LETTER TO THE EDITOR: Fluid particle dynamics simulation of charged colloidal suspensions

An ew method of simulation of the dynamics of charged colloidal suspensions is formulated that is based on the fluid particle dynamics method (Tanaka and Araki 2000 Phys. Rev .L ett. 85 1338) so as to incorporate the electrohydrodynamic interactions properly. The fluid particle approximation allows us to treat dynamic coupling among motions of the three relevant elements of charged colloidal suspensions, i.e., colloidal particles, ion clouds, and liquid, in a physically natura lm anner. The validity of our method is demonstrated for a problem of the electrophoretic deposition of charged colloids. Our simulation results clearly indicate that the electro-osmotic flow causes ‘effective’ long-range attractions between charged particles of the same sign, as previously suggested by experiments and theories. Liquid suspensions containing colloids are of fundamental importance in soft matter physics, surface chemistry, biology, and industry [1–3]. In colloidal suspensions, charges play key roles in stabilizing the dispersions and also in electrically manipulating suspended particles. It is also widely known that they affect various kinetic phenomena of colloidal suspensions, such as sedimentation, rheology, and electrophoresis. When one tries to study the dynamics of charged colloidal suspensions either theoretically or numerically, the most difficult problem arises from the complex dynamic coupling among motions of the three key elements; that is ,c olloidal particles, ions, and liquid molecules. These elements are strongly interacting with each other via both electrostatic and hydrodynamic interactions. Since these static and dynamic interactions are both of long-range nature, we must inevitably deal with a very complex dynamic many-body problem. Because of these difficulties, there have so far been neither theoretical nor numerical studies that take into account the full static and dynamic coupling among the motions of these three key elements of colloidal suspensions, despite the scientific