Formation of Nano-emulsions by Low-Energy Emulsification Methods at Constant Temperature

Abstract

Formation of nano-emulsions has been studied in the system water/Brij 30/decane at 25 °C by three low-energy emulsification methods: (A) stepwise addition of oil to a water-surfactant mixture, (B) stepwise addition of water to a solution of the surfactant in oil, and (C) mixing all the components in the final composition. Nano-emulsions with average droplet size of 50 nm and high kinetic stability have been obtained only at oil weight fractions, R, lower than 0.3 by emulsification method B. Independent of the oil weight fraction, R, emulsions obtained by method B have lower polydispersity than those obtained by methods A and C. Phase behavior studies have revealed that compositions giving rise to nano-emulsions consist of Wm, (O/W microemulsion), LR (lamellar liquid crystalline), and O (oil) phases, at equilibrium. It has been shown that equilibrium properties cannot fully explain nano-emulsion formation. Low values of equilibrium interfacial tensions and phase equilibrium involving a lamellar liquid crystalline phase are probably required but not sufficient to obtain nano-emulsions in this system. The key factor for nanoemulsion formation has been attributed to the kinetics of the emulsification process. The change in the natural curvature of the surfactant during the emulsification process may play a major role in achieving emulsions with small droplet size.

Nano-emulsion formation by emulsion phase inversion

“…In order to illustrate the mechanisms involved in this lowenergy emulsification process, the steps of submicron-droplet formation by phase inversion are given in the following. As the water phase is poured into the oil phase, the system starts as a W/O microemulsion [15]. Upon increasing the volume fraction of water, water droplets merge together and bicontinuous or lamellar [15] structures are formed, which, after the EIP is passed, decompose into smaller oil droplets upon further increasing the water content.…”

“…As the water phase is poured into the oil phase, the system starts as a W/O microemulsion [15]. Upon increasing the volume fraction of water, water droplets merge together and bicontinuous or lamellar [15] structures are formed, which, after the EIP is passed, decompose into smaller oil droplets upon further increasing the water content. Further dilution with water does not change the droplet size at this stage of droplet formation.…”

Spontaneous emulsification of water in oil at appreciable interfacial tensions

“…In the case of ultralow interfacial tension this type of emulsification does not require energy input, as the ultralow interfacial tension leads to a spontaneous emulsification when the phases are brought in contact [1]. The full mechanism behind this phenomenon is still under investigation and is a matter for discussion despite the fact that microemulsions were first recorded in the XIX century [3][4][5][6][7][8][9][10].…”

The use of Brazilian vegetable oils in nanoemulsions: an update on preparation and biological applications

“…Thus, simple and cheaper strategies to obtain NE are the use of low energy approaches based on the spontaneous emulsification (SE, also called solvent displacement or self-emulsification) of oil droplets in oil-water surfactant by modifying the composition or environment (Sajjadi, 2006;McClements, 2012;Yukuyama et al, 2016). Other low-energy methods occur due to temperature variations during the emulsification process (PIT -Phase Inversion Temperature) (Shinoda, Saito, 1969;Forgiarini et al, 2001;Morales et al, 2003) and maintaining the temperature constant and varying the composition of the system (PIC -Phase Inversion Composition or EPI -Emulsion Phase Inversion) (McClements, Rao, 2011).NE have some advantages in relation to other systems. Compared to conventional emulsions (2-20 μm), which have a milky white appearance, NE feature a smaller droplet size (< 1μm) which gives them greater kinetic stability and translucent appearance (Tadros, Kessell, 2004;Constantinides, Chaubal, Shorr, 2008;Gupta et al, 2016).…”