Nanometric-Scaled Emulsions (Nanoemulsions)

Nanotechnology, shortened to nanotech, is the study of the controlling of matter on an atomic and molecular scale. Generally, nanotechnology deals with structures sized between 1 to 100 nanometer in at least one dimension and involves developing materials or devices within that size. The use of nanotechnology in the field of pharmaceutics and drug delivery has grown over the last few years, so remarkably that the pharmaceuticals developed on the basis of this technology are termed as Nanopharmaceuticals. Among the nanopharmaceuticals currently being used or under investiga-fine-dispersed emulsions and so forth) are a group of dispersed particles used as vehicles for pharmaceutical aims and seem to be promising for the future of cosmetics, diagnosis, drug therapies and biotechnologies. Due to the similarities between microemulsions and nanoemulsions, various definitions have been proposed in the literature, regarding nanoemulsions, as follows: Nanoemulsions are non-equilibrium emulsions with a remarkable small droplet size in the range of 20-200 nm, regardless of the preparation method. Nanoemulsions are transparent or translucent systems containing droplets with a mean diameter in the range between 100 – 500 nm, and unlike thermodynamically stable microemulsions, they are kinetically stable. Nanoemulsions are isotropic and thermodynamically stable dispersions consisting of oil, sur-factants, co-surfactants and aqueous phase, usually with a droplet diameter within the range of 10-100 nm. Nanoemulsions are non-equilibrium systems with a spontaneous tendency to separate into the constituent phase, although they may possess a relatively high kinetic stability for a long time, unlike microemulsions which are equilibrium systems (i.e. thermodynamically stable). Nanoemulsions can not be formed spontaneously and consequently energy input is required. However, some authors prefer to use the word " nanoemulsions " only for those emulsions with droplet size in the nanometer range obtained by high shear methods (e.g. high shear stirring, high pressure homogenization and ultrasound generators). These authors believe that the emulsions prepared by methods such as self-emulsifying and phase inversion temperature/composition, although possessing an extremely small droplet size, should not be considered as nanoemulsions, due to the influence of the method of preparation on the droplet size, stability and other emulsion properties. As generally accepted, nanoemulsions are transparent or translucent dispersions, having the droplet size of less than 100 nm (the same droplet length-scale as microemulsions) with ultra low interfacial tension, large o/w interfacial areas and long-term physical stability (they are sometimes referred to as " Approaching Thermodynamic Stability "). The following main advantages have made …