(256e) Smooth and Rough Surface Approaches to Model Inter-Particle Adhesion: Assessing the Extent of Fine Particle Cohesion Reduction Via Surface Modification

Adhesion in particle-to-particle contact significantly influences bulk powder properties. Estimating particle adhesion involves two primary approaches in contact mechanics: the Smooth Surface and the Rough Surface approach. The Smooth Surface approach, including Hertz, JKR, DMT, Maugis, and Dugdale contact models, among others, is applicable over a wide range of particle mechano-physical properties such as surface energy, hardness, and elasticity. However, this approach has inherent limitations in accounting for particle roughness. The Rough Surface approach expands upon the Smooth Surface approach by examining the impact of roughness through van der Waals force estimations, utilizing Hamaker theory via single and multi-asperity contact models. In this talk, we cover different methods incorporating surface energy and van der Waals force approaches, their applicability, and their limitations, specifically in the context of dry coating-based surface modification. The application of analytical models is used for understanding surface modification mechanisms that decrease cohesion in fine particles by altering surface energy or roughness, as well as their relationship with bulk properties at various roughness/surface energy scales. The use of adhesion force models to quantify interparticle forces before and after surface modification is assessed, along with the relative importance of factors contributing to the adhesion reduction mechanism through surface modification. The models are tested through a large number of pharmaceutically relevant fine powders, both the drug materials, and excipients.

The investigation also considers the predictive approach of relating bulk powder properties before and after surface modification with particle-scale measures, specifically the dimensionless parameter Bond number (Bog), while emphasizing existing gaps and challenges. The need to address contact model assumptions to develop accurate prediction models connecting particle-scale properties to bulk behavior is highlighted. The analysis and results presented in this study underscore the significance of a mechanistic understanding of surface modification for advancing model-guided insights into surface modification processes relevant to industry practitioners.