Emulsions with immiscible liquids

The choice of scale-up technique depends on the particular system. As a general guide, constant tip speed is used where suspended solids are involved, where heat is transferred to a coil or jacket, and for miscible liquids. Constant power per unit volume is used with immiscible liquids, emulsions, pastes and gas-liquid systems. Constant tip speed seems more appropriate in this case, and hence the rotor speed should be 0.66 Hz. The... 

A problem with reactions involving immiscible liquids is that the reagents and analyte(s) are often dissolved in different phases. Hence, any reaction between these species can only occur in the interfacial region between the liquids and this is commonly a very slow process. Here sonication can be used to produce very fine emulsions from immiscible liquids. This is the result of cavitational collapse at or near the interface, which causes disruption and impels jets of one liquid into the other to form extremely fine emulsions (Figure 2.31). These emulsions increase the interfacial contact area between the liquids, dramatically increasing the reactivity between species dissolved in the separate liquids. 

The conditions change completely when a dilute soap solution, instead of straight water, is used and it is shaken with an oil. In doing so, a milky liquid develops, which remains in this state without separating for a considerable length of time. Then, a typical emulsion is formed. Therefore, three components are necessary to produce emulsions two immiscible liquids, and a substance which helps to promote the emulsion and to keep it stable, i.e., the emulsifying agent, or emulsifier. 

This type of technique is faced by freewill isotropic fluid microstructures in a colloidal equilibrium dispersion form. Microemulsions with immiscible liquids, especially short-chain alcohols such as methanol, ethanol, 1 -butanol, and ionic or nonionic am-phiphiles, have been studied to reduce the high viscosity of vegetable oils (Demirbas, 2003). Through this method, the problem of the high viscosity of vegetable oils would be solved (Ma Hanna, 1999). Regarding this subject, Ziejewski, Kaufman, Schwab, and Pryde (1984) prepared an emulsion of 53% (vol) alkah-refined and winterized sunflower oil, 13.3% (vol) ethanol, and 33.4% (vol) 1-butanol. Lower viscosities and better spray patterns (more even) were observed with an increase of 1-butanol. 

Some Hints on the Elimination of Emulsions during Extraction WITH Immiscible Liquids... 

The fibers themselves can be modified significantly in the way they are processed. The emulsion of immiscible liquids which are then electrospun creates fibers with a core of one type and a surface of another type. If the internal material is dissolvable, it creates a hollow core [31]. And additives to the polymer do not have to be removed. Blends of inorganic and organic material, which can be purified [32] or heterogenous extracellular matrix components [33], can add bioactive components for interacting cells or change the material s mechanical and chemical properties. 

Liquid-liquid immiscible liquid phases reactions such as the nitration of toluene or benzene with mixed acids, and emulsion polymerisations. 

BDS process. The pore size of the filter (0.2-1.0 xm) is selected such that the liquid phase, which is miscible with the liquid that is used to wet the filter, passes through the filter, while the second liquid phase remains. Thus, an aqueous filter is wet with a liquid, which is miscible with water, but immiscible with oil. The flow rate is chosen so as to prevent solid deposition through the filter. Although, such a separation process can be applied to any oil/water emulsion, it was particularly envisioned as part of a BDS process. One may ask, whether it would be more efficient to break a macroemulsion by filtering than it is by any other means Second, in the case of microemulsions, how efficient would such a filtration process be ... 

The first criterion for the formation of a HIPE is, of course, the presence of two immiscible liquids, one of which is water (or aqueous solution), almost without exception. The nature of the organic, or oil, phase can vary to a considerable extent, although the most stable HIPEs are generally produced with more hydrophobic liquids. However, it is the nature of the surfactant employed to stabilise the HIPE which will ultimately facilitates its formation. Above a certain critical limit of internal phase volume, an emulsion will tend to invert to the opposite type, i.e. an oil-in-water (o/w) emulsion will become the w/o variety, and vice versa. This can be prevented from occurring by careful choice of surfactant, such that it is completely insoluble in the dispersed phase of the emulsion. 

Electrostatic and non-electrostatic biopolymer complexes can also be used as effective steric stabilizers of double (multiple) emulsions. In this type of emulsion, the droplets of one liquid are dispersed within larger droplets of a second immiscible liquid (the dispersion medium for the smaller droplets of the first liquid). In practice, it is found that the so-called direct water-in-oil-in-water (W/O/W) double emulsions are more common than inverse oil-in-water-in-oil (O/W/O) emulsions (Grigoriev and Miller, 2009). In a specific example, some W/O/W double emulsions with polyglycerol polyricinoleate (PGPR) as the primary emulsifier and WPI-polysaccharide complexes as the secondary emulsifying agent were found to be efficient storage carriers for sustained release of entrapped vitamin Bi (Benichou et al., 2002). 

A (macro (emulsion is formed when two immiscible liquids, usually water and a hydrophobic organic solvent, an oil. are mechanically agitated so that one liquid forms droplets in the other one. A microemulsion, on the other hand, forms spontaneously because of the self-association of added amphiphilic molecules. During the emulsification agitation both liquids form droplets, and with no stabilization, two emulsion layers are formed, one with oil droplets in water fo/w) and one of water in oil (w/o). However, if not stabilized the droplets separate into two phases when the agitaliun ceases. If an emulsifier (a stabilizing compound) is added to the two immiscible liquids, one of them becomes continuous and the other one remains in droplet form. 

Unlike micelles, an emulsion is a liquid system in which one liquid is dispersed in a second, immiscible liquid, usually in droplets, with emulsiLers added to stabilize the dispersed system. Conventional emulsions possess droplet diameters of more than 200 nm, and are therefore optically opaque or milky. Conventional emulsions are thermodynamically unstable, tending to reduce their total free energy by reducing the total area of the two-phase interface. In contrast, microemulsions with droplet diameters less than 100 nm are optically clear and thermodynamically stable. Unlike conventional emulsions that require the input of a substantial amount of energy, microemulsions are easy to prepare and form spontaneously on mixing, with little or no mechanical energy applied (Lawrence and Rees, 2000). 

Emulsification The development of an emulsion by mixing two or more immiscible liquids together, such as oil and water. The liquids do not dissolve into each other, but the emulsion consists of distinct microscopic droplets of one or more liquids dispersed into the most abundant liquid (compare with surfactant). 

Example. An emulsion is a dispersion of one immiscible liquid in another. In most cases one of the liquids is aqueous and the other is in some sense, an oil. Emulsions are another kind of colloidal system in which interfacial properties are very important because emulsified droplets have a large interfacial area. Even a modest interfacial energy per unit area can become a considerable total interfacial energy to be reckoned with. 

Emulsion flotation is analogous to carrier flotation. Here, small-sized particles become attached to the surfaces of oil droplets (the carrier droplets). The carrier droplets attach to the air bubbles and the combined aggregates of small desired particles, carrier droplets, and air bubbles float to form the froth. An example is the emulsion flotation of submicrometre-sized diamond particles with isooctane. Emulsion flotation has also been applied to the flotation of minerals that are not readily wetted by water, such as graphite, sulfur, molybdenite, and coal [623]. Some oils used in emulsion flotation include mixed cresols (cresylic acid), pine oil, aliphatic alcohols, kerosene, fuel oil, and gas oil [623], A related use of a second, immiscible liquid to aid in particle separation is in agglomeration flocculation (see Section 5.6.4). 

The relative ease with which two immiscible liquids can be made into an emulsion. 

Partitioning of components between two immiscible or partially miscible phases is the basis of classical solvent extraction widely used in numerous separations of industrial interest. Extraction is mostly realized in systems with dispergation of one phase into the second phase. Dispergation could be one origin of problems in many systems of interest, like entrainment of organic solvent into aqueous raffinate, formation of stable, difficult-to-separate emulsions, and so on. To solve these problems new ways of contacting of liquids have been developed. An idea to perform separations in three-phase systems with a liquid membrane is relatively new. The first papers on supported liquid membranes (SLM) appeared in 1967 [1, 2] and the first patent on emulsion liquid membrane was issued in 1968 [3], If two miscible fluids are separated by a liquid, which is immiscible with them, but enables a mass transport between the fluids, a liquid membrane (LM) is formed. A liquid membrane enables transport of components between two fluids at different rates and in this way to perform separation. When all three phases are liquid this process is called pertraction (PT). In most processes with liquids membrane contact of phases is realized without dispergation of phases. 

Emulsions are a class of disperse systems consisting of two immiscible liquids, one constituting the droplets (the disperse phase) and the second the dispersion medium. The most common class of emulsions is those whereby the droplets constitute the oil phase and the medium is an aqueous solution (referred to as O/W emulsions) or where the droplets constitute the disperse phase, with the oil being the continuous phase (W/O emulsions). To disperse a liquid into another immiscible liquid requires a third component, referred to as the emulsifier, which in most cases is a surfactant. Several types of emulsifiers may be used to prepare the system, ranging from anionic, cationic, zwitterionic, and nonioinic surfactants to more specialized emulsifiers of the polymeric type, referred to as polymeric... 

Emulsions are formed when two immiscible liquids are mixed with each other. The most familiar types are oil-in-water emulsions (O/W emulsions), which consist of colloidal or microscopic oil droplets in water, and water-in-oil (W/O emulsion), where an aqueous solution is emulsified in an outer oil phase [24]. 

Emulsions made by agitation of pure immiscible liquids are usually very unstable and break within a short time. Therefore, a surfactant, mostly termed emulsifier, is necessary for stabilisation. Emulsifiers reduce the interfacial tension and, hence, the total free energy of the interface between two immiscible phases. Furthermore, they initiate a steric or an electrostatic repulsion between the droplets and, thus, prevent coalescence. So-called macroemulsions are in general opaque and have a drop size > 400 nm. In specific cases, two immiscible liquids form transparent systems with submicroscopic droplets, and these are termed microemulsions. Generally speaking a microemulsion is formed when a micellar solution is in contact with hydrocarbon or another oil which is spontaneously solubilised. Then the micelles transform into microemulsion droplets which are thermodynamically stable and their typical size lies in the range of 5-50 nm. Furthermore bicontinuous microemulsions are also known and, sometimes, blue-white emulsions with an intermediate drop size are named miniemulsions. In certain cases they can have a quite uniform drop size distribution and only a small content of surfactant. An interesting application of this emulsion type is the encapsulation of active substances after a polymerisation step [25, 26]. 

By careful selection of the composition of a two immiscible liquid system, one can reduce the surface tension to near zero. In such conditions, with gentle agitation, a very fine dispersion (under micrometer size droplets) may be formed. This is a very stable system for an emulsion. In some conditions the size dispersion may be limited. 

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