Nanoemulsions are kinetically stable, dispersed oil droplets on the nanometer diameter scale. They owe their long-term stability to surfactants, amphiphilic molecules typically with a long carbon tail and a polar head group. Surfactant-stabilized nanoemulsions are widely prevalent in various applications, including oil spill remediation, cosmetics, and pharmaceutical products. Though many studies have been conducted to understand how surfactants of varying charges interact at surfaces, much less is understood about the interfacial behavior and properties of zwitterionic surfactants. Yet, the interest in zwitterionic surfactants is rising due to their enhanced biosafety and biodegradability. In this study, we investigate how the zwitterionic surfactant dodecyldimethylammoniopropanesulfonate (DDAPS) stabilizes nanoemulsions with other additives such as salts and co-surfactants as co-stabilizers. By employing dynamic light scattering (DLS) and pendant drop tensiometry, we determined the stabilizing capacity and surface activity of DDAPS with various co-stabilizers. Further, to better understand the interfacial molecular conformation of DDAPS at the droplet surface, we used vibrational sum frequency scattering spectroscopy (VSFSS) to measure the vibrational modes of the surfactant alkyl tails. We show that DDAPS alone does not form stable, monodispersed nanoemulsions, and requires the aid of co-stabilizers. In conjunction with co-stabilizers, DDAPS not only stabilizes and adsorbs to the droplet surface, it also adopts a net ordering that can be influenced by the type of co-stabilizer, providing insight into how zwitterionic surfactants can be effective in commercial and industrial applications.

Interfacial behavior and molecular conformation of zwitterionic surfactants at the oil/water interface in the presence of co-additives

ACS Spring 2022

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