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 w ere calculated from the small angle neutron scattered intensity. At a chain length of 12 carbons, only small, relatively unstructured aggreg ates 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 chai n length of 20 carbons, micelles were the sole species. The radii of t he 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 effec ts were noted in the two solvents on changing the counterion (I-, Br-, or Cl-).