A Chemical Synthetic Route towards “Colloidal Molecules”

Abstract

A non-exhaustive list of fields in which extensive research has been dedicated to colloidal particles during the past century includes condensed matter physics, biology, optics, materials science, and chemistry. Both our current understanding of various physical phenomena and our capability to fabricate new functional materials have been considerably enriched by the development of synthetic strategies that are capable of generating copious quantities of colloidal entities of good size uniformity. Nevertheless, most of the available monodisperse colloidal materials are spherical, as the minimization of the interfacial free energy strongly drives a particle to adopt such a shape.[1] This strongly limits the number of new structures which can be engineered by using these colloids as building blocks. For instance, the crystallization of spherical colloids into three-dimensional periodic lattices has recently allowed the emergence of a very active field of research-photonic colloidal crystals, known as artificial opals. Nevertheless, the light diffraction properties of these crystals are rather limited because of their face-centered cubic lattice, which results from the packing of spheres. It has been predicted that crystals with a lower degree of symmetry, such as the diamond lattice, can exhibit a full photonic bandgap. To build such photonic crystals, well-defined colloids with nonspherical shapes are required. Van Blaaderen recently introduced the elegant term of "colloidal molecules", [2] which takes into account that spherical colloids can be treated as if they were atoms and that molecules can form more complex materials than can atoms. Therefore, the reproducible fabrication of large amounts of colloids that have a good uniformity in chemical composition, surface properties, size, and shape is a huge challenge.[3] Intensive efforts during the last decade have led to the development of nonspherical colloids of various shapes (such as rods, [4][5][6] wires, [7] triangles, [8] prisms, [9] cubes, [10] ellipsoids, [11] octahedra, [12] tetrapods, [13] ), but few of these samples combined the requirements of a true monodispersity in size and shape and the production of sufficiently large quantities. A promising synthetic procedure involves the use of a physical template to better control these two parameters. Micropatterned charged monolayers [14][15][16][17] or relief structures [18][19][20][21][22][23] on two-dimensional substrates were used to fabricate mono or binary clusters of colloids with high-arrangement accuracies, but in very small quantities. Three-dimensional templates such as liquid [24] or emulsion droplets [25,26] were also exploited to form complex colloidal assemblies with well-controlled sizes and morphologies. For example, a clever approach based on the generation of oil-in-water emulsions containing polymer microspheres and the subsequent controlled oil evaporation was first developed by Manoharan et al., [27][28][29] and led to aggregates that contain a precise number of polymer microspheres. Th...

Colloids with valence and specific directional bonding

“…This difficulty might be overcome by large-scale separations 44 , or developing methods that produce clusters with controlled morphology so that no separation is needed. Indeed, the swelling and functionalization methods we use to make our colloidal particles could readily be adapted for use with clusters made using other recently-developed techniques 22,25,45 .…”

Fabrication, Assembly, and Application of Patchy Particles

“…Thus, clusters with many different sizes result and require subsequent separation. Recent work by Perro et al [89] , addresses the size-selectivity by using silica seeds of varying size to synthetically select one colloidal cluster size over the other, for example, 42 nm silica seeds result in mainly dimers, while 85 nm seeds yield tetramers. An interesting future route would be to employ colloids of identical size but varying surface functionality to form colloidal clusters with patches of varying functionality.…”

One‐Pot Construction of Multipodal Hybrid Periodic Mesoporous Organosilica Nanoparticles with Crystal‐Like Architectures

“…[ 8 ] Tetrapod-shaped CdSe and CdTe NPs, [ 9,10 ] tri-, tetra-, and tree-like multipodal GaP NPs, [ 11 ] via epitaxial connection of branched heteroonanostructures [ 12 ] have been synthesized and the unusual charge separation properties of these materials could have important applications in photovoltaïc energy conversion. NPs with high morphological complexity have been obtained as multipodal colloidal silica clusters, [13][14][15] and various kinds of anisotropic nanoassemblies from NPs building block approaches have been investigated. [ 16 ] Of particular interest is the design of porous multipodal nanosystems that have been scarcely reported.…”