Evolution of polymer conformation during droplet-to-particle formation

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 to precisely handle the polymer droplets in controlled environments. We then couple our experimental platforms 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 three model systems: two water-soluble polymers, poly(vinyl alcohol) and semi-flexible polyelectrolyte sodium carboxymethyl cellulose, and high-glass transition, semicrystalline poly(2, 6-diphenyl-p-phenylene oxide). We investigate the roles of composition (with respect to c* and c**), molecular mass, viscosity, and salt addition. 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.