Quantifying ibuprofen powder adhesion: Impact of surface roughness and substrate material

Powder adhesion influences flow during pharmaceutical processing, where particle-particle and particle-surface interactions often lead to weight variability and unacceptable content uniformity. This study investigates how substrate material and surface roughness affect the effective work of adhesion, Γ of ibuprofen powders using the drop test method. Five substrates; aluminium, acrylic, stainless steel, brass and copper, were examined in both polished and scratched conditions. The effective work of adhesion of the polished aluminium, acrylic, stainless steel, brass and copper were 19.6 ± 2.9 mJ/m 2 , 26.4 ± 4.0 mJ/m 2 , 27.5 ± 5.1 mJ/m 2 , 32.2 ± 2.8 mJ/m 2 and 38.5 ± 2.6 mJ/m 2 , respectively. Contact angle measurements confirmed that surface free energy trends were consistent with the adhesion values. Aluminium’s low adhesion was attributed to its naturally formed oxide layer and rougher surface. A scratch-test rig was utilised to introduce scratches across five substrates, where adhesion values followed the same trend to polished surfaces. Generally, roughness reduced the adhesion except for aluminium, where deeper valleys in the polished state, likely due to polishing and scratching variations, resulted in higher adhesion values. Additionally, we developed an automated algorithm to analyze substrate images and quantify the critical particle diameter and effective work of adhesion. While the results aligned with manual findings for polished surfaces, scratched surfaces showed discrepancies due to higher levels of image noise. • The effective work of adhesion, Г , was determined by employing the drop test method. • Influence of substrate material on effective work of adhesion, Г , is studied. • Effect of surface roughness on effective work of adhesion, Г , is examined. • The surface energy trend from contact angle measurement aligned with adhesion values.