Properties of a Thermotropic Nematic Liquid Crystal Doped with Graphene Oxide

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Graphene oxide (GO) nanoparticles of two different sizes are dispersed in
the nematic liquid crystal (LC) 5CB covering a wide concentration range. The
dielectric properties, as well as the electrooptic behavior, including threshold
voltage, elastic constant, and response times are investigated as a function
of GO concentration. It is found that small graphene oxide flakes of mean
size of 560 nm are better and easier dispersible than larger flakes of 2.8 μm
mean size. The nematic–isotropic transition only increases slightly for the
(GO+LC) hybrid systems. For increasing GO concentrations the threshold
voltage and splay elastic constant dramatically increase, until saturation for
a concentration of ≈1% by weight GO. The field driven switching-on time is
practically independent of concentration, while the switching-off time, which
is purely elastically driven, exhibits a strongly decreasing behavior. Dielectric
spectroscopy reveals a noncollective relaxation which is absent in the neat
liquid crystal. This may be attributed to a drastically slowed down molecular
relaxation related to the rotation around the short axis of the liquid crystal
molecules. When heating the thermotropic liquid crystal into its isotropic
phase, the latter acts as a solvent for the GO particles, and a lyotropic
nematic phase with largely reduced birefringence is formed.

Bibliographical metadata

Original languageEnglish
Pages (from-to)1541-1548
Number of pages8
JournalAdvanced Optical Materials
Issue number10
Early online date15 Jun 2016
Publication statusPublished - Oct 2016

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