Polymer solution droplet-to-capsule drying in levitation and microfluidics

Motivated by ubiquitous spray drying approaches in the manufacturing of polymer particles and composites, we experimentally investigate the mechanism and kinetics of particle formation by controlled solvent extraction and evaporation of polymer solution droplets. We employ microfluidics and acoustic levitation, and couple our experimental platform with small angle neutron scattering (SANS) to elucidate chain conformation under equilibrium conditions and along the particle formation pathway, supplemented by optical and electron microscopies that characterise overall external and internal particle morphologies. We examine semi-flexible polyelectrolyte sodium carboxymethyl cellulose, amorphous polystyrene, and high Tg semicrystalline poly(2, 6-diphenyl-p-phenylene oxide). We investigate the roles of composition, molecular mass, viscosity, and salt addition collapse (for NaCMC) in particle and capsule formation. Equipped with this knowledge, we then predictively design and fabricate polymer particles and capsules with prescribed dimensions, shape, porosity, microstructure and dissolution profile, and discuss complementarity with ‘flash nanoprecipitation’ methods.