Self-Assembled Colloidal Crystals: Visualizing Atomic Crystal Chemistry Using Microscopic Analogues of Inorganic Solids

Abstract

Monodisperse spherical colloids spontaneously crystallize into close-packed crystals, in analogy to the simple crystal structures of many of the elements. Since colloids are orders of magnitude larger than atoms, students can directly observe crystal structure and behavior in a microscope using colloidal crystals. This laboratory exercise provides a modular series of materials science experiments appropriate for undergraduate chemistry and engineering majors. The individual modules include aspects of chemical synthesis (monodisperse SiO2 and polymer spheres), self-assembly (colloidal crystallization), and structural characterization through microscopy (optical and scanning electron microscopies) and optical spectroscopy (optical diffraction and UV–visible spectroscopy). Using these experiments, students learn new inorganic and organic synthetic techniques, study crystal behavior (e.g., coordination, defects, close-packing) in model systems, and apply optical characterization techniques to the analysis of their materials. The experiments can easily be tailored to the desired level of complexity and instrumental availability.