Monte Carlo study of structural ordering in charged colloids using a long-range attractive interaction

Abstract

Monte Carlo simulations have been carried out for aqueous charged colloidal suspensions interacting via an effective pair potential [Formula Presented] which has the long-range attractive term in addition to the usual screened Coulomb repulsion. Simulations are performed over four orders of magnitude of particle volume fractions [Formula Presented] under salt free as well as added salt conditions. The computed pair correlation functions [Formula Presented] at high values of [Formula Presented] show a face centered cubic (fcc) crystalline order, which is found to transform to a body centered cubic (bcc) crystalline order upon lowering of [Formula Presented] The crystalline order is found to melt into a liquidlike order upon the addition of salt. A purely repulsive potential based on Derjaguin-Landau-Vervey-Overbeek theory was earlier claimed to be responsible for the formation of bcc and fcc phases and the associated order-disorder transitions. It is clearly shown here that [Formula Presented] also explains equally well such phenomena and the results are shown to be in close agreement with experimental observations. Simulations in the dilute regime show a vapor-liquid transition upon variation of [Formula Presented] and the coexistence of ordered and disordered regions with voids upon variation of the charge on the particles. These results explain the reported experimental observations, which suggested the existence of a long-range attraction in the interparticle interaction. For very low volume fractions calculated pair correlation functions show only a single peak and are found to be independent of [Formula Presented] The reported results on the direct measurement of the pair potential are discussed in the light of the present results. © 1998 The American Physical Society.