TY - CONF A1 - Schönhals, Andreas T1 - Polymer based nanocomposites as investigated by dielectric spectroscopy and gas transport measurement T2 - Vortrag an der technischen Universität Lodz CY - Lodz, Poland DA - 2008-04-01 PY - 2008 AN - OPUS4-17487 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Molecules in nanometer confinement investigated by dielectric, thermal and neutron spectroscpoy T2 - Vortrag an der technischen Universität Lodz CY - Lodz, Poland DA - 2008-04-01 PY - 2008 AN - OPUS4-17488 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brás, A.R. A1 - Dionísio, M. A1 - Schönhals, Andreas T1 - Confinement and Surface Effects on the Molecular Dynamics of a Nematic Mixture Investigated by Dielectric Relaxation Spectroscopy N2 - Broadband dielectric spectroscopy (10-2-109 Hz) was employed to investigate the molecular dynamics of the liquid crystalline mixture E7 confined in both untreated and lecithin-treated 20 nm Anopore membranes. Because E7 does not crystallize, it was possible to cover a temperature range of more than 200 K, providing an exhaustive dielectric characterization of a liquid crystal confined to Anopore membranes for the first time. In the nematic state, the tumbling (α-) and the δ-relaxation are observed, also under confinement conditions. The analysis of their relative intensities give that the orientation of the E7 molecules is preferentially axial in untreated but opposite radial in lecithin-treated pores. The radial alignment of the liquid crystals in the modified membrane is understood as a tail-to-tail conformation of E7 molecules imposed by the adsorbed lecithin molecules. The relaxation rate of the α-process is enhanced for E7 confined in native Anopore compared with the bulk and E7 in treated pores. This is interpreted as resulting from a less dense molecular packing of E7 in the middle of the pore compared to the bulk. In both untreated and treated membranes, the relaxation rate of the δ-process is higher than in the bulk, and the values of the respective Vogel-Fulcher-Tammann temperatures depend on the actual surface treatment. Additionally, a surface process, due to molecular fluctuations of molecules within an adsorbed layer at the pore wall, was detected. PY - 2008 DO - https://doi.org/10.1021/jp802133e SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 112 IS - 28 SP - 8227 EP - 8235 PB - Soc. CY - Washington, DC AN - OPUS4-17802 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Labahn, Diana A1 - Schönhals, Andreas ED - Co, A. ED - Leal, L. G. ED - Colby, R. H. ED - Giacomin, A. J. T1 - Molecular Dynamics of Ultra-Thin Supported Polysulfone Films N2 - Ultra-thin films of polysulfone are prepared by spin coating down to thicknesses below 10 nm on an aluminum support and investigated by broadband dielectric spectroscopy. As a main result is was found that the glass transition temperature Tg does not depend on the film thickness for thicknesses larger than 10 nm. Secondly from the analysis of the dielectric strength it is concluded that the polysulfone segments form an adsorbed layer with a reduced mobility at the Al support having a thickness of ca. 5 nm. T2 - 15th International Congress on Rheolog, The Society of Rheology 80th Annual Meeting CY - Monterey, CA, USA DA - 2008-08-03 KW - Ultra-thin films KW - Dielectric relaxation KW - Glass transition KW - Polysulfone PY - 2008 SN - 978-0-7354-0549-3 DO - https://doi.org/10.1063/1.2964552 VL - 1027 IS - 1 SP - 1300 EP - 1302 PB - American Institute of Physics CY - Melville, NY, USA AN - OPUS4-17803 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brás, A. R. A1 - Noronha, J. P. A1 - Antunes, A. M. M. A1 - Cardoso, M. M. A1 - Schönhals, Andreas A1 - Affouard, F. A1 - Dionísio, M. A1 - Correia, N.T. T1 - Molecular motions in amorphous Ibuprofen as studied by broadband dielectric spectroscopy N2 - The molecular mobility of amorphous ibuprofen has been investigated by broadband dielectric relaxation spectroscopy (DRS) covering a temperature range of more than 200 K. Four different relaxation processes, labeled as α, β, γ, and D, were detected and characterized, and a complete relaxation map was given for the first time. The γ-process has activation energy Ea = 31 kJ·mol-1, typical for local mobility. The weak β-relaxation, observed in the glassy state as well as in the supercooled state was identified as the genuine Johari-Goldstein process. The temperature dependence of the relaxation time of the α-process (dynamic glass transition) does not obey a single VFTH law. Instead two VFTH regimes are observed separated by a crossover temperature, TB = 265 K. From the low temperature VFTH regime, a Tgdiel(t =100 s) = 226 K was estimated, and a fragility or steepness index m = 93, was calculated showing that ibuprofen is a fragile glass former. The D-process has a Debye-like relaxation function but the temperature dependence of relaxation time also follows the VFTH behavior, with a Vogel temperature and a pre-exponential factor which seem to indicate that its dynamics is governed by the α-process. It has similar features as the Debye-type process observed in a variety of associating liquids, related to hydrogen bonding dynamics. The strong tendency of ibuprofen to form hydrogen bonded aggregates such as dimers and trimers either cyclic or linear which seems to control in particular the molecular mobility of ibuprofen was confirmed by IR spectroscopy, electrospray ionization mass spectrometry, and MD simulations. PY - 2008 DO - https://doi.org/10.1021/jp8040428 SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 112 IS - 35 SP - 11087 EP - 11099 PB - Soc. CY - Washington, DC AN - OPUS4-17866 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Molecular mobility of molecules in nanoscale confinement and close to surface T2 - 5th International Conference on Broadband Dielectric Spectroscopy and its Applications CY - Lyon, France DA - 2008-08-26 PY - 2008 AN - OPUS4-17822 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Glass transition of ultrathin supported polysulfone films studied by dielectric spectroscopy T2 - 5th International Conference on Broadband Dielectric Spectroscopy and its Applications CY - Lyon, France DA - 2008-08-26 PY - 2008 AN - OPUS4-17823 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Relaxation Behavior of Nanocomposites based on Polyethylene and Layered Double Hydroxide T2 - 5th International Conference on NANOSTRUCTURED POLYMERS AND NANOCOMPOSITES CY - Paris, France DA - 2009-04-15 PY - 2009 AN - OPUS4-19307 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Turky, G. A1 - Shaaban, S.S. A1 - Schönhals, Andreas T1 - Broadband dielectric spectroscopy on the molecular dynamics in different generations of hyperbranched polyester N2 - Dielectric spectroscopy (10-2 Hz to 106 Hz) was employed to investigate the molecular dynamics of hyperbranched polyesters where the number of the generation is systematically varied from 2 to 5. As a first result, the dielectric properties depends strongly on the generation of the hyperbranched polymers. For higher generations (3 to 5) at temperatures below Tg two relaxation processes are observed, a γ-process at lower temperatures and a β-process at higher ones. The apparent activation energies are around 100 kJ/mol which seems to be too high for truly localized processes. For the Generation 2, only the γ-process is observed. For all investigated polymers the dielectric α-relaxation could not be observed because of strong conductivity effects. Therefore, the conductivity is systematically analyzed which obeys the peculiarities found to be characteristic for semiconducting disordered materials. Especially, the Barton/Nakajima/Namikawa relationship is found to be valid. KW - Molecular dynamics KW - Polyesters KW - Relaxation KW - Synthesis PY - 2009 DO - https://doi.org/10.1002/app.30046 SN - 0021-8995 SN - 1097-4628 VL - 113 IS - 4 SP - 2477 EP - 2484 PB - Wiley InterScience CY - Hoboken, NJ AN - OPUS4-19484 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Goering, Harald A1 - Costa, F. R. A1 - Wagenknecht, U. A1 - Heinrich, G. T1 - Dielectric properties of nanocomposites based on polyethylene and layered double hydroxide N2 - Nanocomposites with a predominantly exfoliated morphology were prepared by melt blending of organically modified doubled layered hydroxide (LDH) and low density polyethylene (PE). The prepared materials were investigated by differential scanning calorimetry (DSC) and in detail by dielectric spectroscopy. The DSC experiments show that the degree of crystallinity decreases linearly with increasing content of the LDH. The extrapolation of this dependence to zero results in a limiting concentration of ca. 50 wt % LDH were the crystallization of PE is completely suppressed by the nanofiller. The dielectric response of pure polyethylene shows different weak relaxation processes. The intensity of dynamic glass transition (β-relaxation) increases with the concentration of LDH. This is attributed to the increasing concentration of the exchanged anion dodecyl benzene sulfonate (SDBS). The SDBS molecules are strongly adsorbed at the exfoliated LDH layers. Therefore, a detailed analysis of the β-relaxation provides information about the structure and the molecular dynamics in the interfacial region between the exfoliated LDH layers and the polyethylene matrix. This analysis shows that the β-relaxation region consists of two processes: both of them obey glassy dynamics. The difference in corresponding Vogel (ideal glass transition) temperatures is about 30 K. The relaxation process at lower frequency is assigned to polyethylene segments with a reduced molecular mobility close to LDH layers. The process at higher frequencies is related to polyethylene segments in a farer distance for the surface of the nanofiller. In the nanocomposite materials an additional process due to Maxwell-Wagner-Sillars (MWS) polarization was observed. The time constant of this MWS process can be correlated with characteristic length scales in nanocomposites and therefore provides additional information on dispersion and delamination/exfoliation of the LDH layers in these materials. PY - 2009 DO - https://doi.org/10.1021/ma900077w SN - 0024-9297 SN - 1520-5835 VL - 42 IS - 12 SP - 4165 EP - 4174 PB - American Chemical Society CY - Washington, DC AN - OPUS4-19594 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -