Emulsion type

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]. 

There is a common rule, called Bancroft s rule, that is well known to people doing practical work with emulsions if they want to prepare an O/W emulsion they have to choose a hydrophilic emulsifier which is preferably soluble in water. If a W/O emulsion is to be produced, a more hydrophobic emulsifier predominantly soluble in oil has to be selected. This means that the emulsifier has to be soluble to a higher extent in the continuous phase. This rule often holds but there are restrictions and limitations since the solubilities in the ternary system may differ from the binary system surfactant/oil or surfactant/water. Further determining variables on the emulsion type are the ratios of the two phases, the electrolyte concentration or the temperature. 

The solubility of the surfactant of polyethyleneglycol type in different phases can be described by the HLB (hydrophilic-lipophilic-balance) concept [ 27]. This concept attributes to the molecule a HLB number that represents the geometric ratios of the hydrophilic and the hydrophobic moieties. It should, however, be emphasized that the HLB does not represent a fundamental property of the system but is based on experience. For fatty alcohol ethoxylates 

As a rule of thumb, surfactants with 3 HLB 6 are suitable for the preparation of W/O emulsions while surfactants with 8 HLB 18 are O/W emulsifiers. 

The HLB concept assumes that the emulsion type is mainly governed by the curvature of the interface. Large headgroups may need considerable space on the outside of oil droplets in a continuous water phase and cause a positive curvature of the interface. On the other hand, small hydrophilic headgroups can be forced together inside a water droplet whereas large hydrophobic moieties extend into the continuous oil phase. The interface now has a negative curvature. 

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An emulsion may be defined as a mixture of particles of one liquid with some second liquid. The two common types of emulsions are oil-in-water (O/W) and water-in-oil (W/0), where the term oil is used to denote the water-insoluble fiuid. These two types are illustrated in Fig. XIV-1, where it is clear that the majority or outer phase is continuous, whereas the minority or inner phase is not. These two emulsion types are distinguished by their ability to disperse oil or water-soluble dyes, their dilution with oil or water, and their conductivity (O/W emulsions have much higher conductivity than do W/0 ones see Ref. 1 for reviews). 

One may rationalize emulsion type in terms of interfacial tensions. Bancroft [20] and later Clowes [21] proposed that the interfacial film of emulsion-stabilizing surfactant be regarded as duplex in nature, so that an inner and an outer interfacial tension could be discussed. On this basis, the type of emulsion formed (W/O vs. O/W) should be such that the inner surface is the one of higher surface tension. Thus sodium and other alkali metal soaps tend to stabilize O/W emulsions, and the explanation would be that, being more water- than oil-soluble, the film-water interfacial tension should be lower than the film-oil one. Conversely, with the relatively more oil-soluble metal soaps, the reverse should be true, and they should stabilize W/O emulsions, as in fact they do. An alternative statement, known as Bancroft s rule, is that the external phase will be that in which the emulsifying agent is the more soluble [20]. A related approach is discussed in Section XIV-5. 

Metal poHshes may contain emulsifiers and thickeners for controlling the consistency and stabilization of abrasive suspensions, and the product form can be soHd, paste, or Hquid. Liquid and paste products can be solvent or emulsion types the market for the latter is growing. Formulas for metal poHshes are Hsted ia Reference 12. A representative Hquid emulsion product may contain 8—25 wt % abrasive, 2—6 wt % surfactant, 0—5 wt % chelating agents, and 0—25 wt % solvent, with the remainder being water. The abrasive content ia an emulsion paste product is greater than that ia a solvent product. 

The next larger film sizes, considered a medium format, are 120-, 220-, and 70-mm roU films. The first two are about 62-mm wide and unperforated the last is bulk motion-picture stock perforated along both edges. These are also available in a range of emulsion types. 

An unusual method for the preparation of syndiotactic polybutadiene was reported by The Goodyear Tire Rubber Co. (43) a preformed cobalt-type catalyst prepared under anhydrous conditions was found to polymerize 1,3-butadiene in an emulsion-type recipe to give syndiotactic polybutadienes of various melting points (120—190°C). These polymers were characterized by infrared spectroscopy and nuclear magnetic resonance (44—46). Both the Ube Industries catalyst mentioned previously and the Goodyear catalyst were further modified to control the molecular weight and melting point of syndio-polybutadiene by the addition of various modifiers such as alcohols, nitriles, aldehydes, ketones, ethers, and cyano compounds. 

Numerous other examples of enantioselective hydrolysis of esters have been reported. For example chymotrypsin, immobilised in a liquid membrane of kerosene or cydohexane, can be used for resolution of D,L-amino add esters in an emulsion type... 

More recently there have been developed water- resistant phosphorus-based intumescence catalyst. This commercially available product, as an example Phos-Chek P/30 tradename from Monsanto, can be incorporated (with other water insoluble reagents) into water-resistant intumescent coatings of either the alkyd or latex-emulsion type. These intumescent coatings, formulated ac-... 

There has been some evidence of a higher antioxidant effect when both flavonoids and a-tocopherol are present in systems like LDL, low-density lipoproteins (Jia et al., 1998 Zhu et al, 1999). LDL will incorporate a-tocopherol, while flavonoids will be present on the outside in the aqueous surroundings. A similar distribution is to be expected for oil-in-water emulsion type foods. In the aqueous environment, the rate of the inhibition reaction for the flavonoid is low due to hydrogen bonding and the flavonoid will not behave as a chain-breaking antioxidant. Likewise, in beer, none of the polyphenols present in barley showed any protective effect on radical processes involved in beer staling, which is an oxidative process (Andersen et al, 2000). The polyphenols have, however, been found to act synergistically... 

Hand lotions, of the emulsion type, are also, in most cases, oil in water emulsions. A true emulsifying agent is usually used to form the emulsion and for cleansing properties. Vegetable gums, like tragacanth or Irish moss extract, are added, not only to stabilize the emulsion but to increase the emollient properties, because of the added viscosity effect. 

The utilization of the vegetable gums, especially those with good filmforming properties, to suspend the solids in paints of the casein and emulsion types, still offers a wide field for experimentation and application. 

Kelly, W.R. "Relationship Among Emulsion Type, Detergency and Foam," J. Amer. Oil Chem. Soc.. 1966, 43, 358-363. 

Effect of Section Thickness Emulsion Type and Development on Resolution of EM Radioautographs... 

C. B. Lalor, G. L. Flynn, and N. Weiner. Formulation factors affecting release of drug from topical formulations. I. Effect of emulsion type upon in vitro delivery of ethyl p-aminobenzoate. J. Pharm. Sci. 83 1525-1528 (1994). 

CED values can be determined from surface tension measurements, (2) the effects of particular molecular components of surfactant molecules on surface tension and CED can be addressed, and (3) the emulsion type and stability can be evaluated based on either molecular structure surface tension and/or CED. 

J.L. Salager Macro Emulsions Stabilized by an Ethoxylated Fatty Alcohol and an Alkyl Quat Emulsion Type and Stability in View of the Phase Behavior. In Proceedings of the 3rd World Congress on Emulsions 1 -F-107, Lyon, France (2001). 

W/O emulsions are formed by using HLB values between 3.6 and 6, thus suggesting that emulgators that are soluble in the oil phase are generally used. O/W emulsions need HLB values around 8 to 18. This is only a very general observation it must be noted that HLB values alone do not determine emulsion type. Other parameters, such as temperature, properties of the oil phase, and electrolytes in the aqueous phase also have their effect. However, HLB values have no relation to the degree... 

Table 4.4 Typical characteristics of wax emulsion type of dampproofer...

Table 4.6 Effect of a wax emulsion type of dampproofer on the compressive strength of concrete of varying cement content...

When fatty-acid or wax emulsion type damp-proofers are used in conjunction with lignosulfonate or hydroxycarboxylic-based admixtures, heavy air entrainment results with attendant strength reduction. Both these effects decrease waterproofing characteristics. At higher workabilities, ligno sulfonates counteract the reduced bleeding effect obtained with waxes and increase bleeding rates [83]. 

Liquid membranes of the water-in-oil emulsion type have been extensively investigated for their applications in separation and purification procedures [6.38]. They could also allow extraction of toxic species from biological fluids and regeneration of dialysates or ultrafiltrates, as required for artificial kidneys. The substrates would diffuse through the liquid membrane and be trapped in the dispersed aqueous phase of the emulsion. Thus, the selective elimination of phosphate ions in the presence of chloride was achieved using a bis-quaternary ammonium carrier dissolved in the membrane phase of an emulsion whose internal aqueous phase contained calcium chloride leading to phosphate-chloride exchange and internal precipitation of calcium phosphate [6.1]. 

The dielectric properties of water have been extensively used to determine moisture content in food systems. However, only veiy recently have we used the complex dielectric properties of emulsions in the microwave frequency region to characterize both emulsion type and water content [50-52], We have developed both a cavity resonance dielectrometer capable of operating at 8-11 GHz and an interference dielectrometer operating at 23.45 GHz. 

EX duPont deNemours and Company Water-In-Oil Emulsion Type Blasting Agent... 

Ibid, Emulsion Type Explosive Composition Containing Ammonium Stearate or Alkali Metal Stearate , U P 3770522 (1973) CA 80, 49974 (1974) 4) Merck (1976), 75 (No 584)... 

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