MOLECULAR-DYNAMICS SIMULATIONS FOR CHARGED COLLOIDAL DISPERSIONS

Salt-free charged colloidal dispersions are studied by molecular-dynamics simulations based on the primitive model. The system consists of macro ions and counter ions. The counter ions are treated with the continuous density distribution obtained by the Poisson-Boltzmann equation for a given configuration of the macro ions. The macro ions are evolved in time through interaction with the counter ion distribution. Simulations are done for a micellar solution and a latex dispersion. For the latter system, the radius and the volume fraction are set to 160 angstrom and 0.04, respectively, and the colloidal charge Z0 is varied from 50 to 400. Then the height of the first peak of the structure factor, S(k(max)), is plotted as a function of colloidal charge. When this is extrapolated, it becomes much larger than the experimental result from small-angle neutron scattering at Z0 = 850. The S(k(max)) of the simulation is also compared with that arising from the one component system with the Derjaguin-Landau-Verwey-Overweek (DLVO) potential. The results of the one component system are larger than that of the two component system. However, when the charge and another parameters in the DLVO potential are renormalized, the results of the one-component system become comparable to that of the two-component system.