Emulsification spontaneous

True spontaneous emulsification would lead to microemulsions, and those are not the subject of this chapter. There is, however, a closely related topic, that of interfacial turbulence. It has been studied by Stemling and Scriven and by Gouda and Joos.  

It may well be that a combination of fairly gentle stirring (i.e. fairly long deformation times) and the generation of interfacial turbulence may cause formation of small drops. A pre-requisite is that y is very small, which requires a high concentration of surfactant. Moreover, the surfactant must be well soluble in the disperse phase (be it as such or in the form of micelles) and nevertheless be more soluble in the continuous phase. Methods based on these principles may provide nearly the only manner in which reasonably small drops of a very viscous oil in an aqueous phase can be made. The authors are unaware, however, of a systematic experimental study on the role of interfacial instability in practical emulsification. 

Another example is the spontaneous emulsification of xylene/cetyl alcohol mixtures in an aqueous solution of sodium dodecyl sulphate. Here the extreme reduction of the interfacial 

The observation that mixed adsorption layers often provide an extreme reduction of the interfaeial tension and thereby enable easy or even spontaneous emulsification was studied systematically by Shinoda Friberg (1975) using the two surfactants CH3(CH2)g-(0CH2CH2)g50P(0H2) and CH3(CH2)j(0CH2CH2)30P(0H)2. By changing the composition of the mixed components in the system water/heptane conditions for the formation of liquid/crystalline phases and spontaneous emulsification were found. The results support the idea that the use of two suitably compatible emulsifiers is often much more efficient than single surfactant systems. 

The formation of emulsions or microemulsions is conneeted with several dynamic processes the time dependence of surface tensions due to the kinetics of adsorption, the dynamic contact angle, the elasticity of adsorption layers as a mechanic surface property influencing the thiiming of the liquid films between oil droplets, the mass transfer across interfaces and so on. Kahlweit et al. (1990) have recently extended Widom s (1987) concept of wetting or nonwetting of an oil-water interface of the middle phase of weakly-structured mixtures and microemulsions. They pointed out that the phase behaviour of microemulsions does not differ from that of other ternary mixtures, in particular of mixtures of short-chain amphiphiles (cf for example Bourrell Schechter (1988). 

Chapters 10 and 11 are dedicated to nex concepts of flotation and microflotation. As a main act of these processes the formation and stability of thin liquid films are discussed in Appendix 2D. 

Interfacial turbulence [60] Due to a nonuniform distribution of surfactant molecules at the interface or to local convection currents close to the interface, interfacial tension gradients lead to a mechanical instability of the interface and therefore to production of small drops. 

Negative interfacial tension [58,61-66] Due to adsorption of surfactants or cosurfactant molecules, the interfacial tension can become extremely low (less than 1 mN/m) and eventually transiently negative. Therefore, the interface can increase and any fluctuation can break it. 

The two aforementioned mechanisms involve a mechanical instability of the interface that breaks up and produces small droplets. 

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In buffered surfactant-enhanced alkaline flooding, it was found that the minimum in interfacial tension and the region of spontaneous emulsification correspond to a particular pH range, so by buffering the aqueous pH against changes in alkali concentration, a low interfacial tension can be maintained when the amount of alkali decreases because of acids, rock consumption, and dispersion [1826]. 

A similar technique, the so-called spontaneous emulsification solvent diffusion method, is derived from the solvent injection method to prepare liposomes [161]. Kawashima et al. [162] used a mixed-solvent system of methylene chloride and acetone to prepare PLGA nanoparticles. The addition of the water-miscible solvent acetone results in nanoparticles in the submicrometer range this is not possible with only the water-immiscible organic solvent. The addition of acetone decreases the interfacial tension between the organic and the aqueous phase and, in addition, results in the perturbation of the droplet interface because of the rapid diffusion of acetone into the aqueous phase. 

T Niwa, H Takeuchi, T Hino, N Kunou, Y Kawa-shima. Preparations of biodegradable nanospheres of water-soluble and insoluble drugs with d,l-lacti-de/glycolide copolymer by a novel spontaneous emulsification solvent diffusion method, and the drug release behavior. J Control Rel 25 89-98, 1993. 

Bouchemal, K., Briangon, S., Perrier, E. and Fessi, H. (2004) Nano-emulsion formulation using spontaneous emulsification solvent, oil and surfactant optimisation. International Journal of Pharmaceutics, 280, 241-251. 

Spontaneous emulsification, 10 127 Spontaneous fermentations for wine production, 26 468 Spontaneous fission, 21 304-305 Spontaneous ignition temperature, 7 438t... 

C.A. Miller Spontaneous Emulsification Produced by Diffusion—a Review. Colloid Surfaces 29, 89 (1988). 

K. J. Ruschak and C.A. Miller Spontaneous Emulsification in Ternary Systems with Mass Transfer. Ind. Eng. Chem. Fundam. 11, 534 (1972). 

M.J. Rang and C.A. Miller Emulsions and Microemulsions—Spontaneous Emulsification of Oil Drops Containing Surfactants and Medium-Chain Alcohols. Prog. Colloid Polym. Sci. 109, 101 (1998). 

M. J. Rang and C.A. Miller Spontaneous Emulsification of Oils Containing Hydrocarbon, Nonionic Surfactant, and Oleyl Alcohol. J. Colloid Interface Sci. 209, 179 (1999). 

N. Shahidzadeh, D. Boim, and J. Meunier A New Mechanism of Spontaneous Emulsification Relation to Surfactant Properties. Europhys. Lett 40, 459 (1997). R.W. Greiner and D.F. Evans Spontaneous Formation of a Water-Continuous Emulsion from a W/O Microemulsion. Langmuir 6, 1793 (1990). 

J. C. Lopez-Montilla, P.E. Herrera-Morales, S. Pandey, and D.O. Shah Spontaneous Emulsification Mechanisms, Physicochemical Aspects, Modeling and Applications. J. Dispersion Sci. Technol. 23, 219 (2002). 

These equations, referring to completely unstirred systems, are not usually valid in practice complications such as spontaneous interfacial turbulence and spontaneous emulsification often arise during transfer, while, if external stirring or agitation is applied to decrease Ri and R2, the hydrodynamics become complicated and each system must be considered separately. The testing of the above equations will be discussed below, after a consideration of overall coefficients and of interfacial turbulence. 

Diethylamine, transferring from 0.16 M solution in toluene to water, shows such strong spontaneous emulsification and turbulence that quantitative results are precluded 36). If, however, 1.25 mM sodium lauryl... 

The concept of interfacial mesophases promoting spontaneous emulsification (21.22) can be applied to the Tagat TO - Miglyol 812 system, where stable liquid crystalline dispersion phases are adequate to promote the process of self-emulsification. The stability of the resulting emulsion systems can also be accounted for by liquid crystalline interface stabilisation (23.24). Phase separation of material as observed above 55f surfactant, in conjuction with the increased viscosities of such systems, will inhibit the dynamics of the self-emulsification process and hence the quality of self-emulsified systems declines when the surfactant concentration is increased above 55. ... 

Spontaneous emulsification of oils carrying drugs make SEDDS good candidates for the oral delivery of hydrophobic drugs with adequate oil solubility since the drug will be presented as a fine (submicron) emulsion that has a large surface area across which diffusion can take place rapidly, thereby facilitating absorption into the body. 

Spontaneous emulsification and solvent diffusion method Solid lipid nanoparticles 20-80 nm Horn and Rieger, 2001 Cui et al., 2006 Ribeiro et al., 2008... 

Calomel electrodes are used, connected to the water phase on both sides of the black lipid film by KCl-containing capillaries. The water phase is generally 0.25M KC1, which precludes interface contamination by spontaneous emulsification. Carbon tetrachloride is used as the undermost oil layer, which serves exclusively as an electric seal. 

Microemulsions, like micelles, are considered to be lyophilic, stable, colloidal dispersions. In some systems the addition of a fourth component, a co-surfactant, to an oil/water/surfactant system can cause the interfacial tension to drop to near-zero values, easily on the order of 10-3 - 10-4 mN/m, allowing spontaneous or nearly spontaneous emulsification to very small drop sizes, typically about 10-100 nm, or smaller [223]. The droplets can be so small that they scatter little light, so the emulsions appear to be transparent. Unlike coarse emulsions, microemulsions are thought to be thermodynamically stable they do not break on standing or centrifuging. The thermodynamic stability is frequently attributed to a combination of ultra-low interfacial tensions, interfacial turbulence, and possibly transient negative interfacial tensions, but this remains an area of continued research [224,225],... 

When the minimum of y with respect to T is negative (Fig. 3), the interfacial tension is negative in the range of temperatures in which the curve y = y(T) intersects the abscissa. A negative y makes the water oil interface unstable to thermal and mechanical perturbations and a spontaneous emulsification with the formation of globules of oil in water and water in oil takes place. At low temperatures, because of coalescence, only a fraction of the globules of oil survive... 

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