(298a) Flash Nanoprecipitation of Ionomers for the Scalable Production of Salt-Responsive Pickering Emulsifiers

Pickering emulsifiers have been demonstrated as advantageous alternatives to traditional small molecule surfactants, owing to their high interfacial adsorption energy and mechanical functionality. However, translating these benefits on an industrial scale requires continuous fabrication processes with high production yield. One potential solution is flash nanoprecipitation (FNP) which has been demonstrated as a scalable process for the production of polymeric nanocolloids with a rich library of morphologies. While advantageous as a continuous process, FNP of hydrophobic polymers has been limited to dilute polymer solution processing, a consequence of weak electrostatic stabilization during particle formation only afforded by the hydrophobic adsorption of naturally present anions to particle surfaces in water.

In this work, the FNP of homopolymers (polystyrene and polyisoprene) with an ionomer analog (lightly sulfonated polystyrene) is presented as a route for not only enhanced electrostatic stabilization, but also the tunable expression of charge groups on particles for producing Pickering emulsifiers. Anionic groups on adsorbed ionomer chains are shown to promote electrostatic repulsion between aggregating nuclei during FNP, allowing precise control over resultant particle size based on ionomer content and solution concentration. Additionally, ionomer-driven stabilization enables more concentrated solution processing, yielding up to a 10-fold increase in nanoparticle mass output.

Utilizing the tunable quantity of anionic surface charge groups from incorporated ionomers, the interaction between colloids and hydrophobic cations is then studied. As salt concentration is increased, size stability is found to trend non-monotonically, a phenomenon related to differing propensities for charge inversion due to the glassy nature of specific polymers. Lastly, the surface activity of various colloid-salt combinations is demonstrated via the formation of stable Pickering emulsions and tensiometry.