A numerical study of one-patch colloidal particles: from square-well to Janus

We perform numerical simulations of a simple model of one-patch colloidal particles toinvestigate: (i) the behavior of the gas-liquid phase diagram on moving from a sphericalattractive potential to a Janus potential and (ii) the collective structure of a system of Janusparticles. We show that, for the case where one of the two hemispheres is attractive andone is repulsive, the system organizes into a dispersion of orientationally ordered micellesand vesicles and, at low temperature (T), the system can be approximated as a fluid of suchclusters, interacting essentially via excluded volume. The stability of this cluster phasegenerates a very peculiar shape of the gas and liquid coexisting densities, with a gascoexistence density that increases on cooling, approaching the liquid coexistence densityat very low T.