Colloidal dispersions and phase transitions in charged colloids

Abstract

Sterically stabilized as well as charge-stabilized colloidal dispersions mimic most of the phases of condensed matter and serve as excellent model systems to study the cooperative behaviour at micrometer length scales in equilibrium and non-equilibrium conditions. Charged-stabilized suspensions have the advantage of exhibiting structural ordering at much lower volume fractions as compared to sterically stabilized suspensions and is mainly due to the strong electrostatic interaction between the particles. The easy tunability of the interparticle interaction makes these systems ideally suited for studies of ordering phenomenon and the phase transitions under ambient conditions. Apart from novel applications of their ordered structures, it is the richness of the phase behaviour that makes the colloidal systems interesting from a fundamental point of view. Under certain conditions charge-stabilized suspensions are found to become inhomogeneous or undergo macroscopic phase separation. The underlying phase transitions have been identified. The phase separation phenomena observed in bulk suspensions of like-charged particles as well as microscopic investigations under confined geometries have generated considerable interest in reexamining the interparticle interaction in suspension of like-charged particles. This article reviews the structural ordering and phase transitions brought about by parameters such as particle volume fraction, surface charge density, salt concentration and polydispersity. In addition, the recent investigations of a two-dimensional system of charged large size metal balls, which has commonness with the charged colloidal system, are also discussed.