Nanosized droplets

Figure 3 Schematic drawings of thermograms (a) sohdifi cation of pure compound in hulk (h) melting of a pure com pound (c) solidification of a monodispersed pure compound (d) solidification of a polydispersed pure compound (e) melt ing of nanosized droplets (Gaussian function of size distribu tion). dq/dt energy registered by the calorimeter Tgi temperature of solidification Tjjj temperature of melting T most probable temperature of sobdification.

A microemulsion is a thermodynamically stable three-component system two immiscible components (generally water and oil) and a surfactant molecule that lowers the interfacial tension between water and oil resulting in the formation of a transparent solution. Water-in-oil microemulsions involve dispersion of the aqueous phase as nanosized droplets (5-25 nm in diameter) surrounded by a monolayer of surfactant molecules in the continuous hydrocarbon phase. These micellar droplets exhibit a dynamic exchange of their contents, which further facilitates the reactions between reactants dissolved in different droplets. One can synthesize size-controlled crystallites by carrying out a wide variety of chemical reactions in nanodroplets using this micellar exchange. Different types of microemulsions are... 

Electroencapsulation is an application of electrospraying in which liquid is atomized into micro- or even nanosized droplets using electrostatic forces alone. The method allows better controllability of the capsulation process than, e.g., the most commonly used spray drying. Due to the applied electrostatic forces, it also enables production of complex capsule structures, like solid shell covered liquid core particles. In this review, we will focus on electroencapsulation processes used to improve the handling, processing, and administration of porous silicon-based drug delivery systems. 

Microemulsions Processes and Products. In contrast to the above, microemulsions in selected compositional areas ofwater-oil-surfactant systems are thermodynamically stable, isotropic dispersions of nanosized droplets of one liquid in another immiscible liquid... 

The most common technique used for the preparation of PLGA nanoparticles is the emulsification-solvent evaporation technique. This technique allows the encapsulation of hydrophobic drugs and consists of dissolving the polymer and the compound in an organic solvent. The emulsion oil (O) in water (W) is prepared by adding water to a polymer solution. The nanosized droplets are induced by sonication or homogenization. The solvent is then evaporated or extracted and the nanoparticles collected after centrifugation [69,70]. 

Microemulsions in selected compositional areas of water-oil-surfactant systems are thermodynamically stable, and isotropic dispersions of nanosized droplets of one liquid in another immiscible liquid (W/O or O/W) are obtained. The water phase, similarly to the case of macroemulsions, could be water in which an alkoxide is to be added, as well as a sol or an alkoxide solution. The difference between microemulsion and macroemulsion systems consists of the amount of surfactants used (10-40% in the former case and 1-2% in the latter case). 

Fig. 13.11 Injected droplet model proposed to explain how nonvolatile species become heated in a collapsing bubble. Nanosized liquid droplets enter the bubble as a result of interfacial instabilities...

Out of these assemblies, microemulsion droplets and swollen micelles have been widely used as nanoreactors for inorganic nanoparticie synthesis [20-23]. These self-assembled nanosized beakers/droplets provide a robust and tunable environment that permits size-controlled encapsulation of... 

Infrared spectra suggested that a sulfate ion coordinates to two titanium atoms as a bidentate in particles. The maximum particle size was found at Aerosol OT mole fraction of 0.35 in the mixtures. The particle size increased linearly with increasing the concentration of sulfuric acid at any Wo, but with increasing Wo the effect was the opposite at any sulfuric acid concentration. These effects on the particle size can be explained qualitatively in relation with the extent of number of sulfate ions per micelle droplet. These precursor particles yield amorphous and nanosized TiO particles, reduced by 15% in volume by washing of ammonia water. The Ti02 particles transformed from amorphous to anatase form at 400°C and from anatase form to rutile form about at 800°C. In Triton X-100-n-hexanol-cyclohexane systems, however, spherical and amorphous titanium hydroxide precursor were precipitated by hydrolysis of TiCl4 (30). When the precursor particles were calcinated,... 

Over the last decade, o/w nanosized emulsions containing either anionic or cationic droplets have been recognized as interesting and promising ocular topical delivery vehicles for lipophilic drugs. Complete details are available elsewhere [117]. As an overview of this topic, important results on emulsion-based ocular topical drug delivery are covered below and are listed in Table 5. 

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