(245c) Droplet and Particle Formation in the Electrohydrodynamic Atomization Process

The Electrohydrodynamic Atomization (EHDA) method has been used to fabricate polymeric particles, with diameters ranging from the micrometer to the nanometer range. Particles with substantially different sizes and morphologies, such as biconcave-shaped porous particles and spherical particles with either corrugated or smooth surfaces, have been obtained. Such particles can be used as drug delivery vehicles for different applications. For example, compared with spherical non-porous particles of similar mass, biconcave-shaped porous particles are well suited for inhalation drug delivery purposes due to their large aerodynamic diameters. In contrast, spherical particles with a smooth surface can be used for controlled drug delivery implant because the release rate is relatively predictable compared to irregularly shaped porous particles.

In the first part of this study, we investigated the formation of both the primary droplets and the secondary droplets formed in the Single Taylor Cone Single Jet mode in EHDA. Computational fluid dynamic simulations were used to examine the droplet formation process with the fluid-gas interface modeled using a front tracking method. Different operating parameters, such as nozzle and ring electrical potential, are varied to study their effects on droplet size.

In the second part of this study, particular attention was devoted to the effects of the particle formation process on the particle morphology. It was found that the solvent evaporation rate and the polymer diffusion rate inside the droplets play crucial roles in determining the morphology of the final particles. In order to fabricate spherical particles with low porosity and smooth surface morphology, a slow solvent evaporation rate or a high polymer diffusion rate is required.

A modified Peclet number (Pe) was used to characterize how these two parameters affect the morphology of the particles. When Pe is less than order 1, spherical particles with smooth surfaces are obtained. Pe values of around 10 will give spherical particles with corrugated surfaces, while Pe values in excess of 100 will give irregularly shaped porous particles. Computational simulations were also used to investigate the transient changes for the concentration profile of the polymer inside the droplet during the course droplet shrinkage due to solvent evaporation.

The results show that, with prior knowledge of the operating parameters, it is possible to control the size and morphology of the particles fabricated by the EHDA method.