Effective Interactions and Properties of Model Colloidal Suspensions Integral Equation Theory and Molecular Dynamics Simulation Study

Abstract

Colloidal suspensions of charged macroparticles dissolved in electrolyte solutions have received long time scientific interests. They are quite complex systems consisting of mesoscopic polyions (the colloid) and the microscopic solvent molecules and ions. Under most physical conditions, there exists a clear separation of time/length-scales between the microscopic degrees of freedom (such as solvent particles, counter/co-ions and salt etc.) and the mesoscopically sized colloidal particles. This poses significant challenges for theoretical investigation of colloidal suspensions; but makes them excellent model systems to study many phenomena in soft-condensed matter physics, such as melting, freezing and glass transitions, etc. In this work, we study the colloidal suspensions using the description of solvent-solvent, solvent-colloid and colloid-colloid correlations from the formalism of statistical thermodynamics of liquids and asymmetrical mixtures. Molecular dynamic simulations and Integral equation theories have been used to find the correlation functions. Formulae expressing properties in terms of correlation functions are well known. newlineChapter 1 introduces the importance and modelling of colloidal suspensions, basic statistical mechanics leading to pair correlation functions and property calculations, Integral Equation theory, Molecular Dynamics simulation, concept of effective pair potential etc. The gaps in existing research and objectives of this research work have also been discussed. newlineIn Chapter 2, we studied asymmetric binary fluid mixtures using molecular dynamics simulation. The asymmetries are either in particle size, charge, or mass alone and their combinations. Systematic variations in the pair correlation functions and different properties have been observed as a function of size, charge and mass asymmetry. As the size and/or charge increases, the pair correlation functions shift to larger inter-particle distances indicating increase in repulsion between particles. Both the energy as well as the pressu