Micromechanics and strength of agglomerates produced by spray drying

Colloidal suspension spray drying is often used as a route to produce micrometric agglomerates. The morphology and re-dispersion behavior of such agglomerates under fluid dynamic stress is expected to be strongly affected by the operative conditions at which drying is conducted. Motivated by the emerging research area of fluid-activated drug carriers, in this work we studied numerically both the generation mechanism of agglomerates during spray drying, and their mechanical and fragmentation behavior under fluid dynamics stresses. Capillary forces, Brownian motion and the contact mechanics of the particle-particle bonds were kept into account. Results showed that different spray drying conditions lead to substantially different morphologies and mechanical responses of the agglomerates: compact, uniformly dense clusters are obtained for low Péclet number conditions, hollow clusters, with a void core and a thick crust of contacting colloidal particles are instead formed at high Péclet conditions. We also observed that compact agglomerates are considerably stronger than hollow ones, and exhibit brittle rupture under fluid dynamic stresses. Hollow clusters were seen on the contrary to be looser and to undergo noticeable deformation prior to breakup. Finally, this work aims at providing the information needed for selecting spray drying conditions when aiming at a specific morphology and/or re-dispersability properties of colloidal agglomerates.