Isothermal diffusion in a peculiar ternary system: the microemulsion AOT–water–heptane

Abstract

The isothermal diffusion process was studied on the microemulsion system AOT–water–heptane at an H₂O–AOT mol ratio W= 20 and one average concentration, temperature 25 ± 0.01 °C. The system was considered as a ternary system and four diffusion coefficients were obtained : D₁₁= 1.096 × 10^–10, D₁₂=–0.008 × 10^–10, D₂₁= 8.813 × 10^–10, and D₂₂= 0.416 × 10^–10 m² s^–1; subscripts 1 and 2 indicate AOT and water, respectively. The experimental data confirm that water is mainly carried by the detergent droplets even against its own concentration gradient. From the experimental diffusion coefficients and Fick's laws it can be seen that, for a W ratio very near to 20, water diffuses at the same velocity as AOT, confirming our previous results that if W does not change through the diffusion boundary the system behaves as a pseudo-binary system.