Micelles of asymmetric chain catanionic surfactants

The properties of solutions of asymmetric chain catanionic surfactants are reported. The materials are n-propyl-, n-butyl-, n-hexyl- and n-heptylammonium dodecylsulfates (abbreviated as C3-C12, C4-C12, C6-C12 and C7-C12 respectively). At 25°C the critical micelle concentrations (CMCs) were determined by air-water tension, γ, and electrical conductivity, κ, measurements. The mean are per molecule and per hydrocarbon chain were estimated by applying the Gibbs isotherm to pre-CMC γ versus ln(c) data. The mesophase sequences were determined at 25°C using polarizing microscopy. Small-angle neutron scattering experiments and data modelling suggest that the micelles of C4-C12, C6-C12 and C7-C12 are essentially uncharged, and that a cylinder-to-disc transition occurs between chain length nc= 4 and 6.