Packing Patterns of Silica Nanoparticles on Surfaces of Armored Polystyrene Latex Particles

Abstract

Fascinating packing patterns of identical spherical and discotic objects on curved surfaces occur readily in nature and science. Examples include C(60) fullerenes, (1, 2) 13-atom cuboctahedral metal clusters, (3) and S-layer proteins on outer cell membranes. (4) Numerous situations with surface-arranged objects of variable size also exist, such as the lenses on insect eyes, biomineralized shells on coccolithophorids, (5) and solid-stabilized emulsion droplets (6) and bubbles. (7) The influence of size variations on these packing patterns, however, is studied sparsely. Here we investigate the packing of nanosized silica particles on the surface of polystyrene latex particles fabricated by Pickering miniemulsion polymerization of submicrometer-sized armored monomer droplets. We are able to rationalize the experimental morphology and the nearest-neighbor distribution with the help of Monte Carlo simulations. We show that broadening of the nanoparticle size distribution has pronounced effects on the self-assembled equilibrium packing structures, with original 12-point dislocations or grain-boundary scars gradually fading out.

Physical Methods for the Preparation of Hybrid Nanocomposite Polymer Latex Particles

“…A quantitative method based on disk centrifugation was developed to monitor the amount of nanoparticles present in the water phase in solids-stabilized emulsion polymerizations of vinyl acetate, methyl methacrylate, and butyl acrylate. The concentration profile of nanoparticles in the water phase as a function of monomer conversion agreed with theoretical models developed for the packing densities in these systems [120]. Noteworthy was that in the case of silica-nanoparticle-stabilized emulsion polymerization of vinyl acetate, the event of late-stage limited coalescence, leading to small armored nonspherical clusters, could be predicted and explained on the basis of the concentration profiles and particle size measurements.…”

“…Bausch et al [83,84] showed that for large droplets onto which thousands of microspheres were assembled, this rule of 12 defects prevailed in the form of five-and seven-neighbor line defects, or grain boundary scars. Bon and coworkers [85] studied a system of intermediate size (tens to hundreds of particles on a sphere), i.e., the packing patterns of silica nanoparticles on polystyrene latex particles made via Pickering miniemulsion polymerization [86,87]. They found an excellent correlation between the experimental morphology and the nearest-neighbor distribution using metropolis Monte Carlo simulations, using a 12-24 Lennard-Jones potential.…”

“…Moreover, they addressed the effect of the polydispersity of the nanoparticles used in preparing the armored droplets. They found that upon broadening of the particle size distribution, the packing geometry could no longer be described in terms of 12-point dislocations or grain boundary scars [85].…”

“…Key herein was that the sonication process to prepare the armored miniemulsion droplets warranted reversible adhesion of the Laponite clay discs throughout the emulsification step. Bon and coworkers [85] also performed Pickering miniemulsion polymerizations of styrene using spherical silica nanoparticles of approximately 25 nm in diameter (Ludox TM-40), in which the packing arrangements of the silica nanoparticles on the surface were investigated and modeled with the aid of Monte Carlo simulations. Zhang and coworkers used organically modified silica nanoparticles to carry out a Pickering miniemulsion polymerization of styrene [107].…”

Colloidosomes: Synthesis, properties and applications

“…For example, a minimum of 12 pentagonal defects must be present for small monodisperse spheres to pack fully around a larger sphere. 71,72 These defects are often described as line defects or grain boundary 'scars' 73 and have been experimentally observed during bright field and fluorescence microscopy studies of water droplets stabilized using polystyrene 74 or silica 72 particles, respectively. A pentagonal defect within a packed monolayer of spheres has an estimated size of 0.70d, which is significantly larger than the fundamental interstitial dimensions of 0.15d.…”