Local stress control of spatiotemporal ordering of colloidal crystals in complex flows.

We show that spin coating, an unsteady, nonuniform shear flow, produces spatiotemporal variation in the crystal order of concentrated colloidal dispersions that is a universal function of the local reduced critical stress and the macroscopic strain. The dependence of the crystal quality of model poly(methyl methacrylate) colloids on radial and axial position, spin speed, and particle size is quantified by confocal microscopy. The coupling of flow-induced crystallization with the centrifugally driven spin coating flow determines local crystal quality without a priori knowledge of the suspension rheology.