Oil-in-Water Nanosized Emulsions for Drug Delivery and Targeting. Tamilvanan Shunmugaperumal. Читать онлайн. Newlib. NEWLIB.NET

Автор: Tamilvanan Shunmugaperumal
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Химия
Год издания: 0
isbn: 9781119585251
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of the system at any given time, at the frontier between the growth and decrease of the droplets. Consequently, Ostwald ripening is reflected by a linear relationship between the cube radius and time.

      A final remark, which may be of importance here, concerns the influence on the nanosized emulsion destabilization of layer density and structure in the interfacial zone. Indeed, up to now it has been considered that Ostwald ripening is a diffusion‐controlled process, but this assumption does not take into account the fact that surfactants, polymeric emulsifiers or stabilizers can create a thick steric barrier at the droplet interface (Goldberg and Higuchi 1969; Yotsuyanagi et al. 1973). As a consequence, the diffusion of the inner material of the droplets may be slowed down, reducing the ripening rate. The substantial difference in stability between nanoemulsions and nanocapsules (another colloidal API delivery system having polymeric outer shells covered on the dispersed oil droplets) for instance, appears essentially from such details.

      Before proceeding into Chapter 2, a brief description concerning classification of nanosized emulsions is presented below.

       1.1.2.3. Classification of Oil‐in‐Water Nanosized Emulsions

      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 (δk) 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).

      (1.5)

      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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