Films duplex film theory

According to the duplex film theory, the interfacial tension /j is given by the following expression [5],... 

The duplex film theory predicts that the nature of the microemulsion formed depends on the relative packing of the hydrophobic and hydrophilic portions of the surfactant molecule, which determined the bending of the interface. For example, a surfactant molecule such as Aerosol OT,... 

Mixed film theories (4-8) The essential feature of the mixed film theories is to consider the film as a liquid, two dimensional third phase in equilibrium with both oil and water, implying that such a monolayer could be a duplex film, i.e., one giving different properties on the water side than on the oil side (4). According to these theories, the interfacial tension Y is given by the expression,... 

The vapour-expanded films have pressure-area curves with small values of — F0. At low values of the pressure the area becomes so large that the molecules have to lie nearly flat on the surface the thickness of the hydrocarbon part of the film thus becomes so small that there is much less opportunity for the chains to oscillate about the vertical direction than with the smaller areas of the liquid-expanded films. The hydrocarbon part of the film cannot therefore be considered as a liquid layer and the theory of duplex films tends to become inapplicable owing to the molecules being nearly fiat, the expanded state merges into the gaseous without abrupt change of slope. 

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