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 - TY - JOUR A1 - Wlodarska, M. A1 - Schönhals, Andreas A1 - Bak Grzegorz, G. W. A1 - Mossety-Leszczak, B. A1 - Galina, H. T1 - Molecular mobility of diepoxy nematics studied by dielectric spectroscopy N2 - The molecular mobility of four liquid crystalline epoxy compounds was studied by dielectric spectroscopy in a wide range of frequency (10-1–109 Hz). All the investigated materials form a nematic liquid crystalline phase at temperatures above 60 °C, one of them additionally exhibits a smectic A phase. Two of the compounds have molecules composed of a mesogen and two symmetric tails with eight alkyl groups each. Their properties were compared with the homologous pair having two alkyl groups in each tail. The length of the carbon chain influences the temperature range of the mesophase, which was also observed in this study. Characteristic relaxation processes were observed in the different mesophases. These processes were quantitatively analyzed and the estimated parameters were discussed in detail in dependence of the structure of the materials. KW - Dielectric properties KW - Relaxation KW - Electric modulus KW - Liquid crystals and molecular liquids PY - 2010 DO - https://doi.org/10.1016/j.jnoncrysol.2009.07.048 SN - 0022-3093 VL - 356 IS - 11-17 SP - 828 EP - 832 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-21267 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 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 - Fahmy, A. A1 - Mix, Renate A1 - Schönhals, Andreas A1 - Friedrich, Jörg Florian T1 - Structure of plasma-deposited poly(acrylic acid) films N2 - Poly(acrylic acid) films with a thickness of about 150?nm were deposited using a pulsed plasma onto aluminum and glass. The structure/property relationships of these samples were studied in dependence to the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time, volume sensitive methods (FTIR, dielectric spectroscopy, and differential scanning calorimetry) are combined with surface analyses i.e. XPS. For an unambiguous identification of COOH groups by XPS, derivatization with trifluoroethanol was accomplished. Quantitative FTIR investigations give qualitatively a dependence of the concentration of COOH groups upon DC similar to that given by XPS investigations. The observed differences are discussed considering the different analytical depths of both methods. The dielectric measurements reveal that the structure of the plasma deposited films is different from that of the bulk material. Moreover, these measurements show also that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating, where the reaction kinetics depends on DC. PY - 2011 DO - https://doi.org/10.1002/ppap.201000108 SN - 1612-8850 SN - 1612-8869 VL - 8 IS - 2 SP - 147 EP - 159 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-23478 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fahmy, A. A1 - Mix, Renate A1 - Schönhals, Andreas A1 - Friedrich, Jörg Florian T1 - Structure-property relationship of thin plasma deposited poly(allyl alcohol) films N2 - Poly(allyl alcohol) films with a thickness of about 150 nm were deposited by pulse plasma polymerization onto different substrates (inorganic and organic). The structure/property relationships of these samples were studied in dependence on the duty cycle (DC) of the plasma by a broad combination of different techniques and probes. For the first time volume sensitive methods (FTIR and dielectric spectroscopy) are combined with surface analytics by employing XPS for that system. FTIR spectroscopy gives qualitatively the same dependence of the concentration of the OH groups on DC like XPS. The observed differences are discussed considering the different analytical depths of both the methods. The dielectric measurements show that the plasma deposited films are not thermally stable but undergo a post plasma chemical reaction during heating. The results obtained by dielectric spectroscopy are discussed in detail with the data from FTIR and XPS measurements. KW - Allyl alcohol KW - Dielectric properties KW - Plasma polymerization KW - Surface and bulk characterization KW - Thermal stability PY - 2011 DO - https://doi.org/10.1007/s11090-011-9297-0 SN - 0272-4324 VL - 31 IS - 3 SP - 477 EP - 498 PB - Plenum Publ. Corp. CY - New York, NY, USA AN - OPUS4-23671 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -