The data summarized in Table show that the average interfacial area of the surfactants adsorbed at the flat oil-water interface is close to 0.8 𝑛𝑚 2 , which is close to the value (0.9 𝑛𝑚 2 ) obtained from the standard Gibbs' adsorption equation . While a tightly packed hydrocarbon chain occupies an area of about 0.2 𝑛𝑚 2 , one would expect that the average area per molecule in an emulsion or in a vesicle would be higher than this value as they would be more disordered. On the other hand, the average area occupied by the ethylene glycol group of the non-ionic surfactant should be greater than (0.6 𝑛𝑚 2 ), as obtained from the surface pressure-area isotherm. The average area per molecule, as estimated on the basis of the number of hydrocarbon chains) range from 0.34 𝑛𝑚 2 𝑡𝑜 0.4 𝑛𝑚 2 for the emulsions and vesicles (Table and). The fact that this range of values is larger than that 0.2 𝑛𝑚 2 but less than 0.6 𝑛𝑚 2 suggests that the ethylene glycol groups spread above the carboxylic acid groups of the DDA molecules, i.e. the Polyoxyethylene (23) lauryl ether molecules accommodate some of the dodecanoic acid molecules under its umbrella in the self-assembled structures.