A dry powder inhaler (DPI) is effective in treating respiratory diseases if it can deliver consistent and reliable drug dosage with each actuation. De-agglomeration and subsequent detachment of the drug from the carrier particles upon actuation depends on the interaction forces between particle and wall and particles themselves. The particle surface properties such as roughness and moisture sorption, in turn, determine the extent of the interactions. Via combining high speed imaging with non-intrusive electrostatic measurements in an impaction throat model, the contributions of the electrostatic forces arising from de-agglomeration and impaction behaviours of the rough and smooth particulates could be investigated at 60 L/min. Higher flowing charges with limited agglomerate fracture upon impaction were observed for the rough carrier particles while significant agglomerate breakup and 'plume-like' re-entrainment behaviour was noted for the smooth ones. Increased moisture sorption on the larger specific surface area of the rough particles could have facilitated the accumulation of surface charges while the higher dispersive surface energy could have increased the cohesiveness of the rough particles. The smooth particles easily broke up upon impaction. High speed imaging with electrostatic monitoring has proved to be useful in investigating the mechanisms of powder de-agglomeration upon impaction. (c) 2013 Elsevier Ltd. All rights reserved.