Helical graphite

Abstract

One-handed helical graphite films with a structure controlled by that of the original iodine-doped helical polyacetylene (H-PA) films were prepared using the recently developed morphology-retaining carbonization method. The fibrillar structure of the H-PA film remains unchanged even after carbonization at 800 °C. The weight loss of the film due to carbonization was very small; only 10–29% of the weight of the film before doping was lost. Furthermore, the graphite film prepared by subsequent heating at 2600 °C retained the same structure as that of the precursor films. The screw direction, degree of twist, and vertical or horizontal alignment of the helical graphite film were well controlled by changing the sense and pitch of the helix, and the orientation of the chiral nematic liquid crystal (N*-LC) used as an asymmetric LC reaction field. The important potential of these graphite films is exemplified in their electrical properties. The horizontally aligned helical graphite film exhibits an increase in electrical conductivity compared to the nonaligned one. The aligned helical graphite film also shows an electrical anisotropy in which conductivity parallel to the helical axis of the fibril bundle is higher than that perpendicular to the axis. [TANSO 2013 (No. 258) 201–9.]