Reversible gels of patchy particles

In the last years a significant progress in the understanding of the aggregation properties of patchy colloidal particles and of the process of formation of equilibrium gels has taken place. We discuss here how the number of patches (a variable which can be experimentally controlled in current synthesis procedures) affects the equilibrium phase diagram and the relative stability against decomposition into two phases with different colloidal concentration, the analog of the gas-liquid phase separation in simple liquids. For small number of patches, the liquid phase exists as an equilibrium state down to small temperatures, giving rise to empty liquids and equilibrium gels. Finally, we discuss the connection between irreversible and reversible gelation in this class of colloidal systems proposing a conceptual link between elapsed time during the aggregation kinetics and temperature in thermodynamic equilibrium.