Adhesion of dry nano-coated microparticles to stainless steel: A physical interpretation

During the manufacture of pharmaceuticals, it is desirable to modify the surface of powder particles to alter their adhesion characteristics without changing their dissolution rates or their chemical or biological characteristics. In this study, dry silica nanoparticle coatings were applied to spheroidal micron-scale aluminum host particles to alter their surface morphology and adhesion behavior. The host particles were coated with either hydrophobic or hydrophilic fumed nanosilica using a magnetically assisted impact coating technique. The adhesion between polished or unpolished stainless steel and all three particle types, including uncoated aluminum and aluminum coated with either hydrophobic or hydrophilic nanosilica, was examined at 30% relative humidity. On both steel surfaces, the measured adhesion force towards the uncoated aluminum was greater than towards either type of coated aluminum. The uncoated aluminum adhered more strongly to the polished substrate than to the unpolished one. The hydrophobic- and hydrophilic-coated particles adhered to both substrates with roughly the same force, such that there was no effect of either the substrate type or the coating type on the adhesion. To confirm that capillary forces had no influence on the measured adhesion, the adhesion behavior between the uncoated aluminum particles and the steel was measured at 15 and 30% RH, and no change in adhesion force was observed.