Aerodynamic dispersion of cohesive powders: A review of understanding and technology

Dispersion is the desired disintegration of particle clusters down to their primary constituents through the application of external forces, which overcome the interparticle attraction forces. This method is beneficial for many processes but especially for the characterisation of particulate systems and therapeutic drug delivery via the lungs from dry powder inhalers (DPIs). Dry powder dispersion is becoming increasingly popular as a method of sample preparation for a range of instruments such as a laser diffraction measurement device. There are many advantages for dry dispersion compared to wet methods. However, complete dispersion of fine cohesive powders is difficult due to the relatively large interparticle attraction forces compared to separating forces arising from fluid energy. This review identifies the current state of theoretical and experimental understanding of powder dispersing in a gaseous medium. The approaches to relate bulk powder properties to dispersion, the stresses produced on a particulate structure due to aerodynamic forces and possible approaches for linking the two are discussed. Furthermore, the available dispersion technology is reviewed with a discussion of individual dispersers and commercial devices used for dispersing bulk powder. Also, the review highlights the research needed in this field to gain a better understanding of how bulk powders interact with a dispersing fluid.