Micellization of N-alkylpyridinium halides in formamide tensiometric and small angle neutron scattering study

The Krafft temperatures and critical micellar concentrations (cmc) of N-alkylpyridinium halides (C(m)PyX, m = 12, 16, or 20 and X = Cl, Br, or I) in formamide were determined. The size, structure, and charge of the micelles as a function of chain length and nature of counterion were calculated from the small angle neutron scattered intensity. At a chain length of 12 carbons, only small, relatively unstructured aggregates were formed. At a chain length of 16 carbons, some micelles were also observed at a concentration of twice the cmc and above. At a chain length of 20 carbons, micelles were the sole species. The radii of the cores of the spherical micelles in formamide were always lower than the radii of the corresponding micelles in water. The micelles bear a higher charge in formamide than in water, but similar solvation effects were noted in the two solvents on changing the counterion (I-, Br-, or Cl-).