Patterned Colloidal Photonic Domes and Balls Derived from Viscous Photocurable Suspensions

Abstract

Many-body colloidal systems have been studied intensively on account of their phase behavior and photonic characteristics. Direct visualization of colloids using optical microscopy makes it possible to analyze colloidal crystal structures with ease; this allows such systems to be used as ‘‘visible’’ models of atomic or molecular assemblies. The periodic modulation of the refractive index within a colloidal crystal induces photonic bandgaps at wavelengths comparable to the periodicity or lattice constant. Generally, colloidal crystals are prepared by the self-organization of colloidal particles, and therefore the photonic bandgap properties can readily be controlled by adjusting the size and concentration of the particles. More importantly, the fabrication of colloidal photonic crystals via self-organization is simple and cheap compared with the conventional lithography-based approach. However, evaporation-induced self-assembly, the most popular method for fabricating close-packed colloidal crystals, requires long times and subtle fabrication conditions, and inevitably produces crystals with cracks due to non-uniformities in the capillary force. Although dispersion of charged colloidal particles in an aqueous medium and subsequent infiltration of a non-ionic monomer can produce crack-free non-close packed crystals, this approach still requires complicated processes to achieve large scale production. Recently, we developed a novel and simple method for spontaneous crystallization of charged colloidal particles in a photocurable resin. In this method, the viscous suspension is brought into contact with a template and crystallization occurs, starting at the interface between the colloidal suspension and the template. More importantly, the high viscosity of the colloidal suspension and