An Advanced Method for Preparation of Helical Carbon and Graphitic Films Using a Carbonization Substrate

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 degrees C, respectively.