An
advanced method is proposed to prepare helical graphite films
with large domains of left- and right-handed spiral morphologies which
are composed of fibril bundles using oxidized PEDOT films as carbonization
substrates. Helical PEDOT (H-PEDOT) films, as carbonization precursors,
are prepared via an electrochemical polymerization in an asymmetric
reaction solution containing the chiral nematic liquid crystal (N*-LC),
the monomer bis-EDOT, and an electrolyte. The N*-LCs are provided
by mixing a spot of di- or tetra-substituted, axially chiral, binaphthyl
compounds as the chiral dopants with the N-LC. In addition, a new
type of chiral dopant bearing a cyanobiphenyl moiety, which is the
same mesogenic core as that of the parent LC [4-cyano-4′-pentylbiphenyl],
is used for preparing high miscible N*-LC systems. The distances between
the fibril bundles of H-PEDOTs specifically depend on the helical
twisting powers of the chiral dopants. In circular dichroism spectra,
the H-PEDOTs in both neutral and oxidized states exhibit clear Cotton
effects. In the preparation of the helical graphite films, substrates
such as quartz and carbon plates cannot retain the spiral morphologies
because of the substantial difference in the thermal shrinkage between
the substrate and precursor. The oxidized PEDOT film used as a promising
carbonization substrate has almost the same thermal shrinkage as the
H-PEDOT film, which allows for a reduction in the deformation due
to thermal shrinkage during the heat treatment. As a result, helical
carbon and graphite films which have distinguished spiral morphologies
are obtained via heat treatment at 800 and 2600 °C, respectively.