《Formation and stability of paraffin oil-in-water nano-emulsions》.pdf

Journal of Colloid and Interface Science 303 (2006) 557–563 /locate/jcis Formation and stability of paraffin oil-in-water nano-emulsions prepared by the emulsion inversion point method Weirong Liu, Dejun Sun ∗ , Caifu Li, Qian Liu, Jian Xu Key Laboratory for Colloid and Interface Chemistry of Education Ministry, Shandong University, Jinan, Shandong 250100, People’s Republic of China Received 10 June 2006; accepted 23 July 2006 Available online 26 July 2006 Abstract Paraffin oil-in-water nano-emulsions stabilized by Tween 80/Span 80 were prepared using the emulsion inversion point method at different emulsification temperatures. Nano-emulsions with droplet size below 200 nm were formed above a critical surfactant-to-oil ratio of 0.20 at 50 ◦C. The main destabilization mechanism of the systems was found to be Ostwald ripening. An interesting phenomenon was that the Ostwald ripening rate declined as the surfactant concentration rose. Furthermore, flocculation was also found to contribute to the instability of the nano-emulsions, especially for those with low surfactant concentrations. Study on the electrophoretic properties of emulsion droplets revealed a negative value of the zeta potential, which was strongly dependent on the pH of the systems. © 2006 Elsevier Inc. All rights reserved. Keywords: Nano-emulsions; Emulsion inversion point; HLB; Long-term stability; Ostwald ripening; Zeta potential 1. Introduction ical energy stored in the ingredients and produce the nano-