TY - JOUR A1 - Schönhals, Andreas A1 - Schick, C. A1 - Huth, H. A1 - Frick, B. A1 - Mayorova, M. A1 - Zorn, R. T1 - Molecular Mobility of Poly(phenyl methyl siloxane) Investigated by Thermal, Dielectric and Neutron Spectroscopy JF - PMSE preprints PY - 2007 SN - 0743-0515 VL - 97 SP - 948 EP - 949 PB - Division of Polymeric Materials Science and Engineering, American Chemical Society CY - Washington, DC AN - OPUS4-15736 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Goering, Harald A1 - Schick, C. A1 - Frick, B. A1 - Mayorova, M. T1 - Segmental dynamics of poly(methyl phenyl siloxane) confined to nanoporous glasses JF - The European physical journal / Special topics N2 - 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 dynamics is faster than in the bulk which originates from an inherent length scale of the underlying molecular motions. For high temperatures the temperature dependence of the relaxation rates for confined PMPS crosses that of the bulk state. Besides finite states effects also the thermodynamic state of nano-confined PMPS is different from that of the bulk. At a pore size of 5 nm the temperature dependence of the relaxation times changes from a Vogel/Fulcher/Tammann like to an Arrhenius behavior where the activation energy depends on pore size. This is in agreement with the results obtained by NS. The increment of the specific heat capacity at the glass transition depends strongly on pore size and vanishes at a finite length scale between 3 and 5 nm which can be regarded as minimal length scale for glass transition to appear in PMPS. PY - 2007 SN - 1951-6355 SN - 1951-6401 VL - 141 IS - 1 SP - 255 EP - 259 PB - Springer CY - Berlin AN - OPUS4-14602 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Szymoniak, Paulina A1 - Kolmangadi, Mohamed Aejaz A1 - Böhning, Martin A1 - Zamponi, M. A1 - Frick, B. A1 - Appel, M. A1 - Günther, G. A1 - Russina, M. A1 - Alentiev, D. A1 - Bermeshev, M. A1 - Zorn, R. T1 - Microscopic dynamics of highly permeable super glassy polynorbornenes revealed by quasielastic neutron scattering JF - Journal of Membrane Science N2 - 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 methods 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 them promising candidates for active separation layers for gas separation membranes. At least for larger gas molecules it is assumed that the pathways for diffusion require an enlargement of pre-existing micropores in terms of an activated zone. A low temperature relaxation process was found for both polymers by the performed neutron scattering experiments. This process was assigned to the methyl group rotation. It was analysed in terms of a jump diffusion in a three-fold potential. The analysis of the dependence of the elastic incoherent structure factor on the scattering vector yields the number of methyl groups which might be immobilized. For PTCNSi1 (3 methyl groups in the monomeric unit) it was found that all methyl groups take part in the methyl group rotation whereas for PTCNSi2g (6 methyl groups in monomeric unit) a considerable number of methyl groups are blocked in their rotation. This immobilization of methyl groups is due to the sterically demanding arrangement of the methyl groups in PTCNSi2g. This conclusion is further supported by the result that the activation energy for the methyl group rotation is three times higher for PTCNSi2g than that of PTCNSi1. KW - Highly permeably polynorbornenes KW - Polymers of intrinsic microporosity KW - Gas separation membranes KW - Quasielastic neutron scattering PY - 2021 DO - https://doi.org/10.1016/j.memsci.2021.119972 SN - 0376-7388 VL - 642 PB - Elesevier B.V. AN - OPUS4-53508 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, Christina A1 - Zorn, R. A1 - Emmerling, Franziska A1 - Falkenhagen, Jana A1 - Frick, B. A1 - Huber, P. A1 - Schönhals, Andreas T1 - Vibrational density of states of triphenylene based discotic liquid crystals: dependence on the length of the alkyl chain JF - Physical chemistry, chemical physics N2 - 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 liquid crystalline phase at higher temperatures and a quasi isotropic phase at the highest temperatures. The X-ray scattering pattern for the plastic crystalline phase of all materials shows a sharp Bragg reflection corresponding to the intercolumnar distance in the lower q-range and a peak at circa 17 nm-1 related to intracolumnar distances between the cores perpendicular to the columns as well as a broad amorphous halo related to the disordered structure of the methylene groups in the side chains in the higher q-range. The intercolumnar distance increases linearly with increasing chain length for the hexagonal columnar ordered liquid crystalline phase. A similar behaviour is assumed for the plastic crystalline phase. Besides n = 8 all materials under study exhibit a Boson peak. With increasing chain length, the frequency of the Boson peak decreases and its intensity increases. This can be explained by a self-organized confinement model. The peaks for n = 10, 12 are much narrower than for n = 5, 6 which might imply the transformation from a rigid system to a softer one with increasing chain length. Moreover the results can also be discussed in the framework of a transition from an uncorrelated to a correlated disorder with increasing n where n = 8 might be speculatively considered as a transitional state. KW - X-ray scattering KW - Neutron scattering KW - Differential scanning calorimetry PY - 2014 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-304789 DO - https://doi.org/10.1039/c3cp55303e SN - 1463-9076 SN - 1463-9084 VL - 16 IS - 16 SP - 7324 EP - 7333 PB - The Royal Soc. of Chemistry CY - Cambridge AN - OPUS4-30478 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, Christina A1 - Zorn, R. A1 - Frick, B. A1 - Schönhals, Andreas T1 - Thermal properties and vibrational density of states of a nanoconfined discotic liquid crystal JF - Colloid and polymer science N2 - 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 were observed down to the smallest pore size. The decrease of the transition enthalpies versus inverse pore size for both transitions implies an increase of the amount of disordered amorphous material. By extrapolation of its pore size dependence, a critical pore diameter for structure formation of 17 nm is estimated. Similar to the bulk, excess contributions to the VDOS (Boson peak) are also observed for confined HAT6. The Boson peak gains in intensity and shifts to lower frequencies with decreasing pore diameter. This is discussed in the framework of a softening of HAT6 induced by the confinement due to a less-developed plastic crystalline state inside the pores compared to the bulk. KW - Discotic liquid crystals KW - Confinement KW - Neutron scattering KW - Boson peak PY - 2014 DO - https://doi.org/10.1007/s00396-014-3247-3 SN - 0303-402X SN - 1435-1536 VL - 292 IS - 8 SP - 1949 EP - 1960 PB - Springer CY - Berlin AN - OPUS4-31254 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kityk, A.V. A1 - Busch, M. A1 - Rau, D. A1 - Calus, S. A1 - Cerclier, C.V. A1 - Lefort, R. A1 - Morineau, D. A1 - Grelet, E. A1 - Krause, Christina A1 - Schönhals, Andreas A1 - Frick, B. A1 - Huber, P. T1 - Thermotropic orientational order of discotic liquid crystals in nanochannels: an optical polarimetry study and a Landau-de Gennes analysis JF - Soft matter N2 - Optical polarimetry measurements of the orientational order of a discotic liquid crystal based on a pyrene derivative confined in parallelly aligned nanochannels of monolithic, mesoporous alumina, silica, and silicon as a function of temperature, channel radius (3–22 nm) and surface chemistry reveal a competition of radial and axial columnar orders. The evolution of the orientational order parameter of the confined systems is continuous, in contrast to the discontinuous transition in the bulk. For channel radii larger than 10 nm we suggest several, alternative defect structures, which are compatible both with the optical experiments on the collective molecular orientation presented here and with a translational, radial columnar order reported in previous diffraction studies. For smaller channel radii our observations can semi-quantitatively be described by a Landau–de Gennes model with a nematic shell of radially ordered columns (affected by elastic splay deformations) that coexists with an orientationally disordered, isotropic core. For these structures, the cylindrical phase boundaries are predicted to move from the channel walls to the channel centres upon cooling, and vice-versa upon heating, in accord with the pronounced cooling/heating hystereses observed and the scaling behavior of the transition temperatures with the channel diameter. The absence of experimental hints of a paranematic state is consistent with a biquadratic coupling of the splay deformations to the order parameter. PY - 2014 DO - https://doi.org/10.1039/c4sm00211c SN - 1744-683X VL - 10 IS - 25 SP - 4522 EP - 4534 PB - RSC Publ. CY - Cambridge AN - OPUS4-30866 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Frunza, S. A1 - Frunza, L. A1 - Unruh, T. A1 - Frick, B. A1 - Zorn, R. T1 - Vibrational and molecular dynamics of a nanoconfined liquid crystal JF - The European physical journal / Special topics N2 - 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 cylindrical pores with a radius of 1.25 nm. The results obtained by both methods are compared in detail. PY - 2010 DO - https://doi.org/10.1140/epjst/e2010-01329-5 SN - 1951-6355 SN - 1951-6401 VL - 189 IS - 1 SP - 251 EP - 255 PB - Springer CY - Berlin AN - OPUS4-22638 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Zorn, R. A1 - Frick, B. T1 - Inelastic neutron spectroscopy as a tool to investigate nanoconfined polymer systems JF - Polymer N2 - 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 for the study of confined systems. Moreover, Neutrons are sensitive to light nuclei therefore the confined polymers can be investigated directly, more or less independently of the confining host. Resulting findings are firstly, a reduction of the low frequency contributions to the VDOS below the Boson Peak frequency for both polymers. Including literature data, this reduction can be regarded as a more general feature for glass-forming systems confined by hard walls. Secondly, clear deviations in the temperature dependence of the mean squared displacement of the confined molecules compared to the bulk were found close to the thermal glass transition temperature, whereas localized methyl group rotations were only weakly influenced. Furthermore, the molecular dynamics is accessed. The combination of neutron Time-of-Flight with neutron backscattering, thus covering a broad dynamical range from sub ps to ns, reveal clear influence from confinement on the intermediate incoherent scattering function S(q,t). The latter was obtained by combining the inverse Fourier transform of the individual dynamical structure factors measured by the both methods. The time and q dependence of S(q,t) are discussed in detail for the local methyl group rotations and the segmental dynamics, considering both the interaction of the segments with the pore walls and possible geometrical confinement effects. KW - Confinement KW - Density of states KW - Dynamic glass transition PY - 2016 DO - https://doi.org/10.1016/j.polymer.2016.06.006 SN - 0032-3861 SN - 1873-2291 VL - 105 SP - 393 EP - 406 PB - Elsevier AN - OPUS4-38256 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Krause, Christina A1 - Zorn, R. A1 - Frick, B. A1 - Schönhals, Andreas T1 - Quasi- and inelastic neutron scattering to investigate the molecular dynamics of discotic molecules in the bulk JF - The European physical journal - Web of Conferences : proceedings N2 - 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 density of states are found. Therefore it is concluded that these liquid crystals show a glass-like behaviour. Elastic scans further show that in these materials a rich molecular dynamics takes place. T2 - QENS/WINS 2014 - 11th International Conference on Quasielastic Neutron Scattering and 6th International Workshop on Inelastic Neutron Spectrometers CY - Autrans, France DA - 2014-05-11 PY - 2015 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-325477 DO - https://doi.org/10.1051/epjconf/20158302017 SN - 2100-014X VL - 83 SP - 02017-1 EP - 02017-4 PB - EDP Sciences CY - Les Ulis AN - OPUS4-32547 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Schönhals, Andreas A1 - Frick, B. A1 - Zorn, R. ED - Kremer, Friedrich ED - Loidl, Alois T1 - The scaling of the molecular dynamics of liquid crystals as revealed by broadband dielectric, specific heat, and neutron spectroscopy T2 - The scaling of relaxation processes, Advances in dielectrics N2 - 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 heat spectroscopy and neutron scattering. As systems the nematic liquid crystal E7 and a discotic liquid crystalline pyrene are considered. First of all it was proven that both systems show all peculiarities which are characteristic for glassy dynamics and the glassy state. Especially for the nematic liquid crystal E7 it could be unambiguously shown by a combination of dielectric and specific heat spectroscopy that the tumbling mode is the underlying motional process responsible for glassy dynamics. Dielectric investigations on the discotic liquid crystalline pyrene reveal that at the phase transition from the plastic crystalline to the hexagonal columnar liquid crystalline phase the molecular dynamics changes from a more strong to fragile temperature dependence of the relaxation rates. Moreover a combination of results obtained by specific heat spectroscopy with structural methods allows an estimation of the length scale relevant for the glass transition. KW - Broadband dielectric spectroscopy KW - Specific heat spectroscopy KW - Rod-like liquid crystals KW - Discotic liquid crystals PY - 2018 UR - https://link.springer.com/content/pdf/10.1007%2F978-3-319-72706-6.pdf SN - 978-3-319-72705-9 SN - 978-3-319-72706-6 DO - https://doi.org/10.1007/978-3-319-72706-6_9 SN - 2190-930X SN - 2190-9318 SP - 279 EP - 306 PB - Springer International publishing AG CY - Cham, Switzerland ET - 1. AN - OPUS4-45624 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -