SURFACTANT INDUCED INTERFACIAL ANCHORING TRANSITIONS IN NEMATIC LIQUID CRYSTAL DROPLETS ON GLASS SURFACES

The interfacial adsorption of surfactants at planar nematic liquid crystal (NLC)–water interface induces an ordering transition from a tilted to perpendicular anchoring with the increase in surfactant concentration at [Formula: see text], where [Formula: see text] is the Critical Micelle Concentration of surfactants in water. In this study, we show that depending upon the surfactant structure a tilted to perpendicular NLC anchoring transition is observed at [Formula: see text] in 5CB droplets of size 50–70[Formula: see text][Formula: see text]m. Micrometer sized 5CB droplets are deposited on glass surfaces using flow coating of 5CB-in-ethanol solutions. When placed on 5CB drop decorated glass surfaces, the aqueous surfactant solutions of aliphatic chain surfactants (SDS, CTAB and CPBr) at [Formula: see text], result in an optical transition to a bright-cross texture attributed to the tilted anchoring of 5CB molecules at 5CB–water interface. At [Formula: see text], perpendicular anchoring of 5CB molecules at 5CB–water interface results in a droplet texture with a hedgehog defect. In contrast, aqueous solutions of SDBS lead to 5CB droplets with a bright-cross texture regardless of the surfactant concentration in the aqueous phase. These results indicate that the orientation of 5CB molecules is independent of the nature of the surfactant headgroup. In addition, 5CB droplet decorated OTS treated glass substrates show a hedgehog texture which disappears completely on exposure to organic vapors with the response time-dependent on the polarity of the vapor molecules.