Phase inversion transitional

In transitional phase inversion the first step is to prepare an emulsion of the phase that should become the continuous phase (phase f ) in a continuous phase (A). In this case, however, the surfactant system is chosen very carefully, such that at the initial conditions, it favours the formation of a B- d-A emulsion. Then, when this emulsion has been prepared, the conditions are changed such that the properties of the surfactant system changes towards favouring an A-ia-B emulsion. This can be done by temperature, or by changing pH, or by other means, but the effect is of changing the affinity of the surfactants to the two phases. 

Figure 15.24. Transitional phase inversion ean take place by changing the affinity of the surfactant system. There will be a region where a micro-emulsion is formed. By passing the emulsion through this area in the phase diagram, a very fine emulsion of B in A can be formed.

Transitional phase inversion is a very effective process, but it is not used in the food industry due to the properties of the oils commonly used in foods, finding a surfactant system that exhibits this behaviour has not yet succeeded. The process is applied widely, however, in the cosmetic and coating industries. 

A third class is phase inversion. Here, emulsions are made by starting with an emulsion in which the ultimate continuous phase is the dispersed phase and vice versa. Then by adding more and more dispersed phase, one can induce the emulsion to suddenly invert (catastrophic inversion). Alternatively, one can choose the surfactant system such that, for example, by a temperature change, the surfactant system changes from favouring the initial emulsion to favouring an inverted emulsion. This is called transitional phase inversion. 

Two types of phase inversion may be distinguished (a) Catastrophic, e.g. when the disperse phase volume exceeds its maximum packing and (b) transitional, which occurs over a long period of time due to change in the conditions. An example of transitional phase inversion is when the emulsion is subjected to a temperature change. For example, when an emulsion, prepared using an ethoxylated nonionic... 

Brooks and Richmond " studied the dynamics of transitional phase inversion for various combinations of nSOW systems. They found that drop sizes decreased as the transitional inversion point was approached. Figure 6.9 shows the change in drop diameter across the phase transition for the oil-water-NPE system. This change in drop diameter reflects the interfacial tension change through the phase transition. For all the individual mixtures that were studied hy Brooks and Richmond, the locus for the transitional inversion was found to he a straight line. It was also found that, contrary to what was suggested by other workers, when... 

The SIN s from castor oil and the other oils were tough materials, either reinforced elastomers or impact resistant plastics depending on their composition and whether phase inversion had occurred. Impact strengths in the range of 40-60 J/m were obtained. The glass transitions of the rubber phase of the SIN s tended to be a little higher than those shown in Table IV. The polystyrene phase... 

Rgure 1.6. (a) Schematic formulation-composition map. SAD is the surfactant affinity difference it is positive for a lipophilic surfactant and negative for a hydrophilic one. The gray zones are abnormal, (b) Schematic representation of the proposed mechanism for a transitional inversion, (c) Schematic representation of the proposed mechanism for a catastrophic phase inversion. 

B.W. Brooks and H.N. Richmond Phase Inversion in Non-Ionic Surfactant-Oil-Water Systems, I. The Effect of Transitional Inversion on Emulsion Drop Size. Chem. Eng. Sci. 49, 1053 (1994). 

S. Sajjadi, F. Jahanzad, and M. Yianneskis Catastrophic Phase Inversion of Abnormal Emulsions in the Vicinity of the Locus of Transitional Inversion. Colloid and Surfaces A Physicochem. Eng. Aspects 240,149 (2004). 

It seems to be a kind of transition somewhat akin to such phenomena as phase inversion observed in oil/water/ surfactant systems(24), and critical demixing (i5j. 26). 

In the aromatic transition state approach, the basic criterion was that a reaction is allowed in the ground state if and only if there occurs in the transition state aromatic stabilization. This criterion led to the Dewar-Zimmerman selection rule (Equation 11.36), where p. i. = 0 signifies an even number of phase inversions, p. i. = 1 signifies an odd number of phase inversions, and N is the total number of electrons. 

As adsorbate, the polysaccharide dct is sensitive to the DP and polydis-persity (Cohen Stuart et al., 1982). Higher DP polysaccharides are less kinetically active, are therefore slower to accumulate than lower DP polysaccharides because of the time taken for surface orientation, and are thus more inclined to stay adsorbed longer and reach higher concentrations. Agitation increases the rate of physical adsorption. From the foregoing discussion on polysaccharide dispersibility, it is safe to conclude that multilayer adsorption is antecedent to polysaccharide phase inversion and in some instances to sol-gel transition. 

Figure 2 shows tensile-yield strengths for blends of the crystalline EPDM with various levels of LDPE. The curve increases monotonically as expected if no phase inversion occurs. Since amorphous LDPE has a glass-transition temperature near that of EPDM (7) and since the LPDE has only 27 % crystallinity, one should not expect a rubber-to-rigid phase transition. 

According to Zimmermann [101] and Dewar [102], the allowedness of a concerted pericyclic reaction can be predicted in the following way A cyclic array of orbitals belongs to the Hiickel system if it has zero or an even-number phase inversions. For such a system, a transition state with An+ 2 electrons will be thermally allowed due to aromaticity, while the transition state with An electrons will be thermally forbidden due to antiaromaticity. 

Consequently, as shown by (3), is primarily associated with the transition metal d AO (the absolute magnitude of is also less than 1) and there is antibonding associated with this MO, that is, there is a phase inversion on going from M to L in 4 2... 

Values of Gc predicted by the above two models are shown in Figure 2-15. Implicit in the above models is that the experimental value of Gc lies between those of Gx and Gy. For a simple phase-separated system, the lower bound form (isostress) should predict Gc prior to phase inversion when the supporting phase (jc) is the weaker one. It will then show a transition to the upper bound behavior. More complex models... 

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