Counterion Complexation by Calixarene Ligands in Cesium and Potassium Dodecylsulfate Micelles. A Small Angle Neutron Scattering Study

Cesium and potassium dodecyl sulfate micellar solutions have been studied in the presence of three calix[4]arene-crown ethers able to complex cesium and potassium micellar counterions in a selective way (C(8)Cal-6 and C(3)Cal-6 for Csi and C(3)Cal-5 for K(+)). The cesium or potassium dodecyl sulfate micelles are modeled as two-shell ellipsoids. The surfactant dodecyl chains and part of the calix-crown ligands are located in the micelle hydrophobic core. Intermicellar correlations are calculated according to a multicomponent primitive model in a mean spherical approximation with a nonadditive diameter (NARMMSA). We found that calix-crown derivatives addition to cesium dodecyl sulfate micellar solutions leads to a generalized increase of the micelle aggregation number, a consistent decrease of the micelle ionization, and a micellar grow toward elongated ellipsoids. However, the addition of calixarene molecules to potassium dodecyl sulfate produces only a slight decrease of the micellar charge.