Layer-by-layer (LbL) deposition of oppositely charged polyelectrolytes is a technique commonly employed for modifying surface functionalities in various systems. For the design of drug delivery systems, alternating layers of different biopolymers often coat nanoemulsions, which house and protect the cargo until the time and destination of delivery. While several experimental techniques have been employed to study LbL processes on a flat substrate, obtaining structural information at a curved oil/water interface is much more difficult due to experimental limitations with probing spherical droplets. In this work, we investigate both the macroscopic and molecular-level surface properties of nanoemulsions stabilized by a cationic surfactant and two different polymers: anionic poly(styrene sulfonate) (PSS) and partially cationic polyethylenimine (PEI). Taking advantage of the variable charge of PEI with pH, important insights into the interplay between electrosterics and hydrophobicity upon co-adsorption are revealed. To probe interfacial layering properties, we use vibrational sum frequency scattering spectroscopy in tandem with zeta potential measurements to determine the adsorptive behavior and molecular conformational arrangement of the polymer layers. Complementing these interfacial studies are dynamic light scattering experiments measuring the nanoemulsion size distribution and polydispersity index over a 30-day period. Our spectroscopic results of the nanoemulsion surfaces show that the polymer layers display a significant degree of molecular orientation on co-adsorption, which can be controlled by surfactant concentration, PEI concentration, and pH. Together, these results provide an understanding of how molecular surface properties of multi-polymer coated nanoemulsions contribute to synergistic effects and droplet stability, enabling advancements in applications surrounding biopharmaceuticals, cosmetics, and food sciences.

Peeling back the layers: Investigating how multi-polymer layering influences nanoemulsion surface structure and stability

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.