Colloidal Self-Assembly Under Electric Field

Colloidal systems are analogous to atomic systems in exhibiting phase transitions between gas, liquid and solid phases. Therefore, they are widely employed as model systems in studying phase transitions. The advantage of colloidal model systems is that colloidal particles can be investigated at single particle level with a light microscope, which is more challenging to realize in atomic systems. Moreover, crystalline structures obtained through colloidal crystallization or colloidal self-assembly have potential applications in photonic crystals, drug delivery and energy storage. In order to control colloidal crystallization and colloidal self-assembly, it is critical to tailor the interactions between colloidal particles. In this study, we control colloidal interactions through applying an alternating electric field on charged colloidal particles and then study the kinetics of colloidal self-assembly under different conditions. Structures including chains, sheets and body-centered tetragonal structures are formed. It’s found that both the strength and the frequency of electric field have effect on the self-assembly. In addition, we observe a nucleation process that cannot be described by the classical nucleation theory. In a two-dimensional colloidal system with competing long-range repulsion and short-range attraction, chains are formed first in nucleation, and then the chains fold into square structures. In addition, when applying the electric field on an existing three-dimensional face-centered cubic(FCC) structure, a solid-solid transition is induced. As the first step of the solid-solid phase transition, the FCC crystal melts into an amorphous liquid state. From which, body-centered tetragonal structure is nucleated and formed.