Nanoemulsions stabilization

Qian, C. and McClements, D.J. (2011) Formation of nanoemulsions stabilized by model food-grade emulsifiers using high-pressure homogenization factors affecting particle size. Food Hydrocolloids, 25 (5), 1000-1008. 

Figure 15.13 Silicone oil in water nanoemulsions stabilized with HMI (top curve 1.6% w/w HMI bottom curve 2.4% wjw HMI).

The nanoemulsion mean droplet sizes were much smaller than those obtained in other systems using polar oil mixtures (above 500 nm) [18]. The findings verify that the low-energy emulsification methods are valid not only for aliphatic [9,10,13, 75, 76, 79-81] and semipolar oils [82-84], as reported in most studies devoted to low-energy emulsification, but also for polar solvent-preformed polymer mixtures. These nanoemulsions show good kinetic stability at 25 °C over a period of at least 24 h,... 

Klang, V., Matsko, N., Zimmermann, A.M., Vojnikovic, E. and Valenta, C. (2010) Enhancement of stability and skin permeation by sucrose stearate and cydodextrins in progesterone nanoemulsions. International Journal of Pharmaceutics, 393, 152—160. 

Lee, S.J. and McClements, D.J. (2010) Fabrication of protein-stabilized nanoemulsions using a combined homogenization and amphiphilic solvent dissolution/evaporation approach. Food Hydrocolloids, 24, 560-569. 

Wang, L., Tahor, R., Eastoe, J., Li, X., Heenan, R.K. and Dong, J. (2009) Formation and stability of nanoemulsions with mixed ionic—nonionic surfactants. Physical Chemistry Chemical Physics, 11, 9772-9778. 

Yang, H.J., Cho, W.G. and Park, S.N. (2009) Stability of oil-in-water nanoemulsions prepared using the phase inversion composition method. Journal of Industrial and Engineering Chemistry,... 

Yuan, Y., Gao, Y., Zhao, J., Mao, L. (2008). Characterization and stability evaluation of p-carotene nanoemulsions prepared by high pressure homogenization under various emulsifying conditions. Food Research International, 41, 61-68. 

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 this technique, a hydrophobic polymer is dissolved in an organic solvent, such as chloroform, ethyl acetate, or methylene chloride and is emulsified in an aqueous phase containing a stabilizer (e.g., PVA). Just after formation of the nanoemulsion, the solvent diffuses to the external phase until saturation. The solvent molecules that reach the water-air interphase evaporate, which leads to continuous diffusion of the solvent molecules from the inner droplets of the emulsion to the external phase simultaneously, the precipitation of the polymer leads to the formation of nanospheres. The extraction of solvent from the nanodroplets to the external aqueous medium can be induced by adding an alcohol (e.g. isopropanol), thereby increasing the solubility of the organic solvent in the external phase. A purification step is required to assure the elimination of the surfactant in the preparation. This technique is most suitable for the encapsulation of lipophilic drugs, which can be dissolved in the polymer solution. 

Very recently, a method to prepare water-soluble CdTe QDs with excellent chemical stability and quantum yields has been developed (Wang et al. 2006). By integrating these water-soluble with our nanoemulsion- or nanoparticle-based... 

Wooster, T. J., Golding, M., and Sanguansri, P. (2008). Impact of oil type on nanoemulsion formation and Ostwald ripening stability. Langmuir 24, 12758-12765. 

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. 

The stability of nanoemulsions prepared using isohexadecane was assessed by following the droplet size as a function of time. Plots of versus time for four... 

Microemulsions are thermodynamically stable phases, which can be represented by clear areas in equilibrium phase diagrams. Nanoemulsions are really small emulsions, with the main characteristics of emulsions they are not thermodynamically stable and the way they are prepared has a great impact on their physical stability. The only difference with common emulsions is their very small droplet size, which ranges from 10 to 500 nm. Accordingly, nanoemulsions may look bluish, due to light diffusion (brown/yellow by transmission), just like microemulsions close to a critical point. 

Unfortunately, the droplet size distribution of a nanoemulsion prepared by the PIT process is relatively large. Due to the high Laplace pressure, Ostwald ripening takes place rapidly, limiting the lifetime of the nanoemulsions to a few minutes to a few days. The addition of a water-insoluble component can significantly reduce the breakdown kinetics however, long-term stability is rarely achieved with this process. 

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]. 

Therefore, micelle-forming surfactant molecules (e.g., SDS) will be present in three different forms, namely, on the lipid surface, as micelles, and as monomeric surfactant molecules in solution. Lecithin will form liposomes, which have also been detected in nanoemulsions for parenteral nutrition [77], Mixed micelles have to be considered in glycocholate/lecithin-stabilized and -related systems. Micelles, mixed micelles, and liposomes are known to solubilize drugs, and are therefore attractive alternative drug-incorporation sites (especially with respect to the low incorporation capacity of lipid crystals). 

For styrene nanoemulsions prepared with 10 2 M sodium lauryl sulfate and a 1 1 molar ratio of ionic surfactant fatty alcohol, the order of decreasing stability with fatty alcohols of different chain length is Ci6 > Qg > CM > Ci2 > C10. For sodium lauryl sulfate-Ci6 alcohol mixtures, the order of decreasing stability with different sodium lauryl sulfate fatty alcohol ratios is 1 3 > 1 2 > 1 1 > 1 6 > 1 0.5. The 1 3 and 1 2 ratios produce emulsions with stabilities > 1 month. The presence of rodlike liquid-crystalline structures at 1 1 to 1 3 ionic surfactant fatty alcohol ratios is believed to be essential for the preparation of a stable nanoemulsion. (El-Aaser, 1984). 

This method has been used to prepare nanoemulsions of such polymers as cellulose esters and epoxy resins, similar to latexes produced by emulsion polymerization. The nanoemulsions are prepared by direct emulsification of solutions of the polymers in organic solvents, followed by removal of the organic solvent by steam distillation under reduced pressure. The nanoemulsions produced in this fashion had stabilities > 1 year. 

Nanocrystals, anatase Nanocrystals, offretite Nanoemulsion template Nanoparticles agglomerates, MFI Nanoparticles, Au Nanoparticles, Fe203 in MCM-41 Nanoparticles, Sn02 Nanoparticles, surfactant stabilized Nanoparticles, Zr02 in SBA-15 Nanoscopic precursor particles Nanoslabs, silicalite-1 Nanowires in FSM-16 Nanowires, Se in MFI Naphtha isomerisation Naphthalene isopropylation Naphthalene alkylation 25-0-03 25-P-Naphthene ring opening S-Naproxen synthesis... 

These cationic SLN are formulated from a matrix lipid surfactants to stabilize the formulation and cationic lipids to charge the SLN surface positively. The cationic lipids employed are the same used in cationic liposomes for transfection [28]. Eormulation optimization studies revealed that both the cationic lipid and the matrix lipid influence transfection activity [27]. Comparable results were found for the oil component in cationic nanoemulsions for transfection [29]. Several formulations made from different cationic lipids and matrix lipids were tested for in vitro transfection efficiency (Eigure 6.8). The SLN Cp DOTAP made from the wax cetyl pahnitate and the cationic lipid N-[l-(2,3-dioleoyloxy)propyl]-N,N,N-trimethylammonium... 

Nanoscale emulsions have gained technological interest because the transport efficiency of functional components in emulsion food systems is increased when droplets are in the nanoscale (Spernath and Aserin, 2006). In addition, these emulsions are transparent, and they have lower viscosity when compared to conventional emulsions, which make them suitable for use in beverages, for example. In recent years, considerable research effort was made to understand the physical properties, preparation, phase behavior, and stability of micro- and nanoemulsions. 

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