Self-assembly of two-dimensional colloidal clusters by tuning the hydrophobicity, composition, and packing geometry.

We study the structure of binary monolayers of large (3  μm diameter) very hydrophobic (A) and large (3  μm diameter) hydrophilic (B) or small (1  μm diameter) hydrophilic (C) silica particles at an octane-water interface. By tuning the composition and packing geometry of the mixed monolayer, we find that a rich variety of two-dimensional hexagonal superlattices of mixed A/B or A/C clusters are formed, stabilized by short-ranged electrostatic induced dipole interactions. The cluster structures obtained are in excellent agreement with zero temperature calculations, indicating that the self-assembly process can be effectively controlled.