Selective encapsulation by Janus particles

Self-assembly of Janus disks confined in a slit

Using Monte Carlo simulations, we investigate the self-organization of Janus disks confined in two-dimensional slits. Janus particles are modeled as circles composed of attractive and repulsive parts. We consider the slits with identical walls and slits with competing walls (the so-called Janus-like pores). We investigate how the system morphology depends on the slit width, density, and temperature. Different unique orientationally ordered structures are found. The mechanism of formation of these structures is discussed in detail. We show that the anisotropic interactions between the confined molecules, the nature of the "walls," and the slit size strongly affect the self-organization.

Self-assembly in a model colloidal mixture of dimers and spherical particles

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 the 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 χ. For low χ (less than 10%), most guests are isolated and coated with a layer of dimers. As χ progressively increases, clusters grow in size becoming more and more elongated and polydisperse; after reaching a shallow maximum for χ≈50%, the size of clusters again reduces upon increasing χ further. In one case only (χ=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.

Encapsulation of spherical nanoparticles by colloidal dimers

We study by Monte Carlo simulation the coating process of colloidal dimers onto spherical nanoparticles. To this end we investigate a simplified mixture of hard spheres (the guest particles) and hard dimers formed by two tangent spheres of different sizes (the encapsulating agents) in an implicit-solvent representation; in our scheme, the range of effective interactions between the smaller particle in a dimer and a guest sphere depends on their relative size. By tuning the size and concentration of guests, under overall dilute conditions a rich phase behavior emerges: for small sizes and/or low concentrations, the preferred arrangement is compact aggregates (capsules) of variable sizes, where one or few guest particles are coated with dimers; for larger sizes and moderate guest concentrations, other scenarios are realized, including equilibrium separation between a guest-rich and a guest-poor phase. Our results serve as a framework for a more systematic investigation of self-assembled structures of functionalized dimers capable of encapsulating target particles, like for instance bioactive substances in a colloidal dispersion.