Influence\nof Geometries on the Assembly of Snowman-Shaped\nJanus Nanoparticles

Abstract

The self-assembly of micro/nanoparticles\ninto suprastructures is\na promising way to develop reconfigurable materials and to gain insights\ninto the fundamental question of how matter organizes itself. The\ngeometry of particles, especially those deviating from perfectly spherical\nshapes, is of significant importance in colloidal assembly because\nit influences the particle “recognition”, determines\nthe particle packing, and ultimately dictates the formation of assembled\nsuprastructures. In order to organize particles into desired structures,\nit is of vital importance to understand the relationship between the\nshape of the colloidal building blocks and the assembled suprastructures.\nThis fundamental issue is an enduring topic in the assembly of molecular\nsurfactants, but it remained elusive in colloidal assembly. To address\nthis issue, we use snowman-shaped Janus nanoparticles (JNPs) as a\nmodel to systematically study the effect of colloidal geometries on\ntheir assembled suprastructures. Ten types of JNPs with identical\nchemical compositions but with different geometries were synthesized.\nSpecifically, the synthesized JNPs differ in their lobe size ratios,\nphase separation degrees, and overall sizes. We show that by altering\nthese parameters, both finite suprastructures, such as capsules with\ndifferent curvatures, and nonfinite suprastructures, including free-standing\nsingle-layered or double-layered JNPs sheets, can be obtained <i>via</i> self-assembly. All these different types of suprastructures\nare constituted by highly oriented and hexagonally packed JNPs. These\nfindings demonstrate the significance of geometries in colloidal assembly,\nsuch that slightly changing the building block geometries could result\nin a large variety of very different assembled structures, without\naltering the chemistry of the particles.