B. V. R. Tata

Interactions, structural ordering and phase transitions in colloidal dispersions

Abstract The structural ordering in colloidal dispersions is found to be very similar to that of atomic systems, such as crystalline solids, atomic liquids and even glasses. A number of intrinsic as well as extrinsic parameters influence the stability of colloids and induce transitions between different phases. It is the richness of the phase behavior that makes the colloids interesting also from the fundamental point of view. This article reviews the recent advances in the area of ordering and phase transitions brought about by parameters such as particle volume fraction, surface charge density, polydispersity, added electrolyte and external fields, such as shear, electric, magnetic and laser optical fields. Some of the recent experimental techniques that provide insight into the ordering phenomena are also covered. Microscopic investigations of suspensions under confined geometries and their implications on current understanding of the effective interparticle interaction are discussed. Finally, recent efforts in the direction of epitaxial growth of ordered structures on specially designed templates and their applications in synthesizing advanced materials are also briefly reviewed.

On RMSA description of liquid order in dilute charged colloidal suspensions

The principal purpose of this paper is to give an unambiguous test of the self-consistent mean field (SCMF) theory for a fluid of polarizable Lennard-Jones particles with dipoles and quadrupoles. The SCMF approximation replaces the many-body interactions present in polarizable fluids with an effective pair potential, and relates the properties of the system of interest to those of the effective system. In the present work the properties of the effective system are obtained using exact molecular dynamics (MD) calculations and the SCMF/MD results are compared with full MD simulations of the polarizable fluid. This procedure eliminates ambiguities present in previous calculations due to approximate theoretical treatments of the effective system, and provides a clear test of the SCMF reduction of the many-body potential. Also given is a general derivation of the SCMF result for the dielectric constant which is independent of the way in which the properties of the effective system are obtained. Finally, the ti...

Dynamic Light Scattering Studies in Silica/Ethylene Glycol Charged Colloidal System

Multiple scattering of light in colloidal suspensions can be suppressed by suspending the particles in a liquid with matching refractive index. We minimize the multiple scattering of light in charged silica suspensions by dispersing them in a mixed solvent of ethylene glycol/water (EGW). We report here the static and dynamic light scattering investigations carried out on these closely refractive index matched and deionised suspensions over a wide range of volume fractions (φ=0.0006–0.12). The suspensions are found to have a liquid-like order up to a volume fraction φ of 0.02 and a crystalline order beyond this φ value. A liquid-like ordered suspension with φ=0.04, when subjected to sudden compression by centrifugation, the suspension was found to freeze into a colloidal glassy state. The dynamics in liquid-like, crystalline and glassy states of these silica dispersions are analyzed and the results are compared with those reported for aqueous latex suspensions.

Order-disorder transition driven by random interactions

Abstract The role of random interactions in the disruption of crystalline order is investigated using a Monte Carlo (MC) simulation of charge polydisperse colloidal crystals. The static root-mean-square displacement of the equilibrium particle positions with respect to a reference lattice and the configurational entropy shows a jump across the order-disorder (crystalline-to-glass) transition. Lattice relaxations as a function of polydispersity are calculated analytically from a nearest neighbour model. The MC results are in good agreement with those predicted by the model.