Aqueous emulsion polymerisation using free radical chemistry has been the most important process for latex production for at least fifty years. However, the inherently heterogeneous nature of such polymerisations makes them very difficult to study. Various particle nucleation and growth mechanisms have been proposed but to date no-one has sought their verification via in situ scattering techniques. One reason for this omission is that efficient stirring is essential for aqueous emulsion polymerisation because this produces sufficiently small monomer droplets. We have recently developed a bespoke stirrable SAXS cell that enables efficient stirring, see Figure 1. Thus, for the first time we are able to monitor the evolution of structure that occurs during aqueous emulsion polymerisation. To explore the mechanism of particle nucleation and growth, three formulations involving vinyl monomers have been investigated using our bespoke SAXS cell. The simplest formulation comprises just vinyl monomer, ionic initiator and water. The other two formulations involve the same vinyl monomer with the addition of either an anionic surfactant (SDS) or an ultrafine silica sol to produce either SDS-stabilised latex or polymer/silica nanocomposite particles, respectively. The onset of micellar nucleation and subsequent particle growth are explored by in situ SAXS measurements. Moreover, the reaction solution volume within the SAXS cell is approximately 2 mL which allows post mortem characterisation of the latex (or nanocomposite) particles using 1H NMR spectroscopy, TEM and DLS.

In situ SAXS studies during aqueous emulsion polymerisation

2019 Fall National Meeting

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