The optical properties of carbonaceous mesophase

• Published in: Carbon (New York) 1990, Vol.28 (1), p.85-90
• Main Authors: Chuvyrov, A.N, Lebedev, Y.A, Cornilov, V.M
• Format: Article
• Language: English
• Subjects: mesophase; Optical microscopy
• ISSN: 0008-6223; 1873-3891
• DOI: 10.1016/0008-6223(90)90097-I

The optical constants of carbonaceous mesophase and anisotropic carbons from petroleum-derived pitches have been measured over a wide range of wavelengths and heat-treatment temperatures by interferometry and by reflected and transmitted spectrophotometry. The optical properties differ substantially from those of conventional nematic liquid crystals. The intrinsic birefringence Δn measured by polarized interferometry is only 0.02–0.03 and depends weakly on wavelength; the anisotropy of absorption coefficients is of the order of ~0.1 with k ⊥ = 0.03 and k ⊥ = 0.10 ( at T HT = 450° C) and has strong wavelength dependence with a maximum at 560–590 nm (symbols∥ and ⊥ denote that the electric vector of the incident light lies along the optical axis, or perpendicular to it, respectively). The anisotropy of reflectivities ΔR at normal incidence is of the order of ~0.1 with R ⊥ = 0.13 and R ∥ = 0.04 (at T HT = 450° C); ΔR increases with increasing temperature of heat-treatment. To explain the features of optical properties, a theory of light reflection is developed based on a model of carbonaceous mesophase that consists of graphite-like disc-shaped particles having a nematic-like packing. From the reflectivity values the dimensions and the concentration of these particles have been evaluated. The nature and formation of carbonaceous liquid crystals are discussed.