1. S Chandrasekhar Liquid Crystals, (London: Cambridge University Press) (1975)
2. O M Abdul-Aziz, J R Abdul-Karim, A Mohammed and A O Karar J. Babylon University, Pure and Applied Sciences, 21 1764 (2013)
3. G W Gray, KJ Harrison and J A Nash Electron. Lett. 9 130 (1973)
4. B Bahadur, Liquid Crystal, Applications and Uses, 2nd edn. (Singapore: World Scientific Publishing Co. Pte. Ltd.), vol. 3 (1992)
5. H Kelker and B Scheurle Angew. Chem. Int. Ed. 8 884 (1969)