A study of the microstructure of CTAB/1-butanol/octane/water system by PGSE-NMR, conductivity and cryo-TEM

A quaternary microemulsion system of a cationic surfactant (cetyltrimethylammonium bromide, CTAB), octane, water, and 1-butanol has been investigated using conductivity, pulsed field gradient spin-echo NMR measurements, and electron microscopy (Cryo-TEM and freeze fracture electron microscopy (FFEM)). The conductivity behavior has a distinct percolative phenomenon and a bell-shaped curve as a function of water contents. This indicates that the single-phase microemulsion is changed continuously from oil-in water structure via a bicontinuous structure to water-in oil structure. This result is consistent with those of the PGSE-NMR, Cryo-TEM, and FFEM. In the w/o region, the self-diffusion coefficient of water is relatively high (2–7×10−10 m2 s−1) due to the higher solubility of water in the continuous phase which consisted of octane(10 wt.%) and 1-butanol. The penetration of a large amount of octane molecules between surfactant chains results in the self-diffusion coefficient of octane being much lower (1–8×10−10 m2 s−1) in the w/o region.