Valentina Preziosi
University of Naples "Federico II", Italy

The effect of flow on emulsion microstructure in a phase inversion process

In this work, we use a simple low energy emulsification processing to create nanoemulsions. Starting from a system made of oil and surfactants (one hydrophilic and one hydrophobic), with a gel-like behavior at rest, by applying mild flow conditions the system can be reversibly converted into highly viscoelastic nanoemulsions. Once the flow is stopped, the system spontaneously reverts to the starting gel-like state. Our approach is based on dropwise addition of water to a concentrated oil-surfactant solution under stirring, until a striking transition from a transparent, purely viscous Newtonian fluid to a turbid, highly viscoelastic material, climbing up over the impeller, is observed. This pathway is usually exploited in “phase inversion concentration” process [1,4-9] as a means to obtain stable nano and microemulsions. To outline emulsion morphology development and the effect of flow on the microstructure, confocal microscopy and rheological measurements are exploited. Rheological measurements probe the increased viscoelasticity induced by water addition up to the point of bicontinuous phase formation. Confocal microscopy reveals the formation of complex mesoporous structures at the microscale. Moreover, the effect flow on the microstructure along the phase inversion emulsification process is investigated by performing experiments in a microfluidic set-up. [1]C. Solans and I. Solé, Current Opinion in Colloid & Interface Science 17, 246 (2012). [2]H. Kunieda and K. Shinoda, Journal of Dispersion Science and Technology 3, 233 (1982). [3]K. Roger, Current Opinion in Colloid & Interface Science 25, 120 (2016). [4]A. Perazzo, V. Preziosi, and S. Guido, Advances in Colloid and Interface Science 222, 581 (2015). [5]A. Kumar, S. Li, C.-M. Cheng, and D. Lee, Industrial & Engineering Chemistry Research 54, 8375 (2015). [6]J. L. Salager, A. Forgiarini, L. Márquez, A. Peña, A. Pizzino, M. P. Rodriguez, and M. Rondón-González, Adv Colloid Interface Sci 108-109, 259 (2004). [7]N. Anton and T. F. Vandamme, International Journal of Pharmaceutics 377, 142 (2009). [8]K. Piela, G. Ooms, and J. V. Sengers, Physical Review E 79, 021403 (2009). [9]F. Bouchama, G. A. van Aken, A. J. E. Autin, and G. J. M. Koper, Colloids and Surfaces A: Physicochemical and Engineering Aspects 231, 11 (2003).