Microfluidics provides an exceptional platform for the generation of polymer solution droplets and their subsequent manipulation. We describe the formation of polymeric particles and capsules with broad applications in the pharmaceutical and consumer goods industries. Two main routes, generally applicable to neutral polymers and polyelectrolytes, are explored, namely solvent extraction (akin to spray drying) and salt-induced gelation and precipitation. In order to elucidate the molecular conformational changes and kinetics underpinning this liquid-to-solid transformations, we develop microflow approaches to perform small angle neutron scattering (SANS) and phase mapping of multicomponent systems. By contrast to conventional SANS, reconfigurable microfluidic-SANS continually varies solution composition (e.g. during solvent exchange, salt diffusion, or phase mapping), providing spatio-temporal insight and enabling global, constrained data modelling with unprecedented robustness and precision. We can thus establish the thermodynamics and phase behaviour of model systems: neutral polymer polyvinyl alcohol (PVA) with mixed (good and poor) solvents, and polyelectrolytes poly styrene sulfonate (NaPSS) and carboxymethyl cellulose (NaCMC) in aqueous solvent mixtures and upon multivalent salt addition. Solidification and gelation front propagation kinetics and accompanying conformational changes are then established systematically. We obtain a particle and capsule morphology diagram, attaining internal morphologies encompassing nucleated and bicontinuous microstructures, as well as isotropic and non-isotropic external shapes. Equipped with this knowledge, we design and fabricate composite capsules and particles with prescribed dimensions and external shape, microstructure and dissolution profile.