Phase microemulsion characterisation

The most common definition of a microemulsion characterises it as a thermodynamically stable, transparent, optically isotropic, freely flowing surfactant mixture, often containing co-surfactants (e.g. alcohol) and added salts [37]. We restrict the definition further to non-crystalline (disordered) aggregates, since crystalline isotropic phases are better considered as liquid crystalline mesophases. Indeed, the most succinct description of a microemulsion would involve its microstructure. However, this has proven to be a very equivocal issue. So much so that until very recently it was widely believed that microemulsions were devoid of microstructure hence the thermod)mamic definition. 

Aboofazeh, R. Lawrence, M.J. Investigations into the formation and characterisation of phosphohpid microemulsions. II. Pseudo-ternary phase diagrams of systems containing water-lecithin-isopropyl myristate. Int. J. Pharm. 1994, 111, 63-72. 

Kim C-K, Ryuu S-A, Park K-M. Preparation and physicochemical characterisation of phase inverted water/oil microemulsion containing cyclosporin A. Int J Pharm 1997 147 131-134. 

Samples were also taken from the diluted and the long float. The characterisation of the phase behaviour resulted for both floats in a three-phase state, which, in contrast to the short float, is not located at T = 37°C, but at T = 60°C as shown in Fig. 10.7. At the degreasing temperature T = 30°C now a fat-in-water microemulsion coexists with a fat-excess phase, which is turned into a stable fat-in-water emulsion via shearing. 

The results obtained from the characterisation of the phase behaviour and in the beam house imply that Eusapon OD is a suitable alternative allowing for an eco-friendly degreasing of animal skins. However, the understanding of the so far unidentified degreasing mechanism is the key goal for a continuous development of the degreasing process itself. In order to clarify the role of microemulsions in degreasing additional phase behaviour and interfacial tension measurements were conducted. 

For all systems we characterise as physico-chemists, the fundamental issue we deal with is that of whether we have a thermodynamically stable system or not. However, in the case of microemulsions, looking back we can see that it were the spectacular properties of microemulsions that called attention, while issues of whether the system was kinetically or thermodynamically stable were not in focus. Therefore, in the early work, a phase diagram approach, already established for surfactant systems in general, was not applied. 

Any study on microemulsion polymerisation must be preceded by an appropriate formulation and phase diagrams of systems in which the monomer is to be dispersed must be characterised. What is the formulator looking for The main constraint is cost. Systems should contain the highest possible monomer concentration for the smallest possible quantity of surfactants. This is indeed... 

The polymerisation of vinyl acetate in microemulsions stabilised with cetyltrimethylammonium bromide surfactant was investigated as a function of concentrations of monomer and initiator and temperature. Molar mass distributions, phase behaviour and latex characterisations were analysed. 44 refs. 

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