Field-dependent NMR relaxation study of aggregation and dynamics in diluteto concentrated micellar decylammonium chloride solutions

The surfactant aggregation behavior in aqueous decylammonium chloride solut ions for concentrations between 5 and 29 wt % was studied by H-2 nuclear ma gnetic relaxation dispersion in the 0.5-77-MHz frequency range. Below the s econd cmc the micelles can be described as polydisperse fairly small aggreg ates undergoing unhindered Brownian rotation. Above the second cme the mice lles are rod shaped and grow with increasing concentration, and as a conseq uence the tumbling of the micelles eventually becomes restricted by neighbo ring aggregates, which is demonstrated by the low-frequency relaxation data . The restricted reorientation of the micelles in the concentrated solution has been modeled as rotational diffusion in a hard-walled double cone pote ntial of mean torque.