Anionic-cationic surfactant mixture providing the electrically controlled homeotropic surface anchoring of liquid crystals

Abstract In search of a substance able to function as an anionic surfactant applied for the electrically-induced anchoring transitions in liquid crystals, the compound 4-heptyloxybenzoate benzyl dodecyldimethylammonium (HOBBDDA) has been synthesized. Its orienting influence on nematic liquid crystal 4-pentyl-4′-cyanobiphenyl (5CB) has been tested. HOBBDDA dissolved up to 1.4% in 5CB droplets dispersed in polymer film does not change the tangential surface anchoring inherent to polyvinyl alcohol matrix used. Homeotropic surface anchoring is realized if the HOBBDDA content exceeds 1.7%. The molecules of the surfactant in 5CB dissociate into anions and cations. The anions modify the surface anchoring under the action of DC electric field both in the normal and inverse mode. The mixture of HOBBDDA and cetyltrimethylammonium bromide can function as a binary ionic-cationic surfactant which significantly expands the prospects for using the ionic-surfactant method to control liquid crystal materials.