Self-assembly behaviour of hetero-nuclear Janus dumbbells

We investigate the fluid structure and self-assembly of a system of Janus dumbbells by means of aggregation-volume-bias Monte Carlo simulations and Simulated Annealing techniques. In our approach, Janus dumbbells model asymmetric colloidal particles constituted by two tangent (touching) spheres (labelled as h and s) of different sizes and interaction properties: specifically, the h spheres interact with all other spheres belonging to different dumbbells via hard-sphere potentials, whereas two s spheres interact via a square-well potential. By introducing a parameter alpha is an element of [0,2] that controls the size ratio between the h and s spheres, we are able to investigate the overall phase behaviour of Janus dumbbells as a function of alpha. In a previous paper (O'Toole et al., Soft Matter, 2017, 13, 803) we focused on the region where the s sphere is larger than the h sphere (alpha > 1), documenting the presence of a variety of phase behaviours. Here we investigate a different regime of size ratios, predominantly where the hard sphere is larger than (or comparable to) the attractive one. Under these conditions, we observe the onset of many different self-assembled super-structures. Depending on the specific value of alpha we document the presence of spherical clusters (micelles) progressively evolving into more exotic structures including platelets, filaments, networks and percolating fluids, sponge structures and lamellar phases. We find no evidence of a gas-liquid phase separation for alpha <= 1.1, since under these conditions it is pre-empted by the development of self-assembled phases.