Evaporation of Colloidal Suspensions of Aspherical Particles

Recent studies have shown that size-dependent stratification can occur in a rapidly drying suspension of a polydisperse mixture of spherical colloids. In this work we utilize molecular dynamics simulations based on an implicit solvent model to investigate the role of particle shape in such far-from-equilibrium processes. Rigid-body composite particles with various shapes, including spheres, hollow spheres, tetrahedra, cubes, rods, and disks, are prepared using Lennard-Jones beads. Our results reveal that the most important factor in controlling the distribution of the particles in a rapidly dried film is the contrast in their diffusivities and shape does not play a significant role. In a binary mixture of particles, stratification is observed after drying when their diffusion coefficients are sufficiently different, regardless of their shapes. In a similar vein, no stratification is found in a mixture of particles with similar diffusion coefficients, even when their shapes differ strikingly (e.g., rods vs. disks). Our results thus indicate that when using solvent evaporation to assemble, separate, or stratify colloidal particles, it is crucial to tune their diffusivities to control the distribution of the particles in the drying film.