our results clearly rule out the strong corset effect proposed for this polymer from nuclear magnetic resonance (NMR) studies and can be rationalized by assuming that the interactions with the pore walls affect one to two adjacent monomer monolayers.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.3258329
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2009
    detail.hit.zdb_id: 3113-6
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  • 5
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    Correlation of mass fractal dimension and asymmetry
    AIP Publishing ; 2009
    In:  The Journal of Chemical Physics Vol. 130, No. 23 ( 2009-06-21)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 130, No. 23 ( 2009-06-21)
    Abstract: Small-angle X-ray experiments reveal the structure and structural changes of silica embedded in a rubbery host matrix due to the deformation of the surrounding elastomer. The experiments prove that the silica is initially isotropic and becomes anisotropic due to the deformation of the matrix. Increasing the elongation ratio of the polymer results in a larger mass fractal dimension of the silica clusters. The growing mass fractal dimension can be explained simply by a rearrangement of the primary particles within the clusters. However, for the first time, mathematical reasons are presented which clearly demonstrate that self-affine clusters have to be used instead of self-similar ones in order to describe the experiments correctly.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.3154602
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2009
    detail.hit.zdb_id: 3113-6
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  • 6
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    A new ultrasonic transducer sample cell for in situ small-angle scattering experiments
    AIP Publishing ; 2018
    In:  Review of Scientific Instruments Vol. 89, No. 1 ( 2018-01-01)
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 89, No. 1 ( 2018-01-01)
    Abstract: Ultrasound irradiation is a commonly used technique for nondestructive diagnostics or targeted destruction. We report on a new versatile sonication device that fits in a variety of standard sample environments for neutron and X-ray scattering instruments. A piezoelectric transducer permits measuring of the time-dependent response of the sample in situ during or after sonication. We use small-angle neutron scattering (SANS) to demonstrate the effect of a time-dependent perturbation on the structure factor of micelles formed from sodium dodecyl sulfate surfactant molecules. We observe a substantial change in the micellar structure during and after exposure to ultrasonic irradiation. We also observe a time-dependent relaxation to the equilibrium values of the unperturbed system. The strength of the perturbation of the structure factor depends systematically on the duration of sonication. The relaxation behavior can be well reproduced after multiple times of sonication. Accumulation of the recorded intensities of the different sonication cycles improves the signal-to-noise ratio and permits reaching very short relaxation times. In addition, we present SANS data for the micellar form factor on alkyl-poly (ethylene oxide) surfactant molecules irradiated by ultrasound. Due to the flexibility of our new in situ sonication device, different experiments can be performed, e.g., to explore molecular potentials in more detail by introducing a systematic time-dependent perturbation.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.5021370
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2018
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
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  • 7
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    Proton injector operational results on a high-power continuous-wave radio-frequency quadrupole accelerator
    AIP Publishing ; 2000
    In:  Review of Scientific Instruments Vol. 71, No. 2 ( 2000-02-01), p. 767-770
    Details
    In: Review of Scientific Instruments, AIP Publishing, Vol. 71, No. 2 ( 2000-02-01), p. 767-770
    Abstract: A 50 keV proton injector utilizing a dc microwave source has been used to operate a 1.25 MeV continuous wave (cw) radio-frequency quadrupole (RFQ) accelerator. RFQ injection places stringent requirements on beam properties including centroid control, emittance, and phase-space matching. The ion source chosen for these applications is based on a microwave discharge operating at 2.45 GHz with an on-axis magnetic field near 875 G. The injector employs a space-charge-neutralized, two-solenoid-lens, low-energy beam transport (LEBT) system. Proton injector development with a 1.25 MeV RFQ has resulted in meeting the RFQ 75 mA design current specification in cw mode. Details of the ion source and LEBT operation are presented, and simulations for ion beam extraction and transport are compared with the injector measurements. The proton injector has been converted to 75 keV beam operation for injecting into a 6.7 MeV cw RFQ.
    Type of Medium: Online Resource
    ISSN: 0034-6748 , 1089-7623
    URL: Article
    DOI: 10.1063/1.1150288
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2000
    detail.hit.zdb_id: 209865-9
    detail.hit.zdb_id: 1472905-2
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  • 8
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    Structural changes in precipitated silica induced by external forces
    AIP Publishing ; 2010
    In:  The Journal of Chemical Physics Vol. 132, No. 15 ( 2010-04-21)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 132, No. 15 ( 2010-04-21)
    Abstract: The morphology of pure precipitated silica, silica filled in polydimethylsiloxane rubber, and silica filled in styrene butadiene rubber was studied by means of small-angle X-ray scattering experiments. The silica at a length scale of a few nanometers consists of primary particles, which form aggregates, and clusters with aggregates as basic units. It is evidenced that the aggregate branching, represented by the mass fractal dimension, and the aggregate diameter are different if pure silica and silica in rubber are compared. Contrary, the size of the primary particles and their surface are not influenced. It is demonstrated that the change in the aggregate morphology is due to the external mechanical forces appearing during the mixing process. This is achieved by model experiments using a pistil and a mortar and a composite with different silica fractions. By that means, a systematic change in the morphology with grinding time is observed. Then, the experiments on the composite demonstrate that the major contributions to the mass fractal dimensions are due to the external mechanical forces. In order to test reproducibility and universal validity in the case of precipitated silicas, independent experiments on one silica and further silicas are performed. Several important conclusions are obtained from the study. First, it is shown that a comparison of different pure silica samples without knowing their history may be difficult or questionable. Second, it becomes evident that it is not sufficient to provide only a description of the materials, rather than the details of the sample treatment have to be reported. Therefore, solely the characterization of the morphology of the pure silica is not sufficient to be compared to the mechanical properties of the composites.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.3389480
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 3113-6
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  • 9
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    Correlation of mass fractal dimension and cluster size of silica in styrene butadiene rubber composites
    AIP Publishing ; 2010
    In:  The Journal of Chemical Physics Vol. 133, No. 9 ( 2010-09-07)
    Details
    In: The Journal of Chemical Physics, AIP Publishing, Vol. 133, No. 9 ( 2010-09-07)
    Abstract: The morphology of the precipitated silica VN3 filled in styrene butadiene rubber was studied as a function of the volume fraction Φ by means of small-angle X-ray scattering experiments. The wide q-range of 0.008 nm−1 & lt;q & lt;1 nm−1 probes the structures of the primary particles, the clusters, and resolves a part of the larger clusters of the silica. The diameter of the primary particles and their surface roughness are independent from the silica concentration. The size of the clusters and the corresponding aggregation number depend on Φ. This observation could be ascribed to external mechanical forces because of the mixing process and to growing cluster-cluster interactions with increasing filler fraction. In contrast the mass fractal dimension does not depend on Φ, and by that means experimentally proving that there is not necessarily a correlation between the mass fractal dimension and the cluster size.
    Type of Medium: Online Resource
    ISSN: 0021-9606 , 1089-7690
    URL: Article
    DOI: 10.1063/1.3469827
    Language: English
    Publisher: AIP Publishing
    Publication Date: 2010
    detail.hit.zdb_id: 3113-6
    detail.hit.zdb_id: 1473050-9
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