Small‐angle neutron scattering‐measurements on a surfactant system consisting of cationic and anionic surfactant molecules

Abstract

AbstractResults of small‐angle neutron scattering (SANS) experiments are reported on the mixed cationic anionic surfactant system Tetradecyl‐pyridinium‐heptylsulfonate (C14PyC7SO3). In the concentration range between 10 mM and 160 mM, the scattering curves show a correlation peak. The scattering vector at the correlation peaks shifts with the volume fraction of the surfactant with a power low having an exponent 0.43. The data can be explained on the basis of rodlike micelles which become shorter with increasing concentrations. For the two highest concentrations 320 and 640 mM the correlation peak disappeared. This change in the scattering curves is attributed to a change in the aggregation behaviour of the system. It is found that at these concentrations the short chain anionic surfactant bind in a one to one ratio with the anionic surfactant and the micelles are practically uncharged, while in the rodlike concentration range the dissociation degree is higher. In the concentration range of the rodlike micelles the correlation peak becomes weaker with increasing concentration.