(550b) Novel Method for Micro- and Nano- Particle Preparation by Electrohydrodynamic Atomization

Electrohydrodynamic Atomization has been shown to be suitable for the preparation of nearly monodisperse polymeric particles [1]. A solution containing organic solvent and polymer solute is sprayed through a nozzle which is maintained at a high electrical potential. The electrical potential difference between the nozzle and a grounded needle causes the formation of the Single Taylor Cone/Single Jet, in which a liquid cone is formed at the tip of the nozzle and a thin jet is ejected from the apex of the cone. The jet breaks into nearly monodisperse droplets and, with the loss of organic solvent through evaporation from the surface of the droplets, monodisperse polymeric particles can be prepared.

To change the size of the particles, the first step is to change the size of the droplets formed. There are many methods to change the size of the droplets, but most of them require modifications to the physical system or changes in the properties of the solution being atomized. Such methods are unwieldy in industrial applications. To overcome these problems, the present study aims at designing a new method for the preparation of micro- and nano- particles. By applying a secondary electrical field due to a ring electrode surrounding the nozzle, we are able to control the size of the droplets formed, while maintaining the low polydispersity of the droplets that is characteristic of the Electrohydrodynamic Atomization process. Ijsebaert [2] has previously made use of the ring electrode in his study of the production of aerosols, but the ring electrical potential was set to a constant and was thought only to have the effect of focusing the spray.

We have found that, if the electrical potential of the nozzle is kept constant while the electrical potential of the ring electrode is changed, it is possible to change the size of the droplets while maintaining a low polydispersity. Preliminary results from Phase Doppler Particle Analyzer experiments have shown that, by increasing the ring electrical potential, we are able to get droplet sizes that increase almost linearly with increasing ring potential, provided that the spray mode is maintained in the Single Taylor Cone/Single Jet mode. Particles prepared by this method also show the same trend, and we are able to vary the particle size in this simple manner.

The new method is shown to have advantages compared to the conventional methods of size control in Electrohydrodynamic Atomization. Without any modification to either the physical system or the solution, we are able to change the size of the particles in real time by simply changing the electrical potential relative to the grounded needle applied to the ring electrode.

[1] Ding, L., Lee, T., and Wang, C.H., Fabrication of mono-dispersed Taxol loaded particles using electrohydrodynamic atomization, Journal of Controlled Release, 102, 395-413, 2005.

[2] Ijsebaert, J.C., Geerse, K.B., Marijnissen, J.C.M., Lammers, J.W.J., Zanen, P., Electrohydrodynamic Atomization of Drug Solution for Inhalation Purposes, J. Appl. Physiol., 91, 2735-2741, 2001.