Experimental Phase Diagram of Symmetric Binary Colloidal Mixtures with Opposite Charges

• Published in: The journal of physical chemistry. B Vol. 110; no. 26; pp. 13220 - 13226
• Main Authors: Romero-Cano, Manuel S, Caballero, José B, Puertas, Antonio M
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 06.07.2006
• Subjects: Colloids; Gels; Scattering, Radiation
• ISSN: 1520-6106; 1520-5207
• DOI: 10.1021/jp0607162

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.