TY - CONF A1 - Schönhals, Andreas T1 - Molecular Mobility of Molecules in Nanoscale Confinement and Close to Surfaces T2 - Seminar an der Technische Universität Lodz CY - Lodz, Poland DA - 2008-11-14 PY - 2008 AN - OPUS4-18626 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hao, Ning A1 - Böhning, Martin A1 - Wohlrab, Sebastian A1 - Schönhals, Andreas T1 - Polymer Based Nanocomposites with PhenethylPOSS as Nanofilter Investigated by Dielectric Spectroscopy and Gas Transport Measurements N2 - Polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) as nanofiller was incorporated within Poly(bisphenol A carbonate) (PBAC) as matrix. Dielectric spectroscopy proved an almost complete miscibility of PhenethylPOSS up to 7 wt. %. At higher concentrations phase separation yields composites with a PBAC-rich matrix and POSS-rich domains which posses well shaped interfaces. The nanocomposites were also investigated with respect to their gas transport behaviour. An increase of the gas permeability was found at higher PhenethylPOSS concentrations, which is due to the phase separated structure. KW - Dielectric measurements KW - Nanocomposites KW - Permeation KW - Polycarbonates KW - Polyhedral oligomeric silsesquioxanes PY - 2008 DO - https://doi.org/10.1002/masy.200850712 SN - 1022-1360 SN - 0258-0322 SN - 1521-3900 VL - 267 IS - 1 SP - 69 EP - 73 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-17751 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Schönhals, Andreas A1 - Kosslick, H. A1 - Frunza, S. T1 - Relaxation processes of water confined to AIMCM-41 molecular sieves. Influence of the hydroxyl groups of the pore surface N2 - A series of AlMCM-41 molecular sieves was prepared with constant composition (Si/Al = 14.7) and presumably same pore structure but different pore diameters (from 2.3 to 4.6 nm). The pore size distribution is narrow for each sample. The rotational fluctuations of water molecules confined inside the pores were investigated applying broadband dielectric spectroscopy (10-2–107 Hz) over a large temperature interval (213–333 K). A relaxation process, slower than that expected for bulk water, was observed which is assigned to water molecules forming a surface layer on the pore walls. The estimated relaxation time has an unusual non-monotonic temperature dependence, which is rationalized and modeled assuming two competing processes: rotational fluctuations of constrained water molecules and defect formation (Ryabov model). This paper focuses on the defects and notably the influence of the hydroxyl groups of the pore walls. The Ryabov model is fitted to the data and characteristic parameters are obtained. Their dependence on pore diameter is considered for the first time. The found results are compared with those obtained for other types of molecular sieves and related materials. PY - 2008 DO - https://doi.org/10.1140/epje/i2007-10340-y SN - 1292-8941 SN - 1292-895X VL - 26 SP - 379 EP - 386 PB - EDP Sciences CY - Orsay AN - OPUS4-17752 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Glassy dynamics of ultra-thin supported polysufone layers as studied by dielectric spectroscopy T2 - The 15. International Congress on Rheology CY - Monterey, CA, USA DA - 2008-08-03 PY - 2008 AN - OPUS4-17772 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Structure property relationships of different polymer based nanocomposites as investigated by dielectric spectroscopy and gas transport measurements T2 - Kolloquium am Institut für Polmerforschung Dresden CY - Dresden, Germany DA - 2008-07-01 PY - 2008 AN - OPUS4-17768 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Polymer Based Nanocomposites - Interplay between Interfacial and Bulk Effects T2 - Vortrag am Deutschen Kunststoffinstitut CY - Darmstadt, Germany DA - 2009-07-02 PY - 2009 AN - OPUS4-19657 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Dieletric Relaxation of Nanocomposites of Polypropylene and Clay Nanofillers T2 - 2. Jahreskonferenz von VAMAS TWA-33 CY - Rome, Italy DA - 2009-08-30 PY - 2009 AN - OPUS4-19894 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brás, A.R. A1 - Frunza, S. A1 - Guerreiro, L. A1 - Fonseca, I.M. A1 - Corma, A. A1 - Frunza, L. A1 - Dionísio, M. A1 - Schönhals, Andreas T1 - Molecular mobility of nematic E7 confined to molecular sieves with a low filling degree N2 - The nematic liquid crystalline mixture E7 was confined with similar filling degrees to molecular sieves with constant composition but different pore diameters (from 2.8 to 6.8 nm). Fourier transform infrared analysis proved that the E7 molecules interact via the cyanogroup with the pore walls of the molecular sieves. The molecular dynamics of the system was investigated by broadband dielectric spectroscopy (10-2-109 Hz) covering a wide temperature range of ~ 200 K from temperatures well above the isotropic-nematic transition down to the glass transition of bulk E7. A variety of relaxation processes is observed including two modes that are located close to the bulk behavior in its temperature dependence. For all confined samples, two relaxation processes, at frequencies lower than the processes observed for the bulk, were detected. At lower temperatures, their relaxation rates have different temperature dependencies whereas at higher temperatures, they seem to collapse into one chart. The temperature dependence of the slowest process (S-process) obeys the Vogel-Fulcher-Tammann law indicating a glassy dynamics of the E7 molecules anchored to the pore surface. The pore size dependence of both the Vogel temperature and fragility revealed a steplike transition around 4 nm pore size, which indicates a transition from a strong to a fragile behavior. The process with a relaxation rate in between the bulklike and the S-process (I-process) shows no dependence on the pore size. The agreement of the I-process with the behavior of a 5CB surface layer adsorbed on nonporous silica leads to the assignment of E7 molecules anchored at the outer surface of the microcrystals of the molecular sieves. KW - Adsorption KW - Fourier transform spectra KW - Glass transition KW - infrared spectra KW - Molecular sieves KW - Nematic liquid crystals KW - Organic compounds KW - Porous materials PY - 2010 DO - https://doi.org/10.1063/1.3432775 SN - 0021-9606 SN - 1089-7690 VL - 132 SP - 224508-1 - 224508-12 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21510 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Schönhals, Andreas A1 - Frunza, L. A1 - Beica, T. A1 - Zgura, I. A1 - Ganea, P. A1 - Stoenescu, D. T1 - Dynamics of cyanophenyl alkylbenzoate molecules in the bulk and in a surface layer adsorbed onto aerosil. Variation of the lengths of the alkyl chain N2 - The molecular mobility of 4-butyl- and 4-pentyl-4'-cyanophenyl benzoate (CP4B, CP5B) and their composites prepared from aerosil A380 was investigated by broadband dielectric spectroscopy in a large temperature range. Thermogravimetric and infrared investigations were additionally performed. High silica density (larger than 7 g aerosil/1 g of liquid crystal) was selected to observe a thin layer adsorbed on the surface of the silica particles. The data were compared with those of the member of the series with six carbon atoms in the alkyl tail. Bulk CP4B and CP5B show the dielectric behaviour expected for liquid crystals. For the composites one relaxation process is observed at frequencies much lower than those for the corresponding bulk, which was assigned to the dynamics of the molecules in a surface layer. The temperature dependence of the relaxation rates (and of the dielectric strength) shows a crossover behaviour with two distinguished regimes. At higher temperatures the data obey the Vogel-Fulcher-Tammann law, whereas an Arrhenius law is observed at lower temperature, in a close similarity to the behaviour of a constrained dynamic glass transition. The estimated Vogel and crossover temperature is independent on the tail length, while the activation energy for the low temperature branch increases weakly with increasing the alkyl tail. KW - Confined liquid crystals KW - Molecules at surfaces KW - Dielectric properties KW - Relaxation processes KW - Glassy dynamics KW - Crossover phenomenon PY - 2010 DO - https://doi.org/10.1016/j.chemphys.2010.04.031 SN - 0301-0104 SN - 1873-4421 VL - 372 IS - 1-3 SP - 51 EP - 60 PB - Elsevier CY - Amsterdam AN - OPUS4-21588 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Molecular Dynamics of glass-forming materials revealed by a combintaion of broadband dielectric, specific heat and neutron spectroscopy T2 - Joint Softmatter Seminar CY - Jülich, Germany DA - 2010-12-15 PY - 2010 AN - OPUS4-23011 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - GEN A1 - Wang, D. A1 - Costa, F. R. A1 - Leuteritz, A. A1 - Purohit, Purv A1 - Schönhals, Andreas A1 - Vyalikh, A. A1 - Scheler, U. A1 - Wagenknecht, U. A1 - Kutlu, B. A1 - Heinrich, G. ED - Mittal, V. T1 - Polyolefin nanocomposites with layered double hydroxides PY - 2010 SN - 978-1-4398-1454-3 SP - 225 EP - 245 PB - CRC Press AN - OPUS4-23039 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Dielectric relaxation of ultrathin films of supported polysulfone T2 - 10th Laehnwitzseminar on Calorimetry 2008 CY - Rostock, Germany DA - 2008-06-08 PY - 2008 AN - OPUS4-17551 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Dynamics of nearly single cyanobiphenyl and cyanophenylbenzoate molecules adsorbed onto aerosil T2 - 10th Laehnwitzseminar on Calorimetry 2008 CY - Rostock, Germany DA - 2008-06-06 PY - 2008 AN - OPUS4-17552 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Polymer based Nanocomposites - Interplay between interfacial and Bulk Effects T2 - Workshop on Progress in Bio- and Nanotechnology CY - Lodz, Poland DA - 2009-02-12 PY - 2009 AN - OPUS4-18990 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Labahn, Diana A1 - Mix, Renate A1 - Schönhals, Andreas T1 - Dielectric relaxation of ultrathin films of supported polysulfone N2 - The dynamic glass transition (α relaxation, structural relaxation) of ultrathin polysulfone films prepared between aluminum electrodes is investigated by dielectric relaxation spectroscopy. As a main result, it is found that the glass transition temperature Tg does not depend on the thickness of the polymeric layer down to a thickness of 10 nm. For thicknesses lower than 10 nm, an increase of Tg is observed. A more detailed analysis of the temperature dependence of the relaxation rates reveals that the Vogel temperature increases and the fragility decreases systematically with decreasing film thickness d. Further, the dielectric strength Δε decreases with decreasing d. This is discussed by the formation of a surface layer of adsorbed polysulfone segments having a reduced molecular mobility with regard to the time scale characteristic of the glassy dynamics of bulk polysulfone. Plotted versus inverse film thickness Δε decreases linearly with 1/d and becomes zero for an extrapolated length scale of 10 nm. From that it is concluded that the thickness of the adsorbed boundary layer is about 5 nm. Contact-angle measurements were carried out to confirm the strong interaction between aluminum and polysulfone. It is also shown that preparation details like annealing conditions strongly influence the glass transition of supported ultrathin films. KW - Adsorbed layers KW - Aluminium KW - Annealing KW - Contact angle KW - Dielectric relaxation KW - Electrodes KW - Glass transition KW - Polymer films KW - Thin films PY - 2009 DO - https://doi.org/10.1103/PhysRevE.79.011801 SN - 1539-3755 SN - 1063-651X VL - 79 IS - 1 SP - 011801-1 - 011801-9 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-19050 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Schönhals, Andreas A1 - Goering, Harald A1 - Manaila-Maximean, D. A1 - Beica, T. A1 - Frunza, L. A1 - Moldovan, R. T1 - Dynamics of Cyanophenyl Alkybenzoate molecules in a surface layer adsorbed onto Aerosil. I. Cyanophenyl Hexylbenzoate N2 - A composite prepared from aerosil A380 and the liquid crystal (LC) 4-hexyl-4'-cyanophenyl benzoate (CP6B) was investigated by broadband dielectric spectroscopy in a large temperature range. The selected high silica density (ca. 7 g aerosil/1 g of CP6B) allows the observation of a thin layer (two-monolayer structure) adsorbed on the surface of the silica particles. For the composite one relaxation process is observed at frequencies much lower than that of the processes found for bulk CP6B. It is assigned to the dynamics of the molecules in the surface layer. The temperature dependence of its relaxation rates obeys the Vogel-Fulcher-Tammann law, which is characteristic for glass-forming liquids. The quasi 2D character of the observed glassy dynamics in the surface layer is discussed. The temperature dependence of the CP6B relaxation in the composite is compared with that of related hexylcyanobiphenyl molecules in the surface layer of aerosil composite with a similar concentration. KW - Cyanophenyl-alkylbenzoates KW - Dielectric spectroscopy KW - Infrared spectroscopy KW - Liquid crystals KW - Thermal analysis KW - Aerosil composites PY - 2008 DO - https://doi.org/10.1080/15421400802430448 SN - 0026-8941 SN - 1543-5318 VL - 495 SP - 60/[412] EP - 79/[431] PB - Gordon & Breach CY - London AN - OPUS4-19063 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Molecular Dynamics of Polymeric Nanocomposites with Layered Nanofillers T2 - 6th International Discussion Meeting Relaxation in Complex Systems CY - Rome, Italy DA - 2009-08-30 PY - 2009 AN - OPUS4-19947 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Frunza, S. A1 - Kosslick, H. A1 - Schönhals, Andreas T1 - Phase behavior and molecular mobility of n-octylcyanobiphenyl confined to molecular sieves: Dependence on the pore size PY - 2008 DO - https://doi.org/10.1103/PhysRevE.78.051701 SN - 1539-3755 SN - 1063-651X VL - 78 IS - 5 SP - 051701-1 - 051701-11 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-20881 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Vibrational and Molecular Dynamics of Nanoconfined Liquid Crystals T2 - Confit 2010 CY - Grenoble, France DA - 2010-03-03 PY - 2010 AN - OPUS4-20988 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, L. A1 - Frunza, S. A1 - Zgura, I. A1 - Beica, T. A1 - Gheorghe, N. A1 - Ganea, P. A1 - Stoenescu, D. A1 - Dinescu, A. A1 - Schönhals, Andreas T1 - Involvement of cyan and ester groups in surface interactions of aerosil-cyanophenyl alkyl benzoate systems wih high silica density: infrared investigations N2 - Composites prepared from aerosil A380 and liquid crystals (LCs) of 4-n-alkyl-4'-cyanophenyl benzoate type, with four to six carbon atoms in the alkyl chain were investigated by infrared spectroscopy. Their high silica content (of 2-7 g aerosil/1 g of LC) was given by thermogravimetric investigations and allows the observation of a rather thin LC layer on the silica particles. Several surface species onto the external surface of the grains were demonstrated. Arguments are given that monomer and dimer species are present in the bulk cyanophenyl benzoate materials while bulk-like species along with hydrogen-bonded ones coexist in the so-called surface layer of the composites. The main interaction of LC molecules with the aerosil surface is by hydrogen bonding taking place with the involvement of the cyan group. There is a contribution of ester carbonyl group to these surface interactions but this cannot be well quantified. KW - Cyanophenyl alkyl benzoate KW - Aerosil composites KW - Infrared spectra KW - Band shape analysis PY - 2010 DO - https://doi.org/10.1016/j.saa.2009.12.029 SN - 1386-1425 SN - 0370-8322 SN - 1873-3557 SN - 0584-8539 VL - 75 IS - 4 SP - 1228 EP - 1235 PB - Elsevier CY - Amsterdam AN - OPUS4-20997 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Saiter, A. A1 - Delbreilh, L. A1 - Couderc, H. A1 - Arabeche, K. A1 - Schönhals, Andreas A1 - Saiter, J.-M. T1 - Temperature dependence of the characteristic length scale for glassy dynamics: Combination of dielectric and specific heat spectroscopy N2 - The temperature dependence of characteristic length scales associated to the glass transition such as the cooperativity length scale introduced by Adam and Gibbs [cooperative rearranging region (CRR)] or the dynamic heterogeneity as estimated from the four point correlation function X4, is at the center of large interests. Broadband dielectric spectroscopy and temperature modulated differential scanning calorimetry allow to study the CRR size temperature dependence in the temperature range of ergodicity loss for glass-forming liquids, starting from the onset of cooperativity in the crossover region down to the glass transition temperature. Furthermore, the correlation between these two techniques allows to explore a large frequency range (from 1 mHz to 10 MHz). The goal of this work is to follow the cooperativity evolution along the Arrhenius plot for two different polymeric systems: poly(ethylene 1,4-cyclohexylenedimethylene terephthalate glycol) and poly(bisphenol A carbonate). PY - 2010 DO - https://doi.org/10.1103/PhysRevE.81.041805 SN - 1539-3755 SN - 1063-651X VL - 81 IS - 4 SP - 041805-1 - 041805-8 PB - American Institute of Physics CY - Melville, NY AN - OPUS4-21220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -