Spontaneous formation method

Gel emulsions can be prepared by the usual preparation method for W/O emulsions, dissolving a suitable emulsifier in the component that will constitute the continuous phase followed by addition of the component which will constitute the dispersed phase, with continuous stirring. However, they can be prepared according to several other methods that have been proposed specifically for highly concentrated emulsions.In the following, attention will be focused on the multiple emulsion method and spontaneous formation method, - because they constitute interesting novel methods of preparation. 

In the spontaneous formation method, emulsification is achieved by a rapid temperature change of a micellar solution or microemulsion without the need for mechanical stirring.It should be noted that for W/0 gel emulsions the system is below the HLB temperature at the start and emulsification takes place when an O/W microemulsion is rapidly heated from temperatures below to above the HLB temperature. Formation of O/W gel emulsions, by this method, is achieved by quickly cooling a water-in-oil microemulsion from a temperature higher than the HLB temperature of the system to a temperature below it, at which two phases, a micellar solution phase and an oil phase, appear. The emulsification process for a gel emulsion of the W/0 type is depicted in Figure 11.13. 

Different methods are used in microemulsion formation a low-energy emulsification method by dilution of an oil surfactant mixture with water and dilution of a water-surfactant mixture with oil and mixing all the components together in the final composition. These methods involve the spontaneous formation of microemulsions and the order of ingredient addition may determine the formation of the microemulsion. Such applications have been performed with lutein and lutein esters. ... 

Very recently a new method was developed that opens the possibility to polymerize even hydrophobic monomers in aqueous solution. This method is based on the finding that hydrophobic monomers can be made water-soluble by incorporation in the cavities of cyclodextrins. It has to be mentioned that no covalent bonds are formed by the interaction of the cyclodextrin host and the water-insoluble guest molecule. Obviously only hydrogen bonds or hydrophobic interactions are responsible for the spontaneous formation and the stability of these host-guest complexes. X-ray diffraction pattern support this hypothesis. Radical polymerization then occurs via these host-guest complexes using water-soluble initiators. Only after a few percent conversion the homogeneous solution becomes turbid and the polymer precipitates. 

This method is suggested as an alternative method for siRNA-lipoplex formation, when the spontaneous formation of lipoplex did not produce an effective gene silencing effect (See Note 13). It is important to note that application of vortex-mixing to form pDNA-lipoplex is not practicable, since it may damage the structure of pDNA. 

Prota s method cannot be employed in the synthesis of the trichochrome E and F skeleton because it would require the unstable 2H-1,4-benzothiazine 8 as starting material. However, the Italian group observed the spontaneous formation of compound 20 while attempting to prepare 2H- 1,4-benzothiazine... 

The experimental results indicate that in the range of nanometers other rules apply to the stability of different carbon structures than would on a macroscopic scale. This is evident, for example, from the spontaneous formation of various diamond materials with nanoscopic particles in different methods of preparation like CVD or detonation and shock wave synthesis. The products obtained include polycrys-taUine materials with particle dimension of 1-60 (tm that consist of primary par-... 

Later Ebersole et al. described a novel method for the immobilisation of biological species [69] based on the spontaneous formation of avidin and streptavidin monolayers onto gold. The monolayers formed irreversibly from aqueous solutions onto freshly formed gold surfaces of Pz crystals monolayers formed on aged gold surfaces showed lower activity. They demonstrated the use of this method using a DNA hybridisation assay and incorporated their AMISA technique to enhance the measured frequency change. 

Several methods are known for the reconstitution of HDL-like complexes from pure components (i) spontaneous formation of HDL discs from dimyristoylphosphatidyl-choline liposomes (ii) detergent-mediated reconstitution of HDL discs with various PL and (iii) co-sonication of apolipoproteins and lipids to form either discoidal or spherical HDL analogs [19]. 

In some cases under the conditions similar to those corresponding to the formation of lyophilic colloidal systems, a spontaneous formation of emulsions, the so-called self-emulsification, may take place. This is possible e.g. when two substances, each of which is soluble in one of the contacting phases, react at the interface to form a highly surface active compound. The adsorption of the formed substance under such highly non-equilibrium conditions may lead to a sharp decrease in the surface tension and spontaneous dispersion (see, Chapter III, 3), as was shown by A.A. Zhukhovitsky [42,43], After the surface active substance has formed, its adsorption decreases as the system reaches equilibrium conditions. The surface tension may then again rise above the critical value, acr. Similar process of emulsification, which is an effective method for preparation of stable emulsions, may take place if a surfactant soluble in both dispersion medium and dispersed liquid is present. If solution of such a surfactant in the dispersion medium is intensively mixed with pure dispersion medium, the transfer of surfactant across the low surface tension interface occurs (Fig. VIII-10). This causes turbulization of interface... 

Microemulsions can be prepared by controlled addition of lower alkanols (butanol, pentanol, and hexanol) to milky emulsions to produce transparent solutions comprising dispersions of either water-in-oil (w/o) or oil-in-water (o/w) in nanometer or colloidal dispersions (-100 nm). The alkanols (called cosurfactants) lower the interfacial tension between oil and water sufficiently for almost spontaneous formation. The miscibility of oU, water, and amphiphile (surfactant plus cosurfactant) depends on the overall composition, which is systan specific. Phase inversion method is further divided into two types ... 

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