TY - GEN A1 - Yin, Huajie A1 - Madkour, Sherif Aly Hassan Aly A1 - Schönhals, Andreas ED - Kremer, F. T1 - Glass transition of ultra-thin polymer films: A combination of relaxation spectroscopy with surface analytics N2 - The glass transition behavior of ultra-thin supported polymer films is discussed controversially in the literature for around 20 years. Substantial efforts have been archived to understand it. In this contribution, a combination of methods sensitive to bulk properties of a system, like dielectric or specific heat spectroscopy with surface analytics, for instance, atomic force microscopy (AFM), contact angle measurements, and X-ray photoelectron spectroscopy (XPS) were employed to study the glass transition of ultra-thin supported films. All investigations were carried out on identically prepared and treated samples. Different systems with different complexities going from more or less flexible homopolymers over rigid main chain macromolecules to polymer blends have been studied. For the investigated flexible macromolecules, the dynamic glass transition temperature estimated within the frame of the linear response approach is independent of the film thickness down to several nanometers and identical to the bulk value. For polystyrene it was found the thermal glass transition temperatures can depend on the film thickness. This different behavior is not well understood till now and needs further experimental clarification. For the investigated main chain polymers polycarbonate and polysulfone. Dynamic and thermal glass transition temperature estimated from the dielectric measurements increases with decreasing film thickness. This is discussed in the frame of a strong interaction of the polymer segments with the surface of the substrate. In general for homopolymers, the interaction energy of the polymer segments with the substrate surface cannot be considered as the only parameter, which is responsible for the change in the thermal glass transition with the film thickness. For the investigated miscible blend system of polystyrene/poly(vinyl methyl ether) at a composition of 50/50 wt-% a decrease of the dynamic glass transition temperature with decreasing film thickness is found. This is explained by the formation of a poly(vinyl methyl ether)-rich surface layer with a higher molecular mobility. KW - Broadband dielectric spectroscopy KW - Specific heat spectroscopy KW - Photoelectron spectroscopy KW - Contact angle measurements KW - Polystyrene KW - Poly(vinyl methyl ether) KW - Poly(2-vinylpyridine) KW - Polycarbonate KW - Polysulfone KW - Polystyrene/ Poly(vinyl methyl ether) blend PY - 2014 SN - 978-3-319-06099-6 SN - 978-3-319-06100-9 DO - https://doi.org/10.1007/978-3-319-06100-9_2 SN - 2190-930X SN - 2190-9318 SP - 17 EP - 59 PB - Springer AN - OPUS4-31078 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yildirim, Arda A1 - Krause, Christina A1 - Huber, P. A1 - Schönhals, Andreas T1 - Multiple glassy dynamics of a homologous series of triphenylene-based columnar liquid crystals – A study by broadband dielectric spectroscopy and advanced calorimetry N2 - Hexakis(n-alkyloxy)triphenylene) (HATn) consisting of an aromatic triphenylene core and alkyl side chains are model discotic liquid crystal (DLC) systems forming a columnar mesophase. In the mesophase, the molecules of HATn self-assemble in columns, which has one-dimensional high charge carrier mobility along the columns. Here, a homologous series of HATn with different length of the alkyl chain (n = 5,6,8,10,12) is investigated using differential scanning calorimetry (DSC), broadband dielectric spectroscopy (BDS) and advanced calorimetric techniques including fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). The investigation of the phase behavior was done utilizing DSC experiments and the influence of the alkyl chain length on the phase behavior was revealed. By the dielectric investigations probing the molecular mobility, a c-relaxation due to localized fluctuations as well as two glassy dynamics, the acore- and aalkyl-relaxation, were observed in the temperature range of the plastic crystalline phase. Moreover, the observed glassy dynamics were further studied employing advanced calorimetry. All observed relaxation processes are attributed to the possible specific molecular fluctuations and discussed in detail. From the results a transition at around n = 8 from a rigid constrained (n = 5,6) to a softer system (n = 10,12) was revealed with increasing alkyl chain length. A counterbalance of two competing effects of a polyethylene-like behavior of the alkyl chains in the intercolumnar domains and self-organized confinement is discussed in the context of a hindered glass transition. KW - Discotic liquid crystals KW - Broadband dielectric spectroscopy KW - Advanced calorimetry PY - 2022 DO - https://doi.org/10.1016/j.molliq.2022.119212 VL - 358 SP - 1 EP - 10 PB - Elsevier B.V. AN - OPUS4-54721 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 - Broadband dielectric spectroscopy to study soft matter systems 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. Further the application of dielectric spectroscopy to polymerbased nanocomposites and high preformance polymers was discussed in detail. T2 - Kolloquiumsvotrag am Karlsruher Instiut of Technology CY - Karlsruhe, Germany DA - 05.12.2018 KW - Broadband dielectric spectroscopy PY - 2018 AN - OPUS4-46910 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Schönhals, Andreas A1 - Frick, B. A1 - Zorn, R. ED - Kremer, Friedrich ED - Loidl, Alois T1 - The scaling of the molecular dynamics of liquid crystals as revealed by broadband dielectric, specific heat, and neutron spectroscopy N2 - A combination of different complementary methods is employed to investigate scaling of the molecular dynamics of two different liquid crystals. Each method is sensitive to different kind of fluctuations and provides therefore a different window to look at the molecular dynamics. In detail, broadband dielectric spectroscopy is combined with specific heat spectroscopy and neutron scattering. As systems the nematic liquid crystal E7 and a discotic liquid crystalline pyrene are considered. First of all it was proven that both systems show all peculiarities which are characteristic for glassy dynamics and the glassy state. Especially for the nematic liquid crystal E7 it could be unambiguously shown by a combination of dielectric and specific heat spectroscopy that the tumbling mode is the underlying motional process responsible for glassy dynamics. Dielectric investigations on the discotic liquid crystalline pyrene reveal that at the phase transition from the plastic crystalline to the hexagonal columnar liquid crystalline phase the molecular dynamics changes from a more strong to fragile temperature dependence of the relaxation rates. Moreover a combination of results obtained by specific heat spectroscopy with structural methods allows an estimation of the length scale relevant for the glass transition. KW - Broadband dielectric spectroscopy KW - Specific heat spectroscopy KW - Rod-like liquid crystals KW - Discotic liquid crystals PY - 2018 UR - https://link.springer.com/content/pdf/10.1007%2F978-3-319-72706-6.pdf SN - 978-3-319-72705-9 SN - 978-3-319-72706-6 DO - https://doi.org/10.1007/978-3-319-72706-6_9 SN - 2190-930X SN - 2190-9318 SP - 279 EP - 306 PB - Springer International publishing AG CY - Cham, Switzerland ET - 1. AN - OPUS4-45624 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A1 - Szymoniak, Paulina A1 - Heídari, M. A1 - von Klitzing, R. A1 - Schönhals, Andreas T1 - Unveiling the dynamics of self-assembled layers of thin films of poly(vinyl methyl ether) (PVME) by nanosized relaxation spectroscopy N2 - A combination of nanosized dielectric relaxation (BDS) and thermal spectroscopy (SHS) was utilized to characterize the dynamics of thin films of Poly(vinyl methyl ether) (PVME) (thicknesses: 7 nm – 160 nm). For the BDS measurements, a recently designed nano-structured electrode system is employed. A thin film is spin-coated on an ultra-flat highly conductive silicon wafer serving as the bottom electrode. As top electrode, a highly conductive wafer with non-conducting nanostructured SiO2 nano-spacers with heights of 35 nm or 70 nm is assembled on the bottom electrode. This procedure results in thin supported films with a free polymer/air interface. The BDS measurements show two relaxation processes, which are analyzed unambiguously for thicknesses smaller than 50 nm. The relaxation rates of both processes have different temperature dependencies. One process coincidences in its position and temperature dependence with the glassy dynamics of bulk PVME and is ascribed to the dynamic glass transition of a bulk-like layer in the middle of the film. The relaxation rates were found to be thickness independent as confirmed by SHS. Unexpectedly, the relaxation rates of the second process obey an Arrhenius-like temperature dependence. This process was not observed by SHS and was related to the constrained fluctuations in a layer, which is irreversibly adsorbed at the substrate with a heterogeneous structure. Its molecular fluctuations undergo a confinement effect resulting in the localization of the segmental dynamics. To our knowledge, this is the first report on the molecular dynamics of an adsorbed layer in thin films. KW - Broadband dielectric spectroscopy KW - AC-nanochip calorimetry KW - Nanostructured capacitors KW - Thin films PY - 2017 UR - http://pubs.acs.org/doi/pdf/10.1021/acsami.6b14404 DO - https://doi.org/10.1021/acsami.6b14404 SN - 1944-8244 VL - 9 IS - 8 SP - 7535 EP - 7546 PB - ACS Publications CY - Washington DC AN - OPUS4-39291 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas 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 - CONF A1 - Schönhals, Andreas T1 - Broadband dielectric spectroscopy as a complementary tool to characterize polymer systems 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. Further the application of dielectric spectroscopy to polymerbased nanocomposites and high preformance polymers was discussed in Detail. T2 - International Symposium on Polymer Analyisis and Characterization CY - Linz, Austria DA - 11.06.2017 KW - Broadband dielectric spectroscopy PY - 2017 AN - OPUS4-40602 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Polymer-based nanocomposites – Interplay between interfacial and bulk properties N2 - Different types of polymerbased nanocomposites (matrix materials: polyethylene, polypropylene, polylactide, polycarbonate, polystyrene) with a broad variety of nanofillers (fillers: layered silica, layered doubled hydroxides, POSS) are prepared where the concentration of the particles is varied. For layered fillers TEM images show both an intercalated and exfoliated morphology in dependence on the nanofiller and the matrix. All systems are studied in detail by dielectric spectroscopy (BDS) but also complementary methods like WAXS, SAXS, gas transport measurements, calorimetry, and FTIR spectroscopy are employed. Besides the dispersion, the interfacial region between the nanoparticles and the polymer matrix is crucial for the properties of the nanocomposites. Therefore, attention is paid to investigate this interfacial area by BDS because the polar groups of both the surfactant and compatibilizer are located close to the layers. For some systems it is found that the molecular mobility in the interfacial area is essentially higher than in the matrix. In addition a Maxwell/Wagner/Sillars polarization is found due to the blocking of charges at the layers. The time constant of this MWS-process can be correlated with characteristic length scales in the nanocomposites and provides information about the dispersion of the nanofiller. T2 - International Symaposium on Polymer Ananlysis and Characterization CY - Linz, Austria DA - 11.06.2016 KW - Polymer based nanocomposites KW - Broadband dielectric spectroscopy PY - 2017 AN - OPUS4-40604 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Schönhals, Andreas T1 - Broadband dielectric spectroscopy in comparison to other spectroscopic methods applied to functional materials 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 illustrated. Further the application of dielectric spectroscopy to advanced functional materials. T2 - International Summer School on Crystal Growth and Advanced Materials for Energy Conversation CY - Bucharest, Romania DA - 10.07.2017 KW - Broadband dielectric spectroscopy PY - 2017 AN - OPUS4-41024 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yin, Huajie A1 - Chapala, P. A1 - Bermeshev, M. A1 - Schönhals, Andreas A1 - Böhning, Martin T1 - Molecular Mobility and Physical Aging of a Highly Permeable Glassy Polynorbornene as Revealed by Dielectric Spectroscopy N2 - Polymeric membranes represent a cost- and energy efficient solution for gas separation. Recently superglassy polymers with high free volume outperform many conventional dense polymers in terms of gas permeability and selectivity. However, such polymers are prone to pronounced physical aging, resulting in a dramatic reduction in the gas permeability. Molecular mobility of polymer segments plays an important role in the physical aging and the gas transport performance of polymeric membranes. Molecular mobility and physical aging of a representative superglassy polynorbornene with very high gas permeability, PTCNSi2g, was monitored by using dielectric spectroscopy with state-of-the-art high-resolution analyzers. This work helps to shed some light on the structure−property relationship of superglassy polymers on a molecular level and to provide practical “design rules” for the development of high performance polymers for gas separation. KW - Molecular mobility KW - Gas separation membrane KW - Broadband dielectric spectroscopy KW - Polymer KW - Physical ageing PY - 2017 DO - https://doi.org/10.1021/acsmacrolett.7b00456 SN - 2161-1653 VL - 6 IS - 8 SP - 813 EP - 818 PB - ACS CY - Washington DC, USA AN - OPUS4-41354 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hao, Ning A1 - Böhning, Martin A1 - Goering, Harald A1 - Schönhals, Andreas T1 - Nanocomposites of Polyhedral Oligomeric Phenethylsilsesquioxanes and Poly(bisphenol A carbonate) as Investigated by Dielectric Spectroscopy N2 - Nanocomposites were prepared by solution blending of polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) into poly(bisphenol A carbonate) (PBAC). The nanocomposites were investigated by dielectric spectroscopy, differential scanning calorimetry (DSC) and density measurements. PhenethylPOSS shows one relaxation process, the α-relaxation, confirmed by DSC investigations. PBAC shows a β-relaxation at lower and an α-relaxation at higher temperatures. With increasing PhenethylPOSS content the α-relaxation of the composites shifts to lower temperatures. Thus, incorporation of PhenethylPOSS leads to a plasticization of PBAC due to a decrease of the packing density which is rationalized by density measurements. For higher concentrations of PhenethylPOSS (>10 wt %) the α-relaxation of the polycarbonate matrix splits into two peaks. Moreover, close to the α-relaxation of PhenethylPOSS a third process is observed. These results indicate a phase separation into a PBAC matrix with a few percents of molecularly solved POSS and POSS-rich domains. These POSS-rich domains are surrounded by an interfacial layer of PBAC having a higher concentration of POSS than the matrix. A phase diagram is deduced providing a miscibility criterion. For the phase separated nanocomposites an interfacial polarization phenomena is observed. Using a simplified model the time constant of this process is correlated with the size of the PhenethylPOSS-rich domains and theire increasing size with the increase of the concentration of POSS. KW - Polyhedral oligomeric silsesquioxane (POSS) KW - Polymer-based nanocomposites KW - Broadband dielectric spectroscopy KW - Interfacial polarisation PY - 2007 SN - 0024-9297 SN - 1520-5835 VL - 40 IS - 8 SP - 2955 EP - 2964 PB - American Chemical Society CY - Washington, DC AN - OPUS4-14768 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Madkour, Sherif A. A1 - Gawek, Marcel A1 - Penner, P. A1 - Paneff, F. A1 - Zhang, X. A1 - Gölzhäuser, A. A1 - Schönhals, Andreas T1 - Can Polymers be Irreversibly Adsorbed on Carbon Nanomembranes? A Combined XPS, AFM, and Broadband Dielectric Spectroscopy Study N2 - Carbon nanomembranes are synthetic two-dimensional sheets with nanometer thickness, macroscopic lateral dimensions, and high structural homogeneity. They have great application potential in various branches of nanotechnology. Because of their full carbon structure, it is not clear whether macromolecules like poly(methyl methacrylate) (PMMA) can be irreversibly adsorbed on their surface. Here, irreversible adsorption means that the polymer chains cannot be removed by a leaching process, which is assumed in technological transfer processes. However, if polar defects are present on the carbon nanomembranes (CNMs), it may occur that polymers can be irreversibly adsorbed. To address this question, PMMA was spin-coated on top of CNMs, annealed for a specific time at different temperatures, and then tried to be removed by a acetone treatment in a leaching approach. The samples were investigated in detail by atomic force microscopy, X-ray photoelectron spectroscopy, and broadband dielectric spectroscopy, where the latter method has been applied to CNMs for the first time. Unambiguously, it was shown that PMMA can be adsorbed on the surface of CNMs after annealing the sample above the glasstransition temperature of PMMA. The general occurrence of polar defects on the surface of CNMs and the adsorption of polymers open opportunities for advanced innovative hybrid materials combining the properties of the CNM with those of the polymer. KW - Carbon Nanomembranes KW - Irreversible adsorption KW - Broadband dielectric spectroscopy KW - XPS spctroscopy KW - Atomic force microscopy PY - 2022 DO - https://doi.org/10.1021/acsapm.2c01320 SN - 2637-6105 VL - 4 IS - 11 SP - 8377 EP - 8385 PB - ACS AN - OPUS4-56067 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hao, Ning A1 - Böhning, Martin A1 - Schönhals, Andreas T1 - Dielectric Properties of Nanocomposites Based on Polystyrene and Polyhedral Oligomeric Phenethyl-Silsesquioxanes N2 - Nanocomposites were prepared by solution blending of polyhedral oligomeric silsesquioxane with phenethyl substituents (PhenethylPOSS) into polystyrene (PS). The prepared materials were investigated by dielectric spectroscopy, differential scanning calorimetry (DSC), and density measurements. Additional FTIR investigations were carried out. Pure polystyrene shows two relaxation processes, an intermediate β*-process at lower and the α-relaxation at higher temperatures, the latter corresponding to segmental dynamics (dynamic glass transition). The molecular assignment of the β*-process needs further investigation. PhenethylPOSS can be incorporated into PS up to about 40 wt % without any indication of phase separation. With increasing PhenethylPOSS content, the α-relaxation of the composites shifts to lower temperatures and the loss peak broadens. Thus, the main effect of the nanofiller in the polystyrene matrix is to enhance the segmental dynamics, i.e., plasticization. The incorporation of approximately 40 wt % (approximately 5 mol %) PhenethylPOSS shifts the glass transition temperature Tg by 50 K to lower temperatures. The obtained results for polystyrene are discussed together with those reported recently for polycarbonate where a phase-separated morphology is observed for higher concentrations of PhenethylPOSS. The different behavior of PhenethylPOSS in polystyrene and polycarbonate is interpreted in terms of the different interaction of the phenyl rings within the POSS substituents with the phenyl rings of the polymers. For polystyrene, the interaction is stronger than for polycarbonate which probably leads to the enhanced miscibility of PhenethylPOSS into polystyrene. A detailed analysis of the temperature dependence of the dielectric relaxation strengths points also to additional interactions in the nanocomposites when compared to pure polystyrene. The broadening of the loss peak with increasing concentration is discussed in the framework of composition fluctuations. KW - Polyhedral oligomeric silsesquioxane (POSS) KW - Polymer-based nanocomposites KW - Broadband dielectric spectroscopy KW - Polystyrene PY - 2007 DO - https://doi.org/10.1021/ma071777g SN - 0024-9297 SN - 1520-5835 VL - 40 IS - 26 SP - 9672 EP - 9679 PB - American Chemical Society CY - Washington, DC AN - OPUS4-16492 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Böhning, Martin A1 - Hao, Ning A1 - Schönhals, Andreas T1 - Correlation of activation energies of gas diffusivity and local matrix mobility in polycarbonate/POSS nanocomposites N2 - According to basic phenomenological models describing the solution-diffusion based mechanism of penetrant diffusion in dense polymers, a connection between the diffusive transport of gas molecules in a polymeric matrix and the molecular mobility of that matrix on a certain length scale is, in principle, established for a long time. However, experimental data directly showing this correlation are rare. The investigation of a series of nanocomposites based on a polyhedral oligomeric silsesquioxane (POSS) and a polycarbonate matrix allows a systematic change of the molecular mobility on a local length scale (β-relaxation) and of the corresponding activation energy EA, both determined by broadband dielectric spectroscopy. Independently, activation energies of penetrant diffusion (ED) of these nanocomposites were determined for N2, O2, CO2, and CH4 and a clear linear correlation between the two activation energies was established for the first time. KW - Broadband dielectric spectroscopy KW - Diffusion KW - Dielectric properties KW - Gas permeation KW - Molecular mobility KW - Nanocomposites KW - Polyhedral oligomeric silsesquioxane (POSS) KW - Relaxation KW - Beta-relaxation PY - 2013 UR - http://onlinelibrary.wiley.com/doi/10.1002/polb.23381/full DO - https://doi.org/10.1002/polb.23381 SN - 0887-6266 SN - 1099-0488 VL - 51 IS - 22 SP - 1593 EP - 1597 PB - Wiley CY - Hoboken, NJ AN - OPUS4-29284 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 DO - 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 - JOUR A1 - Omar, Hassan A1 - Smales, Glen Jacob A1 - Henning, S. A1 - Li, Z. A1 - Wang, D.-Y. A1 - Schönhals, Andreas A1 - Szymoniak, Paulina T1 - Calorimetric and Dielectric Investigations of Epoxy-Based Nanocomposites with Halloysite Nanotubes as Nanofillers N2 - Epoxy nanocomposites are promising materials for industrial applications (i.e., aerospace, marine and automotive industry) due to their extraordinary mechanical and thermal properties. Here, the effect of hollow halloysite nanotubes (HNT) on an epoxy matrix (Ep) was the focus of the study. The structure and molecular mobility of the nanocomposites were investigated using a combination of X-ray scattering, calorimetry (differential (DSC) and fast scanning calorimetry (FSC)) and dielectric spectroscopy. Additionally, the effect of surface modification of HNT (polydopamine (PDA) and Fe(OH)3 nanodots) was considered. For Ep/HNT, the glass transition temperature (Tg) is was de-creased due to a nanoparticle-related decrease of the crosslinking density. For the modified system, Ep/m-HNT, the surface modification resulted in enhanced filler–matrix interactions leading to higher Tg values than the pure epoxy in some cases. For Ep/m-HNT, the amount of interface formed between the nanoparticles and the matrix ranged from 5% to 15%. Through BDS measurements, localized fluctuations were detected as a β- and γ-relaxation, related to rotational fluctuations of phenyl rings and local reorientations of unreacted components. A combination of calorimetry and BDS dielectric spectroscopy revealed a dynamic and structural heterogeneity of the matrix, as confirmed by two glassy dynamics in both systems, related to regions with different crosslinking densities. KW - Rigid amorphous fraction KW - Epoxy nanocomposites KW - Halloysite nanotubes KW - X-ray scattering KW - Differential scanning calorimetry KW - Broadband dielectric spectroscopy KW - Flash DSC PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-526668 DO - https://doi.org/10.3390/polym13101634 VL - 13 IS - 10 SP - 1634 PB - MDPI AN - OPUS4-52666 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Szymoniak, Paulina A1 - Qu, Xintong A1 - Schönhals, Andreas A1 - Sturm, Heinz ED - Sinapius, M. ED - Ziegmann, G. T1 - Characterization of Polymer Nanocomposites N2 - The complex effect of nanoparticles on an epoxy-based and anhydride cured DGEBA/Boehmite nanocomposite with different particle concentrations is considered in this chapter. A combination of X-ray scattering, calorimetry (fast scanning and temperature modulated calorimetry) and dielectric spectroscopy was employed to characterize the structure, vitrification kinetics and the molecular dynamics of the nanocomposites. Firstly, the unfilled polymer was found to be intrinsically heterogeneous, showing regions with different crosslinking density, indicated by two separate dynamic glass transitions. Moreover, the glass transition temperature decreases with increasing nanoparticle concentration, as a result of changes in the crosslinking density. In addition, it was shown that the incorporation of nanoparticles can result in simultaneous increase in the number of mobile segments for low nanoparticle concentrations and on the other hand, for higher loading degrees the number of mobile segments decreases, due to the formation of an immobilized interphase. KW - Rigid amorphous fraction KW - Epoxy nanocomposites KW - X-ray scattering KW - Differential scanning calorimetry KW - Broadband dielectric spectroscopy KW - Flash DSC PY - 2021 DO - https://doi.org/10.1007/978-3-030-68523-2_4 SP - 55 EP - 77 PB - Springer Nature AN - OPUS4-52698 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Szymoniak, Paulina A1 - Madkour, Sherif A1 - Schönhals, Andreas T1 - Molecular dynamics of the asymmetric blend PVME/PS revisited by broadband dielectric and specific heat spectroscopy: Evidence of multiple glassy dynamics N2 - The molecular mobility of the highly asymmetric miscible blend poly(vinyl methyl ether)/polystyrene was investigated by broadband dielectric (frequency range 10^-1 Hz – 10^9 Hz) and specific heat spectroscopy (frequency range 10^1 Hz – 10^4 Hz). The dielectric spectra revealed a complex molecular dynamic behavior, where three different relaxation processes were observed. At temperatures below the glass transition temperature an α´-relaxation was found, with an Arrhenius-like temperature dependence of its relaxation rates. It is assigned to localized fluctuations of the confined PVME segments within a frozen glassy matrix dominated by PS. Above the thermal glass transition temperature two processes with a VFT behavior of their relaxation rates were detected called α1- and α2-relaxation, both originating from PVME dipoles fluctuating in PS-rich environments, however with diverse PS concentrations. The relevant length scales for the processes are assumed to be different, corresponding to the Kuhn segment length for the former relaxation and to the CRR for the latter one. The observed multiple glassy dynamics result from spatial local compositional heterogeneities on a microscopic level. Additionally, SHS investigations were performed for the first time for this system, proving an existence of a fourth relaxation process (α3-relaxation) due to the cooperative fluctuations of both PS and PVME segments. The separation between the thermal α3- and dielectric α2-relaxation increases dramatically with increasing polystyrene concentration, proving that the thermal response is dominated by PS. KW - Polymer blends KW - Dynamic heterogeneity KW - Broadband dielectric spectroscopy KW - Specific heat spectroscopy PY - 2019 DO - https://doi.org/10.1021/acs.macromol.8b02697 SN - 0024-9297 VL - 52 IS - 4 SP - 1620 EP - 1631 PB - ACS Publications AN - OPUS4-47516 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yildirim, Arda A1 - Bühlmeyer, A. A1 - Hayash, S A1 - Haenle, J. C. A1 - Sentker, K. A1 - Krause, Christina A1 - Huber, Patrick A1 - Laschat, Sabine A1 - Schönhals, Andreas T1 - Multiple glassy dynamics in dipole functionalized triphenylene-based discotic liquid crystals revealed by broadband dielectric spectroscopy and advanced calorimetry – assessment of the molecular origin N2 - A selected series of dipole functionalized triphenylene-based discotic liquid crystals (DLCs) was synthesized and investigated in a systematic way to reveal the phase behavior and molecular dynamics. The later point is of particular importance to understand the charge transport in such systems which is the key property for their applications such as organic field-effect transistors, solar cells or as nanowires in molecular electronics, and also to tune the properties of DLCs. The mesomorphic properties were studied by polarizing optical microscopy, X-ray diffraction, and differential scanning calorimetry, which were compared to the corresponding unfunctionalized DLC. The molecular dynamics were investigated by a combination of state-of-the-art broadband dielectric spectroscopy (BDS) and advanced calorimetry such as fast scanning calorimetry (FSC) and specific heat spectroscopy (SHS). Besides localized fluctuations, surprisingly multiple glassy dynamics were detected for all materials for the first time. Glassy dynamics were proven for both processes unambiguously due to the extraordinary broad frequency range covered. The a1-process is attributed to fluctuations of the alky chains in the intercolumnar space because a polyethylene-like glassy dynamics is observed. This corresponds to a glass transition in a confined three-dimensional space. The a2-process found at temperatures lower than a1-process, is assigned to small scale rotational and/or translational in plane fluctuations of the triphenylene core inside distorted columns. This can be considered as a glass transition in a one-dimensional fluid. Therefore, obtained results are of general importance to understand the glass transition, which is an unsolved problem of condensed matter science. KW - Discotic Liquid Crystals KW - Broadband dielectric spectroscopy KW - Flash DSC KW - Specific heat spectroscopy PY - 2019 DO - https://doi.org/10.1039/c9cp03499d SN - 1463-9076 VL - 21 IS - 33 SP - 18265 EP - 18277 PB - RSC AN - OPUS4-48739 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Szymoniak, Paulina A1 - Gawek, Marcel A1 - Madkour, S. A1 - Schönhals, Andreas T1 - Confinement and localization effects revealed for thin films of the miscible blend Poly(vinyl methyl ether) / Polystyrene with a composition of 25/75 wt% N2 - Thin films (200-7nm) of the asymmetric polymer blend poly(vinyl methyl ether) (PVME)/polystyrene (PS) (25/75wt%) were investigated by broadband dielectric spectroscopy (BDS). Thicker samples ([Formula: see text]37 nm) were measured by crossed electrode capacitors (CEC), where the film is capped between Al-electrodes. For thinner films ([Formula: see text]37 nm) nanostructured capacitors (NSC) were employed, allowing one free surface in the film. The dielectric spectra of the thick films showed three relaxation processes ( [Formula: see text] -, [Formula: see text] - and [Formula: see text] -relaxation), like the bulk, related to PVME fluctuations in local spatial regions with different PS concentrations. The thickness dependence of the [Formula: see text] -process for films measured by CECs proved a spatially heterogeneous structure across the film with a PS-adsorption at the Al-electrodes. On the contrary, for the films measured by NSCs a PVME segregation at the free surface was found, resulting in faster dynamics, compared to the CECs. Moreover, for the thinnest films ([Formula: see text]26 nm) an additional relaxation process was detected. It was assigned to restricted fluctuations of PVME segments within the loosely bounded part of the adsorbed layer, proving that for NSCs a PVME enrichment takes place also at the polymer/substrate interface. KW - Thin polymer films KW - Broadband dielectric spectroscopy PY - 2019 DO - https://doi.org/10.1140/epje/i2019-11870-3 SN - 1292-895X VL - 42 IS - 8 SP - 101, 1 EP - 11 PB - Springer AN - OPUS4-48651 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -