Multiscale Modeling for Surface Composition of Spray-dried Powders
Jie Xiao, Winston Duo Wu and Xiao Dong Chen
School of Chemical and Environmental Engineering
College of Chemistry, Chemical Engineering and Materials Science
Soochow University, Suzhou, China
Spray drying is the most effective process for large-scale manufacturing of various powder products. One of the most important properties of powders is the ability to get wet, which is critically influenced by the powders' surface structure and chemical composition. Furthermore, surface composition also influences the efficiency of production as it affects the stickiness of the powder.
In this work, an innovative multiscale modeling approach is introduced to analyze the surface composition of spray-dried powders produced under various conditions. A molecular-level geometrical packing interpretation is seamlessly coupled with a continuum diffusion analytical model. The predictions are compared with the measurements using X-ray photoelectron spectroscopy (XPS). Sample calculations for the lactose-protein two-component system demonstrate that the integrated multiscale framework actually works quite well in terms of bridging quantitatively the composition result in the thick continuum-scale surface layer and that in the thin layer detected by the XPS instrument (see Figure 1). Moreover, we explore the possibility of integrating the macroscopic diffusion model with a microscopic lattice Monte Carlo model that can characterize evaporation induced self-assembly of solute molecules on the droplet/particle surface. In this way, detailed 3D surface morphology and chemistry (rather than a single value of surface composition) can be revealed. This work provides a good basis for a fruitful area of study towards structure-focused powder quality control that will have a positive impact in industries.
Keywords: Spray drying; surface composition; multiscale modeling; self-assembly; multi-component diffusion; molecular packing