Evaporation-induced alignment of nanorods in a thin film

During the solvent evaporation of a thin film, Brownian rod-shaped particles self-assemble into microstructures and their orientation arrangements change while their volume fractions increase. We have studied the phenomena using a simple model which accounts for the anisotropic diffusion and the mean-field interaction of the particles. By numerically solving the Smoluchowski equation under moving boundary conditions, we obtain the spatiotemporal evolution of volume fractions and order parameters. It is shown that the evaporation dynamics alter the equilibrium orientational configuration of particles to meta-stable states. This alternation is possible by controlling either Péclet numbers or anisotropic diffusion rates. This understanding of the dynamic self-assembly of rod-shaped particles can be useful in manipulating the collective rod-arrangement in printing and coating technologies.