Nanoemulsions spontaneous

Emulsions are two-phase systems formed from oil and water by the dispersion of one liquid (the internal phase) into the other (the external phase) and stabilized by at least one surfactant. Microemulsion, contrary to submicron emulsion (SME) or nanoemulsion, is a term used for a thermodynamically stable system characterized by a droplet size in the low nanorange (generally less than 30 nm). Microemulsions are also two-phase systems prepared from water, oil, and surfactant, but a cosurfactant is usually needed. These systems are prepared by a spontaneous process of self-emulsification with no input of external energy. Microemulsions are better described by the bicontinuous model consisting of a system in which water and oil are separated by an interfacial layer with significantly increased interface area. Consequently, more surfactant is needed for the preparation of microemulsion (around 10% compared with 0.1% for emulsions). Therefore, the nonionic-surfactants are preferred over the more toxic ionic surfactants. Cosurfactants in microemulsions are required to achieve very low interfacial tensions that allow self-emulsification and thermodynamic stability. Moreover, cosurfactants are essential for lowering the rigidity and the viscosity of the interfacial film and are responsible for the optical transparency of microemulsions [136]. 

Santos-Magalhaes et al. [27] reported on PLGA nanocapsules/nanoemulsions for benzathine pencillin G. Nanoemulsions were produced by spontaneous emulsification and nanocapsules by interfacial deposition of the pre-formed polymer. They have observed similar release kinetics from both formulations [27]. 

Phase inversion methods are based on spontaneous O/W nanoemulsion formation induced by controlling the interfacial behavior, from predominantly lipophilic to predominantly hydrophilic, of the surfactants at the O/W interface, in response to changes in system compositions or environmental conditions. ... 

Nanoemulsions do not form spontaneously and so the droplet structure is predominantly a product of the sequence and magnitude of shear stresses used in their formation. These shear stresses have to work against the interfacial... 

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