(76c) Roughness Effects On Particle Adhesion

Surface roughness is influential in many solid processing variables, such as choice of excipients and flowing parameters (compression, pneumatic conveying, etc.) that affect the quality of the final product. Surface roughness is one of the most important parameters in surface/particle engineering.

In this work, we have utilized our experimentally-validated simulation scheme as a tool to estimate the adhesion forces between nanosized silicon nitride and ultra-fine particles (d<10 µm); silica, alumina and alumina coated with nano-silica particles, against a silica surface.

This study focuses on the importance of different physical parameters such as the material, size and surface roughness of the interacting bodies on the force of adhesion between them, with particular attention to particle roughness as the particle size and roughness is varied from the micro- to the nanoscale. The effective Hamaker constant (a force constant for the van der Waals force) for nanoscale particle-substrate systems was derived from experimentally obtained force measurements between a model particles and the substrate of interest, silica surface (polished and unpolished).

By using surface features (geometry and roughness) examined by AFM and SEM imaging of particles, it was determined that surface roughness generally reduces adhesion of both micro- and nanoscale particulates. However, the effect of roughness on the adhesion force is greatly dependent on the particle probe asperities, with asperity diameters below 50 nm, observed in silco. Also, through simulation the adhesion force distribution was related to the distribution of asperities where normal distribution asperities (randomly generated surface) resulted in lognormal adhesion force distributions for all sizes (4 µm, 8 µm, 10 µm, 50 µm). The particle size and geometry can directly influence the adhesion force by altering the area of interaction between the particle and substrate. As a result, it remains an important area of study for particulate systems.