Specific spatial modification of spherical particles with patchy anchor points presents an exciting new area of directed particle assembly. The position of the patches, the patch material and possibly linker molecules assembled onto these patches as well as the patch roughness result in a variety of new parameters important for the assembly, which may allow predicting of structures and directing of particles into desired structures. A combination of attractive and repulsive interactions as well as patch size, and roughness, for example, could be used to predetermine packing densities (cubic vs. hexagonal) as well as the interlayer structures (sheet vs. diamond) by mimicking orbital interactions between atoms in a crystal lattice. Further, the direct liquid-phase synthesis of surface-anisotropic nanocrystals with such specific patch areas is still extremely difficult because of the intrinsic isotropy of the solution-phase approach.
We have developed methods for the synthesis of silver- and gold-capped 2.4 mm polystyrene particles using both template-assisted electroless deposition[1] and physical vapor deposition. We find that electroless deposition results in patches with rough surfaces, while vapor deposition gives much smoother patch surfaces. In addition, we have begun to study the assembly of these so-called Janus particles into two-dimensional monolayer films. Comparison of the two Janus particle types shows a striking difference in their assembly. The rough-patch particles form three-dimensional clusters, while the convective assembly forces the smooth-patch particles into a two-dimensional monolayer. Detailed studies on the relative cap orientation of the particles within the monolayers formed by the smooth-patch particles are underway.
[1] Cui, J.; Kretzschmar, I. "Surface-Anisotropic Polystyrene Spheres by Electroless Deposition" Langmuir 2006, 22, 8281-8284