We study the kinetics of the liquid-to-crystal transformation and of gel formation in colloidal suspensions of oppositely charged particles. We analyse, by means of both computer simulations and experiments, the evolution of a fluid quenched to a state point of the phase diagram where the most stable state is either a homogeneous crystalline solid or a solid phase in contact with a dilute gas. On the one hand, at high temperatures and high packing fractions, close to a substitutionally-ordered/substitutionally-disordered solid-solid coexistence line, we find that the fluid-to-crystal pathway does not follow the minimum free energy route. On the other hand, a quench to a state point far from the substitutionally-ordered/ substitutionally-disordered crystal coexistence border is followed by a fluid-to-solid transition through the minimum free energy pathway. At low temperatures and packing fractions we observe that the system undergoes a gas–liquid spinodal decomposition that, at some point, stops, giving rise to a gel-like structure. Both our simulations and experiments suggest that increasing the interaction range favours crystallization over vitrification in gel-like structures.

J. Phys.: Condens. Matter

Sanz, E., Valeriani, C., Vissers, T., Fortini, A., Leunissen, M. E., van Blaaderen, A., … Dijkstra, M. (2008). Out-of-equilibrium processes in suspensions of oppositely charged colloids : liquid-to-crystal nucleation and gel formation. J. Phys.: Condens. Matter, 20(49, Article number: 494247), 1–10. doi:10.1088/0953-8984/20/49/494247