Aggregation of colloidal spheres mediated by Janus dimers: A Monte Carlo study

We investigate by Monte Carlo simulation the structure and self-assembly of a mixture formed by asymmetric dimers and larger spherical particles. In our model, dimers and spheres interact through a monomer-specific short-range attraction, in addition to hard-core repulsion. The interaction parameters are chosen so as to mimic features of real colloidal mixtures. We find that the dilute mixture at low temperature is characterized by the onset of aggregates of spheres held together by dimers. In particular, when the sphere concentration is sufficiently high, the system stays homogeneous; at intermediate concentrations, very small clusters of spheres coexist with a few lamellar aggregates; finally, for even lower concentrations a single droplet eventually forms. Upon increasing the density, a sponge-like structure emerges for not too high concentrations. If the attraction between dimers and spheres is switched off, leaving only depletion forces to act, neither phase separation nor demixing are found.