The marriage of electrostatics and hydrodynamics: simulating the dynamics of chargedcolloids

Abstract

Charged colloidal particles dispersed in a fluid solvent are omnipresent in nature: inks, paints and many other complex fluids known from everyday life typically consist of highly charged mesoscopic solutes. On the nanoscale, biomaterials such as proteins and DNA solutions represent further prominent candidates for exhibiting charged macromolecules. Furthermore, well-characterized suspensions of polystyrene microspheres are important model systems for studying the principles of phase transformations. A full calculation of the dynamical properties of charged suspensions is therefore important both for fundamental purposes and for many practical applications, e.g. in the rheology of paints. However, a realistic computer simulation of the dynamics of charged colloids is not straightforward since one has to tackle two problems simultaneously: • The strong Coulomb coupling between the highly charged colloidal particles (‘macroions’ or ‘polyions’) and their microscopic counterions left in the solution, which in turn screen the effective interactions between the macroions. This is mainly a problem of electrostatics together with appropriate thermostatistics. • The presence of hydrodynamic interactions mediated via the solvent when the macroions are moving.