Emulsion type theories

J.T. Davies, A quantitative kinetic theory of emulsion type, I, Physical chemistry of the emulsifying agent, in J.H. Schulman (Ed.), Proceedings of the 2nd International Congress of Surface Activity, Butterworths, London, 1957, pp. 426-438. 

Several theories relating to emulsion type have been proposed. The most satisfactory general theory of emulsion type is that originally proposed for emulsions stabilised by finely divided solids (see Figure 10.1). If the solid is preferentially wetted by one of the phases, then more particles can be accommodated at the interface if the interface is convex towards that phase (i.e. if the preferentially... 

Figure 7.3 Illustration of the oriented-wedge theory of emulsion type.

Davies JT. A quantitative kinetic theory of emulsion type. II. Hydrodynamic factors. Proc 3rd Int Congr Surf Activity 1960 2 585-594. 

The A C and A B are called normal O/W and W/O regions, respectively, because the emulsion type matches the interface curvature exp Ted from phase behavior according to the wedge theory and similar rules of thumb. 

The whole phenomenology of phase behavior and emulsion inversion was interpreted wifli a butterfly catastrophe model with amazing quahtative matching between theory and experiment. The phase behavior model used the Maxwell convention which allows the system to split into several states, i.e., phases at equilibrium. On the other hand, the emulsion-type model allows for only one state (emulsion type) at the time, with eventually catastrophic transition and hysteresis, according to the perfect delay convention. The fact that the same model potential permits the interpretation of the phase behavior and of the emulsion inver sion (204, 206) is a symptomatic hint that both phe-nomenologies are linked, probably through formulation and water/oil composition which are two of the four manipula-ble parameters in the butterfly catastrophe potential. 

Figure 7.8 (a and b) Cartoon representing the oriented wedge theory, as presented by Harkins et and Langmuird The monolayers covering emulsion droplets have different frustration energies, which favor one emulsion type over another. Note that the picture shows the macroscopic emulsion droplets and not the surfactant micelles. The theory is wrong because the monolayers are essentially planar on the molecular scale (c and d)... 

To serve as a complete theoretical description of emulsions, a theory must be able to explain and predict all aspects of emulsion formation, stability, and type (O/W or W/0), the influence of environmental factors such as temperature and pressure, the... 

However, the kinetics of PVC emulsion does not foUow the above theory. The rate shows the same increasing behavior with conversion as mass polymerization (94,95). [N depends on [3], but the relationship varies with the emulsifier type (96,97). However, the rate is nearly independent of [N (95). The average number of radicals per particle is low, 0.0005 to 0.1 (95). The high solubiUty of vinyl chloride in water, 0.6 wt %, accounts for a strong deviation from tme emulsion behavior. Also, PVC s insolubiUty in its own monomer accounts for such behavior as a rate dependence on conversion. 

Based on the Smith-Ewart theory, the number of latex particles formed and the rate of polymerization in Interval II is proportional with the 0,6 power of the emulsifier concentration. This relation was also observed experimentally for the emulsion polymerization of styrene by Bartholomeet al. [51], Dunn and Al-Shahib [52] demonstrated that when the concentrations of the different emulsifiers were selected so that the micellar concentrations were equal, the same number of particles having the same size could be obtained by the same polymerization rates in Interval II in the existence of different emulsifiers [52], The number of micelles formed initially in the polymerization medium increases with the increasing emulsifier concentration. This leads to an increase in the total amount of monomer solubilized by micelles. However, the number of emulsifier molecules in one micelle is constant for a certain type of emulsifier and does not change with the emulsifier concentration. The monomer is distributed into more micelles and thus, the... 

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