Dense Packing and Symmetry in Small Clusters of Microspheres

Abstract

When small numbers of colloidal microspheres are attached to the surfaces of liquid emulsion droplets, removing fluid from the droplets leads to packings of spheres that minimize the second moment of the mass distribution. The structures of the packings range from sphere doublets, triangles, and tetrahedra to exotic polyhedra not found in infinite lattice packings, molecules, or minimum-potential energy clusters. The emulsion system presents a route to produce new colloidal structures and a means to study how different physical constraints affect symmetry in small parcels of matter.

Colloids with valence and specific directional bonding

“…The amidinated microsphere clusters were prepared as described by Manoharan et al 5 In a variation to the original report, we used sodium dodecyl sulfate (SDS) as surfactant and changed the shear rate to control cluster distribution. The following two shear experiments were carried out as described in the main document and corresponding to patchy particle distributions in Figure S1: condition a (low shear): 90 seconds at 8000 rpm, 60 seconds at 9500 rpm, and then 60 seconds at 13500 rpm; condition b (high shear): 90 seconds at 8000 rpm, 90 seconds at 9500 rpm, and the 120 seconds at 13500 rpm.…”

“…The past decade has seen an explosion in the kinds of colloidal particles that can be synthesized 1,2 , with many new shapes, such as cubes 3 , clusters of spheres [4][5][6] and dimpled particles 7,8 reported. Because the self-assembly of these particles is largely controlled by their geometry, only a few relatively simple crystals have been made: face-centered and body-centered cubic crystals and variants 9 .…”

Fabrication, Assembly, and Application of Patchy Particles

“…Selective modification of a segment of a particle surface is directly feasible in the case of the PVD technique because of the inherent shadow effect. In addition to the conventional surface modification techniques, [62,63] more recently capillary flow techniques [13,15,[64][65][66][67] and colloidal assembly [68,69] methods have been explored for the fabrication of patchy particles and therefore will be included here.…”

“…We will begin with template-assisted fabrication (Figure 5a), which usually is limited to just one patch, but includes the techniques with the highest associated production volume to-date. [10,11,70] Next, we will introduce evaporation-driven colloidal assembly, as pioneered by Manoharan et al (Figure 5b), [12,68] and particle lithography, as invented by Snyder et al (Figure 5c). [9,16] The commonality between these three techniques is that fabrication/assembly occurs Adapted with permission from ref.…”

“…[68] The originally reported method is based on the emulsification of a suspension of lightly crosslinked polystyrene particles in toluene with an aqueous surfactant solution. In the resulting toluene-in-water emulsion, the polystyrene spheres are trapped at the droplet interfaces by surface tension.…”