(667d) Dynamic Change In Polymer Particle Shape and Size by Simple Emulsion-Diffusion Process

Polymer hollow microspheres have attracted growing attentions in drug delivery, catalyst carriers, and microencapsulation. Here we report a simple preparation of hollow poly(lactic acid) (PLA) microspheres by single emulsion-diffusion method in a turbulent shear flow system. Modified Taylor-Couette mixer was introduced to generate uniform high shear fluid flow, facilitating the formation of hollow structured particles. The critical formation transition of polymer nanospheres to hollow microspheres was studied and controlled. An increasing addition of glycerol into the aqueous phase changed the flow from turbulent inertial to turbulent viscous regime. When the operation temperature was higher than the glass transition temperature of PLA, multiple emulsion droplets were obtained by the inclusion of water droplets during oil drops coalescence. Fast polymer solidification and water entrapping during diffusion process caused the formation of hollow PLA particles. Under harsh conditions, these hollow microspheres collapsed to open structure due to water escaping. Higher mixing speed rate and longer mixing time resulted in more uniform particle size and size distribution. The effects of water to oil ratio, pH of aqueous phase, and electrolyte were investigated for further engineered control of particle shape, size, and size distribution.