Browsing by Author "Schneider, GJ"

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    Position-dependent segmental relaxation in Bottlebrush polymers
    (American Chemical Society, 2024-05-11) Bichler, KJ; Jakobi, B; Klapproth, A; Mole, RA; Schneider, GJ
    Segmental dynamics of specifically labeled poly(propylene oxide), PPO, based bottlebrush polymers, PNB-g-PPO, were studied using quasi-elastic neutron scattering. The focus was set to different parts of the side chains to investigate the hypothetical gradual relaxation behavior within the side chains of a bottlebrush polymer. Different sections of the side chains were highlighted for QENS via sequential polymerization of protonated and deuterated monomers to allow the study of the relaxation behavior of the inner and outer parts of the side chain separately. A comparison of these two parts reveals a slowdown due to the grafting process happening across the different regions. This is seen for the segmental relaxation time as well as on the time-dependent mean-square displacement. Additionally, the non-Gaussian parameter, α, shows a decreasing difference from Gaussian behavior with the distance to the backbone. Altogether, this leads to the conclusion that gradual relaxation behavior exists. © 2024 The Authors. Published by American Chemical Society. - Open Access CC BY licence.
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    Rotational dynamics and coupling of methyl group rotations in methyl fluoride studied by high resolution inelastic neutron scattering
    (American Institute of Physics, 2009-06-07) Kirstein, O; Prager, M; Schneider, GJ
    Methyl group rotations in methyl fluoride were studied using the high flux backscattering spectrometer SPHERES at FRM-II. The asymmetry and width of the low temperature tunneling peak was used to determine if coupled rotations between neighboring methyl fluoride molecules exist. The temperature dependent broadening of the tunneling peak was used to determine the first librational transition and compared to the temperature dependent shift of the position of the tunneling peak. The results obtained by using inelastic neutron scattering confirm previous models that assume rotational coupling. This is the first neutron backscattering experiment with sub-mu eV resolution at energy transfers up to 31 mu eV. © 2009, American Institute of Physics
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    Short-time dynamics of PDMS-g-PDMS bottlebrush polymer melts investigated by quasi-elastic neutron scattering
    (American Chemical Society, 2020-11-10) Bichler, KJ; Jakobi, B; Sakai, VG; Klapproth, A; Mole, RA; Schneider, GJ
    We have studied the short-time dynamical behavior of polydimethylsiloxane (PDMS) bottlebrush polymers, PDMS-g-PDMS. The samples have similar backbone lengths but different side-chain lengths, resulting in a shape transition. Quasi-elastic neutron scattering was used to observe the dynamical changes inherent to these structural changes. The combination of data from three spectrometers enabled to follow the dynamics over broad frequency and temperature ranges, which included segmental relaxations and more localized motions. The latter, identified as the methyl group rotation, is described by a threefold jump model and shows higher activation energies compared to linear PDMS. The segmental relaxation times, τs, decrease with increasing molecular weight of the side chains but increase with momentum transfer, Q, following a power law, which suggests a non-Gaussian behavior for bottlebrush polymers. © 2020 American Chemical Society. This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited.
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    Thermal fluctuations of haemoglobin from different species: adaptation to temperature via conformational dynamics
    (The Royal Society, 2012-11-07) Stadler, AM; Garvey, CJ; Bocahut, A; Sacquin-Mora, S; Digel, I; Schneider, GJ; Natali, F; Artmann, GM; Zaccai, G
    Thermodynamic stability, configurational motions and internal forces of haemoglobin (Hb) of three endotherms (platypus, Ornithorhynchus anatinus; domestic chicken, Gallus gallus domesticus and human, Homo sapiens) and an ectotherm (salt water crocodile, Crocodylus porosus) were investigated using circular dichroism, incoherent elastic neutron scattering and coarse-grained Brownian dynamics simulations. The experimental results from Hb solutions revealed a direct correlation between protein resilience, melting temperature and average body temperature of the different species on the 0.1 ns time scale. Molecular forces appeared to be adapted to permit conformational fluctuations with a root mean square displacement close to 1.2 Å at the corresponding average body temperature of the endotherms. Strong forces within crocodile Hb maintain the amplitudes of motion within a narrow limit over the entire temperature range in which the animal lives. In fully hydrated powder samples of human and chicken, Hb mean square displacements and effective force constants on the 1 ns time scale showed no differences over the whole temperature range from 10 to 300 K, in contrast to the solution case. A complementary result of the study, therefore, is that one hydration layer is not sufficient to activate all conformational fluctuations of Hb in the pico- to nanosecond time scale which might be relevant for biological function. Coarse-grained Brownian dynamics simulations permitted to explore residue-specific effects. They indicated that temperature sensing of human and chicken Hb occurs mainly at residues lining internal cavities in the β-subunits. Copyright © The Royal Society 2012.
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    Universality of time–temperature scaling observed by neutron spectroscopy on bottlebrush polymers
    (American Chemical Society, 2021-05-14) Bichler, KJ; Jakobi, B; Sakai, VG; Klapproth, A; Mole, RA; Schneider, GJ
    The understanding of materials requires access to the dynamics over many orders of magnitude in time; however, single analytical techniques are restricted in their respective time ranges. Assuming a functional relationship between time and temperature is one viable tool to overcome these limits. Despite its frequent usage, a breakdown of this assertion at the glass-transition temperature is common. Here, we take advantage of time- and length-scale information in neutron spectroscopy to show that the separation of different processes is the minimum requirement toward a more universal picture at, and even below, the glass transition for our systems. This is illustrated by constructing the full proton mean-square displacement for three bottlebrush polymers from femto- to nanoseconds, with simultaneous information on the partial contributions from segmental relaxation, methyl group rotation, and vibrations. The information can be used for a better analysis of results from numerous techniques and samples, improving the overall understanding of materials properties. © 2021 The Authors. Published by American Chemical Society. Open Access CC-BY-4.0.