Microfluidic polymer particle and capsule formation: from the molecular to the macroscale

Abstract

In this work the physics underpinning polymer particle formation is explored, particularly probing Å to 100s of nm length scales with small angle neutron scattering (SANS) to macroscopic scales with microscopy. Two approaches are used to generate micron-sized particles from polymer solution droplets; droplet solvent extraction (DSE) concerns the introduction of an `extraction' solvent, which removes the solvent from the polymer-containing droplet, to form a polymer-rich skin and kinetically arrest the shrinking particle. Secondly, ionic gelation occurs upon addition of multivalent ions to a polyelectrolyte solution droplet, which rapidly forms a gel-like front which propagates into the droplet. Micro- and milli-fluidic approaches are used to generate droplets and visualise and map the formation pathways. Chapter 1 introduces background theory and the motivation for investigating these formation pathways. In Chapter 2, SANS measurements of model polymer/solvent/non-solvent mixtures, designed to probe the DSE pathway, are presented. In Chapter 3, the impacts of molecular structure (chain length and chemical substitution), concentration and droplet size on the DSE pathway are established; demonstrated here for model poly(vinyl alcohol) (PVA) to yield particles with well-de fined shape, dimensions and internal microstructure. Chapter 4 presents a comparative study with FlashNanoPrecipitation (FNP); another approach which utilises rapid mixing of ternary mixtures of polymer, solvent and non-solvent under confinement to yield nanoparticles. Chapter 5 details a SANS study on the effect of added mono- and divalent salt on the solution structure of sodium carboxymethyl cellulose (NaCMC). The formation of microcapsules from NaCMC and, instead, trivalent Fe3+ is detailed in Chapter 6. Optical measurements reveal the frontal behaviour and kinetics of the gelation process. Chapter 7 details a SANS study of these 'gelation fronts' to probe the evolution of nanostructure within the gel. Chapter 8 presents brief concluding remarks and an outlook for the future of microfluidic polymer particle and capsule formation.