Bernauer′s Bands

Authors

  • Dr. Alexander Shtukenberg,

    Corresponding author
    1. Department of Chemistry, New York University, 100 Washington Square East, Room 1001, New York, NY 10003 (USA), Fax: (+1) 212-995-3884
    • Department of Chemistry, New York University, 100 Washington Square East, Room 1001, New York, NY 10003 (USA), Fax: (+1) 212-995-3884
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  • Erica Gunn,

    1. Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195 (USA)
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  • Dr. Massimo Gazzano,

    Corresponding author
    1. ISOF-CNR, Via Selmi 2, 40126 Bologna (Italy), Fax: (+39) 051-209-9456
    • ISOF-CNR, Via Selmi 2, 40126 Bologna (Italy), Fax: (+39) 051-209-9456
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  • John Freudenthal,

    1. Department of Chemistry, New York University, 100 Washington Square East, Room 1001, New York, NY 10003 (USA), Fax: (+1) 212-995-3884
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  • Eric Camp,

    1. Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195 (USA)
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  • Prof. Ryan Sours,

    1. Department of Chemistry, Box 351700, University of Washington, Seattle, WA 98195 (USA)
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  • Dr. Elena Rosseeva,

    1. Max-Planck-Institut für Chemische Physik fester Stoffe, Nöthnitzer Strasse 40, 01187, Dresden (Germany)
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  • Prof. Bart Kahr

    Corresponding author
    1. Department of Chemistry, New York University, 100 Washington Square East, Room 1001, New York, NY 10003 (USA), Fax: (+1) 212-995-3884
    • Department of Chemistry, New York University, 100 Washington Square East, Room 1001, New York, NY 10003 (USA), Fax: (+1) 212-995-3884
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Abstract

Ferdinand Bernauer proposed in his monograph, “Gedrillte” Kristalle (1929), that a great number of simple, crystalline substances grow from solution or from the melt as polycrystalline spherulites with helically twisting radii that give rise to distinct bull′s-eye patterns of concentric optical bands between crossed polarizers. The idea that many common molecular crystals can be induced to grow as mesoscale helices is a remarkable proposition poorly grounded in theories of polycrystalline pattern formation. Recent reinvestigation of one of the systems Bernauer described revealed that rhythmic precipitation in the absence of helical twisting accounted for modulated optical properties [Gunn, E. et al. J. Am. Chem. Soc. 2006, 128, 14 234–14 235]. Herein, the Bernauer hypothesis is re-examined in detail for three substances described in “Gedrillte” Kristalle, potassium dichromate, hippuric acid, and tetraphenyl lead, using contemporary methods of analysis not available to Bernauer, including micro-focus X-ray diffraction, electron microscopy, and Mueller matrix imaging polarimetry. Potassium dichromate is shown to fall in the class of rhythmic precipitates of undistorted crystallites, while hippuric acid spherulites are well described as helical fibrils. Tetraphenyl lead spherulites grow by twisting and rhythmic precipitation. The behavior of tetraphenyl lead is likely typical of many substances in “Gedrillte” Kristalle. Rhythmic precipitation and helical twisting often coexist, complicating optical analyses and presenting Bernauer with difficulties in the characterization and classification of the objects of his interest.

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