Formation of Concentrated Nanoemulsion by W/O Microemulsion Dilution Method: Biodiesel, Tween 80, and Water System

In this work, we show the formation of concentrated green O/W nanoemulsion (dispersed phase mass fraction was up to 0.5) by diluting W/O microemulsion in the water/Tween 80/biodiesel system. The mechanism of the formation of nanoemulsions was examined and illustrated by small-angle X-ray scattering (SAXS) and cryogenic transmission electron microscopy (cryo-TEM). At high temperature, nanosized droplets formed spontaneously due to the surfactant migration and inversion upon dilution of W/O microemulsions, but these droplets were highly unstable. When cooled to room temperature, their stability was highly enhanced due to the decrease of collision frequency rate and the enhancement of stabilization of the oil/water interface. Even though, the Ostwald ripening still results in growth of droplets of the nanoemulsions after long-term storage, which limits the practical applications of nanoemulsions. W/O microemulsions are thermodynamic systems. Hence, W/O microemulsions that can form nanoemulsions by simple dilution of water can be used as an alternative to O/W nanoemulsion during storage and transport. Furthermore, biodiesel nanoemulsions could meet the requirements of green chemistry and engineering and be used as new green lubricants in water-based drilling fluid.