Mechanism of Microparticle Formation in the Compressed Antisolvent Precipitation and Photopolymerization (CAPP) Process

Abstract

We investigated the mechanism of particle formation in a new process that combines the principles of photopolymerization and compressed antisolvent processing. In this process, photopolymerization occurs when homogeneous solutions of monomer, initiator, and solvent are exposed to initiating light while being simultaneously introduced into a compressed antisolvent, which can result in highly cross-linked microparticles with a spherical morphology. The resulting particles, when examined using aerodynamic particle sizing, exhibit a bimodal particle size distribution. Ternary phase diagrams of antisolvent, monomer, and solvent solutions were measured and used to explain the mechanism(s) of particle formation. Specific concentration paths from the resulting ternary phase diagrams were investigated, and the significance of crossing the binodal, as well as the importance of where the binodal was crossed, was explained. In addition, manipulation of atomization conditions, varying process residence times, and nucleation rate calculations were used to further investigate the means of particle formation.