Interfacial composition and structural parameters of water/C12-s-C12 x 2Br/n-hexanol/n-heptane microemulsions studied by the dilution method.

The interfacial composition of the stable water/C12-s-C12 x 2Br/n-hexanol/n-heptane microemulsions has been studied in detail by dilution method. The results showed a marked maximum amount of the n-hexanol populating on the surfaces of droplets (represented as a = n(a)i/n(s), where n(a)i and n(s) are respectively the moles of n-hexanol and gemini surfactant on the surface of droplets) with increasing water content. At a constant level of water addition (the molar ratio of water to surfactant W0 = 20), a decreased with increasing the spacer length in the C12-s-C12 x 2Br molecule. The structural parameters of a w/o microemulsion were also estimated by analyzing the data of dilution experiments, and we found that the radius of the water pool was very sensitive to the increment of water content. The radius of the water pool varied from 0.74 to 5.35 nm with increasing W0 from 10 to 50. The variation extent reached 4.61 nm. In the cases of water/CPC/n-butanol/isopropyl myristate and water/CTAB/n-butanol/isopropyl myristate, however, the corresponding variation extents were only 1.22 and 1.68 nm, respectively, when increasing comparable water content. The ratio of N(a)/N(2C), where N(a) and N(2C) are respectively the average numbers of n-hexanol and the total average numbers of alkyl chains of gemini surfactant populating on per droplet surface, decreased obviously with increasing water content at W0 > 15. This indicated that C12-2-C12 x 2Br favored to form large droplets that were suitable to solubilize more water.