Types of emulsions 
Oil in water (o/w): in which oil is the dispersed phase and water is the continuous phase.
Water in oil (w/o): in which water is the dispersed phase and oil is the continuous phase.
Emulsions have a cloudy or opaque appearance because particles scatter light when it passes through them. Since emulsions contain immiscible liquids, they are highly unstable. Various problems such as phase separation, creaming, cracking and flocculation and coalescence are observed. 
To overcome these problems, two novel …show more content…
Both the systems are transparent/ translucent in visibility because the droplet sizes are so small, even less than the visible spectrum of light that the light is passed directly through the system, without scattering.  Microemulsion and nanoemulsion are often argued on the same size range due to their names. However, it is not the size that differentiates microemulsions from nanoemulsions but various other properties. A microemulsion can be easily prepared spontaneously i.e. without any requirement of external energy. It can easily be prepared using gentle stirring and heating to speed up formation.  However, for the formation of a nanoemulsion, high amount of energy is required, such as ultrasonification or high pressure homogenizer. Although both the systems are similar in physical appearance as they are transparent/translucent systems with low viscosity, there are differences in their stability due to the fabrication methods used. Since nanoemulsions are formed due to high input of energy, they are highly kinetically stable, but microemulsions possess high thermal stability.  Since microemulsions are easily formed, they are easily unstabilised as well. Therefore, surfactant concentration required to stabilize the microemulsion is high unlike nanoemulsions, where low concentration of surfactant is required to stabilize the system. Concentration difference of surfactants in microemulsion and nanoemulsion, is supposedly an advantage for nanoemulsions, since high concentration of surfactants can be toxic to human system. [40 Fabrication of microemulsions is cost-effective as compared to nanoemulsions and fabrication methods of nanoemulsions can be easily scaled up to industrial level unlike microemulsions. Since, vortexing and stirring are difficult to be raised to an industrial scale.