Elecrohydrodynamic Atomization (EHDA) has recently been applied to the fabrication of polymeric micro- or nano-particles and fibers for drug encapsulation. EHDA in the cone-jet mode can produce highly monodisperse aerosols. In this process the shape of a liquid droplet is transformed by modulating electrical forces into a conical shape. At the cone apex, a jet with a high charge density occurs which can break up into a number of main droplets with a narrow size distribution, and a number of smaller satellites. Electrical interaction between highly charged droplets causes a size segregation effect. Small droplets will be found at the edge of the spray while large droplets will be found near the spray centre.
In the present study, EHDA is performed in an enclosed glass vessel in which solid particles are fabricated after evaporation of the solvent from sprayed droplets. EHDA process setup consists of glass chamber, nozzle (connected to a syringe pump), ring ( surrounding the nozzle), collecting plate (for neutralizing and collection of the particles) and nitrogen flow. Positive high voltages are applied to nozzle and ring and concurrently the collecting plate is also grounded. Moreover, one additional plate is placed e few centimeters above the collecting plate which is connected to a positive high voltage generator. An idea analogous with “Electrical Field Flow Fractionation (EFFF)” has been used in designing this auxiliary electric field. EFFF is a separation technique where an electric field is applied to a mixture perpendicular to the mixtures flow (in a narrow channel) in order to separate the mixture species due to different mobilities of the various components in the field. Two important differences between these two ideas are, firstly, the channel in this auxiliary electric field is not very narrow and secondly, particle separation is not important in this study. Indeed, the target in this process is the enhancement of particle deposition on the collecting plate.
The present study aims to investigate the effect of auxiliary electric field on particle motion, deposition, size and morphology in the EHDA encapsulation chamber. Furthermore, the influences of this auxiliary electric field on particle collection efficiency and also on the adjacent electric filed are reported.
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