Small-angle neutron-scattering study of bis(quaternary ammonium bromide) surfactant micelles in water. Effect of the spacer chain length on micellar structure

The microstructure of the self-assembly systems, formed by dimeric surfactants in which two quaternary ammonium species (C10H21N+(CH3)(2)) are linked at the polar head groups by a hydrocarbon spacer ((CH2)n(s), n(s) = 2, 3, 4, and 6), has been investigated by small-angle neutron scattering (SANS). The SANS analysis showed that the extent of growth and the variation of shape of the dimeric surfactant micelles strongly depend on the spacer chain length. In particular, it has been found that for the dimeric surfactant with a short spacer (n(s) = 2) both micellar growth and shape variation are more pronounced, while for the surfactant with a long spacer (n(s) = 6) the extent of micellar growth and shape variation becomes very small. We stress that an increase in spacer chain length, within the range n(s) = 2-6, hinders the growth of the micelles formed by the dimeric surfactants in water.