Ion extraction mechanism studied in a lyotropic lamellar phase.

In this paper we used a surfactant-stabilized lyotropic lamellar model system to study the interfacial behavior of an ion-extracting agent: N(1),N(3) dimethyl-N(1),N(3)-dibutyl-2-tetradecylmalonamide (DMDBTDMA). An analysis of small-angle X-ray scattering (SAXS) and polarized attenuated total reflectance-Fourier transform infrared (ATR-FTIR) data enabled us to describe the distribution of the malonamide extractant within the bilayers and its complexation state at the equilibrium. The lamellar phase was diluted with salt water containing varying amounts of complexing salt, and each structural state measured was described using a thermodynamic model based on three elementary equilibria: (i) partition of the extractant polar heads between the core and the polar shell of the bilayers, (ii) the complexation of ions by extractants at the bilayers surfaces, and (iii) the partition of bonded extractants between the core and interfaces of bilayers. This model enabled us to compare the energy cost of each step.