Dynamics of Nanoparticles Assembly at the Interface of a Nematic Liquid Crystal Droplet

Abstract

Up-to-date technological applications of liquid crystal (LC)-based devices have relied on the nematic LC materials in the form of drops or emulsions stabilized by surfactants. Adsorption of nanoparticles at liquid interfaces results in emulsions with exceptional stability. Adsorption of nanoparticles at nematic liquid crystal interfaces provides an alternative promising approach to stabilize nematic emulsions or drops. Improved understanding of the dynamics of the adsorption process of nanoparticles at the nematic LC-water interface is important not only due to its technological significance, but also of interest for the fundamental understanding of non-uniform, ordered fluids. In this work, the dynamic adsorption process of ethyl-cellulose (EC) (with an average radius of 44nm) nanoparticles at the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB) interface is studied by measuring dynamic interfacial tension with the use of a pendant drop tensiometer. Analysis of the dynamic interfacial tension in terms of a model developed by Bizmark et al. (2014) provides information on the adsorption energy of EC nanoparticles that is compared to the adsorption energy values obtained from two other approaches. We conclude that Bizmark’s model for the irreversible adsorption is valid for EC nanoparticle at the isotropic fluid interfaces and also can be applied to study the adsorption of nanoparticles at a nematic liquid crystal interface. Additionally, a model is derived to approximately probe the transient surface (interface) coverage of nanoparticles adsorbed at LC-water interface. Polarized microscopy analysis of 5CB confined between two EC-treated glass substrates confirms that adsorption of EC nanoparticles has no effect on the alignment of 5CB molecules at the interface.