MICELLAR STRUCTURE IN SOLUTIONS OF AN ULTRALONG CHAIN ZWITTERIONIC SURFACTANT

The ''ultralong chain surfactant'' 6-eicosyldimethylammonioperdeuteriohexanoate has been prepared and used in small-angle neutron scattering experiments in H2O:D2O mixtures, of various compositions. The form of the spectra obtained with variation of contrast between the perdeuteriohexanoate group and the rest of the molecule has established that the micelle is spherical in geometry with a hydrocarbon core and a radial shell containing the head groups. The perdeuteriohexanoate group which forms the tether between the positively charged nitrogen atom and the carboxylate group appears to be confined to a radial shell, ca. 3.5 Angstrom thickness. The arrangement of the charged groups at and near the surface of the micelle is also discussed.