  We investigate the structure of a dilute mixture of amphiphilic dimers and
spherical particles, a model relevant to the problem of encapsulating globular
"guest" molecules in a dispersion. Dimers and spheres are taken to be hard
particles, with an additional attraction between spheres and the smaller
monomers in a dimer. Using Monte Carlo simulation, we document the
low-temperature formation of aggregates of guests (clusters) held together by
dimers, whose typical size and shape depend on the guest concentration $\chi$.
For low $\chi$ (less than $10\%$), most guests are isolated and coated with a
layer of dimers. As $\chi$ progressively increases, clusters grow in size
becoming more and more elongated and polydisperse; after reaching a shallow
maximum for $\chi\approx 50\%$, the size of clusters again reduces upon
increasing $\chi$ further. In one case only ($\chi=50\%$ and moderately low
temperature) the mixture relaxed to a fluid of lamellae, suggesting that in
this case clusters are metastable with respect to crystal-vapor separation. On
heating, clusters shrink until eventually the system becomes homogeneous on all
scales. On the other hand, as the mixture is made denser and denser at low
temperature, clusters get increasingly larger until a percolating network is
formed.
