Small-angle neutron scattering study of aggregate structures of multi-headed pyridinium surfactants in aqueous solution

The aggregate structures of a set of novel single-chain surfactants bearing one, two and three pyridinium head groups have been studied using small-angle neutron scattering (SANS). It is found that the nature of aggregate structures of these cationic surfactants depend on the number of head groups present in the surfactants. The single-headed pyridinium surfactant forms the lamellar structure, whereas surfactants with double and triple head groups form micelles in water. The aggregates shrink in size with increase in the number of head groups in the surfactants. The aggregation number (N) continually decreases and the fractional charge (α) increases with more number of head groups on the surfactants. The semi major axis (a) and semi minor axis (b = c) of the micelle also decrease with the increase in the number of head groups in the surfactants. This indicates that hydrocarbon chains in such micelles prepared from multi headed surfactants adopt bent conformation and no longer stay in extended conformation. (author)