Emulsified microdroplets

The transport properties of microemulsions are of great interest both for the information they provide about the physical properties of the systems, and in industrial applications of these materials. The transport of matter or energy through oil in water (0/W) microemulsions is determined both by the volume fraction and geometry of the oil and emulsifier microdroplets (the structure effect") and by possible modifications in the transport properties of the continuous water phase by its interaction with the hydrophilic groups in the surfactant and cosurfactant that stabilize the microemulsion (the "hydration effect"). Through the use of appropriate mixture theories, these two effects can in part be separated. 

Nylon microcapsules are formed by the interfacial polymerization of hexa-methylenediamine with sebacoyl chloride.22 The hexamethylenediamine is initially present in an aqueous enzyme solution, while the sebacoyl chloride is present in an organic phase such as 4 1 hexane/chloroform. The two solutions are mixed to form an emulsion. The nylon-6,10 membrane forms around the emulsified microdroplets, at the organic-aqueous interface ... 

Bulk-like water can be supercooled to temperatures around -16 to -23°C. However, water in thin films or in emulsified microdroplets can be supercooled to temperatures as low as -40°C [211-213]. In surfactant systems, free water is in enough large domains to supercool at -16 to -22°C [54,61,211]. 

It was observed that the titration of a coarse emulsion by a coemulsifier (a macromonomer) leads in some cases to the formation of a transparent microemulsion. Transition from opaque emulsion to transparent solution is spontaneous and well defined. Zero or very low interfacial tension obtained during the redistribution of coemeulsifier plays a major role in the spontaneous formation of microemulsions. Microemulsion formation involves first a large increase in the interface (e.g., a droplet of radius 120 nm will disperse ca. 1800 microdroplets of radius 10 nm - a 12-fold increase in the interfacial area), and second the formation of a mixed emulsifier /coemulsifier film at the oil/water interface, which is responsible for a very low interfacial tension. 

Emulsion Micellar Microdroplets Single- or multistage emulsification Emulsified liquid membrane extractions... 

Pancreatic lipase, with the aid of colipase, digests the triacylglycerols to 2-monoacylglycerols and free fatty acids, which are packaged into micelles. The micelles, which are tiny microdroplets emulsified by bile salts, also contain other dietary lipids such as cholesterol and the fat-soluble vitamins. 

Bile salts, which are produced in the liver from cholesterol obtained from the blood lipoproteins or synthesized from acetyl CoA, are secreted into the bile. They are stored in the gallbladder and released into the intestine during a meal. The bile salts emulsify dietary triacylglycerols, thus aiding in digestion. The digestive products are absorbed by intestinal epithelial cells from bile salt micelles, tiny microdroplets that contain bile salts at their water interface. After the contents of the micelles are absorbed, most of the bile salts travel to the ileum, where they are resorbed and recycled by the liver. Less than 5% of the bile salts that enter the lumen of the small intestine are eventually excreted in the feces. 

Emulsions are defined as dispersions of one liquid in another, stabilized by an interfacial film of emulsifiers such as surfactants and lipids. Emulsion formulations include water in od and oil in water emulsions, multiple emulsions, microemulsions, microdroplets, and liposomes. Microdroplets are unilamellar phospholipid vesicles that consist of a spherical lipid layer with an oil phase inside. 

Hemoglobin solution, isolated from human cells, is emulsified in oil to form a water-in-oil emulsion such as that shown in Fig. 19.2-1. The emulsion is prepared in a blender at 20,000 tpm so that stable microdroplets of hemoglobin rangitrg in size from 1 to 4 [Pg.263]

While microemulsions can be used as potential media for polymerization in which large molecular - weight polymers with narrower molecular weight distribution (MWD) may be achieved. The microemulsion polymerization system consists of three phases an aqueous phase (containing initiator, emulsifier, coemulsifier and some amount of monomer), emulsified monomer microdroplets or the monomer swollen micelles and monomer swollen polymer particles. Water is a most important ingredient of the microemulsion polymerization system. It is inert and acts as the... 

The continuous nucleation of polymer particles during polymerization results from the very high number of monomer-swollen micelles or microdroplets. The ratio of monomer to emulsifier or the monomer concentration at the reaction loci decreases with increasing conversion. The result of these two opposing effects is the appearance of maximal rate at ca. 10 - 20% conversion. The light scattering measurements prove the presence of both the microdroplets and mixed micelles (monomer - starved microdroplets). The ratio of microdroplets to mixed micelles... 

Figure 10.5 Preparation of water-in-oil-in-water (W/O/W) emulsion by the membrane-emulsifying technique. Water-in-oil (W/O) emulsion, prepared by sonica-tion and consisting of numerous vesicles of an aqueous solution of epirubicin, is passed through the porous-glass membrane into saline containing polyoxyethylene 60 stearate. IPSO microdroplets in W/O/W emulsion are almost equal in size and firmly enclose vesicles of epirubicin solution. Indicator 30 jam.

Microemulsions are transparent, thermodynamically stable multicomponent fluids, normally are composed of an aqueous component, an oily eomponent, an amphiphile (used as emulsifying agent) and frequently a co-surfactant. There are two different types of mieroemulsions (a) oil in water microemulsion (o/w-mieroemulsion), in which the hydrophobic part of the surfactant is absorbed on the surfaee of oil mierodroplets while the hydrophilic part is oriented toward the water and (b) water in oil microemulsion (w/o-microemulsion), in whieh the hydrophilic part of the surfactant is absorbed at the surface of water microdroplets while the hydrophobic part is oriented toward the oil. The latter is also... 

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