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 - TY - CONF A1 - Schönhals, Andreas T1 - Molecular Dynamics of Polymers as Studied by Dielectric, Specific Heat and Neutron Spectroscopy. - From the bulk to the confined state T2 - Vortrag an der Technischen Universität Dortmund, Fakultät für Physik CY - Dortmund, Germany DA - 2009-06-16 PY - 2009 AN - OPUS4-19560 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ryabov, Y. A1 - Gutina, A. A1 - Feldman, Y. A1 - Frunza, S. A1 - Frunza, L. A1 - Schönhals, Andreas T1 - Comment on "investigating hydration dependence of dynamics of confined water: Monolayer, hydration water, and Maxwell-Wagner processes" [J. Chem. Phys. 128, 154503 (2008)] N2 - This comment on the experimental methods and the conclusions of the paper "Investigating hydration dependence of dynamics of confined water: Monolayer, hydration water, and Maxwell–Wagner processes" [ J. Sjöström et al., J. Chem. Phys.128, 154503 (2008) ] exposes serious shortcomings in the understanding and the interpretation of the observed relaxation behavior of confined water presented in the article. There are contradictions between the suggested theory and the experimental observations that mislead the reader. In this comment we prove that the Maxwell–Wagner relaxation cannot explain the nonmonotonous temperature dependence for the process observed in confined water. PY - 2010 DO - https://doi.org/10.1063/1.3451102 SN - 0021-9606 SN - 1089-7690 VL - 133 SP - 037101-1 - 037101-2 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21908 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Structure Property Relationsships of Polymeric Nanocomposites with Layered Nanofillers T2 - 6. International Conference on Broadband Dielectric Spectroscopy and its Applications CY - Madrid, Spain DA - 2010-09-07 PY - 2010 AN - OPUS4-21976 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Broadband Dielectric Spectroscopy and its Relationship to Other Spectroscopic Techniques T2 - Satelite Courses at 6. International Conference on Broadband Dielectric Spectroscopy and its Applications CY - Madrid, Spain DA - 2010-09-06 PY - 2010 AN - OPUS4-21977 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wohlrab, Sebastian A1 - Schönhals, Andreas A1 - Goering, Harald A1 - Friedrich, Jörg Florian T1 - Integration of sol-gel derived inorganic nanonetworks into polymers N2 - Nanoparticulate networks as fillers for polymer based nanocomposites offer an optimized, surfactant free distribution of the inorganic component. Additionally, their non-aggregated but interconnected nanoparticulate subunits can lead to new properties owing to special inherent solid state properties and/or spacial restrictions to the polymeric parts. In particular, polymer nanocomposites based on poly(methyl methacrylate) (PMMA) or poly(hydroxyethyl methacrylate) (PHEMA), filled with different nanoparticulate networks of AlOOH were synthesized using two advanced synthesis techniques. An ex situ method, in which a preformed AlOOH-gel was solvent exchanged by methyl methacrylate (MMA) and an in situ method, in which the AlOOH scaffold was prepared within hydroxyethyl methacrylate (HEMA), have been used to produce the materials described here through polymerization. On the MMA based composites the particles were removed by etching, yielding porous polymers. Promising for a broad variety of crystallisable networks within polymers, the phase transition of amorphous AlOOH within PMMA towards crystalline boehmite was performed using a hydrothermal method. The materials were characterized using transmission electron microscopy, X-ray diffraction, gel permeation chromatography, differential scanning calorimetry, IR-spectroscopy, UV/Vis spectroscopy and hardness measurements. Special material properties were investigated using thermogravimetry, thermomechanical analysis and dynamic mechanical analysis. Furthermore, interactions between PMMA segments and the AlOOH network were detailed studied using dielectric spectroscopy. PY - 2010 DO - https://doi.org/10.1039/c0py00105h SN - 1759-9954 SN - 1759-9962 VL - 1 IS - 8 SP - 1226 EP - 1236 AN - OPUS4-21996 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Rittig, F. A1 - Kärger, J. T1 - Self-diffusion of poly(propylene glycol) in nanoporous glasses studied by pulsed field gradient NMR: A study of molecular dynamics and surface interactions N2 - Pulsed field gradient NMR is applied to investigate the self-diffusion of poly(proypylene glycol) in nanoporous glasses (nominal pore sizes of 2.5–7.5 nm). In general, the diffusion is slowed down by the confinement compared to the bulk. For native pore surfaces covered by hydroxyl groups the spin echo attenuation Ψ displays a bimodal behavior versus q2t (q-norm of a generalized scattering vector). This was explained assuming spatial regions of different diffusivities in a two-phase model. The slow component is assigned to segments forming a surface layer close to the pore walls in which the segments have a lower mobility than those located in the center of the pores. By variation of observation time it was concluded that time constant for the dynamic exchange of segments between these two regions is around 100 ms at room temperature. For silanized pores, the bimodal behavior in the spin echo attenuation Ψ shows a stretched exponential decay versus q2t. The estimated diffusion coefficients decrease strongly with decreasing pore size. The temperature dependence of the diffusion coefficient can be approximated by an Arrhenius law where the activation energy increases with decreasing pore size. The observed pore size dependence for the diffusion of poly(propylene glycol) in silanized nanoporous glasses can be discussed assuming interaction and confining size effects. KW - Glass KW - Molecular dynamics method KW - Nanoporous materials KW - Polymers KW - Self-diffusion KW - Spin echo (NMR) PY - 2010 DO - https://doi.org/10.1063/1.3479905 SN - 0021-9606 SN - 1089-7690 VL - 133 IS - 9 SP - 094903-1 - 094903-7 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-22000 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Structure-Property Relationships of Polyolefine based Nanocomposites with Layered Double Hydroxides - Interplay between Matrix and Interfacial Effects T2 - 3. Jahresmeeting VAMA TWA-33 (Poymeric Nanocomposites) CY - Istanbul, Turkey DA - 2010-10-19 PY - 2010 AN - OPUS4-22228 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Schönhals, Andreas A1 - Frunza, L. A1 - Ganea, P. A1 - Kosslick, H. A1 - Harloff, J. A1 - Schulz, A. T1 - Molecular relaxation processes in a MOF-5 structure revealed by broadband dielectric spectroscopy: signature of phenylene ring fluctuations N2 - The molecular mobility of a MOF-5 metal–organic framework was investigated by broadband dielectric spectroscopy. Three relaxation processes were revealed. The temperature dependence of their relaxation rates follows an Arrhenius law. The process observed at lower temperatures is attributed to bending fluctuations of the edges of the cages involving the Zn–O clusters. The processes ('region II') at higher temperatures were assigned to fluctuations of phenyl rings in agreement with the NMR data found by Gould et al. (J. Am. Chem. Soc. 2008, 130, 3246). The carboxylate groups might also be involved. The rotational fluctuations of the phenyl rings leading to the low frequency part of relaxation region II might be hindered either by some solvent molecules entrapped in the cages or by an interpenetrated structure and have a broad distribution of activation energies. The high frequency part of region II corresponds nearly to a Debye-like process: This is explained by a well-defined structure of empty pores. PY - 2010 DO - https://doi.org/10.1021/jp1071617 SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 114 IS - 40 SP - 12840 EP - 12846 PB - Soc. CY - Washington, DC AN - OPUS4-22255 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Friedrich, Jörg Florian A1 - Mix, Renate A1 - Kühn, Gerhard A1 - Retzko, Iris A1 - Schönhals, Andreas A1 - Unger, Wolfgang T1 - Plasma-based introduction of monosort functional groups of different type and density onto polymer surfaces. Part 2: Pulsed plasma polymerization N2 - This new functionalization method consists of the deposition of very thin plasma polymer layers (20 to 100 nm) of functional group bearing monomers in pulsed plasma. With allylalcohol, a maximum of 30 OH groups per 100 C atoms was measured with a selectivity of about 90% and a significant stability at long-time exposure to air. Allylamine was used to produce primary amino groups, with a maximum of 18 NH2 groups per 100 C atoms. Side reactions were observed during the storage in air, such as oxidation of the amino groups. Carboxylic groups could be produced using acrylic acid with a maximum concentration of 24 COOH groups per 100 C atoms. The most prominent side reaction was the decarbonylation/ decarboxylation of the acid group during plasma deposition.___TAGSTART___BR___TAGEND___ The variation of the density of functional groups using the pulsed-plasma polymerization of functional-group-bearing monomers was possible by the chemically-initiated radical copolymerization with either a chain-extending monomer, such as ethylene, or a cross linker, such as butadiene, in plasma. The density of functional groups could be adjusted continuously (0 to 30 OH, 0 to 18 NH2 and 0 to 24 COOH groups per 100 C atoms).___TAGSTART___BR___TAGEND___ The successful application of these densely functionalized polymer surfaces for producing biocompatible surfaces and for use in metal–polymer composites is proposed. KW - Pulsed plasma polymerization KW - Plasma-initiated copolymerization KW - Charcterization of homo- and copolymers PY - 2003 DO - https://doi.org/10.1163/156855403765826874 VL - 10 IS - 2-3 SP - 173 EP - 223 PB - North-Holland CY - New York, NY AN - OPUS4-2706 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Behaviour of ploymers confined to nanoporous glasses studied by dielectric, thermal and vibrational spectroscopy: Cut - off length scale for glass transition? T2 - DPG-Frühjahrstagung (Polymerphysik), Fachverband CPP, Themenkreis 3 CY - Regensburg, Germany DA - 2002-03-11 PY - 2002 AN - OPUS4-3341 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - The Behaviour of Polymers Confined to Nanoporous Glasses Investigated by Relaxation Experiment T2 - Polydays 2004 CY - Potsdam, Germany DA - 2004-10-04 PY - 2004 AN - OPUS4-4354 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Self-Diffusion of Poly(Propylene Glycol) Confined to Nanoporous Glasses by Pulsed Field Gradient NMR T2 - Polydays 2004 CY - Potsdam, Germany DA - 2004-10-04 PY - 2004 AN - OPUS4-4337 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Neutron Spectrocopy on Nanoconfined Polymers T2 - 7. International Conference on Quasi-Elastic Neutron Scattering CY - Arcachon, France DA - 2004-09-01 PY - 2004 AN - OPUS4-4318 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - The Behaviour of Polymers confined to Nanoporous Glasses investigated by Relaxation Experiments T2 - Polydays 2004 CY - Potsdam, Germany DA - 2004-10-04 PY - 2004 AN - OPUS4-4319 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Neutron spectroscopy on polymers confined to nanoporous glasses T2 - Polydays 2004 CY - Potsdam, Germany DA - 2004-10-04 PY - 2004 AN - OPUS4-4320 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -