title: Experimental phase diagram of symmetric binary colloidal mixtures with opposite charges.
abstract: The phase behavior of equimolar mixtures of oppositely charged colloidal systems with similar absolute charges is studied experimentally as a function of the salt concentration in the system and the colloid volume fraction. As the salt concentration increases, fluids of irreversible clusters, gels, liquid-gas coexistence, and finally, homogeneous fluids, are observed. Previous simulations of similar mixtures of Derjaguin-Landau-Verwey-Overbeek (DLVO) particles indeed showed the transition from homogeneous fluids to liquid-gas separation, but also predicted a reentrant fluid phase at low salt concentrations, which is not found in the experiments. Possibly, the fluid of clusters could be caused by a nonergodicity transition responsible for the gel phase in the reentrant fluid phase. Liquid-gas separation takes a delay time after the sample is prepared, whereas gels collapse from the beginning. The density of the liquid in coexistence with a vapor phase depends linearly on the overall colloid density of the system. The vapor, on the other hand, is comprised of equilibrium clusters, as expected from the simulations.
authors.affiliation: Group of Complex Fluids Physics, Department of Applied Physics, University of Almería, 04120 Almería, Spain.
authors.forename: Manuel S
authors.initials: MS
authors.lastname: Romero-Cano
authors.forename: José B
authors.initials: JB
authors.lastname: Caballero
authors.forename: Antonio M
authors.initials: AM
authors.lastname: Puertas
mesh_terms: D003102:Colloids; D005782:Gels; D012542:Scattering, Radiation
chemical_list: D003102:Colloids; D005782:Gels