Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
- Vortrag (10)
- Zeitschriftenartikel (5)
- Posterpräsentation (1)
Sprache
- Englisch (16)
Schlagworte
- Glass transition (16) (entfernen)
Organisationseinheit der BAM
- 6 Materialchemie (9)
- 6.6 Physik und chemische Analytik der Polymere (9)
- 5 Werkstofftechnik (3)
- 5.6 Glas (2)
- 7 Bauwerkssicherheit (2)
- 7.5 Technische Eigenschaften von Polymerwerkstoffen (2)
- 3 Gefahrgutumschließungen; Energiespeicher (1)
- 3.4 Sicherheit von Lagerbehältern (1)
- 5.0 Abteilungsleitung und andere (1)
- 6.7 Materialsynthese und Design (1)
Eingeladener Vortrag
- nein (10)
The pyrolysis and fire behavior of halogen-free flame-retarded DGEBA/DMC, RTM6 and their corresponding 60 vol.-% carbon fibers (CF) composites were investigated. A novel phosphorous compound (DOPI) was used. Its action is dependent on the epoxy matrix. DGEBA/DMC and DOPI decompose independently of each other. Only flame inhibition occurs in the gas phase. RTM6 shows flame inhibition and a condensed phase interaction increasing charring. Both mechanisms decrease with increasing irradiance, whereas in RTM6-CF charring is suppressed at low ones. RTM6+DOPI shows a higher LOI (34.2%) than DGEBA/DMC+DOPI and a V-0 classification in UL 94. Adding CF only enhances the LOI, DOPI+CF leads to a superposition in LOI for DGEBA/DMC-CF+DOPI (31.8%, V-0) and a synergism for RTM6-CF+DOPI (47.7%, V-0).
In this presentation, we report on the Determination of the glass transition temperature of thin layers of Polyvinylmethylether (PVME) depending on the thickness of the polymer layer. The glass Transition of thin polymer layers is currently under much investigation due to the nano-confinement effects proposed to appear in dependence on the layer thicknesses in the nm range. The properties of the polymer, the temperature range, as well as the thicknesses range of the polymer layers pose a serious challenge to the investigation by means of
spectroscopic ellipsometry. By careful choice of experimental parameters, we were able to investigate the thickness change by temperature of PVME layers in the range between 2 and 300 nm and in the temperature range between 200 K and 340 K. By optimizing the analysis process, we were able to determine Tg values within this parameter range with sufficient accuracy to investigate the Tg change due to confinement effects.
Alongside the change of position of the glass transition with thickness, we discuss the details of the ellipsometric analysis and its implications for the resulting thermal properties of the thin polymer layers as well as the accuracy of the Tg value with respect to the method used in the analysis process.
Molecular mobility and conductivity of four bent shaped tetramethylated guanidiniumbased ionic liquid crystals(ILCs) with varying head group configuration (cyclic or acyclic) and alkyl chain length is investigated by a combination of broadband dielectric spectroscopy (BDS) and specific heat spectroscopy (SHS). Two dielectrically active processes observed in the plastic crystalline phase at low and high temperatures are denoted as γ and α1 relaxation. The former is assigned to localized fluctuations of methyl groups including nitrogen atoms in the guanidinium head groups. SHS investigations reveal one calorimetrically active process termed as α2 Relaxation process. The temperature dependencies of the relaxation rates of α1 and α2 are similar for the cyclic ILCwhile for the acyclic counterpart they are different. Possible molecular assignments for the α1 and α2 relaxation are discussed in detail. Alongside relaxation processes, a significant conductivity contribution was observed for all ILCs, where the absolute value of DC conductivity increases by 4 orders of magnitude at the transition from the crystalline to the hexagonal columnar phase. The increase is traced to the change in the underlying conduction mechanism from the delocalized electrical conduction in the Cry phase to ionic conduction in the quasi 1D ion columns formed in the hexagonal columnar mesophase.
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.
Understanding the failure mechanisms that lead to leakage of rubber seals at low temperatures is important. Rubber properties are highly temperature dependent. Changes in behaviour at low temperatures can result from the rubber-glass transition and for some rubbers by partial crystallisation. Experimental results on the low temperature behaviour of different rubber seals were discussed to help understand seal failure processes.
We report the dielectric and calorimetric investigations of an homologous series of Janus polynorbornenes with rigid main backbone and flexible -Si(OR)3 side groups, of differing length alkyl chains (R = Propyl, Butyl, Hexyl, Octyl, Decyl). Dielectric dispersion reveals two active processes at low temperatures, denoted as β- and α- relaxation. The former can be assigned to localized fluctuations, whilst the latter relates to the glassy dynamics of the flexible -Si(OR)3 side groups, that creates a nanophase separation in both the alkyl chain rich and backbone rich domains. Temperature modulated DSC measurements and X-ray scattering experiment confirm the nanophase separation. Fast Scanning Calorimetry employing both fast heating and cooling rates detects the glass transition temperatures of the backbone rich domains, which are beyond or near to their degradation temperatures in terms of conventional DSC. The cooperative length scale of glass transition and the size of the alkyl chain rich domains increases with chain length. Alongside these results, a significant conductivity contribution was observed for all Poly(tricyclononenes) with Si(OR)3 side groups, which is interpreted in terms of a percolation model.
For the first time, dielectric and calorimetric investigations of a homologous series of Janus polynorbornenes with rigid main backbones and flexible −Si(OR)3 side groups of differing length alkyl chains (R = propyl, butyl, hexyl, octyl, and decyl) is reported. Generally, this class of polymers has some potential for applications in the field of gas separation membranes. Two dielectrically active processes are observed at low temperatures, denoted as β- and α-relaxation. The former can be assigned to localized fluctuations, while the latter is related to the glassy dynamics of the flexible −Si(OR)3 side groups, creating a nanophase separation in both the alkyl chain-rich and backbone-rich domains. This is confirmed through temperature-modulated differential scanning calorimetry (TMDSC) measurements and X-ray scattering experiments. The glass transition temperatures of the backbone rich domains, which are beyond or near to their degradation temperatures in terms of conventional DSC, are determined for the first time using fast scanning calorimetry employing both fast heating and cooling rates. This is complemented with scattering experiments that show how the size of the alkyl chain-rich domains increases with the side chain length. Alongside these results, a significant conductivity contribution was observed for all poly(tricyclononenes) with −Si(OR)3 side groups, which is interpreted in terms of a percolation model.
We report the dielectric and calorimetric investigations of an homologous series of Janus polynorbornenes with rigid main backbone and flexible -Si(OR)3 side groups, of differing length alkyl chains (R = Propyl, Butyl, Hexyl, Octyl, Decyl). Dielectric dispersion reveals two active processes at low temperatures, denoted as β- and α- relaxation. The former can be assigned to localized fluctuations, whilst the latter relates to the glassy dynamics of the flexible -Si(OR)3 side groups, that creates a nanophase separation in both the alkyl chain rich and backbone rich domains. Temperature modulated DSC measurements and X-ray scattering experiment confirm the nanophase separation. Fast Scanning Calorimetry employing both fast heating and cooling rates detects the glass transition temperatures of the backbone rich domains, which are beyond or near to their degradation temperatures in terms of conventional DSC. The cooperative length scale of glass transition and the size of the alkyl chain rich domains increases with chain length. Alongside these results, a significant conductivity contribution was observed for all Poly(tricyclononenes) with Si(OR)3 side groups, which is interpreted in terms of a percolation model.
High performance polymers of intrinsic microporosity (PIMs) have emerged as novel materials with broad applications from gas separation to electronic devices. Sufficiently rigid, even contorted polymer chains show only limited molecular mobility, therefore undergo inefficient packing and give rise to intrinsic microporosity with pore size generally smaller than 1 nm and BET surface areas larger than 700 m2/g. Further performance optimization and long-term stability of devices incorporating PIMs rely on our understanding of structure-processing-property relationships and physical aging, in which glass transition plays a key role. Up to now no glass transition temperature (Tg) of PIMs could be detected with conventional thermal analysis techniques before degradation. Decoupling the time scales responsible for the glass transition and the thermal decomposition is a reliable strategy to overcome this. This was achieved by employing fast scanning calorimetry (FSC) based on a chip sensor, which is capable to heat and cool a small sample (ng-range) with ultrafast rates of several ten thousand K/s. FSC provides definitive evidence of glass transition of a series of PIMs with a special consideration on the chain rigidity. The determined glass transition temperature of these PIMs follows the order of the rigidity of their backbone structures. FSC provides the first clear-cut experimental evidence of the glass transition of PIM-EA-TB with a Tg of 663 K, PIM-1 of 644 K and PIM-DMDPH-TB of 630 K at a heating rate of 1Χ104 K/s. Local fluctuations are featured in glass transition of highly rigid PIMs. As conformational changes are prevented by the backbone rigidity, the glass transition must rather be assigned to local small scale fluctuations.
We investigate the molecular dynamics and electrical conductivity for a homologous series of linear shaped guanidinium based cyclic ILCs that vary in alkyl chain length, CLCRs (R = 8, 10, 12, 14, 16) by employing broadband dielectric spectroscopy (BDS), and calorimetry comprised of Fast Scanning Calorimetry (FSC) and temperature modulated FSC (TMFSC). Besides conductivity at high temperatures, the dielectric dispersion reveals two relaxation modes: the fast γ and the slow α1 relaxation. The former is assigned to the localized fluctuations while the latter is due to segmental dynamics of the alkyl chains. The γ mode slows down for long chain length CLCs (12,14,16) compared to their shorter analogues. Calorimetric investigation reveals one process, the α2 process, for all ILCs. The α2 process for CLC10, 12, and 14 has a similar temperature dependence as the dielectric α1 relaxation, while for the CLC8 and 10, it's shifted to a higher temperature. For all CLCRs, the absolute values of DC conductivity increase by 4 orders of magnitude at the transition from the plastic crystalline to hexagonal columnar phase. This increase is due to the change in the underlying conduction mechanism from delocalized electron hopping in the crystalline phase to one-dimensional ion mobility in the columnar phase. The glassy dynamics shifts to higher temperatures with increasing alkyl chain length. Conversely, the DC conductivity drops by 3 orders of magnitude from CLC8 to CLC16.