Microfluidic Solvent Extraction for the Precise Formation of Polymer Particles and Capsules

Microfluidics provides a precise platform for the generation of polymer solution droplets and their subsequent extraction to yield polymeric capsules with a range of applications. Control over particle structure and morphology is predicated, however, on polymer solution thermodynamics, composition pathways and gradients derived from the selective solvent removal, and eventual kinetic arrest. We investigate the role of Mw, degree of hydrolysis and droplet concentration in the formation of poly(vinyl alcohol) capsules. Specifically, aqueous PVA solutions are emulsified in an immiscible carrier phase to form well-defined droplets, which are then immersed into a selective extraction solvent, which is miscible with water but a non-solvent for the polymer. The progressive concentration of the polymer droplets and ingress of non-solvent leads to phase inversion and the formation of internally porous particles with a smooth, polymer-rich skin. By varying initial polymer concentration with respect to the overlap and concentrated crossovers, and separately Mw to tune the overall solution viscosity, we map a plethora of accessible internal morphologies. Further, by inducing anisotropic extraction conditions, non-spherical particles are trivially formed.