Molecular dynamics study of homogeneous and inhomogeneous phase in charged colloids: The influence of surface charge density

Abstract

h i g h l i g h t s• Investigate the dynamic process of crystallization and voids formation in charged colloids.• Influence of surface charge density on homogeneous to inhomogeneous phase transition.• Finite size effects on the phase behavior of charged colloids.• Show that Sogami and Ise theory cannot explain the reentrant transition of highly charged colloidal systems. Compared with previous Mote Carlo (MC) simulations with 432 particles, molecular dynamics (MD) simulations with much larger number of particles have been carried out to investigate the dynamic process of the structural ordering and voids formation in charge stabilized colloidal suspensions. Sogami and Ise (SI) potential which has a long-range attraction is used to represent the interaction between colloidal particles. As increasing the surface charge density on the colloidal particles, the data obtained from the simulations, such as the crystallization, bcc-fcc phase transition, homogeneous to inhomogeneous transition and the voids formation, are in agreement with previous observations of MC simulations and experiments. The effects of particle number used in the simulations are studied in detail. MD simulations in highly charged colloidal system with small sizes show very few crystallized particles, in accord with the results of MC simulations. However, the structure in the system with larger number of particles is always the voids coexisting crystallites instead of a glasslike or disordered inhomogeneous phase, indicating that the glasslike or disordered phase region obtained at very high charge density in small system is an artifact produced by very limited number of particles used in the simulations. Therefore, SI potential is not applicable for explaining the reentrant transition of highly charged colloidal systems.

Polymorph selection and nucleation pathway in the crystallization of Hertzian spheres

“…So far, most studies of crystallization have focused on systems with hard divergent repulsions at a short distance. These systems include the simplest and well-known hard spheres [14,17,18], the Lennard-Jones model [6][7][8], chargestabilized colloids which have repulsive Yukawa interactions [5,[22][23][24][25], etc. On the contrary, there are some systems consisting of soft particles whose interactions are even core softened, e.g., emulsions, soft colloids, microgels, many macromolecules, and their self-assembled entities.…”

Effect of void structures in crystalline structure on the shear moduli of charged colloidal crystals

“…For instance, it was shown [24] that in the bcc-fcc transition process of colloidal crystallization, the shear moduli are much smaller than theoretical expectations and this can be chalked up to crystalline imperfection due to not-well-equilibrated structure during the transition state. Another example demonstrating the structural imperfection is that there exist some void structures in the crystal region of crystals formed by highly-charged colloidal suspensions [12,13,23].…”

“…Previous study [13,25] shows that there is structural imperfection of voids and also Sogami-Ise (SI) interaction potential is more suitable than Yukawa potential for colloidal crystals of highly-charged particles. In this study these two factors were taken into account as modifications to the shear moduluspotential model.…”

“…In this respect the elasticity of the colloidal crystals has been studied in recent years both experimentally and theoretically [10][11][12][13][14]. Experimentally, shear elastic moduli of the colloidal crystals are usually measured through the method of torsional resonance spectroscopy (TRS) in which standing waves are excited when rotary oscillations are imposed on the colloidal crystals [15][16][17].…”