Order-disorder transition in colloidal suspensions

Abstract

The disorder-order transition observed in aqueous suspension of charged macroions is investigated with use of both simulations and a simple theoretical model. Molecular-dynamics (MD) simulations were performed by assuming that the interaction between the charge stabilized particles interact via a modified Debye-H\"uckel potential. The parameters of the potential were chosen to mimic the experimental study of Lindsay and Chaikin. Simulation results predict that the liquid freezes into a bcc phase in accord with the experimental findings. For comparison, the phase diagram with use of the self-consistent phonon theory (SCP) is presented. It is shown that the predictions of the SCP theory in the weak screening limit are in disagreement with both the MD results and the experiments. Possible reasons for this failure are pointed out. Finally, similar calculations have been carried out for the Yukawa potential. It is found that for the parameters considered here, this is an unphysical model for the suspensions of polystyrene spheres. No evidence for reentrant transitions is found in either of these models. This is in agreement with the predictions of the self-consistent phonon theory.