Density and refractive index measurements in hexaheptyloxytriphenylene, a discotic liquid crystal

Density and refractive index measurements in the discotic liquid crystal hexaheptyloxytriphenylene were performed in the hexagonal columnar Colho and isotropic I phases. The temperature dependence of the density ρ(T) for this compound was obtained by combining small angle X-ray data and capillary methods. The ordinary n o extraordinary n e and isotropic liquid n i refractive indices were measured using a modified Abbe refractometer to an accuracy of about 10−3. To check the consistency of the density and the refractometry experiments we used the Lorentz–Lorenz relation. An anomaly in the empirical relationship at the Colho–I phase transition, which holds for many uniaxial liquid crystals, was detected. A discrepancy between low birefringence Δn∼0.109 and a relatively high local electric field anisotropy for hexaheptyloxytriphenylene is discussed.