Synthesis, assembly, and image analysis of spheroidal patchy particles

We report a method to synthesize and image Janus spheroid and "kayak" shaped patchy particles that combine both shape and interaction anisotropy. These particles are fabricated by sequentially combining evaporative deposition of chrome and gold with the uniaxial deformation of the colloidal particles into spheroids. We introduce combined reflection and fluorescence confocal microscopy to image each component of the patchy particle. Image analysis algorithms that resolve patch orientation from these image volumes are described and used to characterize self-assembly behavior. Assemblies of the Janus spheroid and kayak particles produced at different salt concentrations demonstrate the functional nature of the patch-to-patch interactions between the particles. Selective gold-to-gold patch bonding is observed at intermediate salt concentrations, while higher salt concentrations yield gel-like structures with nonselective patch-to-patch bonding. At intermediate salt concentrations, differences in the orientational order of the assemblies indicate that both the preferential gold-to-gold patch bonding and the particles' shape anisotropy influence the self-assembled structure.