TY - CONF A1 - Schönhals, Andreas T1 - Relaxation Phenomena and Cooperative Length Scale at Dynamic Glass Transition in Glass Forming Liquids T2 - Condensed Matter in Paris 2014 CY - Paris, France DA - 2014-08-24 PY - 2014 AN - OPUS4-31081 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Quasi- and Inelastic Neutron Scattering to Investigate the Molecular Dynamics of Discotic Liquid Christals in the Bulk and in the Nanoconfined State T2 - QENS2014/WINS2014 CY - Autrans, France DA - 2014-05-11 PY - 2014 AN - OPUS4-31016 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fahmy, Alaa A1 - Schönhals, Andreas T1 - Reaction of CO2 gas with (radicals in) plasma-polymerized acrylic acid (and formation of COOH-rich polymer layers) N2 - In contrast to most of the existing literature on plasma polymerization of acrylic acid (AA), not only the chemical structure and film thickness of the deposits were studied, but also a new way to obtain COOH-rich surfaces. This is an important aspect when applying the obtained coatings for biomedical and electronics applications. Therefore, acrylic acid/CO2 polymer films with a thickness of ca. 150 nm were deposited in the pulsed plasma regime onto polyethylene and aluminium as organic and inorganic substrates. Their structure–property relationships were studied in dependence on the mixture ratio of acrylic acid monomer and CO2 gas. The influence of the CO2 gas on the regularity and functionality of plasma deposited poly(acrylic acid) (PAA) was studied in detail using bulk-sensitive (dielectric spectroscopy and Fourier transforms infrared spectroscopy) as well as surface-sensitive methods such as X-ray photoelectron spectroscopy. For a clear identification of the functionality of the deposited films, the COOH groups were estimated after derivatization with trifluoroethanol by XPS measurement as well as by the quantitative analysis of the FTIR data. Results show, in presence of a small amount of CO2 gas within the acrylic acid plasma, a structure of poly(acrylic acid) with high concentration of COOH groups was obtained. However, the excess of CO2 gas in the plasma chamber leads to fragmentation of the monomer or/and degradation of the layer which is already deposited. A polymer network is obtained with an increasing abundance of branched groups for AA/CO2 with increasing CO2 gas in the mixture. KW - Poly(acrylic acid) KW - Plasma polymerization KW - COOH rich surfaces PY - 2016 DO - https://doi.org/10.1002/ppap.201500128 SN - 1612-8850 VL - 13 IS - 5 SP - 499 EP - 508 PB - Wiley-VCH Verlag CY - Weinheim AN - OPUS4-36058 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Influence of a nanoscale confinement on the dynamics of discotic liquid crystals investigated by inelastic neutron scattering and relaxation spectroscopy N2 - Discotic liquid crystals (DLCs) are self-assembled materials where self-assembly is driven by non-covalent intermolecular interactions. The corresponding molecules consist of a flat and rigid aromatic core substituted by flexible aliphatic side chains. While the former is responsible for the π-stacking, the latter gives rise to an increased solubility, processability, and rich thermotropic behavior. The disc-shaped molecules form columns that further assemble into two-dimensional arrays with a hexagonal mesophase. The alkyl chains fill the intracolumnar space giving rise to a nanophase separated state. Two different homologous systems based on triphenylene derivatives were investigated as model systems for DCLs where the length of the aliphatic side chains is widely varied. Measurements were carried out in the bulk state and confined to the nanometre wide channels of anodic aluminum membranes (Pore diameter 20 nm, 40nm, 80 nm and 180 nm) by means of inelastic and quasielastic neutron scattering. These investigations were accompanied by calorimetry and dielectric relaxation spectroscopy. From the neutron scattering experiments the vibrational density of states (Boson Peak) from neutron time-of-flight spectroscopy, the molecular dynamics on a time scale of ca. 1 ns (elastic scans from neutron backscattering spectrometers) as well as quasielastic neutron scattering by a combination of time-of-flight spectroscopy and backscattering were considered. Structural information is retrieved by X-ray diffraction carried out on a synchrotron. The dynamics of these unique soft matter materials are discussed in detail considering their structure (length of the aliphatic side chain), the effect of self-confinement (of the aliphatic chains in the intracolumnar space) and of outer confinement (influence of the pore size). Comparison is further made to pyrene based system. T2 - 18. International Seminar on Neutron Scattering Investigations in Condensed Matter CY - Poznan, Poland DA - 12.05.2016 KW - Discotic liquid crystals KW - Nanoconfinement KW - Neutron scattering PY - 2016 AN - OPUS4-36059 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Melnichu, I. A1 - Choukourov, A. A1 - Krakovsky, I. A1 - Biedermann, H. A1 - Schönhals, Andreas T1 - In situ nanocalorimetric investigations of plasma assisted deposited poly(ethylene oxide)-like films by specific heat spectroscopy N2 - In the recent years, highly crosslinked plasma polymers have started to unveil their potential in numerous biomedical applications in thin-films form. However, conventional diagnostic methods often fail due to their diverse molecular dynamics conformations. Here, glassy dynamics and the melting transition of thin PEO-like plasma assisted deposited (ppPEO) films (thickness 100 nm) were In situ studied by a combination of specific heat spectroscopy, utilizing pJ/K sensitive AC-calorimeter chip, and composition analytical techniques. Different crosslinking densities were obtained by different plasma powers during the deposition of the films. Glassy dynamics was observed for all values of the plasma power. It was found that the glassy dynamics slows down with increasing the plasma power. Moreover, the underlying relaxation time spectra broaden indicating that the molecular motions become more heterogeneous with increasing plasma power. In a second set of experiment, the melting behavior of the ppPEO films was studied. The melting temperature of ppPEO was found to be decreasing with increasing plasma power. This was explained by a decrease of the order in the crystals due to formation of chemical defects during the plasma process. KW - Plasma deposited polymers KW - Nanocalorimetry KW - Thin polymer films KW - Glass transition PY - 2016 DO - https://doi.org/10.1021/acs.jpcb.6b01355 SN - 1520-6106 SN - 1520-5207 VL - 120 IS - 16 SP - 3954 EP - 3962 PB - American Chemical Society CY - Washington, DC, USA AN - OPUS4-35922 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frunza, S. A1 - Frunza, L. A1 - Ganea, C. P. A1 - Zgura, I. A1 - Bras, A. R. A1 - Schönhals, Andreas T1 - Rod-like cyanophenyl probe molecules nanoconfined to oxide particles: Density of adsorbed surface species N2 - Surface layers have already been observed by broadband dielectric spectroscopy for Composite systems formed by adsorption of rod-like cyanophenyl derivates as probe molecules on the surface of oxide particles. In this work, features of the surface layer are reported; samples with different amounts of the probe molecules adsorbed onto oxide (nano) particles were prepared in order to study their interactions with the surface. Thermogravimetric analysis (TGA) was applied to analyze the amount of loaded probe molecules. The density of the surface species ns was introduced and its values were estimated from quantitative Fourier transform infrared spectroscopy (FTIR) coupled with TGA. This parameter allows discriminating the composites into several groups assuming a similar interaction of the probe molecules with the hosts of a given group. An influence factor H is further proposed as the ratio of the number of molecules in the surface layer showing a glassy dynamics and the number of molecules adsorbed tightly on the surface of the support: It was found for aerosil composites and used for calculating the maximum filling degree of partially filled silica MCM-41 composites showing only one dielectric process characteristic for glass-forming liquids and a bulk behavior for higher filling degrees. KW - Cyanophenyl molecules KW - Nanoconfinement KW - Surface Species PY - 2016 DO - https://doi.org/10.1140/epjp/i2016-16027-5 SN - 2190-5444 VL - 131:27 IS - 2 SP - 1 EP - 9 PB - Springer AN - OPUS4-35364 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yin, Huajie A1 - Madkour, Sherif Aly Hassan Aly A1 - Schönhals, Andreas T1 - Unambiguous evidence for a highly mobile surface layer in ultrathin polymer films by specific heat spectroscopy on blends N2 - Despite the decade long controversial discussion on the effect of nanometer confinement on the glass transition temperature (Tg) of ultrathin polymer films, there is still no consistent picture. Here, the dynamic calorimetric glass transition of ultrathin films of a blend, which is miscible in the bulk, is directly investigated by specific heat spectroscopy. By a self-assembling process, a nanometer thick surface layer with a higher molecular mobility is formed at the polymer/air interface. By measuring the dynamic calorimetric Tg in dependence on the film thickness, it was shown that the Tg of the whole film was strongly influenced by that nanometer thick surface layer, with a lower Tg. Since the observed thickness dependence of the dynamic Tg is similar to the thickness dependence of the Tg for thin films of homopolymers, it is concluded that also for homopolymer a highly mobile surface layer is relevant for the widely observed Tg depression. PY - 2015 DO - https://doi.org/10.1021/acs.macromol.5b01259 SN - 0024-9297 SN - 1520-5835 VL - 48 IS - 14 SP - 4936 EP - 4941 PB - American Chemical Society CY - Washington, DC AN - OPUS4-33841 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Füllbrandt, Marieke A1 - Ermilova, E. A1 - Asadujjaman, Asad A1 - Hölzel, R. A1 - Bier, F.F. A1 - Von Klitzing, R. A1 - Schönhals, Andreas T1 - Dynamics of linear poly(N-isopropylacrylamide) in water around the phase transition investigated by dielectric relaxation spectroscopy N2 - The molecular dynamics of linear poly(N-isopropylacrylamide) (pNIPAM) in aqueous media at temperatures below and above the lower critical solution temperature (LCST) are investigated using broadband dielectric relaxation spectroscopy in a frequency range from 10–1 to 1011 Hz. Below the LCST, two relaxation processes are observed in the megahertz and gigahertz region assigned to the reorientation of dipoles of the solvated polymer segments (p-process) and water molecules (w-process), respectively. Both relaxation processes are analyzed using the Havriliak–Negami (HN) function, taking special attention to the w-process. Above the LCST, the dielectric spectra of the pNIPAM solutions resemble that of pure water, showing only the high frequency relaxation process of the water molecules with a more or less Debye-type behavior. The non-Debye behavior of the w-process below the LCST is mainly induced by the interactions between water and pNIPAM chains via hydrogen bonding. The relaxation time and strength of the w-process is studied with dependence on the concentration, temperature, and the polymer chain length (molecular weight). The information obtained is useful for a deeper understanding of the dehydration behavior at the phase transition. The suggestion of dehydration of the pNIPAM chains at the LCST is confirmed by calculating a dehydration number. PY - 2014 DO - https://doi.org/10.1021/jp501325x SN - 1520-6106 SN - 1520-5207 SN - 1089-5647 VL - 118 IS - 13 SP - 3750 EP - 3759 PB - Soc. CY - Washington, DC AN - OPUS4-30578 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yildirim, Arda A1 - Kolmangadi, Mohamed Aejaz A1 - Bühlmeyer, A. A1 - Huber, P. A1 - Laschat, S. A1 - Schönhals, Andreas T1 - Electrical conductivity and multiple glassy dynamics of crow-ether based columnar liquid crystals N2 - The phase behavior of two unsymmetrical triphenylene crown ether-based columnar liquid crystals (CLCs) bearing different lengths of alkyl chains, KAL465 and KAL468, was investigated using differential scanning calorimetry (DSC). A plastic crystalline (Cry), columnar liquid crystalline (Colh) and an isotropic phase were observed along with two glass transitions in the Cry phase. The molecular mobility of the KAL compounds was further studied by a combination of broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques. By the BDS investigations, three dielectric active relaxation processes were observed for both samples. At low temperatures, a γ-process in the Cry state was detected and is assigned to the localized fluctuations taking place in the alkyl chains. An α2-process takes place at higher temperatures in the Cry phase. An α3 process was found in the Colh mesophase. The advanced calorimetric techniques consist of fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS) employing temperature modulated DSC and FSC (TMDSC and TMFSC). The advanced calorimetric investigations revealed that besides the α2 process in agreement with BDS, a second dynamic glass transition (α1-process) is present which is not observed by dielectric spectroscopy. The results are in good agreement with the glass transitions detected by DSC for this process. The temperature dependences of the relaxation rates of the α1 , α2 and α3 processes are all different. Therefore, different molecular assignments for the relaxation processes are proposed. In addition to the relaxation processes, a conductivity contribution was explored by BDS for both KAL compounds. The conductivity contribution appears in both Cry and Colh phases, where the conductivity increases by ca. one order of magnitude at phase transition from the crystalline to the hexagonal phase. KW - Columnar Liquid Crystal PY - 2020 DO - https://doi.org/10.1021/acs.jpcb.0c06854 VL - 124 IS - 39 SP - 8728 EP - 8739 PB - ACS AN - OPUS4-51374 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Thermal behavior of high preformance polymers - Fast Scanning Calorimetry and more N2 - The glass tranistion behavior of polymers of intrinsic microporosity and polynornornes is discussed. T2 - Flash DSC Conference 2021 CY - Online meeting DA - 06.12.2021 KW - Polymer of Intrisic Maicroporosity KW - Highly permeable polynorbornenes PY - 2021 AN - OPUS4-53938 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fahmy, Alaa A1 - Saied, M. A. A. A1 - Morgan, N. A1 - Abdelbary, H. A1 - Bahy, S. M. A1 - Schönhals, Andreas A1 - Friedrich, J. F. T1 - Modified polyvinyl chloride membrane grafted with an ultra-thin polystyrene film: structure and electrochemical properties N2 - The work explores the synthesis and the properties of a novel composite membrane System based on modified polystyrene (PS) grafted onto a polyvinyl chloride (PVC) membrane. PVC membranes were prepared by solution-casting followed by exposure to an atmospheric pressure dielectric barrier discharge (DBD) with O2 to obtain an activated Surface for grafting PS to it. Moreover, the thus prepared membranes were chemically modified furthermore by amination with polyethyleneimine or sulfonation with 4 M sulfuric acid. The membrane surface characteristics such as wettability, structure and morphology were investigated using water contact angle measurements, attenuated total reflection Fourier transform infrared spectroscopy and scanning electron microscopy experiments. The thermogravimetric stability and electrolytic responses of the membranes were studied utilizing TGA, ion exchange capacity (IEC), and solvent uptake. A significant result of plasma and chemical modification was to produce a membrane material with low permeability. Thus, the methanol permeability of the sulfonated membranes measured for 12 h was measured to 2.34$10� 8 cm2 s� 1 compared to 177.00$10� 8 cm2 s� 1 of Nafion 117®which is considered as a benchmark. This result indicates that the prepared sulfonated samples are an innovative and effective material for decreasing the methanol crossover in fuel cells to a great extent. This makes the PVC-g-St membranes are promising and attractive as new materials for polyelectrolyte membrane for fuel cells. KW - Electrolyte membrane KW - Fuell cells PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-526794 DO - https://doi.org/10.1016/j.jmrt.2021.04.018 VL - 12 SP - 2273 EP - 2284 PB - Elsevier B.V. AN - OPUS4-52679 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -