Filters

20154

More filters

2022 - 20234
Reset filters

Settings

search.filters.applied.f.access: openAccess × End date: 2016 × Start date: 2015 × DDC: 660 × Has files: Yes × Type: Article × WGL Institute: IPF ×

Search Results

Now showing 1 - 4 of 4
  • Thumbnail Image
    Item
    Reversible thermosensitive biodegradable polymeric actuators based on confined crystallization
    (Washington, DC : ACS Publ., 2015) Stroganov, Vladislav; Al-Hussein, Mahmoud; Sommer, Jens-Uwe; Janke, Andreas; Zakharchenko, Svetlana; Ionov, Leonid
    We discovered a new and unexpected effect of reversible actuation of ultrathin semicrystalline polymer films. The principle was demonstrated on the example of thin polycaprolactone-gelatin bilayer films. These films are unfolded at room temperature, fold at temperature above polycaprolactone melting point, and unfold again at room temperature. The actuation is based on reversible switching of the structure of the hydrophobic polymer (polycaprolactone) upon melting and crystallization. We hypothesize that the origin of this unexpected behavior is the orientation of polycaprolactone chains parallel to the surface of the film, which is retained even after melting and crystallization of the polymer or the “crystallization memory effect”. In this way, the crystallization generates a directed force, which causes bending of the film. We used this effect for the design of new generation of fully biodegradable thermoresponsive polymeric actuators, which are highly desirable for bionano-technological applications such as reversible encapsulation of cells and design of swimmers.
  • Thumbnail Image
    Item
    Carbon-Based Materials at Nanoscale
    (New York, NY : Hindawi Publ., 2015) Xia, Dan; Otyepka, Michal; Li, Xi; Liu, Wei; Zheng, Qingbin
    [No abstract available]
  • Thumbnail Image
    Item
    Review on quality assurance along the CFRP value chain - Non-destructive testing of fabrics, preforms and CFRP by HF radio wave techniques
    (Amsterdam [u.a.] : Elsevier, 2015) Heuer, H.; Schulze, M.; Pooch, M.; Gäbler, S.; Nocke, A.; Bardl, G.; Cherif, Ch.; Klein, M.; Kupke, R.; Vetter, R.; Lenz, F.; Kliem, M.; Bülow, C.; Goyvaerts, J.; Mayer, T.; Petrenz, S.
    Eddy current testing is well established for non-destructive testing of electrical conductive materials [1]. The development of radio frequency (RF) eddy current technology with frequency ranges up to 100 MHz made it possible to extend the classical fields of application even towards less conductive materials like CFRP [2][3](Table 2). It turns out that RF eddy current technology on CFRP generates a growing number of valuable information for comprehensive material diagnostic. Both permittivity and conductivity of CFRP influence the complex impedance measured with RF eddy current devices. The electrical conductivity contains information about fiber texture like orientations, gaps or undulations in a multilayered material. The permittivity characterization influenced by dielectric properties allows the determination of local curing defects on CFRP e.g. hot spots, thermal impacts or polymer degradation. An explanation for that effect is seen in the measurement frequency range and the capacitive structure of the carbon rovings. Using radio wave frequencies for testing, the effect of displacement currents cannot be neglected anymore. The capacitive structures formed by the carbon rovings is supposed to further strengthen the dielectric influences on eddy current measurement signal [3]. This report gives an overview of several realized applications and should be understood as a general introduction of CFRP testing by HF Radio Wave techniques.
  • Thumbnail Image
    Item
    Ultralow percolation threshold in polyamide 6.6/MWCNT composites
    (Barking : Elsevier, 2015) Krause, Beate; Boldt, Regine; Häußler, Liane; Pötschke, Petra
    When incorporating multiwalled carbon nanotubes (MWCNTs) synthesised by the aerosol-CVD method using different solvents into polyamide 6.6 (PA66) by melt mixing an ultralow electrical percolation threshold of 0.04. wt.% was found. This very low threshold was assigned to the specific characteristic of the MWCNTs for which a very high aspect ratio, a good dispersability in aqueous surfactant dispersions, and relatively low oxygen content near the surface were measured. The investigation of the composites by transmission electron microscopy on ultrathin cuts as well as by scanning electron microscopy combined with charge contrast imaging on compression moulded plates illustrated a good MWCNT dispersion within the PA66 matrix and that the very high aspect ratio of the nanotubes remained even after melt processing. Additionally, the thermal behaviour of the PA66 composites was investigated using differential scanning calorimetry (DSC) showing that the addition of only 0.05. wt.% MWCNT leads to an increase of the onset crystallization temperature of 11. K.