Transitional behavior of polymeric hollow microsphere formation in turbulent shear flow by emulsion diffusion method

Polymeric hollow microspheres have attracted growing attention because of their unique properties and extensive applications. We report a facile emulsion diffusion process to fabricate polylactic acid (PLA) hollow microspheres driven by viscous turbulent fluid flow. The process involves the emulsification of PLA–ethyl acetate solution in the water–glycerol medium under high viscous turbulent shear flow where emulsion droplets coalesce into multiple emulsions, and the solidification of PLA by the diffusion of ethyl acetate. The addition of glycerol changed the viscosity of the continuous aqueous phase, resulting in the transition of fluid flow from inertial turbulent to viscous turbulent dominant regime and thus PLA particle size and shape from solid nanospheres to hollow microspheres. The emulsification temperature also needs to exceed the glass transition temperature of PLA to form hollow microstructure. This method allows the easy control of PLA particle shape and size for different applications.