Bernauer's bands

Alexander Shtukenberg, Erica Gunn, Massimo Gazzano, John Freudenthal, Eric Camp, Ryan Sours, Elena Rosseeva, Bart Kahr

Research output: Contribution to journalArticlepeer-review

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 bulls-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, 14234-14235]. 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. Twisted crystals: Ferdinand Bernauer proposed in "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 concentric optical bands between crossed polarizers (see picture). In fact, 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.

Original languageEnglish (US)
Pages (from-to)1558-1571
Number of pages14
JournalChemPhysChem
Volume12
Issue number8
DOIs
StatePublished - Jun 6 2011

Keywords

  • crystal growth
  • crystal twisting
  • linear birefringence
  • mesocrystallography
  • spherulites

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics
  • Physical and Theoretical Chemistry

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