New Low-Energy Method for Nanoemulsion Formation: pH Regulation Based on Fatty Acid/Amine Complexes

Phase inversion composition methods and phase inversion temperature methods are the common methods for nanoemulsion formation. The mechanisms governing both PIC and PIT are the same: composition or temperature can trigger a change in the surfactant spontaneous curvature during the emulsification process. It is anticipated that pH may also induce a change in the spontaneous curvature of pH-responsive surfactants to prepare nanoemulsions. Therefore, fatty acid/amine complexes were synthesized through electrostatic interactions. Based on these complexes, nanoemulsions were successfully prepared by pH regulation. Electrical conductivity and pH measurements were employed to determine the phase inversion process. Dynamic light scattering, digital fluorescence microscopy, and transmission electron microscopy were employed to characterize the droplet size and morphology of the nanoemulsion. The effects of complex concentration, NaCl concentration, and pH of the system were investigated. The developed method, phase inversion pH (PIpH) method, is a moderate and easy-control method. Using this method, the size distributions of nanoemulsion are monomodal and narrow. Nanoemulsion prepared by PIpH has a unique pH-responsive behavior that can be controllably regulated among nanoemulsions, emulsions, and phase separation systems.