TY - CONF A1 - Schönhals, Andreas T1 - Broadband Dielectric Spectroscopy - Basics and Selected Applications N2 - The basics of broadband dielectric spectroscopy were introduced in detail. The analysis of the data was discussed. As application of broadband dielectric spectroscopy the alpha-relaxation (dynamic glass transition) and the chain dynamics of polymers were ilustrated. T2 - 9th International Conference on Broadband Dielectric Spectroscopy and its Applications CY - Pisa, Italy DA - 11.09.2016 KW - Broadband Dielectric Spectroscopy PY - 2016 AN - OPUS4-37386 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas A1 - Madkour, Sherif A1 - Yin, Huajie A1 - Szymoniak, Paulina T1 - Behavior of Ultra-Thin Films of Blends of Polystyrene/ Poly(vinyl methyl ether) by Nanosized Relaxation Spectroscopy N2 - In the course of miniaturizing modern technology down to the molecular scale, understanding the materials behavior has to be investigated and deviations from the bulk that might arises from confinement effects has to be understood. Here, a combination of nano-sized relaxation spectroscopies (Broadband dielectric spectroscopy (BDS) and Specific heat spectroscopy (SHS); employing AC nanochip calorimetry) were utilized to investigate the glassy dynamics of ultra-thin films of blends of Poly (vinyl methyl ether) (PVME) / Polystyrene (PS) 50:50 wt-%, which are miscible bulk (thicknesses: 8nm - 200nm, film thickness was controlled by ellipsometry, film topography by AFM). Both methods are sensitive to different probes; where SHS senses entropy fluctuations while BDS measures dipole fluctuations. For BDS measurements, a recently developed nano-structured electrode sample arrangement is employed; where ultra-thin films are spin-coated on an ultra-flat highly conductive silicon wafer, sandwiched between a wafer with nanostructured SiO2 nano-spacers with heights between 35 nm and 70 nm. The method was applied for film thicknesses up to 50 nm. For thicker films, the samples were prepared between crossed electrodes. It was proven that, for 50 nm films, both contact methods will lead to identical results. By measuring the dynamic Tg in dependence of the film thickness, SHS showed that the Tg of the whole film was strongly influenced by a nanometer-thick surface layer at the polymer/air interface due to a self-assembling process [1]. The dynamic Tg obtained from the SHS measurements decrease with decreasing film thickness, evidencing the importance of a mobile surface layer at the polymer/air interface for the glass transition of the whole film. Compared to the SHS results, the BDS measurements show a completely different behavior. At high temperatures, the temperature dependence of the relaxation times of the films follows that of bulk-like PS/PVME; obeying the VFT-law. With decreasing temperature, the temperature dependence deviates from the VFT to an Arrhenius law; where the apparent activation energy decreases with decreasing film thickness. This is the first example where confinement induced changes were observed by BDS for ultra-thin films. All results were analyzed in details in a comprehensive discussion. T2 - 9th International Conference on Broadband Dielectric Spectroscopy and its Applications CY - Pisa, Italy DA - 11.09.2016 KW - Ultra-Thin films KW - Broadband Dielectric Spectrscopy KW - Nanostructured Electrodes PY - 2016 AN - OPUS4-37387 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas A1 - Lohstroh, Wibke A1 - Zamponi, Michaela A1 - Zorn, R. A1 - Frick, Bernhard T1 - Neutron and dielectric spectroscopy - taking advantage of the strengths of each technique in confinement studies: Vibrational and molecular dynamics of nanoconfined liquid crystals N2 - The effect of a nanometre confinement on the molecular dynamics of liquid crystals was studied by broadband dielectric and neutron spectroscopy. As confining host the molecular sieve Al-MCM-41 (Si/Al=60) with a mean pore diameter of 3 nm was selected. As guest the liquid crystals 8CB and E7 were chosen where the latter does not crystallize but undergoes a glass transition forming a nematic glass. Dielectric spectroscopy shows that for the confined systems one relaxation process is observed. Ist characteristic relaxation time is much lower compared to that of the bulk. No signature of the Phase transition characteristics of the bulk liquid crystal is detected. The temperature dependence of the relaxation time of this relaxation process has to be described by the Vogel-Fulcher-Tammann equation and thus shows similarities to glassy dynamics. The vibrational density of states measured by neutron spectroscopy (IN6, ILL; TOFTOF, MLZ) Shows excess contributions with respect to the Debye density of states (boson peak). For the confined systems the low frequency contributions of the boson peak are suppressed, an effect which is also found for conventional glass forming systems. In addition elastic scans were carried out at the backscattering spectrometer (BS) IN10 at ILL. Such measurements provide an overview about the temperature dependence of the microscopic dynamics. Assuming a Gaussian form for the elastically scattered intensities the effective mean square displacement was calculated. For the nanoconfined samples the mean square displacement is strongly reduced in comparison to the bulk. Also these measurements show the signature of a glass Transition indicated by a change in the temperature dependence of the mean square displacement. For confined E7 the extracted glass transition temperature is shifted by more than 20 K to higher temperatures. Broadband inelastic neutron scattering was carried out by combining time-of-flight (IN6, ILL; TOFTOF, MLZ) and backscattering (IN10, ILL; SPHERES, MLZ) experiments in the time domain. The time dependence of the incoherent intermediate scattering function Sinc(q,t) shows two Relaxation processes which were quantitatively analyzed by fitting the KWW function to the data. The process at shorter times shows a close similarity the methyl group rotation found for polymeric systems. The process at longer times was assigned to glassy dynamics. The obtained data are compared in detail in their temperature dependence to the dielectric results. T2 - Deutsche Neutronenstreutagung 2016 CY - Kiel, Germany DA - 20.09.2016 KW - Neutron scattering KW - Broadband dielectric spectroscopy PY - 2016 AN - OPUS4-37516 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Zorn, R. A1 - Frick, B. T1 - Inelastic neutron spectroscopy as a tool to investigate nanoconfined polymer systems N2 - The effect of a nanometer scale confinement (pore sizes 7.5 nm down to 2.5 nm) on the vibrational density of states (VDOS) and on the molecular dynamics of Poly(dimethyl siloxane) (PDMS) and Poly(-methyl phenyl siloxane) (PMPS) is studied by inelastic Neutron scattering. The high penetration depth of neutrons makes neutron scattering a suitable tool for the study of confined systems. Moreover, Neutrons are sensitive to light nuclei therefore the confined polymers can be investigated directly, more or less independently of the confining host. Resulting findings are firstly, a reduction of the low frequency contributions to the VDOS below the Boson Peak frequency for both polymers. Including literature data, this reduction can be regarded as a more general feature for glass-forming systems confined by hard walls. Secondly, clear deviations in the temperature dependence of the mean squared displacement of the confined molecules compared to the bulk were found close to the thermal glass transition temperature, whereas localized methyl group rotations were only weakly influenced. Furthermore, the molecular dynamics is accessed. The combination of neutron Time-of-Flight with neutron backscattering, thus covering a broad dynamical range from sub ps to ns, reveal clear influence from confinement on the intermediate incoherent scattering function S(q,t). The latter was obtained by combining the inverse Fourier transform of the individual dynamical structure factors measured by the both methods. The time and q dependence of S(q,t) are discussed in detail for the local methyl group rotations and the segmental dynamics, considering both the interaction of the segments with the pore walls and possible geometrical confinement effects. KW - Confinement KW - Density of states KW - Dynamic glass transition PY - 2016 U6 - https://doi.org/10.1016/j.polymer.2016.06.006 SN - 0032-3861 SN - 1873-2291 VL - 105 SP - 393 EP - 406 PB - Elsevier AN - OPUS4-38256 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Broadband dielectric spectroscopy as an orthogonal tool to mechanical analysis – From theory to applications N2 - The basics of broadband dielectric spectroscopy were introduced in detail. The analysis of the data was discussed. As application of broadband dielectric spectroscopy the alpha-relaxation (dynamic glass transition), the chain dynamics of polymers, and the behavior of a high performance polymer were illustrated. T2 - Geesthachter Polymertage CY - Geesthcht, Germany DA - 08.11.2016 KW - Broadband dielectric spectroscopy PY - 2016 AN - OPUS4-38185 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Behavior of Ultra-Thin POLYMER Films investigated by Nanosized Relaxation Spectroscopy N2 - The glass transition behavior of ultra-thin polymer films is discussed in detail. Further nanosized relxation spectroscopy is introduced in the form of AC chip calorimetry and dielectric spectroscopy employing nanostructured electrodes. These methods arre applied to ultra-thin films. T2 - Soft Matter Seminar Jülich CY - Jülich, Germany DA - 15.12.2016 KW - Ultra-thin polymer films PY - 2016 AN - OPUS4-38714 LA - eng 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 U6 - 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 A1 - Krause, Christina A1 - Frick, B. A1 - Zorn, R. 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 - Konnertz, Nora A1 - Böhning, Martin A1 - Schönhals, Andreas T1 - Dielectric investigations of nanocomposites based on matrimid and polyhedral oligomeric phenethyl-silsesquioxanes (POSS) N2 - Matrimid and Matrimid/PhenethylPOSS nanocomposites films were prepared by solution casting. They can be considered as potential membrane materials for gas separation. Theire dielectric properties were investigated using Broadband Dielectric Spectroscopy (BDS) in combination with standard techniques. Matrimid shows one relaxation process assigned as beta*-relaxation and a conductivity contribution. The relaxation process has a high activation energy of 99 kJ/mol. Thus this process is supposed to be of cooperative nature due to a π-π stacking of the phenyl rings of Matrimid. The influence of the thermal history on Matrimid was analyzed with BDS as well where an annealing effect is found. The Matrimid/PhenethylPOSS nanocomposites show up to a concentration of about 4 wt% PhenethylPOSS a miscibility on a molecular level. For higher concentrations a phase separated structure was indicated. The conductivity of both systems is explained by π-π stacking of the phenyl rings which enhances charge transport. KW - Matrimid KW - POSS KW - Nanocomposites KW - Broadband dielectric spectroscopy PY - 2016 U6 - https://doi.org/10.1016/j.polymer.2016.02.060 SN - 0032-3861 VL - 90 SP - 89 EP - 101 PB - Elsevier Science AN - OPUS4-35616 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Madkour, Sherif A1 - Szymoniak, Paulina A1 - Heidari, Mojdeh A1 - von Klitzing, Regine A1 - Schönhals, Andreas T1 - Evidence of a three-layered structure in ultra-thin PVME and PVME/PS blend films by nano-sized relaxation spectroscopy N2 - Despite the many controversial discussions about the nanometric confinement effect and the predictions of the three-layer model, much remain not understood and/or experimentally unproven. Here, a combination of Broadband Dielectric Spectroscopy (BDS), Specific Heat Spectroscopy (SHS), and ellipsometry was utilized to investigate the glassy dynamics of ultra-thin films of Poly (vinyl methyl ether) (PVME) and PVME/Polystyrene (PS) 50:50 wt-% miscible blend (thicknesses: 8nm - 200nm). For BDS measurements, a recently developed nano-structured sample arrangement; where ultra-thin films are spin-coated on an ultra-flat highly conductive silicon wafer and sandwiched between a wafer with nanostructured silica nano-spacers, was used. For PVME films, two processes were observed and interpreted to be the α-processes of a bulk-like layer and an absorbed layer to the substrate. BDS and SHS showed that glassy dynamics are bulk-like. However, for films lower than 15nm, BDS showed weakly slowed dynamics. For PVME/PS blend, by a self-assembling process, a nanometer-thin surface layer with a higher molecular mobility is formed at the polymer/air interface. By measuring the dynamic Tg in dependence on the film thickness, both BDS and SHS, showed that the Tg of the whole film was strongly influenced by that nanometer thick surface layer, with a lower Tg. T2 - 80. Jahrestagung der DPG und DPG-Frühjahrstagung CY - Regensburg DA - 06.03.2016 KW - Ultra-thin films PY - 2016 AN - OPUS4-35540 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -