TY - JOUR A1 - Behrens, H. A1 - Bauer, U. A1 - Reinsch, Stefan A1 - Kiefer, P. A1 - Müller, Ralf A1 - Deubener, J. T1 - Structural relaxation mechanisms in hydrous sodium borosilicate glasses N2 - Borosilicate glasses (16Na2O–10B2O3–74SiO2, NBS) with water contents up to 22 mol% H2O were prepared to study the effect of water on structural relaxation using DTA, viscometry and internal friction measurements. The results show that the glass transition temperature Tg of DTA and the isokom temperature T12, of viscometry are in excellent agreement, confirming the equivalence of enthalpy and viscous relaxation for NBS glass. Combining Tg data with water speciation data demonstrates that OH groups are mainly responsible for the decrease of Tg with increasing hydration, while molecular water plays only a minor role. Internal friction spectra at 7.125 Hz confirm the decisive influence of water on mechanical relaxation. The temperature range of α-relaxation (glass transition) strongly decreases while two β-relaxation peaks (sub-Tg) progressively appear with increasing water content. A high temperature β-relaxation peak, attributed to the presence of OH groups, shifts from 670 to 450 K as total water content increases from 0.01 to 5 wt%. A low temperature β-relaxation peak, attributed to molecular water, appears at 380 K and 330 K in glasses containing 3 and 5 wt% H2O, respectively. These findings suggest that relaxation mechanism of different hydrous species at low temperature may contribute to fatigue of stressed glasses. KW - Borosilicate glass KW - Water KW - Relaxation KW - Internal friction KW - Glass transition PY - 2018 U6 - https://doi.org/10.1016/j.jnoncrysol.2018.05.025 VL - 497 SP - 30 EP - 39 PB - Elsevier B.V. AN - OPUS4-45608 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 U6 - 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 - Böhning, Martin A1 - Niebergall, Ute A1 - Adam, Adeline A1 - Stark, Wolfgang T1 - Influence of biodiesel sorption on temperature-dependent impact properties of polyethylene N2 - In a previous paper we investigated the influence of sorbed biodiesel or diesel on mechanical properties of a typical polyethylene grade for tank applications. Besides the basic sorption and desorption behavior of these two fuels, the study addressed the concentration-dependent mechanical properties as revealed by a non-instrumented Charpy impact test and dynamic mechanical analysis (DMA). In the present paper we extend this investigation focusing on the temperature-dependent impact fracture behavior. Therefore, an instrumented Charpy impact test was employed, allowing a more detailed analysis of the fracture behavior. Furthermore, from the load-time-diagrams obtained from the instrumented impact test, corresponding fracture times can be calculated, allowing a clear correlation of the fuel sorption induced changes in fracture toughness with the enhanced ß-relaxation observed by DMA. As in the previous study, the fracture surfaces of the impact tested specimens were analyzed in order to confirm the brittle or ductile character of the fracture indicated by impact strength and the corresponding load-deflection diagrams. KW - Biodiesel KW - Fuel sorption KW - Impact strength KW - Charpy impact test KW - Dynamic-mechanical analysis KW - Relaxation KW - PE-HD PY - 2014 U6 - https://doi.org/10.1016/j.polymertesting.2014.09.001 SN - 0142-9418 VL - 40 SP - 133 EP - 142 PB - Elsevier Science CY - Amsterdam [u.a.] AN - OPUS4-31583 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Das, A. A1 - Dufresne, E.M. A1 - Maaß, Robert T1 - Structural dynamics and rejuvenation during cryogenic cycling in a Zr-based metallic glass N2 - Subjecting metallic glasses repeatedly to liquid nitrogen temperature has become a popular method to homogeneously rejuvenate the material. Here we reveal the atomic-scale structural dynamics using in- situ x-ray photon correlation spectroscopy (XPCS) during and after cryogenic cycling of a Zr-based metallic glass in two structural states (plate and ribbon). Heterogeneous structural dynamics is observed at 300 K that changes to monotonic aging at 78 K. It is found that cryogenic cycling homogenizes the relaxation time distribution. This effect is much more pronounced in the ribbon, which is the only structural state that rejuvenates upon cycling. We furthermore reveal how fast atomic-scale dynamics is correlated with longtime structural relaxation times irrespective of the structural state, and that the ribbon exhibits unexpected additional fast atomic-scale relaxation in comparison to the plate material. A structural picture emerges that points towards heterogeneities in the fictive temperature as a requirement for cryogenic energy storage. KW - Structural dynamics KW - Metallic glass KW - Relaxation KW - Rejuvenation KW - Cryogenic cycling PY - 2020 U6 - https://doi.org/10.1016/j.actamat.2020.06.063 SN - 1359-6454 VL - 196 SP - 723 EP - 732 PB - Elsevier Ltd. AN - OPUS4-51311 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Konnertz, Nora A1 - Ding, Yi A1 - Harrison, W.J. A1 - Budd, P.M. A1 - Schönhals, Andreas A1 - Böhning, Martin T1 - Molecular mobility of the high performance membrane polymer PIM-1 as investigated by dielectric spectroscopy N2 - The increasing demand for energy efficient separation processes fosters the development of new high performance polymers as selective separation layers for membranes. PIM-1 is the archetypal representative of the class of polymers of intrinsic microporosity (PIM) which are considered most promising in this sector, especially for gas separations. Since their introduction, PIMs stimulated a vast amount of research in this field and meanwhile evolved to the state of the art in membrane technology for gas separation. The major obstacle for extending the practical membrane application is their strong tendency to physical aging. For the first time, investigations by broadband dielectric spectroscopy (BDS) addressing molecular dynamics and conductivity in PIM 1 are presented. As chain packing during film formation from the casting solution and physical aging are key factors determining the separation performance of PIMs as membrane materials, characterization of the molecular mobility in such materials as revealed by BDS will provide valuable information for further development and optimization. KW - PIM-1 KW - BDS broadband dielectric spectroscopy KW - Relaxation KW - Membrane PY - 2016 U6 - https://doi.org/10.1021/acsmacrolett.6b00209 SN - 2161-1653 VL - 5 IS - 4 SP - 528 EP - 532 PB - ACS American Chemical Society CY - Washington, DC, USA AN - OPUS4-35798 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Qiao, Linan A1 - Herbrich, Uwe A1 - Nagelschmidt, Sven T1 - Describing Relaxation Behavior of Metal Seals Using Time-Temperature Superposition Principle N2 - In order to study the time- and temperature-dependent long-term behavior of metal seals, experimental investigations on special metal seals have been carried out at five different temperatures in a temperature range between 20 and 150°C for more than 7 years. Experimental results indicate a noticeable change of relevant sealing properties like seal force and usable resilience depending on time and temperature. In this study, the metal seals are treated as a homogeneous material block so that the identified decrease in seal force can be treated as a material relaxation effect. For the time-dependent behavior of seal force, an enhanced power-law model is introduced for the first time and is compared with the currently used power-law model. Additionally, regarding the influence of temperature, the timetemperature superposition principle is applied to metal seals for the first time with a clearly defined process. Thus, possible mistakes in the application of principle could be avoided. The introduced method is widely available for different applications regarding effects the principle with time and temperature. KW - Metal seals KW - Relaxation KW - Thermo-viscoplasticity KW - Time-temperature superposition PY - 2018 UR - https://ascelibrary.org/doi/abs/10.1061/%28ASCE%29EM.1943-7889.0001424 U6 - https://doi.org/10.1061/(ASCE)EM.1943-7889.0001424 SN - 0733-9399 VL - 144 IS - 4 SP - 04018016-1 EP - 04018016-8 PB - American Society of Civil Engineers AN - OPUS4-44676 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schumacher, G. A1 - Darowski, N. A1 - Zizak, I. A1 - Klingelhöffer, Hellmuth A1 - Neumann, W. T1 - Two-stage relaxation of damage structure in strongly creep-deformed single crystal superalloy SC16 measured by means of X-ray diffraction KW - Superalloys KW - SC16 KW - Creep-deformation KW - Relaxation KW - X-ray diffraction PY - 2009 U6 - https://doi.org/10.1016/j.scriptamat.2008.09.009 SN - 1359-6462 SN - 1872-8456 VL - 60 IS - 2 SP - 88 EP - 91 PB - Elsevier CY - Oxford AN - OPUS4-18304 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schönhals, Andreas A1 - Schick, C. A1 - Huth, H. A1 - Frick, B. A1 - Mayorova, M. A1 - Zorn, R. T1 - Molecular dynamics in glass-forming poly(phenyl methyl siloxane) as investigated by broadband thermal, dielectric and neutron spectroscopy KW - Neutron diffraction/scattering KW - Dielectric properties KW - Relaxation KW - Electric modulus KW - Glass transition PY - 2007 SN - 0022-3093 VL - 353 IS - 41-43 SP - 3853 EP - 3861 PB - North-Holland Publ. Co. CY - Amsterdam AN - OPUS4-15898 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Turky, G. A1 - Shaaban, S.S. A1 - Schönhals, Andreas T1 - Broadband dielectric spectroscopy on the molecular dynamics in different generations of hyperbranched polyester N2 - Dielectric spectroscopy (10-2 Hz to 106 Hz) was employed to investigate the molecular dynamics of hyperbranched polyesters where the number of the generation is systematically varied from 2 to 5. As a first result, the dielectric properties depends strongly on the generation of the hyperbranched polymers. For higher generations (3 to 5) at temperatures below Tg two relaxation processes are observed, a γ-process at lower temperatures and a β-process at higher ones. The apparent activation energies are around 100 kJ/mol which seems to be too high for truly localized processes. For the Generation 2, only the γ-process is observed. For all investigated polymers the dielectric α-relaxation could not be observed because of strong conductivity effects. Therefore, the conductivity is systematically analyzed which obeys the peculiarities found to be characteristic for semiconducting disordered materials. Especially, the Barton/Nakajima/Namikawa relationship is found to be valid. KW - Molecular dynamics KW - Polyesters KW - Relaxation KW - Synthesis PY - 2009 U6 - https://doi.org/10.1002/app.30046 SN - 0021-8995 SN - 1097-4628 VL - 113 IS - 4 SP - 2477 EP - 2484 PB - Wiley InterScience CY - Hoboken, NJ AN - OPUS4-19484 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 U6 - 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 -