Preparation of spherical colloidal crystals by spray drying

Abstract

In this study, evaporation-induced self-assembly method was used to prepare spherical colloidal crystals. Firstly, we prepared three-dimensionally ordered macroporous spherical particles by using polymer assemblies as templates and inorganic materials as matrix. Compared to the available methods that are typically complex and time consuming, the present aerosol-assisted self-assembly, is simple and operates very fast. Our experimental system consisted of a droplet generator, temperature controlled reactor and filter. In a part of the reactor, water evaporated from a droplet and then the nanoparticles of silica/titania and polystyrene (PS) beads of a few hundred nanometers inside of the drop were consolidated into into composite particles. Then, PS particles were removed in the remaining part of the reactor. There was an optimum condition to obtain the well-ordered arrangement of pores both on the surface and inside of the spherical microstructured particle. The size of macropores was proportional to the PS latex particle size, therefore we could control the pore size. Secondly, we prepared three-dimensionally ordered spherical colloidal crystals from PS beads in the size range of 200nm-350nm. We generated uniform PS colloid droplets by electrohydrodynamic atomization (EHDA) under D.C. electric field. And then, the droplets turned into colloidal crystals by evaporation-induced self-assembly in confined geometry. Our crystals were micron-sized colloidal assemblies with narrow size distribution and an ordered surface and internal structures that consisted of close packed monodisperse latex particles. The droplet shape and size were measured by optical microscope and the structures of their dried particles were observed by scanning electron microscope. The PS colloidal crystal suspension displayed different colors according to the incident angles of light.