Self-Assembly of Octapod-Shaped Colloidal Nanocrystals into a Hexagonal Ballerina Network Embedded in a Thin Polymer Film

Abstract

Nanoparticles with unconventional shapes may exhibit different types of assembly architectures that depend critically on the environmental conditions under which they are formed. Here, we demonstrate how the presence of polymer (polymethyl methacrylate, PMMA) molecules in a solution, in which CdSe(core)/CdS(pods) octapods are initially dispersed, affects the octapod-polymer organization upon solvent evaporation. We show that a fast drop-drying process can induce a remarkable two-dimensional (2D) self-assembly of octapods at the polymer/air interface. In the resulting structure, each octapod is oriented like a “ballerina”, that is, only one pod sticks out of the polymer film and is perpendicular to the polymer–air interface, while the opposite pod (with respect to the octapod’s center) is fully immersed in the film and points toward the substrate, like a ballerina performing a grand battement. In some areas, a hexagonal-like pattern is formed by the ballerinas in which the six nonvertical pods, which are all embedded in the film, maintain a pod–pod parallel configuration with respect to neighboring particles. We hypothesize that the mechanism responsible for such a self-assembly is based on a fast adsorption of the octapods from bulk solution to the droplet/air interface during the early stages of solvent evaporation. At this interface, the octapods maintain enough rotational freedom to organize mutually in a pod–pod parallel configuration between neighboring octapods. As the solvent evaporates, the octapods form a ballerina-rich octapod-polymer composite in which the octapods are in close contact with the substrate. Finally, we found that the resulting octapod-polymer composite is less hydrophilic than the polymer-only film.

Limiting the valence: advancements and new perspectives on patchy colloids, soft functionalized nanoparticles and biomolecules

“…Over the last few decades, the availability of monodisperse nonspherical particles at the nano-and micro-scale [134][135][136] 145,146 or bowl-shaped colloids. 147 The particle shape plays an important role in the self-assembly of target structures with tailored properties.…”

Nanorings in planar confinement: the role of repulsive surfaces on the formation of lacuna smectics

“…Non-spherical particles confined in narrow planar slits are found to exhibit the formation of a variety of structures with symmetries not observed under bulk conditions [34][35][36][37][38][39][40][41][42].…”

“…Examples include branched particles [38,41,68], dimpled, bowllike and lens-like particles [69][70][71][72][73][74][75][76], non-convex platelets [77,78], and planar rings [79][80][81]. Modelling non-convex particles generally presents an added challenge due to the complex interactions that emerge due to the complexity in shape such as interlocking, entanglement, and interpenetration, which can hinder the equilibration of the system [67].…”

Phase behaviour and gravity-directed self assembly of hard convex spherical caps

“…A variety of shapes in bulk and under the influence of external fields have been explored including spherocylinders [15][16][17][18] , cut-spheres 23 [24][25][26][27][28] , dimers [29][30][31] , bowl-like particles [32][33][34] , concave spherical caps [35][36][37] , polyhedra [38][39][40][41][42] , and a variety of branched particles [43][44][45][46] , just to mention few examples. An assumption behind these studies is that the effect of gravitational forces is negligible, corresponding to a situation of colloidal particles embedded within a density matched (implicit) medium.…”