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Hermann, Rudolf Nikolaus (1940) Partial coagulation of emulsions in soap solution by addition of salts of bivalent ions. Doctoral thesis, Sir John Cass Technical Institute.
Emulsions stabilised by sodium oleate are partly broken by adding bi- and higher-valent kations and the amounts of coagulated oil determined. For a good understanding of the process of coagulation the nature of the soap film at the interface oil/water is studied. By analysing the equilibrium liquid and calculating the total interfacial area we infer the presence of monomolecular soap layers at the interface. A distinction is made between the process of emulsification and that of stabilisation. The last mentioned process depends upon the formation of stable homogenous or composite films of adsorbed molecules of ions. Due to dissociation or dipole action of the molecules at the interface there is electrostatic repulsion between the emulsion droplets. Evidence is given that the electro-kinetic potential determined by electrophoresis is not the only factor of stability.
When coagulating emulsions by different electrolytes, the added electrolyte reacts not only with the sodium oleate free in the aqueous phase, but also with the acid soap which forms the interfacial film. The product of this second reaction is often different from that of the first. The specific coagulating effects of electrolytes are due to the proportion of the electrolyte which reacts at the interface and to the nature of this reaction. The products of the reaction between a number of bi- and higer-valent kations and sodium oleate in an emulsion are analysed. The ability of metal soaps to stabilise W/O [water-in-oil] emulsions and the special behaviour in this respect of magnesium oleate are discussed. The influence of dilution and of different oil phases on the coagulation of O/W [oil-in-water] emulsions are investigated.
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