**1. Introduction**

### **1.1 Nano-emulsions**

Nano-emulsions can be defined as ternary systems composed of nano-sized droplets (20–500 nm) dispersed in a continuous phase and stabilized by amphiphilic molecules known as surfactants [1–4]. The nature of the droplets and continuous phase can be aqueous or oily, forming oil-in-water (O/W) or water-in-oil (W/O) nano-emulsions. Regarding surfactants, these molecules must possess a
