Effect of the Polymer Glass Transition on Size Stability in Salted Colloidal Dispersions

Polymeric nanoparticles (NPs) offer a wide range of available chemistries for use in applications such as interfacial adsorption, self-assembly, and encapsulation. However, to maintain the advantageous properties enabled by their size, NPs must be stabilized via repulsive interactions to minimize aggregation over time. While ionic strength is commonly used to adjust properties of charged NP dispersions, additional formulation handles for tuning species-specific interactions would allow for greater control over dispersion properties and enable use of multi-component particle morphologies.

In this work, the size stability of salted NP dispersions is demonstrated to directly correlate with the glassy behavior of constituent polymers. Using flash nanoprecipitation as a versatile fabrication technique, dispersions of rubbery and glassy polymers are produced and their stability in the presence of non-adsorbing and adsorbing salts is measured. For a non-adsorbing salt such as KCl, rubbery NPs exhibit a higher critical coagulation concentration than glassy NPs whereas for hydrophobic adsorbing salts, glassy NPs underwent surface potential inversion corresponding with reentrant stability trends. Using these findings, dispersions are formulated to enable their use as Pickering emulsifiers.