Charge and Salt Driven Reentrant Order-Disorder and Gas-Solid Transitions in Charged Colloids

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Monte Carlo simulations have been performed for aqueous charged colloidal suspensions as a function of charge density on the particles and salt concentration. We vary the charge density in our simulations over a range where a reentrant solid-liquid transition in suspensions of silica and polymer latex particles has been reported by Yamanaka et al. [Phys. Rev. Lett. 80 5806 (1998)]. We show that at low ionic strengths a homogeneous liquid-like ordered suspension undergoes crystallization upon increasing charge density. Further increase in charge density resulted once again a disordered state which is in agreement with experimental observations. In addition to this reentrant order-disorder transition, we observe an inhomogeneous to homogeneous transition in our simulations when salt is added to the disordered inhomogeneous state. This inhomogeneous to homogeneous disordered transition is analogous to the solid-gas transition of atomic systems and has not yet been observed in charged colloids. The reported experimental observations on charged colloidal suspensions are discussed in the light of present simulation results.