Capillary forces between non-spherical colloids

Uncharged, spherical colloidal particles at an air-water interface experience no significant interaction forces if their radii are below a critical size. However, strong attraction and repulsion can still be observed when the shape of the particles deviates even slightly from an ideal sphere. We show that $nm$-scale deviations from sphericity on $\mu m$-sized particles lead to interaction energies in excess of thermal energies, resulting in positional and orientational ordering at the interface. Dendritic or lattice-like rafts are observed, the latter showing hexagonal positional and herringbone orientational order.