Light‐Responsive Nematic Colloids and Colloidal Crystals

Abstract

Rational control over the periodic arrangement of particles by means of external stimuli is a technologically important aspect of colloidal science with important physical underpinnings. Here, robust structural control of particle assemblies in a nematic liquid crystal (NLC) is demonstrated by dissolving trace amounts of light-responsive azo-dendrimer molecules, which spontaneously get adsorbed on the particle surface. The azo-dendrimer molecules in the presence of external UV irradiation undergo conformational change (trans-cis); as a result, they transmit the mechanical torque to surrounding LC molecules and alter the near-field director orientation. The director re-orientation at the surface of the particles causes topological defect transformation, which involves elastic dipoles, quadrupoles, and hexadecapoles. The defect transformation can be emulated in colloidal assemblies toward different purposes such as rotation of chains and restructuring of 2D colloidal crystals. In this study, various topological aspects of light-activated defect transformation and its application in the collective manipulation of colloidal assemblies are presented.