Junpei Yamanaka

5 – Colloidal Crystals

Submicron-sized colloidal particles dispersed in a liquid medium self-assemble to form ordered “crystal” structures in which the particles are regularly arranged in body-centered or face-centered cubic lattice structures. Colloidal crystals have been useful models for studying crystallization in general. They have also attracted considerable attention as novel materials. In this chapter, we describe the physical basis and experimental studies of colloidal crystallization, in particular those of charged colloids. We first present a general introduction to the physical background on the stability and interaction of colloids. Then we report our studies on the crystallization of charged colloids, including charge-induced crystallization, unidirectional crystallization, gel immobilization, and exclusion of impurities. Finally, we review recent research topics in this field, including those on opal crystals and complex structures.

Unidirectional crystallization of charged colloids

Submicron-sized colloidal particles dispersed in liquid medium self-assemble into ordered crystal structures, where the particles are regularly arranged in the body-centered-or face-centered-cubic lattice symmetries. Because of large sizes and long characteristic times of the colloidal particles relative to atoms, the colloidal crystallization has been a useful model to study the phase behavior of atomic systems in general. In addition, since the Bragg wavelengths of the colloidal crystals usually lie in visible light regime, the colloidal crystals have attracted considerable attention as novel photonic materials. Here we report the charge-induced crystallizations, unidirectional crystallizations under gradients of pH and temperature, and gel immobilizations of the charged colloidal crystals.