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

Abstract

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 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.

Two-dimensional mixture of amphiphilic dimers and spheres: Self-assembly behaviour

“…(1). Overall, the results are similar to those found in three dimensions: 22 for T * = 0.10 (top panel), n(s) has gaps for large s at moderate concentrations, indicating a low propensity of the largest aggregates to add/lose particles. In particular, for χ = 50%, a broad maximum is visible for s ≈ 100, while the smaller the mean size of clusters, the more we deviate from equimolarity.…”

“…As a general setup, particles are initially distributed at random in the simulation box; then, after setting the reduced temperature T * ≡ k B T / at either 0.15 or 0.10, the MC simulation is started. In a previous study, 22 we had checked that using as initial condition the configuration obtained at the end of a slow cooling process from high temperature does not make any substantial difference in the structural properties of the ensuing steady state, even when the state probed is located inside a spinodal region. This is due to the fact that the simulated systems are overall dilute.…”

“…19,20 Recently, we have investigated by Monte Carlo simulation the low-temperature structure of a dilute mixture of dimers (made up of two spherical monomers of unequal size) and spheres. [21][22][23] In these studies, an additional attraction takes place between spheres and the small monomers. This model aims to represent, within an implicit-medium description, a colloidal dispersion made up of a guest species and an amphiphilic dimer where the small monomer is lyophobic and has a strong affinity for the guest.…”

Influence of Polymer Bidispersity on the Effective Particle–Particle Interactions in Polymer Nanocomposites

“…59 This circumstance sets the second virial coefficient as a suitable tool for quickly predicting the changes in the phase behavior of self-assembling systems. 60,61 The general definition of the second virial coefficient for a potential without an angular dependence can be written as: 62…”

Self-Assembled Structures of Colloidal Dimers and Disks on a Spherical Surface

“…Recently, we studied in 3D space [ 30 ] and on a plane [ 31 ] an implicit-solvent description of the dispersion of two colloidal species, namely, an amphiphilic dimer and a guest spherical/circular particle, where the smaller monomer in the dimer was solvophobic and had a strong affinity for the guest particle. In this paper, we consider the same system embedded in a spherical surface.…”