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

Abstract

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.

Conjugated polymer-based carbonaceous films as binder-free carbon electrodes in supercapacitors

“…The carbonization precursor films can also be directly synthesized by using a very simple electrochemical polymerization procedure with a short reaction time of 1 h. Moreover, we have recently developed to produce carbonaceous and graphitic materials with hierarchical helical morphologies or highly aligned structures from electrochemically synthesized or solid-state polymerized PEDOT materials. 13,20 We believe that the capacities are expected to be more enhanced than the present carbonaceous films by using the morphology-controlled carbon materials as supercapacitor electrodes owing to their ordered structures. This morphological controllability for the PEDOT-based carbon materials is also a superior point for the development of advanced supercapacitor electrodes.…”

“…We have recently discussed that the degree of crystallinity of the graphitic film prepared from a perchlorate ion (ClO 4 − )-doped PEDOT film up to 2600 °C is higher than that prepared from an undoped PEDOT film. 13 Since a highly crystalline carbon film usually has high electrical conductivity, the ClO 4 − -doped PEDOT film was used as a carbonization precursor polymer film in the present study. The amount of doped ClO 4 − in the PEDOT film was determined by using elemental analysis: C, 40.38; H, 2.75; S, 18.06; and Cl, 5.53.…”

“…We have recently prepared a variety of morphology-controlled carbonaceous and graphitic films from various conjugated polymers, such as polythiophene derivatives, 13 polyacetylenes (PAs), 14–17 and polyphenylene derivatives. 18 In particular, freestanding carbonaceous films have been prepared from poly(3,4-ethylenedioxythiophene) (PEDOT) and PA films that have been synthesized through electrochemical and interfacial chemical polymerization methods in an isotropic solvent, respectively.…”

“… 18 In particular, freestanding carbonaceous films have been prepared from poly(3,4-ethylenedioxythiophene) (PEDOT) and PA films that have been synthesized through electrochemical and interfacial chemical polymerization methods in an isotropic solvent, respectively. 13–16 The PEDOT film with hierarchical porous morphology can be directly obtained via the oxidative polymerization of EDOT as a monomer on an anode surface. In contrast, the interfacial polymerization method affords a PA film with a random fibril morphology.…”

Photoinvertible Chiral Liquid Crystal that Affords Helicity‐Controlled Aromatic Conjugated Polymers

“…In fact, helical PEDOT (H‐PEDOT) is useful as a carbonization precursor for helical carbon and graphite bearing spiral morphology. [ 11,48 ] We previously reported the synthesis of H‐PEDOT by electrochemical polymerization of EDOT in N*‐LCs or LC‐based ionic liquids that include ordinary chiral compounds. [ 11,48–50 ] However, two types of chiral compounds with opposite helicity were needed because these chiral compounds had neither thermally invertible nor photoinvertible helical senses.…”