Macroemulsions multiple

Double or Multiple Macroemulsions. These macroemulsions are formed by two or more than two immiscible phases which are separated by at least two emulsifier films. Multiple emulsions can also be subdivided as single emulsions in two categories (0/W/0) and (W/O/W) emulsions (14). For a 0/W/0 system, the immiscible water phase separates the two oil phases, whereas for a W/O/W system, the immiscible oil phase separates the two aqueous phases. These emulsions are schematically shown in Figure 2. 

An emulsion is a significantly stable suspension of particles of liquid of a certain size within a second, immiscible liquid. The term significantly stable means relative to the intended use and may range from a few minutes to a few years. Investigators in this field distinguish between three different types of emulsions, based upon the size of the dispersed particles (1) macroemulsions, the most well-known type, opaque emulsions with particles >400 nm (0.4 pm), easily visible under a microscope (2) microemulsions, transparent dispersions with particles <100 nm (0.1 pm) in size and (3) nanoemulsions (miniemulsions), a type that is blue-white, with particle sizes between those of the first two types (100-400 nm [0.1-0.4 pm]. Multiple emulsions (Matsumoto, 1976), in which the dispersed particles are themselves emulsions, have been the subject of considerable investigation. 

Simple anulsions consist of dispersion of droplets of one liquid phase in another inunisable liqnid phase. Based on the type of the internal phase, two types of simple emulsions exist, namely, wato-in-oil (w/o) and oil-in-water (o/w) emulsions (Figures 58.6a and b). In w/o emulsions, the water disperses in the oil continuum phase, whereas, oil phase remains as dispersed in the water continuum phase in o/w emulsions. Emulsifiers are added to fecilitate the reduction in the surface tension amongst the immiscible phases. The type of the emulsions formed is determined by the type of the anulsifier used. Based on the size of the internal phase, simple emulsions can be divided in microemulsions and macroemulsions. If the emulsions contain more than two phases, then they are regarded as multiple emulsions. 

An important drawback of the process (so far) is that the products are by and large only single and multiple oxides. Not much attempt is apparently on record on macroemulsion-assisted synthesis of sulfides or metals, so commonly achieved via microemulsions, or nitrides and oxynitrides as precursor powders for advanced ceramics. 

The unfavorable aspect of having an emulsion arises outside the reservoir conditions. Although it is well known that macroemulsions are thermodynamically unstable, the presence of multiple... 

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