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Abstract

Carbon nanotubes can be aligned by dispersing them in a liquid
crystalline matrix. To control and optimize the obtained alignment it
is important to understand the interactions between the molecules of
the liquid crystal host phase and the carbon nanotubes. To this end we
have carried out resonant Raman spectroscopy investigations of
dispersions of single-wall carbon nanotubes (SWCNTs) in a liquid
crystal coma pound comprising molecules with a biphenyl rigid core
structure. We detect a distinct wavenumber shift of the radial
breathing modes, confirming that the carbon nanotubes interact with the
surrounding liquid crystal molecules, most likely through aromatic
interactions (Ti-stacking). The interactions between liquid crystal
host and nanotube guests are also evident from a polarizing microscopy
study of the liquid crystal -isotropic phase transition in the
proximity of bundles of nanotubes. The ordered liquid crystal phase is
stable up to higher temperatures around the bundles than in areas
without visible signs of CNTs. Conversely, the transition from the
disordered isotropic phase to the liquid crystal phase on cooling
always nucleates at the carbon nanotube bundles. (c) 2006 WILEY-VCH
Verlag GmbH & Co. KGa.A, Weinheim.