Dispersion nanoemulsion

Phase inversion along the dilution path (by addition of water to the oil/surfactant mixture) followed for nanoemulsion preparation was confirmed by conductivity measurements, and was found to be essential for obtaining finely dispersed systems, as transparent dispersions were not obtained if the order of addition of the components was changed following an experimental path with no phase inversion (Figure 6.2). 

Figure 6.4 TEM image of the dispersion of nanoparticles obtained after evaporation of the solvent of a nanoemulsion with an O/S of 70 30 and a water content of 90wt% and negative staining with a phosphotungstic acid solution. Reproduced with permission from [54].

Maruno, M. and da Rocha-Filhoa, P.A. (2010) O/W nanoemulsion after 15 years of preparation a suitable vehicle for pharmaceutical and cosmetic applications. Journal of Dispersion Science and Technology, 31, 17-22. 

The drug dissolved or dispersed in the melted lipid is poured into an aqueous emulsifier phase of the same temperature. By means of a rotor-stator homogenizer (e.g., an Ultra-Turrax), an o/w preemulsion is prepared and is then homogenized at high pressure and at a temperature at least 10°C above the melting point of the lipid. In most cases, nanoemulsion arises after only three to live homogenization cycles at 500 bar. Nanoparticles are formed by cooling the nanoemulsion to room temperature. 

When a NAPL reaches the subsurface, it may by subject to mechanical forces that lead to the formation of a mixed NAPL-water micro-/nanoemulsion characterized by the presence of micro- and nanodroplets of organic compounds. These micro- and nanoemulsions are transparent or translucent systems, kinetically (nano-) or thermodynamically (micro-) stable, and display an apparent increase in aqueous solubility as compared to the intrinsic solubility of the NAPL itself (Tadros 2004). The very small droplet size (50-200 nm in the case of a nanoemulsion) causes a large reduction in the force of gravity, enabling the system to remain dispersed and... 

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]. 

In principle, in the preparation of medicated nanoemulsions, the drug is initially solubilized or dispersed together with an emulsifier in suitable single oil or oil mixtures by means of slight... 

Although many areas of nanotechnology do not directly deal with colloidal dispersions (such as nanoelectronic devices [952]) other areas do, such as the use of colloidal ink dispersions in robocasting to build near-nanometre scale three-dimensional structures. The possible use of nanoemulsions for intravenous delivery and in medical diagnostics has already been mentioned in Sections 14.4 and 14.5. Some other application areas include ... 

Fig. 26 Morphology of dispersed A18749 nanoemulsion held at 350 °C as a function of time prior to slow cooling (a) 5 min (b) 10 min (c) 30 min (d) 60 min. Black arrows indicate regions in the insets white arrows (in d) indicate highly retracted upper edges of lamellae...

Fig.27 Morphology of dispersed A18749 nanoemulsion sintered (a) on mica (350 °C for 30 min) and (c) in the presence of adventitious NaCl on glass (350 °C, 2 h). (b) Epitaxially oriented bands of a nanoemulsion similar to A18749 sintered at 350 °C for 30 min on mica...

One example that can demonstrate the effectiveness and great promise of nanoencapsulation is the curcumin nanoemulsions. Curcumin is the major yellow pigment in turmeric Curcuma longa Linn). In South and Southeast Asia, curcumin preparation or turmeric has been used extensively to treat inflammatory conditions and chronic diseases (Reddy and Rao 2003). Orally administered curcumin usually has low systemic bioavailability. Only trace amounts of curcumin (or its metabolites) appear in the blood, and most of ingested curcumin is excreted in the feces. One reason is that curcumin has low solubility and does not disperse for absorption. The absorbed curcumin is rapidly metabolized in the intestine and liver to several reduction products (di-, tetra-, and hexa-hydrocurcumin and hexahydrocurcuminol) and... 

Several classes of formulations of disperse systems are encountered in the chemical industry, including suspensions, emulsions, suspoemulsions (mixtures of suspensions and emulsions), nanoemulsions, multiple emulsions, microemulsions, latexes, pigment formulations, and ceramics. For the rational preparation of these multiphase systems it is necessary to understand the interaction forces that occur between the particles or droplets. Control of the long-term physical stability of these formulations requires the application of various surfactants and dispersants. It is also necessary to assess and predict the stability of these systems, and this requires the application of various physical techniques. 

One of the main problems with nanoemulsions is Ostwald ripening which results from differences in solubility between the small and large droplets. The difference in the chemical potential of dispersed phase droplets between different-sized droplets as given by Lord Kelvin [17],... 

CDC are defined only by their size (most scientists agree on sizes below 1 pm others set 0.5 pm as the upper limit). CDC are very heterogeneous in all other aspects (e.g., thermodynamic stability, chemical composition, and the physical state, including solid, liquid, or liquid-crystalline dispersions) [ 1 ]. The most prominent examples are nanoparticles, nanoemulsions, nanocapsules, liposomes, nanosuspensions, (mixed) micelles, microemulsions, and cubosomes. Some CDC have reached the commercial market. Probably the best known example is the microemulsion preconcentrate of cyclosporine (Sandimmun-Neoral), which minimized the high variability of pharmacokinetics of the Sandimmun formulation. In addition, intravenous injectable CDC have been on the commercial market for many years. Examples include nanoemulsions of etomidate (Etomidat-Lipuro) and diazepam (Diazepam-Lipuro) [2-4], mixed micelles (Valium-MM, Konakion), and liposomes (AmBisome) [5]. 

An emulsion is a significantly stable suspension of particles of liquid of a certain size within a second, immiscible liquid. The term significantly stable means relative to the intended use and may range from a few minutes to a few years. Investigators in this field distinguish between three different types of emulsions, based upon the size of the dispersed particles (1) macroemulsions, the most well-known type, opaque emulsions with particles >400 nm (0.4 pm), easily visible under a microscope (2) microemulsions, transparent dispersions with particles <100 nm (0.1 pm) in size and (3) nanoemulsions (miniemulsions), a type that is blue-white, with particle sizes between those of the first two types (100-400 nm [0.1-0.4 pm]. Multiple emulsions (Matsumoto, 1976), in which the dispersed particles are themselves emulsions, have been the subject of considerable investigation. 

Maali A and Hamed Mosavian MT. (2013). Preparation and application of nanoemulsions in the last decade (2000-2010). Journal of Dispersion Science and Technology, 34, 92-105. 

Emulsions and nanoemulsions are heterogeneous systems consisting of two immiscible liquids, with one liquid phase being dispersed as droplets into another continuous liquid phase and stabilized through an appropriate emulsifier. In particular, nanoemulsions are characterized by a nanometric size (<100 nm), while emulsions are in the submicrometric and micrometric range. 

Curcumin Tween 20/Glycerol monooleate/Medium chain triglycerides/water Multiple layer nanoemulsions Microemulsion Solubilization and dispersion in food systems [183]... 

Nanoemulsion is a kinetically stable clear dispersion of two immiscible phases, oil phase and water phase, in combination with surfactant molecules. Small particles or droplets, with a size range of 5—200 nm usually comprise the dispersed phase (Shah and Bhalodia, 2011). 

---