Structural Characterization of Nematic Colloids at Liquid Crystal-Air Interfaces Prepared Via Photopolymerization

Research at the intersection of interfacial and colloidal science has led to the development of two-dimensional colloid assemblies applicable in systems ranging from photonics to microlithography. Traditionally, colloids must first be prepared through an independent synthesis step before being assembled using common techniques such as sedimentation or spin coating. However, by leveraging polymerization-induced phase separation and elastic interactions found in liquid crystal (LC) phases, we demonstrate the preparation of colloidal crystals at nematic LC-air interfaces by simultaneous photopolymerization and assembly. Polymer colloids are produced by polymerization-induced phase separation of 2-hydroxyethyl methacrylate in the non-reactive LC 4-cyano-4'-pentylbiphenyl (5CB) using an open-cell setup. Colloids adsorbed to the nematic 5CB-air interface form non-close-packed hexagonal crystals that cover the entire interface area. To analyze these structures, a set of MATLAB functions and scripts was developed that couples file management and image processing to quickly and efficiently quantify optical microscopy images of colloid assemblies. A wide range of metrics quantifying the positional and orientational order are calculated and visualized within generated figures to allow for easy data compilation and analysis. A comprehensive structural characterization of the colloid assemblies confirmed that field standards for positional and orientational order were achieved by this one-step fabrication process.