Emulsions direct

The preparation of a ferrofluid emulsions is quite similar to that described for double emulsions. The starting material is a ferrofluid oil made of small iron oxide grains (Fe203) of typical size equal to 10 nm, dispersed in oil in the presence of an oil-soluble surfactant. The preparation of ferrofluid oils was initially described in a US patent [169]. Once fabricated, the ferrofluid oil is emulsifled in a water phase containing a hydrophilic surfactant. The viscosity ratio between the dispersed and continuous phases is adjusted to lie in the range in which monodisperse fragmentation occurs (0.01-2). The emulsification leads to direct emulsions with a typical diameter around 200 nm and a very narrow size distribution, as can be observed in Fig. 1.33. 

The study of inverse adhesive emulsions has revealed the same features as direct emulsions [112,113]. Here again, it was shown that adhesion is favored when the surfactant becomes less soluble in the continuous phase [113]. This can be tested experimentally by using binary mixtures of oils, one in which the surfactant is soluble and another one in which the surfactant is insoluble. For example, water droplets can be stabilized in mineral oil by sorbitan monooleate (Span 80). This surfactant is soluble in dodecane whereas it is not in silicon oil. The affinity of the surfactant for the organic solvent can be tuned by mixing dodecane and silicon oil. As shown in Fig. 2.38, the energy of adhesion between water droplets strongly varies as the ratio of the mixture is changed. A sharp rise is noted as the surfactant... 

As for direct emulsions, the presence of excess surfactant induces depletion interaction followed by phase separation. Such a mechanism was proposed by Binks et al. [ 12] to explain the flocculation of inverse emulsion droplets in the presence of microemulsion-swollen micelles. The microscopic origin of the interaction driven by the presence of the bad solvent is more speculative. From empirical considerations, it can be deduced that surfactant chains mix more easily with alkanes than with vegetable, silicone, and some functionalized oils. The size dependence of such a mechanism, reflected by the shifts in the phase transition thresholds, is... 

The previous experimental observations reported in the preceding text are, at least to a certain extent, in agreement with the well-known Bancroft rule. Indeed, a double W/O/W emulsion turns into a simple direct one when a sufficient quantity of the water-soluble surfactant is added. Similarly, by shaking a 1 1 mixture of water and oil, each phase containing one of the two types of surfactants, a direct emulsion is obtained if the aqueous phase contains a large amount of water-soluble... 

Polymer emulsions can be produced by the direct and the inverse emulsion process. The direct emulsion polymerization can be performed in a batch, semibatch and continuous process. 

FIG. 9 Stability behavior of dodecane-water emulsions ( = 0.5) at various salt (NaN03) concentrations (indicated above) around the inversion point (a) stability of direct emulsions decreases with increasing salt activity (b) stability of inverse emulsions increases with increasing salt concentration. The polyelectrolyte emulsifier is 60C12Na. (From Ref. 151.)... 

High HLB numbers are characteristic of hydrophilic surfactants which stabilize direct emulsions the highest numbers correspond to micelle-forming surfactants. Oppositely, low HLB numbers are typical for oleophilic surfactants which act as stabilizers of inverse emulsions. 

Stabilization of emulsions by powders can be viewed as a simple example of structural- mechanical barrier, which is a strong factor of stabilization of colloid dispersions (see Chapter VIII, 5). The stabilization of relatively large droplets by microemulsions, which can be formed upon the transfer of surfactant molecules through the interface with low a (Fig. VII-10), is a phenomenon of similar nature. The surfactant adsorption layers, especially those of surface active polymers, are also capable of generating strong structural mechanical barrier at interfaces in emulsions. Many natural polymers, such as gelatin, proteins, saccharides and their derivatives, are all effective emulsifiers for direct emulsions. It was shown by Izmailova et al [49-52]. that the gel-alike structured layer that is formed by these substances at the surface of droplets may completely prevent coalescence of emulsion drops. 

The processes of emulsion breaking are similar in their nature and mechanisms to those of foam breaking [59]. Sedimentation of droplets takes place in dilute emulsions. Depending on the difference in densities of dispersed phase and dispersion medium, the sedimentation may proceed either in downward or upward directions. At lower density of dispersed phase the emulsion droplets float in an upward direction (the so-called creaming, typical for most direct emulsions [1]), while at higher density of dispersed phase sedimentation proceeds in a downward direction. 

One key to achieving the best combination of stencil profile and surface roughness lies in the selection of the stencil material. The right dual-cure emulsion must be selected for its wet-on-wet coating properties, solids content, and print definition. The fact is that you may have to accept a little give and take between print clarity and ink transfer. In photorealistic CID printing, Rz values for direct emulsion stencils generally are measured on a Rz scale from 4-10. 

Cam F, Colin A, Richard MF, Deleuze H, Seiler E, Birot M, et al. Inorganic monoliths hierarchically textured via concentrated direct emulsion and micellar templates. J Mater Chem 2004 14 1370-6. 

Silane-modified emulsion copolymers may be prepared by direct emulsion copolymerization of suitable silanes with other monomers, but it would be much more convenient to modify existing emulsion polymers by simple additions of silanes. 

The final step in preparing the screen for use is to coat it with a photosensitive emulsion. The so-called direct emulsion is initially in liquid form. To... 

Water in direct emulsion, containing the same concentration in Na2S04 and other salts as the acidified spent caustic (around 5 to 20% water depending on separation conditions). 

The TMPTA monomer and the Darocur 1173 photoinitiator are encapsulated in polyurethane microcapsules by in situ pol5mierization. Microcapsules are obtained by in situ pol)unerization in direct emulsion (OilAVater). At room temperature, deionized water and polyvinyl alcohol PVOH (3 wt. %) are mixed in a reactor equipped with a mechanical stirrer. Then, an organic solution of monomer (Hexamethylene diisocyanate HMDI/chloroform) containing the monomer (TMPTA) and photoinitiator (Darocur 1173) to be encapsulated is added to the aqueous solution leading to a stable QU/Water emulsion. After 5 minutes of stabilization, a hydrophilic monomer (Ethylene Diamine EDA in excess) is added to the emulsion - Figure 9. The reaction is continued until stabilization of the pH (around 5 hours). 

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