Nematic liquid crystal micro-droplets on solid surfaces and their ordering transition in bulk aqueous solution

Abstract

Here, we report the establishment of an experimental system based on liquid crystal (LC) micro-droplets on solid surfaces. These micrometre-sized LC droplets were formed by the dispersion of 0.5% (v/v) 4-cyano-4'-pentylbiphenyl (5CB) dissolved in n-heptane onto an octadecyltrichlorosilane (OTS)-treated glass. Polarised microscopy revealed a dandelion shape or a double-rod shape when LC micro-droplets were immersed in 4mm in the depth of non-surfactant solution, while distinct diamond-shaped textures were obtained when contacted with the bulk surfactant solution. Different types of optical textures were observed due to various configurations of the local director n. In non-surfactant solution, a parallel configuration led to a bright white-coloured dandelion shape or double-rod shape, while in surfactant solution the colourful diamond-shaped textures were caused by normal configuration. The unprecedented observations we report in this paper will lead to further insight into the properties of sessile LC micro-droplets on solid surfaces. The experimental system established in this paper can be broadly applied to report the liquid-liquid interfacial phenomena, and provide important guidance to the design of surface-anchored LC micro-droplets as chemo-responsive materials for use in optical sensors.