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Proceedings Paper

Alignment and electrooptic effects in nanoparticle-doped nematic liquid crystals
Author(s): Brandy Kinkead; Martin Urbanski; Hao Qi; Heinz-S. Kitzerow; Torsten Hegmann
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Paper Abstract

It is well known that doping nematic liquid crystals with nanoparticles can alter the electrooptic response of the nematic host as well as the alignment of the liquid crystal molecules on various substrates. In addition, nanoparticles dispersed in a nematic matrix often induce defects and defect patterns justifying the necessity for more detailed optical and electrooptic investigations including effects of nanoparticle size, coating, concentration and core material. We studied the local alignment of nematic LC molecules in such dispersions by means of fluorescence confocal polarizing microscopy. The results of two- and three-dimensional imaging indicate that frequently observed birefringent stripes, which are induced by the presence of metal nanoparticles and semiconductor quantum dots, correspond to twist disclinations located at the LC/substrate interface. The luminescence of dispersed quantum dots shows that the ends of these disclination threads are pinned to conglomerates of nanoparticles that stabilize these line defects. By performing (x,z)-scans, it can be shown that the defects are not walls extending through the entire cell gap, but lines that are located at the substrate surface. Our experiments also confirm, as hypothesized before, that the nanoparticles preferably reside at the liquid crystal/substrate interfaces. Finally, detailed electrooptic investigations also revealed that a contrast inversion observed earlier is initiated by a change from parallel to homeotropic anchoring, thereby causing an instability, which in turn leads to the appearance of convection rolls (Kapustin-Williams domains). This electrohydrodynamic instability is likely an example for the behavior of (+, -) systems predicted by de Gennes, which was only recently experimentally observed for the first time.

Paper Details

Date Published: 18 August 2010
PDF: 11 pages
Proc. SPIE 7775, Liquid Crystals XIV, 77750C (18 August 2010); doi: 10.1117/12.858831
Show Author Affiliations
Brandy Kinkead, Univ. of Manitoba (Canada)
Martin Urbanski, Univ. of Paderborn (Germany)
Hao Qi, Univ. of Manitoba (Canada)
Heinz-S. Kitzerow, Univ. of Paderborn (Germany)
Torsten Hegmann, Univ. of Manitoba (Canada)


Published in SPIE Proceedings Vol. 7775:
Liquid Crystals XIV
Iam Choon Khoo, Editor(s)

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