Microstructures of the Gemini surfactant microemulsion system 14-4-14/1-propanol/n-heptane/water

A comprehensive experimental investigation on the microstructures of microemulsion constructed with Gemini surfactant has been carried out. The structural transition of the microemulsion system, 14-4-14/1-propanol/n-heptane/water, from water-in-oil (W/O) to bi-continuous (B.C.) has been characterized by electrical conductivity and cyclic voltammetry. Being a typically percolative system, spherical nanodroplets are observed in the W/O system, while interlinks of water and oil continuous phases are observed in the middle phase, as confirmed by cryo-TEM. Most importantly, the role of water is clearly revealed. Increasing the water content results in size enhancement as well as improvement of micropolarity and diffusion behavior. Results of DSC measurements suggest that free water dominates only at high total water content. The unfrozen water which is not detected by DSC takes a considerable amount in the W/O system at low total water content, while the interphasal water reaches over 50% of total water in the middle phase system.