Electrohydrodynamic Dispersion of Dry Fine Powders

Abstract

Dispersion of fine dry powders in the size range 1.0 to 10.0 mum in aerodynamic diameters requires a high energy dispersive force since the powders in this size range are very cohesive and their dispersion by vibrational, centrifugal or by aerodynamic force (using air currents) is inefficient in most cases. The adhesive force, that includes van der Waals, electrostatic, and liquid bridge forces, is, in general, proportional to the diameter d of the particles, whereas, the vibrational and centrifugal detachment forces are proportional to d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , and the aerodynamic shear force for detachment is proportional to d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Thus smaller the diameter d the higher is the dispersion force needed for efficient dispersion for forming aerosol from a sample of powder that will contain the primary particles present in the powder. We report here dispersion of fine powders deposited on a dielectric substrate by applying a traveling electric field using embedded electrodes. The dispersed particles are aerosolized by passing a gentle air current over the substrate. The dispersion of the powder forming an aerosol particle is achieved here by both electrodynamic force and air current. A brief discussion of van der Waals, electrostatic, and capillary forces between individual particles within a bulk powder and the dispersive forces applied by a using a low frequency three-phase electric field are reported. The electrostatic force of dispersion is proportional to qE, where q is proportional to d <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and E is the applied electric field. The charged particle cloud produced by the combination of electrohydrodynamic and aerodynamic shear forces were characterized with respect their size and electrostatic charge distributions by using an ESPART analyzer. The dispersive properties of the electrodynamic forces are analyzed for powders of different size distributions and conductivities. The traveling wave is produced by placing a series of electrodes, embedded, just beneath the surface of the substrate. The required power consumption needed for dispersion is less than 5 mW and requires only a few seconds for dispersion. The possible applications of breath actuated air flow in conjunction with electro-hydrodynamic dispersion for respiratory drug delivery are discussed.