Length control in rigid cylindrical nanoassembly by tuning molecular interactions in aqueous solutions

We have studied aqueous micellar solutions of nonionic surfactant (pentaethylene glycol mono-n-dodecyl ether, C12E5) doped by cationic surfactant (dodecyl trimethylamoniumbromide, DTAB) as a function of doping level, using small angle neutron scattering. At a doping level of at least 6 mol %, rigid cylindrical micelles formed and the local cylindrical structure of the doped micelles showed no variation across the range of doping levels covered in this study (0-10 mol %). However, the total micellar length decreased rapidly as doping level increased, following well the prediction of micellar aggregation number based on molecular-thermodynamic theory. There was no synergistic interaction between surfactants, leading to monotonically decreasing the micellar aggregation number (shortening of the micellar length).