Relative permittivity emulsions

Fig. 7.18.2 shows measured permittivities for three different kinds of ordinary diesel fuels, kerosene, and RME. The sensor has been calibrated with air (relative permittivity 1) and a standard liquid of known permittivity (cyclohexane, er=2.023 at 20°C). The measurement frequency was 100 kHz. It can be seen that all diesel fuels roughly show relative permittivities confined in a fairly narrow interval around 2.1 whereas RME yields values well above 3.1. Accordingly a mixture should yield permittivities between these values, which allows for the determination of the mixing ratio. Strictly this holds only as long as no emulsion is formed [9]. 

Emulsions in foods are macro emulsions, mainly mixtures of oil and water. The less polar phase of an emulsion (of lower relative permittivity) is referred to as the oil, while water is the second phase of the emulsion. Emulsions in food are of two types. An oil-in-water (o/w) emulsion (oil is the dispersed phase and water is the dispersion medium) contains small droplets of oil that are dispersed in water. Alternatively, a water-in-oil (w/o) emulsion has small droplets of water (dispersed phase) that are dispersed in oil (dispersion medium). Like all hydrophobic colloids, macro emulsions are unstable, because the dispersed phase tends to coalescence (small drops aggregate into larger drops and possibly even into a continuous phase, a layer) and the emulsions can then be divided into two phases, usually irreversibly. According to the density of the dispersion medium, the dispersed phase can be concentrated either on the surface or settle to the bottom of the container. 

The stability of an emulsion depends not only on the surfactant type, but also on die nature of the organic phase. To characterize die oil phase, the concept of a necessary (required) HLB number is used. This number is taken to be equal to die HLB number of die surfactant which ensures the best possible emulsification of the oil. Tables of necessary HLB numbers for various oils were published in Ref 258. For example, with respect to oil-in-water emulsions, the necessary HLB number is 17 for oleic acid, 15 for toluene, 14 for xylene and cetyl alcohol, 10.5 to 12 for mineral oils, 7.5 to 8 for vegetable oils, 5 to 7 for vaseline, and 4 for paraffin. In Refs 263 and 264 the necessary HLB numbers for various oils are compared with the relative dielectric permittivity of the oil e. In the series of saturated hydrocarbons, a weak inverse dependence between the necessary HLB number and e was observed (264) e.g., e =... 

In this model it is assumed that the CCI3F hydrate formation starts at the droplet interface. As the clathrate hydrate grows to the center of the droplets, a shell (with a permittivity typical of hydrates) forms. By inserting the dielectric parameters (Table 1) the experimentally obtained spectra may be fitted to model spectra for emulsion systems having different relative thicknesses of the shell. Hence, it is possible to calculate the amount of free water converted into clathrate hydrates. By using such a procedure it has been possible to evaluate the kinetics of hydrate formation in W/O emulsions (13). 

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