H.-W. Schmidt

University of Bayreuth , Bayreuth, Bavaria, Germany

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Publications (30)112.71 Total impact

  • M. Kersch · L. Pischke · H.-W. Schmidt · V. Altstädt ·
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    ABSTRACT: The influence of two different trisamide-based additives on the morphological and mechanical behavior of isotactic polypropylene (PP) is investigated. Morphological investigations by wide-angle X-ray scattering (WAXS) show that only 0.04 wt.-% of one of the additives is enough to induce 80% beta modification in the crystalline part of. the polymer. The materials are investigated with quasistatic (tensile testing) as well as short-time dynamic (Charpy impact strength) methods and for the first time fatigue crack growth measurements are performed on alpha- and beta-nucleated PP. In all cases a much higher toughness of the material containing the beta-nucleating agent (beta NA) can be observed. The crack growth propagation rate is one order of magnitude smaller with the use of the beta-nucleating agent compared to the alpha polymer. Scanning electron microscopy (SEM) pictures are used to support the correlation of the mechanical behavior with the morphological changes.
    Polymer 06/2014; 55(15). DOI:10.1016/j.polymer.2014.05.030 · 3.56 Impact Factor
  • Andreas Hess · L. Heymann · N. Aksel · M. Pretzl · A. Fery · C. Neuber · H.-W. Schmidt ·

    Rheologentagung 2010 und 17. Ostwald-Kolloquium, Karlsruhe, Germany; 03/2010
  • D.P. Erhard · R. Giesa · V. Altstädt · H.-W. Schmidt ·
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    ABSTRACT: The performance of a polymeric electret material depends on many parameters, and besides chemical structure, charging conditions, and application temperature, other factors, such as grade, manufacturer, processing history, and additive package, are critical. Commercial polyetherimide (PEI) Ultem®1000 films exhibited satisfying electret properties as revealed by an isothermal potential decay (ITPD) to 75% of the initial surface charge after 24 h at 90°C. It was found that after purification by reprecipitation this value drops to 34% and that the same PEI synthesized by two different methods revealed to be a very poor electret with charge retention of almost zero. Assuming that an additive in the commercial material might be responsible for this behavior, we identified an organophosphonite which is commonly used as antioxidant in high-temperature polymers. We incorporated this additive by melt compounding into purified PEI and found a dramatic increase in charge retention to 79% of the initial charge at an additive load level of 0.5 wt %. By immersing Ultem®1000 films in water, the electret behavior was further improved and almost 100% charge retention was achieved.
  • W. Jenninger · J. Wagner · H.-W. Schmidt · D.P. Erhard ·
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    ABSTRACT: Composition comprises at least one polycarbonate and at least one isoindole 1,3-dione derivative (I). Composition comprises at least one polycarbonate and at least one isoindole 1,3-dione derivative of formula (I). R 1-R 6, R 1 3-R 1 6H, (pseudo)halo, OH, NH 2, NO 2, 1-20C alkyl, 1-20C cycloalkyl, 2-20C alkenyl, 2-20C alkynyl, 1-20C aryl, 1-20C alkoxy, 1-20C acyl, 1-20C aldehyde, 1-20C carboxylic acid, 1-20C carboxylic acid ester, amide or acyl halo; m, n : 0-10; and T 1, T 2organic group. Independent claims are included for: (1) the isoindole 1,3-dione derivative (I), where m and n are 1-10 and T 2 is phenoxy phenyl moiety of formula (II); (2) a polymer element comprising the composition; (3) preparing the polymer element from the composition by pressing, scraping, spreading, centrifuging, spraying, extrusion, blow molding and/or compacting; (4) an electret element comprising the polymer element that is charged; (5) preparing the electret element, comprising producing the polymer element and charging it; and (6) electromechanical converter comprising the polymer element or the electret element. R 6 1-R 7 4H, (pseudo)halo, OH, NH 2, NO 2, 1-20C alkyl, 1-20C cycloalkyl, 2-20C alkenyl, 2-20C alkynyl, 1-20C aryl, 1-20C acyl, 1-20C aldehyde, 1-20C carboxylic acid, 1-20C carboxylic acid ester, amide or acyl halo.
    Ref. No: EP2159222 (A1), Year: 03/2010
  • D.P. Erhard · D. Lovera · W. Jenninger · J. Wagner · V. Altstädt · H.-W. Schmidt ·
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    ABSTRACT: An electret is a dielectric material exhibiting a quasi-permanent electric charge. The aim of this work is to give access to polycarbonate (PC) electret materials with a distinctly improved electret performance. In this context, the charge storage capabilities of corona charged films of several PC grades were investigated by isothermal potential decay measurements at 90°C. The most promising PC grade was further improved by a new class of bisimide additives. The best additive at the most efficient concentration in combination with a physical aging step yielded excellent PC electrets maintaining almost their complete applied charge even at 90°C.
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    ABSTRACT: The charge decay in isotactic polypropylene (i-PP) films of 50 µm thickness, containing three kinds of additives, namely a trisamide, a bisamide and a fluorinated compound, with concentrations in the range 0.004–1 wt% was studied. Compression molding was used to produce the films. The samples were either surface-charged by a corona method or volume-charged by mono-energetic electron beams of different energies, having penetration depths up to 6 µm. In all cases, surface potentials of about 200 V were chosen. After charging the films, the decay of the surface potential was studied either by an isothermal discharge method at 90 °C or by thermally stimulated discharge measurements. The results show a dependence of the decay rate on the kind of additive used, on additive concentration and on the energy of the injected charges. In particular, for samples with fluorinated additives, the stability of the surface potential decreases markedly with increasing electron energy, while such a dependence is very weak for samples containing the bisamide additive and does not exist at all for samples with the trisamide additive. These observations are tentatively explained by the radiation-induced generation of relatively mobile negative ions originating from the bisamide and fluorinated additives.
    Journal of Physics D Applied Physics 02/2009; 42(6):065410 (8pp). DOI:10.1088/0022-3727/42/6/065410 · 2.72 Impact Factor
  • D.P. Erhard · R. Giesa · H.-W. Schmidt ·

    8th International Technical Symposium on Polyimides & High Performance Functional Polymers (STEPI 8); 06/2008
  • D. Lovera · V. Altstadt · H.-W. Schmidt ·
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    ABSTRACT: The charge storage behavior is a fundamental property of polymers used in electromechanical-transducer applications. Polymer blends can potentially show a higher charge storage capability than the neat constituents, since the phase boundaries between the individual components can act as trapping sites. In this work, the charge storage behavior of polyphenylene ether (PPE) is enhanced by the addition of selected amounts of polystyrene (PS) and poly(styrene-isobutylene-styrene) (SIBS). While the binary blends PPE/PS are miscible and are expected to form one homogeneous phase, the ternary blends PPE/PS/SIBS are multiphasic. The blend charge storage behavior was related to the macro- and micro- morphology as well as to the charging method.
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    ABSTRACT: In the present paper, the effect of several additives on charge transport in specially prepared polypropylene PP samples is investigated.
  • N. Behrendt · V. Altstadt · X. Zhang · G. Sessler · H.-W. Schmidt ·
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    ABSTRACT: Cellular polymer films have an enhanced charge storage capability, since the charge drift across the film is hindered by the presence of voids. Furthermore, modulating the morphology of those cellular polymer structures, very high piezoelectric activities can be obtained. In this work, polypropylene (PP) and polyetherimide (PEI) cellular films were produced using novel methods and their morphology, charge storage properties and piezoelectricity were investigated.
  • D. Lovera · V. Altstadt · H.-W. Schmidt ·
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    ABSTRACT: In this study, multiphasic blends were prepared by the addition of different styrene-based-copolymers to a blend PPE/PS of 75/25 composition. The aim is to give insights into the influence of the polymer chemical structure on the charge storage of polymer blends.
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    ABSTRACT: Enhancing the charge storage capability of thermoplastic polymers can be achieved at least by (i) the creation of obstacles such as highly elongated pores in the polymer film to substantially lengthen the pathway for charge recombination, (ii) the tailored chemical modification of the polymer backbone, and (iii) the addition of functional additives to create charge traps. This work focuses on the functional additive approach. Novel compounds to improve the electret performance of isotactic polypropylene (i-PP) were synthesized, which act as charge traps.
  • D.P. Erhard · R. Giesa · V. Altstadt · H.W. Schmidt ·
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    ABSTRACT: The aim of the present work was to synthesize PEIs with different degrees of fluoro substitution in order to further improve the electret performance of the promising Ultemreg1000 and to better understand the correlation of the polymer chemical structure with the electret properties.
    Electrets, 2008. ISE-13. 13th International Symposium on; 01/2008
  • N. Mohmeyer · C. V. Salis-Soglio · V. Altstadt · H.-W. Schmidt ·
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    ABSTRACT: A comparative study on the influence of chemical structure and solubility of a series of low-molecular-weight 1,4-phenylene-bisamides in isotactic polypropylene (i-PP) was conducted to explore their performance as electret additives. The effect of the symmetry of the molecules, of the type of substitution and of the length of the alkyl chain on the solubility in the i-PP melt and on the charge storage properties was investigated.
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    ABSTRACT: In this paper we describe the use of combinatorial vapor deposition techniques for the optimization of blue organic light emitting diodes (OLEDs). In these devices the star shaped molecule 1 with a triphenylamine core and three fluorene side groups serves as hole transport and emitting layer. Compound 2 with a much lower lying HOMO and a larger bandgap is used as hole blocking layer. Using combinatorial vapor deposition 42 OLEDs with thickness gradients of both the hole transport and the hole blocking layer have been simultaneously prepared on one substrate. The physical characterization of the devices clearly shows that a hole blocking layer of the star shaped molecule 2 is necessary in order to obtain pure blue emission with CIE coordinates of x = 0.15 and y = 0.15. A thickness of only 5 nm of the blocking layer is sufficient, and with increasing layer thickness the brightness of the blue devices drops. The blue devices exhibit a brightness of 400 cd m–2 and a luminous efficiency of 2 cd A–1. The thickness variations of both the hole transport and the hole blocking layer have been made in one combinatorial evaporation experiment on a single substrate using a set of movable masks. This demonstrates how efficient combinatorial methods can be used for the development of OLEDs.
    Advanced Functional Materials 11/2007; 17(17):3456 - 3461. DOI:10.1002/adfm.200700223 · 11.81 Impact Factor
  • D Lovera · C Bilbao · V Altstädt · H W Schmidt · R Giesa ·

    Microscopy and Microanalysis 09/2007; 13. DOI:10.1017/S1431927607082220 · 1.88 Impact Factor
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    ABSTRACT: A negative tone photoresist film, consisting of a molecular glass, a photoacid generator, and an acid labile crosslinker, was prepared by physical vapor deposition, a solvent-free process. Subsequent to deposition, the coevaporated monomers were exposed using 365 nm radiation, subjected to a post exposure bake step, and developed in aqueous base to produce sub-micron patterns. Combinatorial techniques were used to aid optimization of the photoresist by systematic variations in composition and exposure dose. Development factors such as concentration and time were also optimized.
    Advanced Functional Materials 08/2007; 17(14):2336 - 2342. DOI:10.1002/adfm.200600717 · 11.81 Impact Factor
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    ABSTRACT: The paper presents the synthesis of azobenzene-functionalized block copolymers based on a poly(methyl methacrylate) (PMMA) segment and an azobenzene-functionalized poly(hydroxyethyl methacrylate) segment, and a basic study of blending these block copolymers with homopolymers is given. Two diblock copolymers, prepared via different routes, were synthesized by a living anionic polymerization followed by a polymer analogous reaction to attach the azobenzene side groups. Self-assembly of the block copolymers resulted in phase-separated morphologies on the nanometer scale. The photoaddressable azobenzene segments are dispersed in the PMMA matrix and locally confined. Special focus is given to the preparation and characterization of block copolymer blends with PMMA homopolymer in order to dilute the phase-separated azobenzene morphology and reduce the optical density while maintaining the confinement. The block copolymer blends were characterized with respect to their morphology and initial holographic experiments were performed.
    Macromolecules 03/2007; 40(6-6):2100-2108. DOI:10.1021/ma0624907 · 5.80 Impact Factor
  • Michael Haeckel · Lothar Kador · Daniela Kropp · H.-W. Schmidt ·
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    ABSTRACT: A homogeneous polymer blend based on azobenzene containing polymer and a similar but nonabsorbing polymer was used as a stable rewritable volume holographic media. The proper optical density was adjusted by blending the block copolymer with a polystyrene homopolymer, thus diluting the continuous polystyrene matrix while maintaining the microphase separation. Transmission electron microscopy on similar polymer blends revealed that the domain size of the minority phase is maintained while the spacing between the domains increases upon dilution. The polymer blend can be processed by injection molding to prepare samples of any desired shape. The reorientation of the azobenzene side chains is reversible and it is possible to erase all information written in the entire medium by heating it above the glass transition temperature. The results show that multiplexing a large number of volume holograms is possible in polymer blends with azobenzene-containing block copolymers.
    Advanced Materials 01/2007; 19(2):227 - 231. DOI:10.1002/adma.200601458 · 17.49 Impact Factor
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    ABSTRACT: In the present work, the development of cellular films by stretching isotactic polypropylene (i-PP) filled with NA11 (2,2'-methylene-bis-(4,6-di-tert-butylphenyl)-phosphate) particles and hollow glass spheres is reported. Morphology, electret properties and piezoelectric activity are investigated. An enhancement of the charge storage stability for the cellular films is due to the formation of cavities, which retard the drift of charges through the volume of the film. Furthermore, the cellular stretched i-PP films with hollow glass spheres were made piezoelectric by suitable corona poling method. Films were stretched to draw ratios of 3.5:3.5 (medium stretched) and selected samples were drawn to ratios of 5:5 (highly stretched). The applied draw ratio was found to directly influence the cavity formations and by this the electret and piezoelectric properties. Excellent electret properties were obtained in the case of highly stretched i-PP films containing 10 wt% of NA11, known as a nucleating agent additive for i-PP. Additionally, piezoelectric activity (d<sub>33</sub>=179 pC/N) was observed in these films. i-PP films with glass spheres showed piezoelectric coefficients between 17 and 170 pC/N, depending on glass sphere size and concentration as well as on draw ratio
    IEEE Transactions on Dielectrics and Electrical Insulation 11/2006; 13(5-13):992 - 1000. DOI:10.1109/TDEI.2006.247824 · 1.28 Impact Factor

Publication Stats

410 Citations
112.71 Total Impact Points


  • 2002-2014
    • University of Bayreuth
      • • Chair of Macromolecular Chemistry I
      • • Bayreuth Institute of Macromolecular Research (BIMF)
      Bayreuth, Bavaria, Germany