Encapsulation of spherical nanoparticles by colloidal dimers

Abstract

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.

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

“…In our system, a dimer is modeled as a pair of tangent hard spheres with different diameters, σ 1 and σ 2 . We hereafter assume a fixed size ratio σ 2 /σ 1 of 3, which ensures that the dimers effectively isolate the guest from the solution in those cases where capsules form [33].…”

“…In this paper we explore by Monte Carlo simulation the self-assembly of the same mixture studied in Ref. [33], allowing the overall density and the sphere concentration to span over a wider range than previously considered. In the present analysis, the sphere size is fixed to that of the large monomers.…”

“…Interestingly, a wide variety of patterns is also observed in simpler systems of Janus dimers [18][19][20][21][22][23][24][25][26][27], i.e., heterodimers where one monomer is lyophilic and the other one is lyophobic. In essence, Janus dimers represent the "molecular" analogue of Janus spheres [28-31]; like their "atomic" counterparts, Janus dimers are able to organize into various super-structures, such as micelles and bilayers, as well as to separate into vapor and liquid [32].Very recently, we have proposed heteronuclear dimers as encapsulating agents for spherical particles [33]. Aside from its fundamental interest, the reversible formation of capsules [34,35] around a dissolved target species ("guest") is an issue of growing importance in the pharmaceutical field, where it finds application in drug delivery [36][37][38], and for food industry as well, as a tool to improve the delivery of bioactive substances into foods [39,40].In our model [33], a dimer consists of a pair of tangent hard spheres of different size, with an additional square-well attraction between small monomers and spheres.…”

Depletion-Induced Encapsulation by Dumbbell-Shaped Patchy Colloids Stabilize Microspheres against Aggregation

“…Patchy model systems for the formation of empty virus capsids 2−5 and the assembly of virus capsids around a core particle 6 have been studied in theory and simulations. Recently, Munaò et al 7 presented simulations of the encapsulation of spherical particles by Janus dumbbells. However, this paper provides a first experimental investigation of encapsulating a spherical template particle by patchy colloidal particles.…”

Second virial coefficient of rod-shaped molecules and molecular dynamics simulations of the isotropic phase

“…9 of Ref. [16], O f relevance to this work, RISM has been applied recently to tetrahedral colloidal particles, [17], homonuclear hard dumbbells [18], and m-interaction center fused rods [19], Fundamental measure density functional (FMDFT) theory is another approach, which has been used to model elongated particles in the bulk [20][21][22][23][24], and confine ment [25]. FMDFT has been tested for nonconvex bodies, in particular, hard dumbbells [26], which as this work is concerned with fused sphere rods is relevant to the present study.…”