Nano-emulsions are emulsions with droplet sizes from 20 nm up to 200-500 nm, thermodynamically unstable, and appear transparent or translucent to the naked eye. Nano-emulsions are very useful in many industries; such as food, pharmaceutical, cosmetic, and chemical. Forming nano-emulsions using a method that requires energy input from a mechanical device is known as a ‘high-energy method’, while a method using chemical energy stored in the components is referred to as a ‘low- energy method’. The low-energy method can be classified into three categories: the Phase Inversion Temperature method, Phase Inversion Composition method or Emulsion Inversion Point method and the Spontaneous Emulsification method. To study nano-emulsification using the low-energy methods, phase diagrams are used to determine the phase behavior of the components and specify the temperature and concentrations at which various structures exist at equilibrium with desired properties. Most research focuses on droplet size and polydispersibility of nano-emulsions, because these properties influence physicochemical properties, appearance and stability of nano-emulsions. There have been many studies on the effect of composition and the major determining factors in the emulsification process on droplet size and polydispersibility of nano-emulsions such as surfactant type, concentration, location, oil type, surfactant-to-oil ratio, salt, stirring speed, and temperature.
The surface-oil contents of microcapsules with differing oil droplet-to-microcapsule size ratios were estimated based on a two-dimensional percolation model to examine the effects of differences in the ratio distribution. In the model, squares were divided into equal lattices that were sized to obey a log-normal distribution. The surface-oil contents of microcapsules with various volumetric oil fraction and different variances of the ratio were evaluated. The variance in the distribution of the oil droplet-to-microcapsule size ratio had no significant effect on the surface-oil content at any oil fraction in the microcapsules.