Tuning the Morphology and Structure of Supraparticles Composed of Ellipsoids

Evaporating droplets of colloidal dispersions on superamphiphobic surfaces is a versatile way to fabricate supraparticles with complex shape and internal morphology. Here, we investigated experimentally the formation of supraparticles consisting of polystyrene (PS) ellipsoids, with aspect ratios ranging from 4 to 11, and of sphere-ellipsoid mixtures. We demonstrated that the final supraparticle morphology can be tuned from buckled to spherical through the addition of the surfactant sodium dodecyl sulfate (SDS), which stabilizes the colloids within the drying droplet. At low evaporation speeds, we observed the ordering of the ellipsoidal colloids into small nematic bundles inside the supraparticle and into smectic domains on the supraparticle surface, which is consistent with results from previous computer simulations. The orientational ordering of ellipsoidal colloids was disrupted in the binary supraparticles consisting of sphere-ellipsoid mixtures, even at low sphere concentrations.