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.