Tamilvanan Shunmugaperumal - Oil-in-Water Nanosized Emulsions for Drug Delivery and Targeting

Figure 1.2. Classification of oil‐in‐water (o/w) nanosized emulsions based on emulsifier molecules.

According to Capek (2004), the stability of the electrostatically‐ and sterically‐stabilized o/w nanosized emulsions can be controlled by the charge of the electrical double layer and the thickness of the droplet surface layer formed by non‐ionic emulsifier, respectively. In spite of the similarities between electrostatically‐ and sterically‐stabilized emulsions, there are large differences in the partitioning of molecules of ionic and non‐ionic emulsifiers between the oil and water phases and the thickness of the interfacial layers at the droplet surface (Capek 2004). The thin interfacial layer (the electrical double layer) at the surface of electrostatically stabilized droplets does not create any steric barrier for mass transfer. This may not necessarily be true for the thick interfacial layer formed by a non‐ionic emulsifier. The sterically‐stabilized oil droplets, however, can favor the transfer of materials within the intermediate agglomerates. Hence, the stability of electrosterically‐stabilized emulsion ( δ k) is controlled by the ratio of the thickness of the non‐ionic emulsifier adsorption layer ( δ ) to the thickness of the electrical double layer ( k −1) around the oil droplets (Capek 2004).

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This section says that although the o/w nanosized emulsions belong to MS category in terms of stability aspects, many competing forces actually determine the stability of emulsions. The group of API molecules suitable to be incorporated into the o/w nanosized emulsions is carefully revived by interpreting the physicochemical properties (molecular size and structure, melting point, log P value, etc.) of individual APIs along with their solubility and permeability characteristics.

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