Emulsion type determination

An aqueous phase is added (incrementally) to a finite amount of oil which contains a known amount of surfactant. The mixture is agitated by a turbine blender for 15 s on each addition and the emulsion type determined. A plot of EIP vs. HLB is made where ... 

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. 

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... 

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. 

Later we discover another parameter, the phase inversion temperature(PIT), which helps us to predict the structure of emulsions stabilized by nonionic surfactants. The PIT concept is based on the idea that the type of an emulsion is determined by the preferred curvature of the surfactant film. For a modern introduction into the HLB and PIT concepts see Ref. [546],... 

There can even be more complex emulsion types [2] Figure 1.2 shows an example of a crude oil W/O/W/O emulsion. The type of emulsion that is formed depends upon a number of factors. If the ratio of phase volumes is very large or very small then the phase having the smaller volume is frequently the dispersed phase. If the ratio is closer to one then other factors determine the outcome. See Chapter 11 (especially Table 11.1) for examples of petroleum emulsion types. 

Not all emulsions exhibit the classical milky opaqueness with which they are usually associated. A tremendous range of appearances is possible, depending upon the droplet sizes and the difference in refractive indices between the phases. An emulsion can be transparent if either the refractive index of each phase is the same, or alternatively, if the dispersed phase is made up of droplets that are sufficiently small compared with the wavelength of the illuminating light. Thus an O/W microemulsion of even a crude oil in water may be transparent. If the droplets are of the order of 1 pm diameter a dilute O/W emulsion will take on a somewhat milky-blue cast if the droplets are very much larger then the oil phase will become quite distinguishable and apparent. Physically the nature of the simple emulsion types can be determined by methods such as [95] ... 

If the oil phase fluoresces then fluorescence microscopy can be used to determine the emulsion type as long as the drop sizes are larger than the microscope s limit of resolution (> 0.5 pm). See [66],... 

There is some evidence to suggest that, depending upon the phase volume ratios employed, the emulsification technique used can be of greater importance in determining the final emulsion type than the H LB values of the surfactants themselves [434], As an empirical scale the HLB values are determined by a standardized test procedure. However, the HLB classification for oil phases in terms of the required HLB values is apparently greatly dependent on the emulsification conditions and process for some phase-volume ratios. When an emulsification procedure involves high shear, or when a 50/50 phase volume ratio is used, interpretations based on the classical HLB system appear to remain valid. However, at other phase-volume ratios and especially under low shear emulsification conditions, inverted, concentrated emulsions may form at unexpected HLB values [434]. This is illustrated in Figures 7.4 and 7.5. 

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 volume applied per unit area is fixed by the pressure and the size of the nozzle (assuming that the number of nozzles per unit length of boom and the speed of the sprayer are constant), and in combination with the phase ratio of the emulsion, this determines the toxicant deposit per unit area. The phase ratio in turn is the main factor which determines the viscosity of the spray liquid. The viscosity, the size and type of... 

Physically the nature of the simple emulsion types can be determined by methods such as... 

Davis, H.T., Factors determining emulsion type HLB and beyond, in Proc. First World Congress on Emulsion, 19-22 Oct., Paris, 1993, p. 69. 

Direct and inverse emulsions are found in everyday-life products. For instance, both types of emulsion are common in food oil-in-water emulsions include milk, cream, and mayonnaise butter and margarine are examples of water-in-oil emulsions. Furthermore, recent studies were carried out, with the help of professional sensory panelists, to determine the influence of emulsion type on the perception of taste [36], In relation to the breakdown mechanisms of emulsions (creaming/sedimentation, flocculation, coalescence, and Ostwald ripening), controlling emulsion type can be regarded as a key parameter to design stabilization/destabilization processes. In cosmetic... 

Emulsion type, i.e., O-W or W-O. This determines several properties see Section 9.1. 

There are many industrial processes in which the formation of low internal phase or concentrated emulsions needs to be controlled in terms of formation, stability, destruction or prevention. Examples range from asphalt emulsions to personal care products, and to food products. Success in emulsion control requires achieving the right physical chemistry and also the right fluid mechanics. In addition to HLB (see Section 7.2.1), both the nature of the emulsification method and the oil-water ratio are critical in determining the produced emulsion type. It appears that the emulsification technique (applied shear and oil-water ratio) used can be of greater importance in determining the final emulsion type than the HLB values of the surfactants themselves. 

The. second intent to numerically characterize (he formulation concept was the so-called phase inversion temperature (PIT), originally introduced by K. Shitioda in 1964 as (he temperature at which a polyethoxylated nonionic surfactant switched its dominant afitnity from the aqueous phase to the oil phase to produce a change in emulsion type. This was both easy to determine experimentally and simple to undersund as far as the related phenomenology was concerned (48-50). 

The energy required to form emulsions is quite low in most cases. Further study is required on a wide variety of emulsions to determine if there is a relation ship to oil properties or to emulsion types. 

Emulsions can be found as two basic types, i.e., 0/W and W/O, but in some particular cases, multiple or double emulsions labeled Wj/0/W2 and Oj/W/02 also occur. The emulsion type may be determined by different methods. In most applications the aqueous phase contains one or various electrolytes, and thus conducts electricity somehow, whereas the oil or organic phase does not. Consequently, the measurement of electrolytic conductivity is a handy way to ascertain the emulsion type. Moreover, the continuous monitoring of the electrolytic conductivity allows the determination of the change in emulsion type which is referred to as emulsion inversion. 

Once the emulsion type is determined as one of the two simple cases, i.e., OAV or W/0, the emulsion structure is characterized by its drop size, or more exactly by its drop size statistical distribution. As a matter of fact, this is quite logical since most emulsions are made by a stirring process that often involves turbulence and thus random effects. Moreover, the emulsion is the result of opposite phenomena, i.e., drop breaking and coalescence, that cannot be described but in some statistical fashion. It may be said that the drop size distribution is the fingerprint of the emulsion. 

The bidimensional mapping does not take into account several secondary factors that are, however, known to influence the emulsion type and properties. Recent research has shown that they may be accounted for as a modification of the bidimensional map character istics. First, it was found that an increase in surfactant concentration tends to widen the A zone (195), i.e., the region in which the emulsion type is determined by the formulation. 

Davis, H. T., Factors determining emulsion type hydro-phile-lipophile balance and beyond. Colloid Surf. A, 91, 9-24 (1994). 

Different types of water-based emulsions are used in EPI adhesives. The most common are poly(vinyl acetate) (PVAc) emulsion, ethylene vinyl acetate (EVAc) emulsion, vinyl acetate-acrylate copolymerized (VAAC) emulsion, acrylic-styrene (AcSt) emulsion or styrene-butadiene rubber (SBR) latex or modified versions of these emulsion types [1, 8, 9], It has also been reported that tri- or ter-polymer emulsions like vinyl acetate-butyl acrylate-hydroxypropyl methacrylate or emulsions with different combinations of block copolymers can be used [4], Emulsion polymers containing cross-linking functional groups are especially well suited [4,6, 9]. The choice of emulsion(s) will, to a large extent, influence the adhesive properties such as setting time, bond quality, heat resistance, and moisture resistance. EPI adhesive systems are, however, very complex and the total composition (including the choice of cross-linker) and the interaction between the different components will determine the properties of the adhesive. Due to this it is difficult to describe in detail the effect of choosing one type of emulsion over the other. 

This test method involves a rapid quantitative determination of the residue in bitumen emulsion using a moisture analyser. It is applicable to all non-solvent-containing emulsion types, anionic, cationic, non-polymer-modified or polymer-modified bitumen emulsions. 

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